In Sigray, Inc. v. Carl Zeiss X-Ray Microscopy, Inc.,1 , the U.S. Court of Appeals for the Federal Circuit held that the Patent Trial and Appeal Board (PTAB) engaged in implicit and erroneous claim construction, and concluded that the claimed magnification range of an X-ray imaging system of a patent owned by Zeiss is inherently disclosed in an anticipatory prior art reference. The Sigray decision is an important reminder of two principles: (1) that an inherent disclosure can anticipate claims even if the inherent feature is unrecognized, unintentional, or undesirable, and (2) that the claim language governs the scope and meaning of the claim.
The PTAB had found, in an Inter Partes Review (IPR) initiated by petitioner Sigray, that certain challenged claims of U.S. Patent No. 7,400,704, directed to an X-ray imaging system, were not shown by Sigray to be unpatentable. The Federal Circuit found that the PTAB had engaged in implicit and erroneous claim construction of the claimed magnification range, and that the magnification range was anticipated by the inherent disclosure of a scientific paper (Jorgensen) in view of the correct claim construction.
Claim 1 of Zeiss's patent recites an X-ray imaging system that includes a projection X-ray stage and an optical stage, “wherein a magnification of the projection x ray stage is between 1 and 10 times.” The magnification (M) is determined, according to the disclosure of the patent, by the equation
M = (Ls+Ld)/Ls,
where Ls is the distance between the X-ray source and the sample, and Ld is the distance between the sample and the detector. M of 1 indicates that there is no magnification. All parties agreed that the presence of any divergence in the X-ray source would cause magnification greater than 1.
In its IPR final written decision, the PTAB declined to hold any claims of Zeiss's patent unpatentable, noting that Sigray has not met its burden to show that Jorgensen discloses a diverging X-ray beam that inherently produces projection magnification within the claimed range. Sigray appealed.
A claim is considered anticipated under 35 U.S.C. § 102 if each and every element in the claim is found, either expressly or inherently described in a single prior art reference. Furthermore, anticipation by inherent disclosure is appropriate only when the reference discloses prior art that must necessarily include the unstated limitation.
In Sigray, the Federal Circuit reviewed the PTAB's legal analysis without deference. Although the PTAB stated that it had not engaged in any claim construction, the court noted that such a statement by the PTAB is not dispositive as to whether it actually did or did not engage in claim construction. Upon reviewing the PTAB's decision, the Federal Circuit concluded that the PTAB had in fact implicitly engaged in a claim construction exercise. As a result, the court reviewed the PTAB's legal conclusions as to claim construction de novo. That is, the appellate court engaged in its own claim construction – a legal question – which then allowed it to also engage in a renewed and independent application of the facts at hand.
The parties' arguments focused on the presence or absence of divergence in the X-ray source of Jorgensen. The Federal Circuit found that the PTAB's use of the word “enough” to describe divergence disclosed in Jorgensen – that is, that Sigray had failed to show that the X-ray beam in Jorgensen diverges “enough” to result in projection magnification—supported the conclusion that Jorgensen disclosed at least some divergence of the X-ray.
The Federal Circuit further pointed out that the evidence the PTAB relied upon to arrive at the decision also supports the presence of divergence. For example, the PTAB's assertion that collimation is a technique for minimizing beam divergence, consideration of Jorgensen's X-ray focal spot that subtends a very small angle, and expert testimony such as “collimated X-ray beam is a beam where … no meaningful divergence is present,” all led to the indication that some divergence is necessarily disclosed by Jorgensen, however small the amount, even if Jorgensen is not attempting to achieve magnification. The Federal Circuit further noted that M equal to 1 can only be achieved by setting the distance between the sample and the detector to be zero. To this end, the Federal Circuit also relied on Zeiss's admission that absolute, theoretical parallelism cannot be achieved as a practical matter. The court concluded that the PTAB construed, implicitly and erroneously, the claim phrase “between 1 and 10” to exclude small amounts of magnification.
The Federal Circuit then conducted the anticipation analysis anew, based on the evidence-supported conclusion that Jorgensen inherently discloses projection magnification M necessarily greater than 1. Thus, the court concluded that Jorgensen anticipates the claimed magnification range by inherent disclosure. The Federal Circuit emphasized that at all times, the language of the claims govern their scope and meaning, and unless the intrinsic evidence compels a contrary conclusion, the claim language carries the meaning accorded those words in the usage of skilled artisans at the time of invention. Challenged claims 1, 3 and 4 of Zeiss's patent were thus held to be anticipated by Jorgensen.
The outcome of Sigray highlights the importance of being cognizant regarding undisclosed features that are present in prior art references, even if such features are unrecognized, unintentional, or undesirable, such as impurities present in a substance. In particular, claims incorporating a broad numerical range should be closely scrutinized, as a single overlapping point, through express or implicit disclosure in the prior art reference, may anticipate the claim. Furthermore, care should be taken in selecting specific claim terms to understand their ordinary and customer meaning. Where necessary or appropriate, inclusion of explicit definitions in the specification should be considered if different or contrary interpretation of the terms is required or desired. These are important considerations for the patent drafter and prosecutor alike.
Footnote
1. Sigray, Inc. v. Carl Zeiss X-Ray Microscopy, Inc., No. 2023-2211, Fed. Cir. (May 23, 2025)
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