1 The parties are competitors in the production of synthetic diamonds grown using chemical vapour deposition (“CVD”). At its simplest, under this process, a substrate (which is also known as a diamond seed) is placed in a reactor containing a mixture of gases, including methane (CH4) and hydrogen (H2). Upon exposure to high energy, the gaseous molecules break up into plasma containing carbon (or “C”) atoms. The C atoms are then deposited on the substrate, growing the synthetic diamond layer by layer. ¹

2 The appellant, a company incorporated in Singapore, claims to be a major manufacturer of CVD diamonds and has a diamond-growing facility in Singapore. ² The respondent, a company incorporated in the United Kingdom, is part of the Element Six Group. The Element Six Group is a member of the De Beers Group, which is itself a subsidiary of the Anglo American PLC. ³ The De Beers Group is an international diamond business and a diamond producer, while the Anglo American PLC is a global mining company. According to the respondent, the Element Six Group is a global leader in the design, development and production of “synthetic diamond supermaterials”. ⁴ The respondent claims that its CVD diamonds have potential technical applications in various industries, including optics, semiconductors and sensors. ⁵

3 In HC/S 26/2016 (“Suit 26”), the respondent claimed that the appellant had infringed two of its patents registered in Singapore, Singapore Patent No 115872 (“SG 872”) and Singapore Patent No 110508 (“SG 508”). To prove infringement, the respondent relied on three samples of diamonds, which were labelled Sample 2, Sample 3 and Sample 4 (collectively, the “Samples”), allegedly purchased from the appellant or the appellant’s related entities or distributors. It claimed that the Samples were made from CVD diamond material synthesised by the appellant and that the appellant must have used the method of growth taught in Claims 62 to 71 of SG 872. ⁶ In its defence, the appellant denied infringing the patents and, in any case, disputed their validity. ⁷ The appellant also sought the revocation of both patents by way of a counterclaim. ⁸ On 7 February 2020, the trial judge (the “Judge”) declared that SG 508 was invalid and revoked it on the basis that it was neither novel nor inventive (Element Six Technologies Ltd v IIa Technologies Pte Ltd [2020] SGHC 26 (“Judgment”) at [291] and [478(d)]–[478(e)]). This was a complete defence to the respondent’s claim for infringement in so far as SG 508 was concerned (Judgment at [416]). However, the Judge found that SG 872 was valid and declined to revoke it. She further found that the appellant had infringed specific claims in SG 872. In this appeal, although both parties proceeded on the basis that Claims 1ii), 1iii), 57, 58 and 62 of SG 872 were infringed, ⁹ it is not entirely clear whether the Judge confined her finding of infringement to specific limbs of Claim 1 (Judgment at [9], [416], [443], [454], [456] and [478(a)]). But this difficulty need not detain us. Even taking Claims 1ii) and 1iii) as the point of departure for our analysis on invalidity, our conclusions affect the entirety of Claim 1 and the outcome of the appeal will not change even if the Judge had found the whole of Claim 1 to be infringed.

4 On 6 March 2020, the appellant filed CA/CA 41/2020 (“CA 41”) appealing against the Judge’s rejection of its defence that SG 872 is invalid and its counterclaim to revoke the entirety of SG 872. It also challenged the Judge’s finding that Claims 1ii), 1iii), 57, 58 and 62 in SG 872 had been infringed. ¹⁰ The respondent has not cross-appealed against the Judge’s findings in respect of SG 508.

5 The Judge delivered her decision on costs (the “Judge’s Costs Decision”) on 30 March 2020, holding that the respondent was entitled to the costs of Suit 26 on a standard basis as well as costs of $3,000 (all in) for the costs hearing which took place on 30 March 2020. On 25 June 2020, the appellant filed CA/CA 96/2020 (“CA 96”) appealing against the entirety of the Judge’s Costs Decision.

6 This judgment deals only with CA 41.

7 On 17 August 2020, the appellant filed CA/SUM 87/2020 (“SUM 87”), seeking leave to admit further evidence from Dr Werner Kaminsky (“Dr Kaminsky”, the appellant’s expert) for the purpose of challenging the evidence of Dr Anthony Michael Glazer (“Dr Glazer”, the respondent’s expert) on his gap theory (“Gap Theory”) (see [36] below for relevance of the Gap Theory in this appeal). We dismissed SUM 87 on 16 September 2020.

8 As appears below, the technical background to SG 872 – including the physical properties of diamonds, how SG 872 seeks to enhance the quality of CVD diamonds grown and the measurement or evaluation of the improvement brought about by SG 872 – is highly complex. The following steps greatly assisted us in coming to grips with the difficult material:

(a) On 19 April 2021, we directed the parties to prepare a “Primer” (with a 50-page limit) setting out their points of agreement and divergence on topics including the common general knowledge (such as different methods of growing diamonds and types of defects in diamonds), the state of the art (including other patents) and the inventive concept of SG 872.

(b) We also convened a “Technology Tutorial” that was conducted on 2, 3 and 4 August 2021. Each party was allowed to nominate up to two presenters from among their expert witnesses to address these topics as well as provide an introduction to SG 872 and the Metripol system. ¹¹ The parties filed and exchanged Powerpoint slide decks prepared by their presenters seven days before the Technology Tutorial.

In the section that follows, we outline the salient aspects of the background to SG 872 as presented in the Primer and Technical Tutorial, which will set the context for our analysis of its validity.

9 Following the Technology Tutorial, CA 41 was heard over three half-day hearings on 20, 24 and 25 January 2022.

10 Subsequently, on 14 September 2022, we wrote to the parties to clarify whether each product claim in SG 872 covers a class of products as opposed to an individual product. The significance of this point, as well as of the parties’ responses on 21 September 2022, will become clear when we analyse whether SG 872 should be revoked in its entirety.

11 We first set out the technical background to SG 872. As we later elaborate, SG 872 discloses a new single crystal CVD diamond material, at least 0.5mm in thickness, which possesses one or more properties stated in the patent. One such property is low “optical birefringence” (henceforth referred to as “birefringence”). It is the respondent’s case that without the new CVD growth process taught within SG 872, the single crystal CVD diamond material manufactured would not display the properties defined in the product claims of SG 872. It is said that these properties are indicative of a high-quality diamond. ¹²

12 Diamonds are a form of solid C (meaning carbon) in which each C atom is bonded to four neighbouring C atoms to form a tetrahedral structure. Many of these tetrahedral structures come together to form a diamond lattice. A “single crystal” diamond, which is claimed in SG 872, is one in which the crystal lattice of the entire sample is continuous and unbroken. In contrast, a polycrystalline diamond consists of many single crystals. ¹³

13 Diamonds may form naturally within the Earth’s crust or be manufactured in a laboratory. ¹⁴ CVD is one of the main ways of manufacturing diamonds, the other of which involves applying high-pressure-high-temperature (“HPHT”) on a C source mixed with a catalyst. ¹⁵

14 In reality, no diamond (natural or man-made) is an array of equally spaced atoms which are purely C. Diamonds will contain impurities and defects. We make this point to provide context to what the respondent/patentee sought to achieve through the new growth processes taught in SG 872. As will become clear, the type and extent of defects in a diamond bear on its physical properties, such as its strength, ¹⁶ and hence its potential industrial use(s) and application(s). The respondent sought to produce CVD single crystal diamonds with certain qualities which were required for specific industrial applications. Allegedly, such diamonds could only be produced using the processes claimed in SG 872. What follows elaborates on the nature of defects or impurities arising in diamonds and the relationship between these imperfections and a diamond’s physical properties.

