Center for Advanced Study & Research on Innovation Policy


CASRIP Newsletter - Winter/Spring 1999, Volume 5, Issue 4

No Doctrine of Equivalents if the Warner-Jenkinson Presumption Applies

Sextant Avionique S.A. v. Analog Device Inc.1

In Litton Systems,2 the Federal Circuit affirmed its own patent-friendly case law on prosecution history estoppel. However, Judge Gajarsa's dissenting opinion to the denial of en banc hearing in the same case3 highlights disagreements among the Federal Circuit judges as to the impact of the presumption introduced by the Supreme Court in Warner-Jenkinson.4 According to Judge Gajarsa, patentees should not be entitled to any scope of equivalents when the disputed limitation was introduced during the prosecution as a means of overcoming prior art. In Sextant, Judge Lourie developed a theory that leads to a similar conclusion as that of Judge Gajarsa. Judge Lourie's theory makes it difficult to show a reason for introducing disputed limitations, and completely prevents application of the doctrine of equivalents when a patentee is unable to show a reason.

Sextant's two patents in suit were directed to an accelerometer sensor in which a test body sways between capacitor plates in response to an accelerative force, with the variation in distance between the plates resulting in a detectable change in capacitance. The two patents were not formally related to each other (e.g., through a continuation or divisional application) but the second patent, issued to Boura, was explained in its specification as an improvement of the first patent, which was issued to Marcillat. During prosecution of the Marcillat patent, the examiner rejected the claim alleged by Sextant, citing Rudolph, a patent on a similar sensor made by a semiconductor processing technique using a test body formed in monocrystalline silicon that was converted into a conductor by doping with impurities. To overcome Rudolph's prior art, Sextant clarified the nature of the capacitor plates by including a limitation "metallization," and also introduced other limitations. As a result, the amended claim was allowed.

After the Marcillat claim was allowed, patentee received an office action to reject the sole independent claim of the Boura patent for indefiniteness under U.S.C. Section 112 Paragraph 2, and for obviousness in light of a different prior art sensor. To secure a quick allowance, patentee amended the claims in the Boura patent to make them uniform with the Marcillat patent claim, emphasizing the improved features in the "wherein" clause. Thus, the "metallization" limitation and other limitations introduced to overcome the prior art cited against Marcillat were included in the claims of Boura. Although different examiners examined the two patents, the claims of Boura were allowed soon after the amendment.

The accelerometer sensor that Sextant alleged was an infringement of its two patents was made by semiconductor processing technology, but its test body used a deposited doped polysilicon. Defendant argued that the metallization limitation limited the material of the capacitor plate to a deposited metallic material. It also argued that prosecution history estoppel bars the patentee from asserting the doctrine of equivalents with respect to either of the two patents. The district court agreed with defendant and granted judgment as a matter of law (JMOL) that there was no infringement, either literally or equivalently.

On appeal heard by a three-judge panel, the Federal Circuit affirmed the district court's finding of no infringement, either literal or under the doctrine of equivalents. In construing the "metallization" limitation, the court noted that the term connotes the use of metallic materials and found no basis in the specification to change the meaning. Further, the prosecution history of the Marcillat patent, in which applicant distinguished his "metallized" structure from the "doped silicon" structure of another patent, strongly supported the court's construction that the term covers only metallic materials. This led to a conclusion that the defendant's sensor using doped silicon does not literally infringe any of Sextant's claims that require the use of metallization material.

The court then examined patentee's arguments objecting to the district court's application of prosecution history estoppel following Warner-Jenkinson. With respect to the Marcillat patent, patentee did not deny that the "metallization" limitation was introduced for a patentability-related reason, because the amendment was made to overcome the examiner's citation to the Rudolph patent. However, patentee argued that defendant's accused devices differed so substantially from the device disclosed in Rudolph that prosecution history estoppel did not preclude a conclusion that defendant infringed the Marcillat patent under the doctrine of equivalents. The court did not agree and found that the effect of Marcillat's amendment and argument on metallization was to surrender all silicon materials, whether poly- or monocrystalline, made conductive by doping. The court rejected patentee's argument that the doped polysilicon is different from the prior art, the doped monosilicon, and thus not within the scope of the estoppel. The court emphasized that an accused device may have a defense under prosecution history estoppel even if it does not have the defense of the accused device being the prior art or its obvious variation.5 This court said these two defenses constitute separate and independent "policy-oriented" limitations on the doctrine of equivalents.

To avoid application of prosecution history estoppel with respect to the Boura patent, patentee argued that the "metallization" limitation was introduced to overcome the examiner's indefiniteness rejection and was not for a reason "related to patentability" as required by the Supreme Court in Warner-Jenkinson for applying the estoppel. Before examining the merits of this argument, the court noted that neither the Supreme Court nor the Federal Circuit has resolved the issue whether an amendment to overcome an indefiniteness rejection constitutes an amendment made for reasons of patentability. The court nevertheless did not address this issue in Sextant because it found that the amendment was not made only for overcoming an indefiniteness rejection. Instead, the court found that the situation in Sextant parallels that in Warner-Jenkinson. Since the Deval patent, the prior art sensor cited against the Boura patent, included a capacitor plate using a metallization layer, the court found that the "metallization" limitation was not necessary to overcome an obviousness rejection. Boura argued that his claims were distinguishable from Deval based on Boura's placement of the metallization on the edge of the test body, as opposed to Deval's placement of it on the sides. Therefore, while the prosecution record disclosed the reason for the "edge" limitation, it disclosed no reason why the patentee introduced the "metallization" limitation. Accordingly, the court concluded that under Warner-Jenkinson it must presume that the limitation was added for a reason "related to patentability." The court found that the patentee did not rebut this presumption, and thus, that prosecution history estoppel applied to the limitation.

