• Federal Circuit Narrows Application of the Doctrine of Equivalents
  • April 29, 2003 | Author: Brian M. Hoffman
  • Law Firm: Fenwick & West LLP - San Francisco Office
  • On November 29, 2000, the Federal Circuit limited a patentee's ability to apply the doctrine of equivalents to a patent's claims. In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558 (Fed. Cir. 2000) (en banc), an eight to four majority of the court held that the doctrine of prosecution history estoppel bars application of the doctrine of equivalents to claims narrowed for reasons substantially related to patentability during prosecution. Because most patent claims are amended during prosecution, this wide-ranging rule is likely to significantly impact both the prosecution and litigation of patents.

    The Doctrine of Equivalents
    The doctrine of equivalents is a well-established part of patent law that expands the scope of a patent's claim beyond its literal language. In general, the doctrine is intended to give the patentee protection against those who would make minor changes to a patented invention that would be enough to take the copied matter outside the literal scope of the claims. Graver Tank & Mfg. v. Linde Air Prods. Co., 339 U.S. 605 (1950).

    In Graver Tank, the Supreme Court stated the well-known "triple-identity" test for determining whether an accused device infringes a claim under the doctrine: an accused device infringes if it performs substantially the same function in substantially the same way to obtain the same result. 339 U.S. at 608. Later, the Federal Circuit revised the test slightly to ask whether there are "insubstantial differences" between the claimed invention and the accused product or process. Hilton Davis Chem. Co. v. Warner-Jenkinson Co., 62 F.3d 1512, 1521-1522 (Fed. Cir. 1995), rev'd, 520 U.S. 17 (1997). Upon review of this decision, the Supreme Court restated the test for equivalence as simply: "Does the accused product or process contain elements equivalent to each claimed element of the patented invention?" Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 40 (1997).

    Equivalence is determined on an element-by-element basis. Id. As a result, one element in a claim may be entitled to a broad range of equivalents while other elements may be limited to only the literal claim language.

    Prosecution History Estoppel
    A claim element's range of equivalents is limited by the doctrine of prosecution history estoppel. See Hughes Aircraft Co. v. United States, 717 F.2d 1351 (Fed. Cir. 1983), overruled by Festo, 234 F.3d at 574-75. Essentially, this doctrine states that a patentee cannot use the doctrine of equivalents to recapture subject matter given up during prosecution.

    For the most part, courts have followed a "flexible bar" approach when limiting the range of equivalents. Under this approach, the range of equivalents for a claim element amended to overcome a prior art rejection is limited only with respect to the given amendment. The claim element is still entitled to equivalents unrelated to the amendment.

    For example, assume a claim element initially recites "a buffer held in a memory" but is narrowed during prosecution to "a buffer held in a display memory" to avoid a reference showing a buffer in a main memory. Prosecution history estoppel precludes the range of equivalents for the claim element from encompassing buffers in main memory. However, under the flexible bar approach, the claim might still be entitled to a range of equivalents covering buffers stored in other memories.

    The Festo Opinion
    In Festo, the Federal Circuit explicitly overruled Hughes and rejected the flexible bar approach to prosecution history estoppel. Id. Under Festo, "prosecution history estoppel acts as a complete bar to the application of the doctrine of equivalents when an amendment has narrowed the scope of a claim for a reason related to patentability." Id. at 574 (emphasis added). As a result, most claims having elements amended during prosecution are no longer entitled to a range of equivalents for those elements.

    The reasons for this decision are primarily rooted in the public notice function and need for certainty in interpreting claim scope. The court explained that the flexible bar approach was unworkable because it was impossible to determine the scope of a claim prior to an appellate decision. Id. at 575. As a result, the marketplace could not look to patent claims for guidance in conducting its affairs. Id. Therefore, the court reasoned, a complete bar "best serves the notice and definitional function of patent claims." Id. at 576. The public can examine the prosecution history of a claim and, if a claim element was amended in a manner that creates prosecution history estoppel, know that the element's scope of protection is defined by its literal terms.

    Festo requires a two-part analysis to determine whether a claim amendment gives rise to prosecution history estoppel and therefore completely bars application of the doctrine of equivalents:

    (1) does the amendment narrow the literal scope of the claim? and

    (2) is the amendment being made for reasons substantially related to patentability?