15 Impurities refer to non-C atoms bonded into the diamond’s lattice structure. Common impurities include nitrogen (N2) and boron. The concentration of nitrogen and boron is expressed in parts per million (“ppm”) or parts per billion (“ppb”). ¹⁷ Based on its purity, a diamond can be categorised into two main types: Type I and Type II. These can be further sub-divided into Types Ia, Ib, IIa and IIb. Type I diamonds contain relatively large amounts of nitrogen – up to 0.3% (5ppm to ~ 3000ppm). Most of the nitrogen atoms in Type Ia diamonds are found in clusters, but this is not the case in Type Ib diamonds. ¹⁸ Type II diamonds contain nitrogen below 5ppm. The only impurity in Type IIa diamonds is nitrogen, whereas impurities in Type IIb diamonds consist of nitrogen and boron. ¹⁹

16 When impurities (meaning non-C atoms) enter the diamond’s structure, a point defect is created in the lattice structure. ²⁰ Extended defects, on the other hand, are structural defects caused by disruptions to the diamond lattice that extend across the crystal. ²¹ One example of an extended defect is a stacking fault, which occurs where the relative positioning of two adjacent layers (or planes) of crystal structure does not conform with the rest of the crystal:

Another type of extended defect is a dislocation. Dislocations occur where there are atoms out of position in the crystal structure that, among other things, form an extra line of atoms within the structure (that is, an edge dislocation): ²²

17 Extended defects can be visualised using X-ray topography images where stacking faults appear as dark planes (Figure 3) and dislocations appear as dark lines (Figure 4). Thicker and relatively darker lines show bundles of dislocations: ²³

18 Dislocations cause strain, or distortion to the position of atoms, in the diamond structure. ²⁴ The strain extends across the full length of the dislocation, which typically runs all the way across the diamond. ²⁵ Strain weakens the chemical bonds, which then can be broken with lower energy. This reduces the strength of the diamond to withstand external pressure. ²⁶ According to Dr Christoph Erwin Nebel (“Dr Nebel”), the appellant’s principal expert, ²⁷ if there is strain, electrons between the atoms are no longer homogenously distributed, resulting in an electric field that may interact with light and increase birefringence in the diamond (a property we explore in some detail at [20]–[27] below). ²⁸

19 Dislocation density refers to the number of dislocations per square cm or mm of surface. Dislocations extend across the diamond like a line (hence, “line defects”) and terminate only on the surface: ²⁹

Dislocation termination points reveal themselves as etch pits. An optical evaluation of the number of etch pits across the surface area of the diamond will reveal its dislocation density:

20 Birefringence is a physical property of diamonds relevant to the key claims in SG 872. We shall therefore explore this concept in some detail.

21  Birefringence, stated generally, is related to how light interacts with a certain object. Light is made of waves of electric and magnetic fields. These waves oscillate in all directions perpendicular to the direction of the transmission of light. The distance travelled when an electromagnetic wave goes through one full oscillation cycle is called wavelength, which is denoted by λ. The wavelength of light determines its colour. ³⁰

22 While normal light consists of electric fields oscillating in all directions in the plane perpendicular to the direction of propagation, a polariser filter may be used to only allow light containing electric fields oscillating in a single direction to pass through. “Polarised light” therefore has only one direction of oscillation. ³¹

23 The atomic arrangement in a material affects the speed at which light travels through it. The speed of light in an optical material is determined by the material’s refractive index. The denser the material, the higher its refractive index and the slower that light travels through it. ³²

24 Where the internal structure of the crystalline material is perfect, in that it has no impurities or defects, the crystalline material is highly symmetrical. Such material is referred to as isotropic. In isotropic materials, the refractive index is the same in all directions. This means that light passes through an isotropic crystal at a single velocity.

25 But for anisotropic materials, the refractive index may vary in different directions. Although a diamond may theoretically be isotropic due to its highly symmetrical uniform lattice of C atoms, in reality, diamonds are anisotropic due to strain caused by dislocations. ³³ When polarised light is passed through a diamond with strain, the light splits into two relevant components which travel at different velocities. One component travels faster along the path in the material with the smallest refractive index (n”) and the other travels slower along the path in the material with the largest refractive index (n’). The difference between the smallest and largest available refractive index is called birefringence (Δn = |n’ – n’’|). ³⁴ In other words, strain in diamonds results in birefringence. ³⁵

26 The gap between the faster and slower components of light when they emerge out of the material is defined as the optical retardation (also referred to as “retardation” or “path difference”). Light of any wavelength which passes through a sample of an anisotropic material having birefringence Δn, where the sample has a thickness of “L”, will display retardation of L·Δn. Dr Nebel depicted birefringence and retardation as follows: ³⁶

27 For light of a particular wavelength (or λ), retardation can also be represented as phase shift “δ”: ³⁷

Dr Nebel represented the components of the above equation, using the following diagrams of light components that have split up when passing through an object: ³⁸

28 This appeal concerns SG 872, which was filed on 20 November 2003. In essence, the patent covers a new optical quality synthetic single crystal CVD diamond material and the method for its production. ³⁹ The patent contains both product and process claims. A product claim is one which “asserts exclusive rights over a new thing, such as new machines, items or articles of manufacture and composition of matter”. Although the patentee may describe only one use of his invention, he has the right to stop others from using it for other purposes (Susanna H S Leong, Intellectual Property Law of Singapore (Academy Publishing, 2013) (“Susanna Leong”) at para 18.002). We will henceforth refer to a diamond falling within any of the product claims in SG 872 as an “SG 872 Diamond”. On the other hand, “a process claim covers a new activity such as a process or method of manufacturing and logically, in a method or process claim, it is the process used and not the end result which must be new to justify patentability.” (Susanna Leong at para 18.003).

29 The pivotal product claim, which all subsequent claims refer back to, is Claim 1:

30 Single crystal CVD diamond material falling within Claim 1 has low strain and exhibits at least one of the optical properties defined in the eight limbs of Claim 1. ⁴⁰ Two of these limbs, limbs ii) and iii), assume significance in this dispute. Following the terminology used by the parties and the Judge, we will refer to these two limbs as “Claim 1ii)” and “Claim 1iii)” respectively. As the respondent pleads that Claims 1ii) and 1iii) were infringed (see Judgment at [417]), ⁴¹ we elaborate on these. Claims 1ii) and 1iii) assert a monopoly over single crystal CVD diamond material with low birefringence. Low birefringence is quantified in Claim 1ii) as a sample (a) remaining in the first order (δ does not exceed ); and (b) with the modulus of the sine of the phase shift (that is, |sin δ|) not exceeding 0.9. Low birefringence is quantified in Claim 1iii) as a sample (a) remaining in the first order (δ does not exceed ); and (b) with the maximum value of Δn[average] (that is, the average birefringence across the thickness of the sample) not exceeding 1.5 x 10-4.

31 We highlight four key points pertaining to Claims 1ii) and 1iii) which the parties do not dispute. First, the term “first order” for the purposes of SG 872 (and Claims 1ii) and 1iii) in particular) has been defined in a specific way. The parties’ experts, when explaining certain technical concepts (see above at [27] and below at [191]), ⁴² referred to each “order” as a multiple of 2π, with “first order” covering a range of values where δ does not exceed 2π (or again, expressed as an equation, δ ≤ 2π). However, SG 872 defines “first order” in a much more limited sense, namely, where δ does not exceed (or again, expressed as an equation, δ ≤ ) (the “SG 872 First Order”). ⁴³

32 Second, it is undisputed that SG 872 directs the person skilled in the art (“PSA”) to use a Deltascan (which has been renamed as the Metripol since 2001) ⁴⁴ or a “similar instrument with similar resolution” to determine the value of |sin δ| and Δn[average]. ⁴⁵ The Metripol is an optical microscope-based imaging system, ⁴⁶ which was developed by Dr Glazer (the respondent’s expert), Dr Kaminsky (the appellant’s expert), and Dr Morten Geday (“Dr Geday”) (the appellant’s witness) in or around 1995. The Metripol has a polariser that rotates in fixed multiples of different angles (for example, by 30o, 60o, 90o) (“Rotation Angles”). At each angle, polarised light passes through the specimen and is captured by a camera. The Metripol calculates the intensities of light received by the camera at different Rotation Angles, and thereafter computes |sin δ|, which is a function of δ.