Further, the court interpreted the Supreme Court's statement in Warner-Jenkinson that in circumstances where the presumption applies, prosecution history estoppel bars the application of the doctrine of equivalents as to that element. The Sextant court found that this statement announced a different rule of scope to be applied in cases in which estoppel applied by presumption, as opposed to cases in which estoppel applied because amendments were clearly made for reasons "related to patentability." The court stated that its reading of Warner-Jenkinson was supported by the Supreme Court's emphasis on the public notice function of claims. Under this policy rationale, a patentee's failure to clarify the reasons for a limitation and thereby rebut the presumption should not work to the detriment of the public by leaving an uncertain range of equivalency as to that limitation. Moreover, where the presumption is operative, reference to prior art or the patentee's arguments are not of assistance in assessing the scope of the estoppel, because the record is unclear as to the reason for the amendment.

Based on the above analysis, the court found that because the patentee was unable to show a reason for introducing the "metallization" limitation, the patentee could not assert infringement under the doctrine of equivalents as to this limitation. Thus, the court found no error in the district court's JMOL denying both literal and equivalent infringement.

In his dissenting opinion, Senior Judge Smith objected to the majority's analysis of Boura's reason for introducing the "metallization" limitation. He believed that the prosecution history clearly showed that Boura added the "metallization" limitation in order to distinguish his invention from the prior art, and that this was done not by requiring metallization per se, but by requiring the metallization to be on the edge of the test body and not on the side. The majority closely parsed the claim limitation into two parts, "metallization" and "on-the-edge," and found that the metallization part could not have been added to distinguish prior art, because Deval also disclosed capacitors formed from metallization. The dissent stated that the majority's analysis conflicted with Federal Circuit precedent which rejected a patentee's argument that an amendment that is not necessary to overcome a prior art rejection cannot have been made to overcome prior art.6 Thus, the court should have found Sextant's amendment to the Boura patent to constitute an amendment made for a reason of patentability. Judge Smith was also uneasy that the presumption was applied for the first time on appeal, because he thought that the patentee was not given a fair opportunity to show a reason for the amendment.

Judge Smith also objected to the district court's importation of the Marcillat patent's prosecution history into the Boura patent. According to the dissent, the Federal Circuit had never based a finding of prosecution history estoppel on a statement made by a different applicant during prosecution of an unrelated application, and had never suggested that competitors be burdened with examining the file histories of applications other than the one in suit in order to determine the scope of equivalents that may be accorded the patentee.

This case clearly shows the difficulty of clearly defining the scope of the estoppel resulting from an amendment and argument during the prosecution. As the majority emphasized, the Federal Circuit has developed two separate doctrines to limit the doctrine of equivalents. The first doctrine is the prior art limitation defense. This doctrine limits the scope of equivalents based on the prior art, which is a very objective element. The policy behind the doctrine is that the patentee should not claim to cover what he would not have been able to cover as of the filing date. If the accused device is anticipated or obvious from the prior art, the patentee would not have been able to obtain a patent had the patentee known of the accused device as of the filing date.

The second doctrine is prosecution history estoppel. This doctrine limits the scope of equivalents based on the scope surrendered by the patentee, regardless of the scope that the patentee could have obtained due to the related prior art. The policy behind this doctrine is that a patentee cannot recapture a scope that was already surrendered during the prosecution under the doctrine of equivalents. Although the case law requires the surrendered scope to be defined objectively as how one skilled would find the surrendered scope from the record of prosecution, in practice, it is very difficult or almost impossible to objectively define what is actually surrendered. Because of this difficulty, the prosecution history introduces extensive disputes as to what was surrendered. Courts are struggling to develop a standard for objectively determining the surrendered scope.

One main reason that U.S. courts maintain two very closely related but separate doctrines is that a court applying prosecution history estoppel does not need to address difficult questions associated with nonobviousness, such as the analogous art doctrine and the suggestion test. However, the majority in Sextant suggests that courts applying estoppel also need to examine the nonobviousness question to see whether the limitation was necessary to overcome the prior art. This would make it less attractive and more cumbersome for U.S. courts to resort to prosecution history estoppel to limit the doctrine of equivalents.

Further, as Judge Smith properly pointed out, the Federal Circuit has developed significant case law that supports applying prosecution history estoppel whenever an amendment was made for overcoming the prior art. In examining the scope left over after application of the estoppel, courts tend to find a broad scope of surrender regardless of the necessity of limitation introduced by the amendment. In short, the analysis adopted by Sextant majority directly conflicts with long-established practice in the Federal Circuit. This introduces further confusion in an area that is already very confused.

Toshiko Takenaka

  1. 49 USPQ2d 1865 (Fed. Cir. 1999).
  2. Litton Sys. v. Honeywell, Inc., 140 F.3d 1449, 46 U.S.P.Q.2d 1321 (Fed. Cir. 1998)
  3. Litton Sys. v. Honeywell, Inc., 145 F.3d 1472, 1478, 47 U.S.P.Q.2d, 1106 (Fed. Cir. 1998) (Gajarsa, J., dissenting from denial of rehearing en banc)
  4. Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997).
  5. Wilson Sporting Goods Co. v. David Geoffrey & Assoc., 904 F.2d 677, 14 U.S.P.Q.2d (BNA) 1942 (1990).
  6. Bai v. L & L Wings, Inc., 160 F.3d 1350; 48 U.S.P.Q.2d 1674 (Fed. Cir.1998).

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