    Id. at 586. If the answers to both questions are "yes," then the complete bar applies to the amended claim element.

    The Festo opinion does not provide explicit guidance for determining whether an amendment narrows a claim element. From the facts of the case, voluntarily amending an independent claim to include a dependent claim is a narrowing amendment. Id. at 589. It is unclear, however, whether amending a dependent claim into an independent claim is a narrowing amendment. The opinion also points out that a narrowing amendment made to an independent claim also narrows all dependent claims that recite the narrowed element. Id. at 590 n.9. The opinion also notes that an amendment replacing means-plus-function language with corresponding structure narrows the scope of the claim. Id. at 589.

    Under Festo, virtually any claim amendment made to comply with a statute is "made for reasons substantially related to patentability." Obviously, amendments made in response to anticipation or obviousness rejections under §§ 102-3 are substantially related to patentability. In addition, amendments made under § 101 to limit the claim scope to patentable subject matter or under § 112 to clarify the meaning of terms in the claim are also so related. Id. at 567. Voluntary amendments, amendments made in response to improper rejections and amendments for which no reasons are established are also substantially related to patentability. Id. at 568, 576, 578.

    Festo's Dissents
    Several judges filed dissenting-in-part opinions disagreeing with the majority's "complete bar" rule. Judges Michel and Newman argued that the Supreme Court supported the flexible bar in Warner-Jenkinson and numerous older opinions. Festo, 234 F.3d at 608-09, 631. Judge Michel also reasoned that the complete bar will lead to inequitable results, especially in the biotechnology area, because copyists can now "readily avoid liability despite practicing the substantial equivalent of the claimed invention." Id. at 616-17.

    Multiple judges also argued that the complete bar rule is ill-suited to the standard practice of prosecuting a patent. Judge Linn noted that "it is quite difficult for claim drafters to draft initial claims that adequately and accurately cover the 'invention' on the day the patent application is filed" and, consequently, claims are commonly amended during prosecution. Id. at 622. Judge Michel likewise stated that the majority's holding will "'subvert the various balances' inherent in the process of patent prosecution." Id. at 618 (citing Warner-Jenkinson, 520 U.S. at 32 n.6).

    In Judge Rader's opinion, the doctrine of equivalents protects patentees against equivalent technologies that arise after invention. He found it illogical to hold that an applicant can surrender claim coverage over something that did not yet exist through a minor narrowing amendment. Id. at 619.

    Prosecution Practice Tips in View of Festo
    Because patent practitioners often find it necessary to narrow claims in response to rejections, practitioners will sometimes have no option but to subject a claim element to the complete bar. Nevertheless, there are certain steps that a practitioner can take to minimize the negative implications of Festo.

    Perhaps the most obvious step is to include independent claims of varying scope in an application as filed. A narrow claim that is allowed without amendment may have broader scope than a broad claim amended to recite the same narrow limitations. Practitioners should also consider filing an appeal rather than making minor claim amendments to satisfy an obstinate examiner. The appeals process may be lengthy, but the resulting claims may provide broader protection against would-be infringers.

    Means-plus-function claims may also have new value in the post-Festo world. The majority opinion acknowledged that means-plus-function claims are still entitled to § 112 ¶ 6 equivalence, even when amended. Festo, 234 F.3d at 589. Although the range of equivalents under § 112 ¶ 6 is less than under the doctrine of equivalents, the range is still broader than the literal claim language. Therefore, practitioners should consider adding a set of means-plus-function claims to new and pending patent applications.

    If possible, practitioners should include remarks explaining why amendments did not narrow the scope of the claims or explaining that the amendments were made for reasons not substantially related to patentability. If there are no remarks in the record stating the reason for an amendment, a court may construe the amendments against the patentee. Practitioners may also wish to avoid making minor amendments, such as amendments fixing insignificant § 112 problems, if such an amendment might be found to narrow the scope of the claim.

    In sum, any narrowing amendment made to a claim in order to comply with statutory requirements is likely to completely bar application of the doctrine of equivalents to the amended claim element. This bar applies to all issued patents and pending applications. Because the majority of claims are amended during prosecution, the scope of many patents will be reduced under Festo.