33 It will be recalled that δ is the optical retardation of light of a particular wavelength that passes through a material, and is related to the birefringence of the material by the formula set out at [27] above. ⁴⁷ As appears from the three graphs below (in particular, the green arrows in graphs (b) and (c)), |sin δ| is the amplitude of a sinusoidal curve (meaning half the distance from the highest point of the curve to its lowest point). This sinusoidal curve is derived by plotting the intensity of polarised light that passes through the diamond specimen on the y-axis, against the polariser’s Rotation Angle on the x-axis. ⁴⁸ Depending on whether and the extent to which the intensity of light varies when the polariser is angled differently, |sin δ| will assume a different value: ⁴⁹

34 Third, after computing |sin δ|, the Metripol produces colour-coded images of the material, where the different colours represent different |sin δ| values at any place within the image (the “Metripol |sin δ| Map”). ⁵⁰ The Metripol is capable of refining the |sin δ| value at each pixel position in the Metripol |sin δ| Map. ⁵¹ An illustration of the Metripol |sin δ| Map can be found in the following diagram, taken from the respondent’s Technology Tutorial slides:

The same Metripol |sin δ| Map can also be represented in greyscale. The patent specification of SG 872 states that the spatial variation of |sin δ| can be appreciated from these images. ⁵² The patent specification also states that for each sample, sets of |sin δ| images are to be recorded for analysis. ⁵³

35 Fourth, it is agreed between the parties that the Metripol data on its own does not tell the PSA whether the δ value of a diamond falls within the SG 872 First Order (the “Metripol Uncertainty Problem”). ⁵⁴ The Metripol does not calculate δ. As mentioned, it generates the value of |sin δ|. ⁵⁵ However, each |sin δ| value corresponds to many δ values, and only one of these δ values lies within the SG 872 First Order. ⁵⁶ From the |sin δ| value alone, the PSA cannot derive a corresponding δ value and will not know whether the δ value of a diamond is within or outside the SG 872 First Order. This point can be illustrated in Figure 13 below, where δ1 is the value that lies within the SG 872 First Order: ⁵⁷

If the Metripol shows that the |sin δ| value of the diamond is 0.9, the corresponding δ value can be 1.12, 2.02, 4.26, 5.16, or any other higher value not reflected in Figure 13 above. ⁵⁸ δ will only be within the SG 872 First Order if it has a value of 1.12, as that is the only value that does not exceed (see above at [31]). The rest of the values lie outside the SG 872 First Order. From this range of possible δ values, the PSA relying solely on the Metripol reading cannot determine the δ value of the diamond, and accordingly, cannot ascertain whether δ is within the SG 872 First Order.

36 In this appeal, as they did in the proceedings below, the parties diverge on the issue of whether the PSA knew of solutions to overcome the Metripol Uncertainty Problem at the relevant time. The thrust of the appellant’s contention is that the PSA, faced with the Metripol Uncertainty Problem and with no knowledge of any workable solution at the relevant time, would not be able to determine whether the δ value of the diamond was within the SG 872 First Order and hence within the scope of the asserted monopoly. For this reason, the appellant contends that SG 872 is insufficient. ⁵⁹ In turn, the respondent’s case is that the PSA would have no difficulty ascertaining that the δ value of the diamond was within the SG 872 First Order by using various methods, such as the Gap Theory proposed by Dr Glazer. ⁶⁰ We will deal with this issue in our analysis later.

37 We now turn to Claim 62, the main process claim in SG 872 to which all other process claims in SG 872 refer. Claim 62 specifies a method of producing low-strain single crystal CVD diamond material that exhibits optical properties defined in the product claims in SG 872. Claim 62 states as follows:

38 Certain terms relating to the growth process, which are referred to subsequently, call for further explanation. The “source gas” in the CVD chamber comprises several gases, including a “C” source which is typically methane (CH4) and a source of atomic hydrogen which is typically hydrogen (H2). The parties agree that other gases, such as an inert gas (like argon) and a dopant gas (like nitrogen, boron or phosphorous), a source of impurities which is used to affect the electrical or optical properties of a diamond, are also used depending on the desired characteristics of the CVD diamond. ⁶¹ Each input gas is controlled by a mass flow controller (“MFC”). The flow of gases across MFCs is measured as cubic centimetres of gas flowing through the MFC per minute (expressed as standard cubic centimetres per minute or “sccm”). The concentration of each gas is represented as a percentage, ppm or ppb. ⁶² As for the “plasma etch” performed on the substrate prior to the commencement of the CVD process, this involves “exposing the substrate to a plasma formed by hydrogen (H2) and/or oxygen (O2) at high temperature in a CVD chamber.” ⁶³ The specification of SG 872 states that such in situ plasma etching minimises the surface damage of the substrate. ⁶⁴ We note, however, that the respondent disputes ⁶⁵ whether the use of a plasma etch to achieve this effect is common general knowledge to a PSA (we will explain the concepts of common general knowledge and the PSA at [63]–[75] below).

39 The respondent claims that the production of low-strain single crystal CVD diamond material disclosed in Claims 1 to 61 and 72 to 78 was not possible prior to the discovery of the process in Claim 62. ⁶⁶ The respondent argues that the growth process in Claim 62, specifically, the addition of 300ppb to 5ppm nitrogen to the synthesis atmosphere (the “Claim 62 Nitrogen Range”), is novel because it runs contrary to previous thinking that adding nitrogen to the synthesis atmosphere would have a deleterious effect on the quality of the diamond produced; nitrogen was regarded as an impurity. ⁶⁷ As the Judge noted, the common general knowledge at the material time was that the addition of nitrogen would increase birefringence. The Claim 62 Nitrogen Range is therefore the inventive concept asserted in Claim 62 (see Judgment at [253]). We agree. According to the specification of SG 872, the Claim 62 Nitrogen Range is not too high because it accomplishes the aim of “prevent[ing] or reduc[ing] local strain generating defects whilst being low enough to prevent or reduce deleterious absorptions and crystal quality degradation.” ⁶⁸ Nor is the range too low, because, according to SG 872, “material grown under conditions with essentially no nitrogen, or less than 300ppb nitrogen has a comparatively higher level of local strain generating defects”. ⁶⁹ Dr Philippe Bergonzo (“Dr Bergonzo”), one of the respondent’s experts, depicted the benefits of operating within the Claim 62 Nitrogen Range as follows (see the curve in black): ⁷⁰

40 As against this, the appellant regards the purported benefits of using the Claim 62 Nitrogen Range as “illusory” and “false”. ⁷¹ It questions why, in the 17 or so years since SG 872, not a single paper has been published discussing or evidencing this discovery. However, as we shall explain, even assuming that the purported benefits of the Claim 62 Nitrogen Range are scientifically true, there are other issues undermining the validity of the patent.

41 Against the appellant’s arguments to the contrary, the Judge held that Claims 1 and 62 of SG 872 were valid. For brevity, we will only summarise the Judge’s reasons for rejecting the appellant’s contentions on insufficiency, and only in so far as they are relevant to the determination of this appeal.

42 The Judge observed that the appellant had relied on s 25(5) of the Patents Act (Cap 221, 2005 Rev Ed) (“Patents Act (2005 Rev Ed)”), ⁷² which provided that claims shall be “clear and concise” in s 25(5)(b). Citing this court’s decision in First Currency Choice Pte Ltd v Main-Line Corporate Holdings Ltd and another appeal [2008] 1 SLR(R) 335 (“First Currency Choice”) at [72], the Judge held that the requirement of clarity was not a ground for revocation under the Patents Act (2005 Rev Ed). She emphasised that what was important was whether the invention has been disclosed sufficiently for a PSA to perform it (Judgment at [191]–[192]), and proceeded to consider the appellant’s contentions on why Claim 1 was insufficient. One of these contentions was that Claim 1 of SG 872 was insufficient because the Metripol could not identify whether δ was within the SG 872 First Order (Judgment at [193]–[196]). She eventually rejected that contention because she accepted Dr Glazer’s evidence that the PSA would know how to determine whether δ was within the SG 872 First Order using the Gap Theory (Judgment at [200]–[206]).

43 The Judge also found that Claim 62 had sufficiently disclosed the claimed invention. The appellant argued that the PSA would not know how to calibrate the other growth conditions to the chosen nitrogen concentration to grow an SG 872 Diamond. ⁷³ The Judge rejected this submission given Dr Bergonzo’s evidence that the missing details would be known to a PSA with a working knowledge of the research and development of CVD diamond synthesis (Judgment at [285]).

44 Another of the appellant’s submissions was that the insufficiency of Claim 62 was demonstrated by how the single crystal CVD diamond material grown in Examples 1 and 14 of SG 872 as well as Examples 4 and 6 of SG 508 had different qualities, even though these examples disclosed a growth process where the synthesis atmosphere had 300ppb to 5ppm nitrogen. The Judge rejected this submission, noting that the respondent had explained that the difference in other parameters of the growth process (such as gas flow and methane concentration in the synthesis atmosphere) between SG 508 and SG 872 resulted in a diamond with different qualities being grown. She also observed that these other parameters did not, in any event, constitute the inventive concept of SG 872 (Judgment at [286]–[287]).

45 Given her finding that Claims 1 and 62 of SG 872 were valid, the Judge did not revoke SG 872 and proceeded to find that both Claims 1 and 62 had been infringed (Judgment at [416]). In particular, she found that the Samples infringed Claim 1 on the basis that they fulfilled limbs ii) and iii) of Claim 1 (Judgment at [431]–[443]). The Judge therefore made the following orders, amongst others (Judgment at [478(a)]–[478(c)]):

46 The appellant’s attack on the Judge’s decision cuts across many areas of patent law, such as novelty, inventive step, and sufficiency. Much reliance has also been placed on concepts recognised in English law which have not been recognised locally, such as “Biogen insufficiency”. For the purposes of the present appeal, we only need to focus on two parts of the appellant’s case, both of which concern the non-fulfilment of the sufficiency requirement and are determinative of this appeal.

