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Although the Federal Circuit attempted to clarify the legal landscape for patent claim construction in the 2005 case Phillips v. AWH Corp., (1) the ruling will not stop plaintiffs and defendants from continuing to vigorously litigate the scope and meaning of claims in patent infringement cases. For plaintiffs who receive an adverse claim construction ruling, however, asserting infringement under the doctrine of equivalents may prove to be a viable option.
This article is in two parts, with the first part having run last month in the April issue of this journal. The first part of the article reviewed the key claim construction cases and described a court's process for construing claims.
In this issue, the second part of this article describes the requirements for proving infringement, either literally or under the doctrine of equivalents, and considers the defenses to doctrine of equivalents claims. This part will also explain that the most foreboding of all the independent barriers to finding infringement under the doctrine of equivalents may be the doctrine of claim vitiation.
To prove literal infringement of a claim, the patentee must show that the accused product or process has every limitation of the claim as construed. (2) The accused product or process must fall within the literal scope of the claim language, as construed by the court. (3) "If even one limitation is missing or not met as claimed, there is no literal infringement." (4)
Doctrine of Equivalents
A product or process that is not within the literal scope of the claims can still be found to infringe under the doctrine of equivalents.The doctrine of equivalents is supposed to prevent the defendant from avoiding infringement by making insubstantial changes to the claimed invention. (5)
Infringement under the doctrine of equivalents occurs "when a claimed limitation and the accused product perform substantially the same function in substantially the same way to obtain substantially the same result." (6) This analysis for determining the differences between an accused element and a claim limitation is performed for each limitation of a claim. (7) The Federal Circuit has stated that infringement, "either literal or by equivalents, is a question of fact." (8)
There is a tension between the doctrine of equivalents and the public notice function of requiring patentees to "particularly point out and distinctly claim the subject matter which the applicant regards as his invention." (9) On the one hand, absent the protection afforded by the doctrine of equivalents, the value of patents "would be greatly diminished. (10) On the other hand, "[t]here can be no denying that the doctrine of equivalents, when applied broadly, conflicts with the definitional and public-notice functions of the statutory claiming requirement." (11) As the Supreme Court noted in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.:
Unimportant and insubstantial substitutes for certain elements could defeat the patent, and its value to inventors could be destroyed by simple acts of copying. It is true that the doctrine of equivalents renders the scope of patents less certain. It may be difficult to determine what is, or is not, an equivalent to a particular element of an invention. If competitors cannot be certain about a patent's extent, they may be deterred from engaging in legitimate manufactures outside its limits, or they may invest by mistake in competing products that the patent secures. In addition the uncertainty may lead to wasteful litigation between competitors, suits that a rule of literalism might avoid. (12)
It has been in seeking to balance these competing interests that the courts, most notably the Federal Circuit, have crafted limitations on the doctrine of equivalents.
Defenses to Doctrine of Equivalents Claims
Failure of Proof
To succeed on a doctrine of equivalents claim, a patentee must prove "substantial identity as to each of the function, way, and result prongs of the doctrine of equivalents." (13) This requirement is supposed to prevent the jury from merely comparing the overall similarity between the claim and the accused device.
In addition, the patentee is "required to provide evidence on a limitation-by-limitation basis.... That evidence must ... include particularized testimony and linking argument." (14)
Disclosed but Unclaimed Subject Matter
In Johnson & Johnston Assocs. v. R.E. Seru. Co., (15) the court resolved a conflict among panel opinions on the issue of whether an embodiment of an invention that was disclosed in a patent application but not claimed may be "recaptured" under the doctrine of equivalents. The court held that one who discloses but does not claim subject matter in a patent application has disclaimed that unclaimed subject matter and may not rely on the doctrine of equivalents to prove infringement, even when the specification explicitly taught the equivalency of that matter. The court justified this conclusion by noting: (1) it is the claims, not the specification, that provides the measure of the patentee's right to exclude; (2) when a patentee discloses but declines to claim subject matter, the unclaimed subject matter is dedicated to the public; and (3) any other outcome would encourage a patentee to present a broad disclosure in the specification and file narrow claims and thus hope to avoid prosecution scrutiny by the PTO but later, after issuance, to use the doctrine of equivalents to establish infringement because the specification discloses equivalents.