47 The first relates to the insufficiency of Claim 62 on the basis that the patent specification fails to teach the “novel” growth process clearly and completely enough for it to be performed by a PSA. In particular, the appellant faults Claim 62 for not disclosing “what ranges of temperature, gas flow rate or methane concentration will give diamond material within claim 1iii) or any other product claims for that matter.” ⁷⁴ We shall refer to these variables, and any other variables in the patented CVD growth process (other than the concentration of nitrogen), as the “Other Growth Conditions”. The appellant argues that it is not enough to point to the examples in SG 872 because these “do not support a claim of the breadth of claim 62.” ⁷⁵ As a result, the PSA is “left with a long and extensive research project to find out what ranges of these other process parameters are required to obtain claim 1iii) or 1ii) diamond material” and that, therefore, SG 872, is insufficient. ⁷⁶

48 The appellant contends that the respondent’s own arguments under novelty establish insufficiency. Relevantly, the respondent argues that Examples 4 and 6 of SG 508, which teach the use of 2.5ppm and 3.8ppm of nitrogen in the synthesis gas mixture respectively, do not anticipate SG 872 because there are “a lot of differences” in terms of gas flow, temperature and methane concentration between those examples and Claim 62. ⁷⁷ The respondent asserts on this basis that Examples 4 and 6 in SG 508 do not anticipate Claim 62 because following those examples will not inevitably lead to the production of an SG 872 Diamond. ⁷⁸ But if this is correct, the appellant points out that it must mean “there are other ranges of essential parameters for the process in SG 872 to ‘work’” and that their omission from Claim 62 or the specification of SG 872 means that the invention is insufficiently disclosed. ⁷⁹

49 Before proceeding further, we note the respondent’s submission that pursuant to O 57 r 9A(5B) of the Rules of Court (2014 Rev Ed), the appellant cannot impugn the clarity and completeness of SG 872 as this ground of insufficiency is not particularised in the Appellant’s Case (the “O 57 Objection”). ⁸⁰ Notwithstanding the respondent’s contentions, we are inclined to consider the appellant’s arguments on this issue (see Oxley Consortium Pte Ltd v Geetex Enterprises Singapore (Ptd) Ltd and another matter [2021] 2 SLR 782 at [45]; Global Yellow Pages Ltd v Promedia Directories Pte Ltd and another matter [2017] 2 SLR 185 at [22]). Although the Appellant’s Case focused on another type of insufficiency that we will turn to next, it foreshadowed the possibility of other insufficiency arguments arising “depending on how the Respondent trie[d] to avoid invalidity.” ⁸¹ And in its Reply, the appellant developed its submissions on this point in direct response to the Respondent’s Case. The respondent also did not press the O 57 Objection in oral submissions and instead dealt substantively with the appellant’s arguments in question. ⁸² There is therefore no procedural impropriety afoot and/or prejudice to the respondent that precludes the appellant from relying on this ground of insufficiency.

50 The second part of the appellant’s case which we will focus on concerns the insufficiency of Claim 1 arising from ambiguity or uncertainty. The appellant argues that the Judge erred in failing to consider this type of insufficiency, which arises where the PSA does not know whether he is inside or outside the claim. ⁸³ On the facts, it argues that the Claim 1 and SG 872 are insufficient because the PSA cannot tell whether the δ value of a particular single crystal CVD diamond was within the SG 872 First Order and hence within the scope of the asserted monopoly.

51 The respondent supports the Judge’s findings that SG 872 is not anticipated, obvious or insufficiently disclosed.

52 Its case is that SG 872 claims a new single crystal CVD diamond material with exceptionally low strain and a new method of producing said diamond material. ⁸⁴ By way of a letter dated 21 September 2022, which was sent in response to our query (see above at [10]), the respondent accepts that each product claim in SG 872 covers a class of products. The distinction between a single product and a class of products is relevant to the issue of insufficiency. If the claim is to a single product, then it is sufficient if it enables the making of that one product. If, on the other hand, the claim is to a class of products, that class of products is sufficiently enabled only if the skilled man can work the invention in respect of all members of the class (Regeneron Pharmaceuticals Inc v Kymab Ltd and another [2016] EWHC 87 (Pat) at [209]). We return to these principles at [108]–[112] and [184] below.

53 In response to the appellant’s submission that the patent is insufficient because it fails to teach the Claim 62 growth process clearly and completely enough, the respondent argues that the correct test is whether the patent’s specification as a whole discloses the invention sufficiently. ⁸⁵ It argues that the specification of SG 872 (in particular Example 1 read with Example 9) gives full disclosure of the Other Growth Conditions, including temperature, pressure and gas flow rates. It stresses that the burden is on the appellant to show that the invention is unworkable by the PSA who is “trying to give practical meaning to the patent specification.” ⁸⁶

54 Next, as to the appellant’s submission that the Judge erred in failing to consider a further type of insufficiency brought about by ambiguity or uncertainty, the respondent submits that the Judge rejected the appellant’s argument on insufficiency arising from “ambiguity”, on the basis that in First Currency Choice we held that lack of clarity under s 25(5)(b) of the Patents Act (2005 Rev Ed) is not a ground for revocation. ⁸⁷ It further submits that the appellant has not explained how the Judge erred in following First Currency Choice, or why the court should depart from the position at law that lack of clarity is not a basis for revocation. ⁸⁸ On the facts, the respondent submits that the PSA can determine that δ is within the SG 872 First Order by using four different methods. ⁸⁹

55 In light of the foregoing, the issues we shall address in this decision are as follows:

56 To set the context for the analysis that follows, we first touch on some foundational principles that guide us, beginning with the objectives of the patent regime and how these are advanced. Where relevant, we also explain principles of patent law which are engaged in the reasoning of this judgment, or which provide context to our analysis.

58 To ensure that patents effectively incentivise innovation in furtherance of the first aim, the patent regime only grants monopolies over deserving inventions. An invention must be novel, contain an inventive step and be capable of industrial application, before it will be patentable (ss 13–16 of the Patents Act (2005 Rev Ed)). If any one of these requirements is not met, the patent may be revoked (s 80(1)(a) of the Patents Act (2005 Rev Ed)). We briefly introduce the concepts of novelty and inventive step as the parties have made submissions on them (although, as foreshadowed at [46] above, we will not analyse the parties’ submissions on these requirements in this judgment).

59 Novelty requires the invention to be new, in that it does not form part of the state of the art (s 14(1) of the Patents Act (2005 Rev Ed)). If directions forming part of the state of the art (meaning a piece of prior art) lead inevitably to something that would infringe the patent, the invention lacks novelty and the patent can be revoked (Mühlbauer AG v Manufacturing Integration Technology Ltd [2010] 2 SLR 724 (“Mühlbauer”) at [17]). The state of the art comprises all matter (whether a product, a process, information about either, or anything else) which has at any time before the priority date of that invention been made available to the public (whether in Singapore or elsewhere) by written or oral description, by use or in any other way (s 14(2) of the Patents Act (2005 Rev Ed)). By default, the “priority date” of an invention is the filing date of the patent application (s 17(1) of the Patents Act (2005 Rev Ed)). Under certain conditions, a patentee can depart from this default position by claiming that the priority date of the invention takes reference from the date of filing of an earlier patent application or applications (see s 17(2) of the Patents Act (2005 Rev Ed)), which has the effect of limiting the state of the art to what it was at that earlier date. On the other hand, a later priority date may widen the pool of material which may anticipate the invention.

61 Separately, the second aim of the patent regime, namely knowledge dissemination, is advanced by the “sufficiency” or “enabling disclosure” requirement, which provides that the patent specification must disclose the invention in a clear and complete manner for it to be performed by a PSA. This requirement is statutorily embodied in ss 25(4) and 80(1)(c) of the Patents Act (2005 Rev Ed), with the latter providing for the revocation of the patent if the patent specification is insufficient.

63 Another point of commonality is that the court, when undertaking the novelty, obviousness and sufficiency inquiries, as well as in construing the claims, dons the mantle of the PSA, that is, someone in the field of technology relevant to the invention in question and who possesses, amongst other characteristics, common general knowledge in the art (Mühlbauer at [18] (novelty); ASM Technology Singapore Pte Ltd v Towa Corp [2018] 1 SLR 211 at [78] (obviousness); First Currency Choice at [60]–[61] (sufficiency); Lee Tat Cheng v Maka GPS Technologies Pte Ltd [2018] 1 SLR 856 (“Lee Tat Cheng (CA)”) at [41] (claim construction)). Common general knowledge is information which, at the relevant date, is common knowledge in the art to which the alleged invention relates, so as to be known to duly qualified persons engaged in that art (British Thomson-Houston Co Ltd v Stonebridge Electrical Co Ltd (1916) 33 RPC 166 at 171; Terrell at para 8-61).

65 Further, the precise assumptions applicable to the PSA are not identical in all areas of patent law. For instance, in matters of claim construction and sufficiency, the PSA is assumed to have the patent specification in his hands whereas when considering the issue of obviousness, the PSA is deemed only to be considering the prior art without the patentee’s invention in front of him (Terrell at para 8-19).

66 The central issues concerned in our decision relate to claim construction and insufficiency. To reiterate, the former identifies the invention that is the subject of the claims, whilst the latter entails a consideration of whether the patent specification sufficiently enables a PSA to perform that invention. It is in this context that we now turn to examine the characteristics of the PSA relevant to our reasoning in the present judgment, and the common general knowledge he (or, the notional team comprising the PSA) would possess.

67 The PSA, apart from possessing common general knowledge in the art, also has a practical interest in the subject matter of the patent and is likely to act on the directions given in it with the desire to make the directions in the patent work. He is a reasonably intelligent but unimaginative workman or technician who has the skill to make routine workshop developments, but not to exercise inventive ingenuity or think laterally (Ng Kok Cheng v Chua Say Tiong [2001] 2 SLR(R) 326 (“Ng Kok Cheng”) at [21]; First Currency Choice at [28]; Ng-Loy at para 30.1.12).

68 The PSA may be an individual person or a notional team of people. The need for a notional team may arise where it is clear that the patent specification engages more than one set of skills which in the real world would be possessed by more than one person. This may be the case where the art is one that concerns a highly developed technology. In such circumstances, the specification can be said to be addressed to a team, with each member contributing his or her individual skill which would in turn be employed in combination in interpreting and carrying into effect the instructions in the patent (Terrell at paras 8-35–8-36; The General Tire & Rubber Company v The Firestone Tyre and Rubber Company Limited and others [1972] RPC 457 (“General Tire”) at 483; Schlumberger Holdings Ltd v Electromagnetic Geoservices AS [2010] EWCA Civ 819 at [33]; Halliburton Energy Services, Inc v Smith International (North Sea) Ltd [2006] RPC 2 at 46; see also Institut Pasteur and another v Genelabs Diagnostics Pte Ltd and another [2000] SGHC 53 (“Genelabs (HC)”) at [194]). For the avoidance of doubt, the formation of such a notional team does not mean that the common general knowledge of the PSA is only that which is common to persons with these different backgrounds (Inhale Therapeutic Systems Inc v Quadrant Healthcare Plc [2001] All ER (D) 211 (Jun) at [39]–[42]; First Currency Choice at [31]).

69 As noted at [65] above, when considering the issues of claim construction and sufficiency, the PSA is assumed to have the patent specification in his hands and have the same attributes for both inquiries (see Terrell at para 8-19). The PSA, for the purposes of the insufficiency inquiry, is “trying to carry out the invention and achieve success” (Zipher Ltd v Markem Systems Ltd and another [2008] EWHC 1379 (Pat) (“Zipher”) at [366]). It is through the eyes of the PSA that the patent will fall to be interpreted, and the PSA must know how to perform the invention upon reading the specification in light of his common general knowledge.

70 Moving now to the PSA in the present case, the Judge found that the PSA, for the purpose of claim construction, would be a notional team of persons working in the field of growing CVD diamonds, with expertise in diamonds (including natural, HPHT and CVD diamonds) and the sciences (including applied physics, optical engineering and material sciences) (Judgment at [14]):

71 The parties have not challenged the Judge’s finding in that passage of the composition and qualifications of the notional team of persons. Further, as already mentioned at [69] above, the PSA for the purposes of claim construction and sufficiency will be the same. However, before us, the appellant seeks to impute the PSA with the specific purpose of growing single crystal CVD diamond material for use in the most demanding optical applications – “etalons and anvils”. ⁹⁰ The respondent rejects this imputation. ⁹¹ Although this dispute between the parties mainly arises in the course of their submissions on novelty and obviousness, a proper identification of the PSA’s practical interest is also important in the context of claim construction and sufficiency.

72 As earlier stated, the PSA is trying to carry out the invention (see [69] above) and has a practical interest in the “subject matter of the patent” (see [67] above). What the subject matter of the patent is should be determined by reference to the patent specification. Having regard to the specification of SG 872, we are satisfied that the PSA’s interest would not be limited to producing etalons and anvils. The patent specification describes the invention in SG 872 in more general terms – a single crystal CVD diamond material which possesses certain desirable characteristics, and which can be used in connection with a wide range of optical applications which “include but are not limited to” optical windows, laser windows, optical reflectors, optical refractors and lenses, diffractive optical elements, etalons, ornamental use and anvils [emphasis added]. ⁹² Accordingly, the PSA’s practical interest lies in using the growth process taught in SG 872 to grow low-strain diamonds for a range of optical applications.

73 As already noted, the PSA is imputed with common general knowledge in the art. He draws upon such knowledge to understand a patent and in his attempts to carry it into effect. As mentioned at [63] above, common general knowledge is information which, at the relevant date, is common knowledge in the art to which the alleged invention relates, so as to be known to duly qualified persons engaged in that art. The relevant art to which the alleged invention is to be gathered from the patent specification itself (First Currency Choice at [30]).

74 Common general knowledge is ordinarily established, where not agreed, by expert evidence which is usually supported by reference to textbooks or other reference works which the PSA would be expected to have access to and acquire his information from. The publication at or before the relevant date of such documents may be prima facie evidence tending to show that the statements contained in them were part of the common general knowledge, but that is far from complete proof as those statements may well have been discredited, forgotten or ignored (Terrell at paras 8-75–8-77). It is also not sufficient just to point out that it was said in a scientific paper that has been well circulated. A particular disclosure does not become common general knowledge merely because it is widely read, and still less because it is widely circulated. To prove that a particular disclosure in scientific paper has become common general knowledge, it must be shown that it is generally known and generally regarded as a good basis for further action by the bulk of those who are engaged in the particular art to which the disclosure relates (General Tire at 480–481).

75 In the present case, as identified by the Judge, the art relates to the growth of CVD diamonds (Judgment at [14]). In our view, this includes methods of measuring the physical properties of the CVD diamonds grown. Based on the Primer, ⁹³ the parties are agreed that the information set out at [11]–[27], [32]–[35] and [38] above constituted common general knowledge in the art of growing CVD diamonds at the relevant time. There are further points of agreement on what was part of the common general knowledge and they will be mentioned, where relevant, when we apply the principles of sufficiency to the facts of this case. But before going into the issue of sufficiency, it is pertinent for us to first consider how the claims, in particular the product claims, ought to be construed. It is to this issue that we now turn.

76 The question here is whether the product claims in SG 872 cover a single product or a class of products. As we shall see, this affects what, in law, must be enabled by the specification of SG 872 (see [108]–[112] below), and whether the claims in SG 872 are in fact insufficient (see, eg, [184]–[185] below).

77 Whether the patent claims a single product or a range of products is a question of construction of the claim(s) in the patent (Regeneron Pharmaceuticals Inc v Kymab Ltd [2021] 1 All ER 475 (“Regeneron (SC)”) at [3]. Before setting out the principles on claim construction in detail, we touch on the relevance of the priority date(s) of the product claims in SG 872 to their interpretation.