In the case, the claim was specifically limited to "a sheet of aluminum" to be used as a substrate. The specification, however, read: "[w]hile aluminum is currently the preferred material for the substrate, other metals, such as stainless steel or nickel alloys may be used." The court stated "[h]aving disclosed without claiming the steel [sheets], Johnston cannot now invoke the doctrine of equivalents to extend its aluminum limitation to encompass steel." (16)
To soften the seeming harshness of this holding, the court pointed out that the patent applicant with the broad disclosure and too narrow claims is not without a remedy; he can file for reissuance or file a continuation application under [section] 120.
In Toro Co. v. White Consol. Indus., (17) the court held that the dedication-disclosure rule is a question of law. The Tow court also held that intent "is not part of the Johnson & Johnston disclosure-dedication analysis.'' (18) In addition, it clarified that the level of disclosure required for dedication-disclosure issues is not the same as the 112 requirement. Instead, the disclosure need only be understood by one of ordinary skill in the art.
If a claim is narrowed for any reason related to patentability, a presumption arises "that the patentee surrendered the territory between the original claims and the amended claims.'' (19) The presumption can be overcome if an amendment could not reasonably be viewed as surrendering a particular equivalent (1) if the equivalent may have been unforeseeable at the time of the application, (2) the rationale underlying the amendment may bear no more than a tangential relation to the equivalent in question, or (3) the patentee for some other reason could not reasonably be expected to have described the insubstantial substitute in question. In these circumstances, a patentee could overcome the presumption that prosecution history estoppel bars a finding of equivalents. (20)
This amendment-based estoppel applies to all of the claims that contain the limitation at issue, regardless of whether the patentee amended a particular claim or simply converted a dependent claim into an independent claim. (21) In either situation, the estoppel applies. It is also of no import whether the patentee amended the limitation itself, as the relevant inquiry is whether the patentee narrowed the claim scope. (22) As such, there is a presumption that the patentee surrendered all equivalents of the newly added limitation.
In addition to amendment-based estoppel, patentees may be precluded from asserting that an accused device or process infringes under the doctrine of equivalents based on statements made during prosecution of the patent. (23) ''Unmistakable assertions made by the applicant to the Patent and Trademark Office (PTO) in support of patentability, whether or not required to secure allowance of the claim, also may operate to preclude the patentee from asserting equivalency between a limitation of the claim and a substituted structure or process step." (24) Such limiting statements can be made in, for example, information disclosure statements, petitions to make special, or the specification. (25)
Ensnaring the Prior Art
In DeMarini Sports v. Worth, Inc., the Federal Circuit stated: "[T]here can be no infringement under the doctrine of equivalents if the asserted scope of equivalency would encompass the prior art.'' (26) Judge Rich explained:
[A] patentee should not be able to obtain, under the doctrine of equivalents, coverage which he could not lawfully have obtained from the PTO by literal claims. The doctrine of equivalents exists to prevent a fraud on a patent, ... not to give a patentee something which he could not lawfully have obtained from the PTO had he tried. Thus, since prior art always limits what an inventor could have claimed, it limits the range of permissible equivalents of a claim. (27)
The Growing Importance of the Vitiation Defense to DOE Claims
The doctrine of equivalents cannot be used to vitiate a claim limitation. Under this rule, if the court finds that a claim limitation would be effectively eliminated by a finding of equivalents, then the court is to grant summary judgment of noninfringement. Such a rule has the potential to swallow the doctrine of equivalents and has been invoked by the Federal Circuit with regularity in recent years. In addition, it presents difficult conceptual issues that go to the core of patent …