78 In Lee Tat Cheng (CA) at [53] and [55], we held that the relevant date for claim construction is the date of the patent application (meaning its filing date) (see also Lee Tat Cheng (HC) at [49]). However, it does not appear that the patentee there claimed that its invention took priority from an earlier filing. If the patentee there had claimed priority, a conundrum noted by the authors of Terrell would have arisen. That conundrum arises from the fact that the English cases are divided over whether the relevant date for patent construction is the priority date or filing date of the patent application, or the publication date of the patent (see Terrell at paras 9-08–9-014). At present, the respondent does claim priority from GB Patent Application No 0227261.5 (“GB 261”), which was filed on 21 November 2002. The parties agree that Claim 1ii) takes priority from 21 November 2002 but disagree on whether Claims 1iii) and 62 enjoy the same priority. ⁹⁴ This specific complication did not present in Lee Tat Cheng (CA). However, nothing in this case turns on which of the three dates should be adopted in law and the parties do not submit otherwise. We therefore prefer to leave this issue for an appropriate case and proceed on the basis that the relevant date for patent construction is the filing date of SG 872 (that is, 20 November 2003). Consequently, any common general knowledge which may be relevant to patent construction must be shown to exist by this date. In addition, whether the asserted priority date is granted only assumes significance in this case in relation to the issues of novelty and obviousness. However, as stated at [46], we need not reach or address the latter issues in this judgment.

79 Turning to the substantive principles on claim construction, in Lee Tat Cheng (CA), we reaffirmed the correctness of construing a patent’s claims purposively (at [41] and [55]). This entails, among other things, viewing the claims through the lens of the PSA (at [41]):

80 The patent “specification”, referred to in the passage above, comprises the description of the invention, drawings (if any) and the claims (Halsbury’s Laws of Singapore vol 13(3) (LexisNexis, 2020 reissue) (“Halsbury’s Singapore IP”) at para 160.321). Examples illustrating how to carry out the invention also form part of the patent’s specification (see rr 19(3) and 19(5)(e) of the Patents Rules (1996 Rev Ed)). However, the claims serve a different purpose from the rest of the patent’s specification, as explained by Floyd LJ in Adaptive Spectrum & Signal Alignment Inc v British Telecommunications PLC [2014] EWCA Civ 1462 at [45]:

81 The parties initially appear to have approached this appeal on the basis that each product claim is a claim to a single product – a new CVD diamond material. For instance, the Appellant’s Case states that “Claim 1 is a product claim, so the eight alternates in Claim 1 disclose the same physical thing – a particular CVD diamond material, characterised in eight different ways”. ⁹⁵ The Respondent’s Case states that “SG 872 claims a new diamond material” [emphasis in original omitted; emphasis added in italics]. ⁹⁶ Both parties took similar positions in their written closing submissions in the second tranche of the trial. ⁹⁷

82 We wrote to the parties on 14 September 2022 seeking clarification on this issue. The appellant confirmed its view that SG 872 teaches the PSA a new method to “grow one product, i.e. a CVD single crystal diamond material having one or more of the specified parameters.” It argued that the “different ranges and combination of properties in each product claims [were] therefore variations of the same product grown from the one process described in SG 872” [emphasis added]. ⁹⁸ In contrast, the respondent took the view that each product claim could be said to cover a class of products. In particular, the respondent noted that “given that the product claims of SG 872 claim, inter alia, a range of values (or depend on a claim which does), these would cover a class of products meeting the values within that range as opposed to an individual product.” ⁹⁹

83 We agree with the respondent. Properly construed, each claim asserts a monopoly over a class of single crystal CVD diamond materials.

84 We turn first to Claim 1, which, as noted above, is the claim that all the other product claims refer back to. In our judgment, Claim 1 can be infringed by various types of single crystal CVD diamond materials, each with a different combination of the physical properties defined in the limbs of Claim 1. That the diamond materials falling within Claim 1 may possess different combinations of physical properties is clear from the words in the chapeau of Claim 1: “A CVD single crystal diamond material which shows at least one of the following characteristics” [emphasis added]. Our reading of the plain language of Claim 1 is fortified by the description of the invention in the specification of SG 872. The relevant portion of the description reads as follows: ¹⁰⁰

The “above properties” referred to in the passage include optical homogeneity, effective refractive index, birefringence, optical absorption, optical scatter, laser damage threshold, thermal conductivity, parallelism, flatness and mechanical design strength. ¹⁰¹ Thus, the description indicates that the invention covers a range of single crystal CVD diamonds possessing different combinations of physical properties.

85 Further, as noted in Lee Tat Cheng (CA) at [41(c)], the language of the claim must be construed through the eyes of a PSA. In this regard, we found the evidence of Dr Mark Edward Newton (“Dr Newton”), the respondent’s expert witness, to be instructive. As the respondent alluded to in its letter of 21 September 2022, ¹⁰² Dr Newton testified that the various limbs in Claim 1 cover optical properties which “may be related but remain different” [emphasis added in bold italics]. ¹⁰³ He added that “[m]any are not directly derivable one from another”. ¹⁰⁴ It is not clear if these observations also apply to Claims 1ii) and 1iii), which both relate to birefringence. Dr Newton’s evidence nevertheless reinforces our understanding that diamonds which fulfil different combinations of limbs in Claim 1 are in fact different diamonds. Our conclusion would be different if the measurements in each limb of Claim 1 were different ways of quantifying the same property.

86 Although Dr Nebel’s first report dated 13 May 2019 (“Dr Nebel’s 1st Report”) stated that a diamond satisfying one limb of Claim 1 will also satisfy all remaining limbs, and that the properties mentioned in Claim 1 are “merely ... different measurement techniques for a common aspect of the diamond” [emphasis added in bold italics], we reject this. ¹⁰⁵ For one, he offered no credible evidence in his Reply Report dated 26 June 2019 or oral testimony to support this assertion. In his reply report, Dr Nebel asserted that measurements like “dislocation density, Raman peak width, X-ray rocking curve width and birefringence” measure “strain in diamond ... and any change in strain in a diamond reflects a proportional change in these measurement parameters.” ¹⁰⁶ But Dr Nebel did not explain nor has the appellant otherwise shown that the optical properties or measurements described in each limb of Claim 1, including optical homogeneity, free spectral range, contrast ratio, insertion loss and variation in refractive index, merely measure a common property or will necessarily be present if one limb of Claim 1 is fulfilled. Crucially, Dr Nebel’s evidence does not square with the specification of SG 872. The “Summary of the Invention” states clearly that the CVD single crystal diamond material invented “may not be endowed with all of the above properties in all cases”, but should show “at least one, preferably at least two, more preferably at least three, and even more preferably at least four” characteristics which are listed. The listed characteristics in the Summary of the Invention correspond to properties defined under the limbs in Claim 1, and include optical homogeneity (see Claim 1i)), birefringence (see Claims 1ii) and 1iii)), effective refractive index (see Claim 1iv)), free spectral range (“FSR”) (see Claim 1v)) and contrast ratio (see Claim 1vi)). ¹⁰⁷ Moreover, in its submissions below, the appellant did not appear to dispute the correctness of the portion of Dr Newton’s evidence that we have accepted at [85] above. ¹⁰⁸

87 Turning now to the subsequent product claims, these likewise cover a range of diamonds. These claims may be placed into three categories based on their phraseology, all of which incorporate Claim 1. The first category of claims incorporates all preceding claims, including Claim 1. An example is Claim 6, which states: “A CVD single crystal diamond material according to any one of the preceding claims, which has a value of effective refractive index of 2.3964 to within an accuracy of +/-0.001” [emphasis added]. ¹⁰⁹ The second category of claims expressly incorporates a preceding claim, the latter of which incorporates Claim 1. An example is Claim 7, which states: “A CVD single crystal diamond material according to claim 6, which has a value of effective refractive index of 2.39695 to within an accuracy of +/-0.0005.” By referring back to Claim 6, Claim 7 likewise incorporates Claim 1. The third category consists only of Claim 72. It reads: “A CVD single crystal diamond material produced by a method according to any one of claims 62 to 71.” Claims 62 to 71 disclose a process that purportedly enables a PSA to produce a CVD diamond in one or more of Claims 1 to 61. By referencing all of these process claims, Claim 72 includes the range of diamonds defined under Claim 1.

88 Once a subsequent product claim incorporates Claim 1, it asserts a monopoly over a range of products. This is because any diamond within the class of products in Claim 1, which also fulfils the additional parameter expressed in the subsequent claim, will fall within that subsequent claim. It is irrelevant that the additional parameter in the subsequent claim is a specific or single value of a particular physical property (for instance, Claim 6, in so far as the additional parameter, “effective refractive index of 2.3964 within an accuracy of +/-0.001”, expresses a single value of an effective refractive index) or a binary condition that is or is not satisfied (for instance, Claim 50, which has an additional requirement that the CVD diamond be formed into a polished gemstone). For reference, these claims state as follows:

In these instances, the PSA would be satisfied that the patentee contemplated multiple diamonds in the Claim 1 range fulfilling the additional parameter in Claims 6 and 50. This is because the claim incorporates the entire range of diamonds in Claim 1 and there is nothing in the language of Claims 6 and 50, or for that matter in any other similar claim, to justify limiting the monopoly to a single product. We approach this on the basis that the respondent should be afforded the full extent of the monopoly that is supported by the language it has adopted.

89 It is even more the case that where the additional parameter in the subsequent claim is itself expressed as a range of values, the claim covers a range of products. One example of this is Claim 4, which states: “A CVD single crystal diamond material according to any one of the preceding claims, wherein the modulus of the sine of the phase shift, |sin δ|, for at least 98% of the analysed area remains in first order and does not exceed 0.4” [emphasis added in bold italics]. The phrase “does not exceed 0.4” indicates that Claim 4 monopolises a class of CVD single crystal diamond materials which have different |sin δ| values falling within the range of less than or equal to 0.4 (and which fulfil any preceding claim). By way of example, a CVD single crystal diamond material for which |sin δ| is equal to 0.2 as well as a CVD single crystal diamond material for which |sin δ| is equal to 0.3 could fall within the scope of Claim 4, subject to the diamond material also satisfying a preceding claim.

90 We find support for our construction of the product claims in the court’s analysis in Anan Kasei Co. Ltd and another company v Neo Chemicals and Oxides Ltd (formerly Molycorp Chemicals and Oxides (Europe) Ltd) and another company [2019] EWCA Civ 1646 (“Anan”). The patent contained a product claim for ceric oxide, which stated as follows: “A ceric oxide consisting essentially of a ceric oxide, and wherein said ceric oxide has a specific surface area of not smaller than 30.0 m2/g when subjected to calcination at 900˚C for 5 hours.” (at [8]). One issue which arose was whether a claim limited by reference to a desirable physical characteristic, namely high specific surface area, and specifying that it remained the same after being subjected to a high temperature, insufficiently described the invention and was invalid. In analysing this issue, Floyd LJ (with whom Lewison and Peter Jackson LJJ agreed) noted that the claim covered a class of products (at [53]):

91 Regeneron (SC) is also illuminating. The patent in the suit contained a product claim which read as follows:

Lord Briggs summarised the claim in these terms (at [15]):

92 Relevantly, the appeal in Regeneron (SC) proceeded on the basis that the claim covered a range of transgenic mice, which differed based on the amount of human antibody genes implanted into the genome of the mouse (see [7], [16]–[17] and [81]). However, it bears highlighting that this issue of claim construction was resolved by the courts below and was not an issue in the appeal before the UK Supreme Court (“UKSC”).

93 In the present case, by defining parameters using ranges of values or incorporating claims which do so, each product claim in substance claims or asserts a monopoly over a range of single crystal CVD diamonds, each with a different combination of physical properties.

94 Before leaving this issue, we note that while Dr Newton’s evidence assisted us in construing the product claims, the expert evidence is not entirely clear as to whether each product claim covers a class of products or not. Be that as it may, claim construction is ultimately a task for the court. In particular, while expert evidence is useful in explaining the technical terms and technical features of the invention, the nature of the invention for which a patent is granted must be ascertained by the judge and not an expert (Brooks v Steele and Currie (1896) 13 RPC 46 at 73 and Dyson Appliances Ltd v Hoover Ltd [2002] RPC 22 at [13], cited in Terrell at paras 9-182 and 9-184). For the reasons given above, we hold that each of the product claims in SG 872 covers a range of products.

95 The sufficiency or enabling disclosure requirement finds statutory expression in ss 25(4) and 80(1)(c) of the Patents Act (2005 Rev Ed). Section 25(4) of the Patents Act (2005 Rev Ed), in the context of prescribing the requirements of a patent application, states that:

96 Non-compliance with s 25(4) of the Patents Act (2005 Rev Ed) is a ground for revoking the patent, as provided for in s 80(1)(c) of the Patents Act (2005 Rev Ed):

97 It is this requirement that compels the inventor to tell the world how his invention works so that, after the expiry of the patent when his invention falls into the public domain, a PSA will have sufficient information to work the invention and build on it (see Ng-Loy at paras 29.1.3 and 30.3.1).

98 English case law may be instructive when interpreting the scope of the sufficiency requirement under our Patents Act (2005 Rev Ed). Section 25(4) of the Patents Act (2005 Rev Ed) is in materially similar terms as s 14(3) of the UK Patents Act 1977 (c 37) (“UK Patents Act 1977”), which reads:

99 Section 80(1)(c) of the Patents Act (2005 Rev Ed) is also materially similar to s 72(1)(c) of the UK Patents Act 1977, which states:

100 Although the word “enough” is omitted in ss 25(4) and 80(1)(c) of the Patents Act (2005 Rev Ed) (and, for that matter, the same provisions in the Patents Act 1994 (2020 Rev Ed)), the sufficiency requirement in Singapore is not stricter. Our courts have held that a patent specification suffices if it is “clear enough” and “complete enough”; absolute clarity and completeness are not uncompromisingly required. This is because under ss 25(4) and 80(1)(c) of the Patents Act (2005 Rev Ed), as long as the specification is sufficiently clear “for [the invention] to be performed by a person skilled in the art”, it does not matter that the specification does not state every single step required for performance. After all, the PSA does not have to be told what is self-evident or what is part of his common general knowledge (First Currency Choice at [73]; Ng Kok Cheng at [47] and [49]). In this regard, the local position is in line with the ss 14(3) and 72(1)(c) of the UK Patents Act 1977.

101 That said, not every aspect of English law on insufficiency is applicable in our context. The UK Patents Act 1977 was passed to give effect to the Convention on the Grant of European Patents, 5 October 1973, 1065 UNTS 199 (“European Patent Convention”). Section 130(7) of the UK Patents Act 1977 provides that certain provisions, including ss 14(3) and 72(1)(c) of the UK Patents Act 1977, were “so framed as to have, as nearly as practicable, the same effects in the United Kingdom as the corresponding provisions of the European Patent Convention”. The English courts have thus approached the law in these respects with the objective of striving for consistency between European and English patent law (Regeneron (SC) at [30]; Generics (UK) Ltd and others v H Lundbeck A/S [2009] 2 All ER 955 (“Generics v Lundbeck (HL)”) at [86] per Lord Neuberger; Merrell Dow Pharmaceuticals Inc and another v H N Norton & Co Ltd and another; Merrell Dow Pharmaceuticals Inc and another v Penn Pharmaceuticals Ltd and another (1997) 33 BMLR 201 at 205). In interpreting and developing the jurisprudence under ss 14(3) and 72(1)(c) of the UK Patents Act 1977, the English courts have therefore introduced certain concepts into English law from European patent law to give effect to this harmonising objective. Such concepts, however, are not necessarily applicable to ss 80(1)(c) and 25(4) of the Patents Act (2005 Rev Ed), and their applicability falls to be determined with reference to the text and legislative objective of ss 80(1)(c) and 25(4) as well as the Patents Act (2005 Rev Ed) as a whole.

102 We begin by noting the policy that undergirds the sufficiency requirement. Both English and local case law have recognised that the sufficiency requirement lies at the heart of what is sometimes called the “patent bargain”. As already alluded to above at [57], the inventor/patentee is rewarded with a limited-term monopoly over the claimed invention, in exchange for enabling a PSA to work the claimed invention and dedicating it to public use after the monopoly has expired (Rohm and Haas Electronic Materials CMP Holdings, Inc (formerly known as Rodel Holdings, Inc) v NexPlanar Corp and another [2018] 5 SLR 180 (“Rohm”) at [161]; Warner-Lambert Company LLC v Generics (UK) Ltd t/a Mylan and another [2019] 3 All ER 95 at [17]). The patent bargain breaks down if the patent does not sufficiently teach a PSA how to perform the invention, in which case it makes little sense to reward the inventor/patentee with a monopoly. It is for this reason that the failure to satisfy the sufficiency requirement is a ground for patent revocation.

103 We now turn to set out general principles applicable to the legal requirement of sufficiency in Singapore. References to English jurisprudence will be made where appropriate.

104 It is well-settled under Singapore law that the burden of proving insufficiency rests on the party challenging the validity of a registered patent (Ng Kok Cheng at [48]).

105 The assessment of whether the legal requirement of sufficiency is met proceeds in two steps. The first step involves identifying the invention and deciding what it claims to enable the PSA to do. The second steps asks whether the specification enables him to do it (Kirin-Amgen Inc and others v Hoechst Marion Roussel Ltd and others; Hoechst Marion Roussel Ltd and others v Kirin-Amgen and others [2005] RPC 169 (“Kirin-Amgen”) at [103] per Lord Hoffmann, cited with approval in First Currency Choice at [61]). Indeed, the court can only ascertain whether the disclosure has been sufficient after ascertaining what needs to be disclosed (meaning the invention).

106 Both steps of the inquiry require the court to don the mantle of a PSA possessing common general knowledge of the art. The first step involves the construction of the patent claims from the perspective of the PSA. Claim construction principles as set above at [79]–[80] are applied (see Towa Corp v ASM Technology Singapore Pte Ltd and another [2017] 3 SLR 771 at [66] and Main-Line Corporate Holdings Ltd v United Overseas Bank Ltd and another (First Currency Choice Pte Ltd, third party) [2007] 1 SLR(R) 1021 at [72]). At the second step, the PSA uses his common general knowledge to supplement the information contained in the specification in order to perform the invention (see Genelabs (CA) at [61]–[63]). The sufficiency inquiry at the second stage is undertaken with reference to the date of filing of the patent application (Biogen Inc v Medeva PLC [1997] RPC 1 (“Biogen”) at 54 per Lord Hoffmann, followed in Kirin-Amgen Inc v Transkaryotic Therapies Inc [2003] RPC 3 at 70). This is sensible, since s 25(4) of the Patents Act (2005 Rev Ed) imposes the requirement of sufficiency at the time the patent application is made (see also Genelabs (HC) at [202]; Susanna Leong at para 16.266). As an aside, since we are regarding the relevant date for construing the patent claims (see at [78] above) and assessing insufficiency as the date of filing of SG 872, and we do not intend to discuss the issues of novelty and obviousness, we need not rule on the respondent’s claim for priority from GB 261.

107 Where the invention is a process, enablement at the second step requires that process to be carried out by the PSA; where the invention is a product, enablement requires the PSA to be able to make that product (Generics v Lundbeck (HL) at [20]; Roughton, Johnson & Cook, The Modern Law of Patents (LexisNexis, 5th Ed, 2022) (“The Modern Law of Patents”) at para 4.37).

108 Regardless of the nature of the invention, the patent specification must enable the invention to be performed by the PSA over the full breadth of the monopoly claimed, as we explain further below. Lord Hoffmann, who delivered the leading decision in the House of Lords in Biogen, observed that this is a long-established principle in English law (at 48) (see also Idenix Pharmaceuticals, Inc v Gilead Sciences, Inc and others [2014] EWHC 3916 (Pat) (“Idenix (HC)”) at [468]; Regeneron (SC) at [3] and [80]). Later in Kirin-Amgen at [102], Lord Hoffmann expressly applied this principle to s 72(1)(c) of the UK Patents Act 1977, which embodies the concept of sufficiency in the context of patent revocation:

This court in First Currency Choice at [61] cited Kirin-Amgen at [102] with approval when setting out the applicable principles in relation to s 80(1)(c) of the Patents Act (2005 Rev Ed).

109 To illustrate what it means for a specification to enable the invention to be performed to the full extent of the monopoly claimed, Lord Hoffmann gave the following illustrations in Biogen at 48:

Subsequently, in H Lundbeck A/S v Generics (UK) Ltd and others [2008] RPC 437 at [34], Lord Hoffmann re-iterated that where a claim is to a class of products, the class of products is enabled only if the PSA can work the invention in respect of all members of the class. The specification can show that this is empirically demonstrated or disclose a principle which can reasonably be expected to apply across the class.

110 However, the patent need not set out every detail necessary for the performance of the invention across its entire scope. As mentioned at [100] above, the patentee can leave the PSA to employ his skill and common general knowledge to work out what needs to be done. But the PSA must not be expected or required to exercise inventive ingenuity or exert undue effort in order to perform the invention across its entire breadth.

111 The requirement of enablement across the full breadth of the claim can be understood with reference to the patent bargain. The inventor/patentee should only be entitled to the full extent of the monopoly claimed if he has fulfilled his end of the bargain by disclosing the full scope of the invention clearly and completely enough. Only if this is done can the second aim of the patent regime, knowledge dissemination, be achieved by way of allowing the public to benefit from the invention after it falls into the public domain. A patent system which allows the inventor/patentee to monopolise more than that which he has sufficiently enabled may unduly stifle research, contrary to its primary aim of encouraging innovation (see Regeneron (SC) at [23]; Lionel Bently et al, Intellectual Property Law (Oxford University Press, 6th Ed, 2022) at pp 607–608). Hence, even where a patent specification is clear and complete enough to teach a PSA how to perform part of the claimed invention, that does not justify a monopoly over the entire breadth of the invention and the patent may be revoked pursuant to s 80(1)(c) of the Patents Act (2005 Rev Ed).

112 Before leaving this point, we note in passing that the majority of the UKSC in Regeneron (SC) held that it is enough if the patent enables the PSA to make “substantially all the types or embodiments of products within the scope of the claim” (at [56(iv)]) [emphasis added]. This threshold appears to be satisfied where there remain a “tiny or inconsequential number of embodiments which are not enabled” such that the scope of non-enablement is de minimis (at [36] and [56(v)]). The standard of substantiality was endorsed by the majority because it was the position in EU law (at [31]–[32] and [36]), and s 130(7) of the UK Patents Act 1977 requires interpretative consistency between European and UK patent law. We are not bound by a similar obligation. Without the benefit of submissions, we shall defer consideration of this aspect of Regeneron (SC) to an appropriate case. In any event, as we shall see, the threshold of substantiality does not have a material bearing on this case.

113 Next, although insufficiency is a single ground of objection to the validity of a patent contained in s 80(1)(c) of the Patents Act (2005 Rev Ed), there are distinct ways in which a patent may be insufficient (see Zipher at [362]; Anan at [22]). As will become clear, the appellant’s case engages different aspects of the rule on patent sufficiency, two of which are determinative of this appeal. We now turn to consider the different ways a patent may be insufficient under English and/or Singapore law.

114 The first way in which a patent may be insufficient is where the patent specification is not clear and complete enough to enable the PSA to perform the invention across the whole breadth of the claim(s) without an undue burden (see Terrell at para 13-31). This objection, termed “classical insufficiency”, is well-established in English and local jurisprudence (see First Currency Choice at [60]–[62]). In evaluating the merits of this allegation, the court has to assess the steps which would be necessary for the PSA to take under the patent’s specification to carry out the invention (see Zipher at [363]).

115 Under English law, a patent specification which enables a PSA to perform the full breadth of the claim without undue effort (meaning that it is not classically insufficient), may nonetheless suffer from another type of insufficiency, known as “Biogen insufficiency”. This form of insufficiency arises where the scope of the claim exceeds the technical contribution to the art made by the invention (see Terrell at para 13-09), whereas classical insufficiency is concerned with the mismatch between the scope of the claim and the method of performance taught in the patent specification. The “technical contribution to the art” does not refer to the technicalities of performing the claimed invention, but, more generally, to how the invention has in a practical sense added to or advanced the state of the art (that said, we note that the precise concept of “technical contribution to the art” has been articulated in various ways (see Generics v Lundbeck (HL) at [95] per Lord Neuberger, at [45] per Lord Mance and at [30] per Lord Walker)).

116 Consider, for example, a claim to “a heavier than air flying machine” in a patent which only discloses how to make an airplane. Assume for the moment that an airplane is a new and non-obvious invention, and the patent specification is clear and complete enough for a PSA to make an airplane. The airplane is a machine that is (a) capable of flight and (b) heavier than air, and by teaching the PSA how to make an airplane, the patent specification has enabled performance of every integer (or “element”, see Rohm at [103] and [179]) of the claim. In other words, the patent specification has sufficiently enabled the full breadth of the claim and can avoid a classical insufficiency attack. Yet, because the language of the claim has defined the invention in such general terms, the monopoly asserted by the claim is capable of extending to all other forms of heavier than air flying machines that are not airplanes and which may be manufactured by a wholly different process. The breadth of the claim thus exceeds what the patentee has contributed to the state of the art, in this example, how to make an airplane. This gives rise to Biogen insufficiency (see Anan at [52], citing Biogen at 52).

117 At present, Singapore patent law has not recognised the concept of Biogen insufficiency under s 80(1)(c) of the Patents Act (2005 Rev Ed), and it is unclear whether it should. We observe that Biogen insufficiency was first recognised by Lord Hoffmann in Biogen at 54, in the light of the jurisprudence under the European Patent Convention: