Chapter §16.05 Legal Limitations on the Doctrine of Equivalents

• Jurisdiction: United States

§16.05 Legal Limitations on the Doctrine of Equivalents

[A] Overview

The Supreme Court instructed in the critical footnote 8 of its 1997 Warner-Jenkinson decision that a patentee may not avail itself of the doctrine of equivalents if certain legal limitations preclude it from doing so.¹⁴⁸ If these limitations are triggered, an infringement case may be resolved on summary judgment or other pre-trial motion and the fact question of technologic equivalency may never reach the fact finder.¹⁴⁹

In keeping with the Supreme Court's guidance in Warner-Jenkinson, the primary legal limitations on the doctrine of equivalents that Federal Circuit case law has applied are the following:

Prosecution history estoppel: The doctrine of prosecution history estoppel (PHE) provides that a patentee may not seek to ensnare under the doctrine of equivalents any subject matter that it surrendered in order to obtain the patent from the USPTO. Prosecution history estoppel is the most frequently encountered legal limitation on the doctrine of equivalents. ¹⁵⁰

All-limitations rule: If even a single claim limitation is not met, either literally or equivalently, in the accused device, there is no infringement. Every limitation of a claim is considered material and must be met in the accused device in order to have infringement. ¹⁵¹

Vitiation of a claim limitation: The doctrine of equivalents must not be applied so broadly as to entirely vitiate or effectively eliminate a particular claim limitation. ¹⁵²

Prior art: A patentee cannot obtain coverage through the doctrine of equivalents over subject matter that it could not have obtained from the USPTO in the first instance. In short, one who merely "practices the prior art" does not infringe under the doctrine of equivalents. ¹⁵³ In practice, this limitation has involved the use of a "hypothetical claim" analysis described below, ¹⁵⁴ and is sometimes referred to as the "ensnarement defense." ¹⁵⁵

Dedication to the public: The patentee may not attempt to cover through the doctrine of equivalents any subject matter that it disclosed but did not claim in its patent application, thereby avoiding USPTO examination of that subject matter. ¹⁵⁶

Foreseeability: A patentee may not encompass through the doctrine of equivalents reasonably foreseeable alterations to claimed structure, when it had an opportunity to negotiate broader claim coverage in the USPTO but did not do so. ¹⁵⁷

These legal limitations on the doctrine of equivalents are separately discussed below.

[B] Prosecution History Estoppel

[1] Definition

Like the doctrine of equivalents, the doctrine of prosecution history estoppel is judge-made law. Because the question whether prosecution history estoppel applies is a question of law, the Federal Circuit reviews a district court's conclusion on this issue without deference.¹⁵⁸

The most commonly asserted legal limitation on the doctrine of equivalents, prosecution history estoppel is based on the notion that if a patent applicant surrendered certain subject matter in the USPTO in order to obtain its patent (e.g., by narrowing the scope of a claim through amendment in order to distinguish subject matter described in a prior art reference), it cannot thereafter rely on the doctrine of equivalents to obtain exclusionary rights over that same subject matter. By reading the patent and its prosecution history in order to determine what the patentee surrendered, competitors should be provided a reasonable degree of certainty that so long as they operate within the confines of the surrendered subject matter, they will not be found to infringe under the doctrine of equivalents.

The most common form of prosecution history estoppel results from narrowing amendments made to the patent application claims during prosecution.¹⁵⁹ For example, the patent allegedly infringed in Dixie USA, Inc. v. Infab Corp.¹⁶⁰ was directed to a type of plastic "stretcher" for use in transporting hospital patients. Claim 1 of Dixie USA's issued patent recited:

1. A patient shifting aid comprising:

a plastic slab having rounded corners forming a rectangular support surface upon which a patient is adapted [sic] to be placed and having sufficient thickness to support the weight of a patient placed thereon while enabling the obtaining of x-rays through the plastic slab to determine the extent of patient injury without the necessity of additional shifting of the patient;

a plurality of openings in said slab and disposed adjacent the periphery of said support surface providing means for gripping the plastic slab to effect sliding movement of the plastic slab and the patient support [sic, supported] thereon;

said plurality of openings comprising generally rectangular openings having rounded corners and rounded openings for grasping the slab for moving a patient; . . . ¹⁶¹

Notably, the corresponding claims of the patent application as originally filed did not limit the nature of the openings. Rather, the claims merely required that the stretcher comprise "a plurality of openings in said slab and disposed adjacent the periphery of said support surface providing means for gripping the plastic slab to effect sliding movement of the plastic slab and the patient support [sic, supported] thereon."¹⁶²

In due course the USPTO rejected the claims as obvious under 35 U.S.C. §103 in view of several prior art references. The patent applicant responded by amending the claims to add the "rectangular openings and rounded openings" limitation (emphasized above). In remarks accompanying the amendment, the applicant contended that what distinguished the claimed invention from the relevant prior art was the presence of both round and rectangular openings, emphasizing to the examiner that "regarding [the amended] claim . . . , none of the cited patents discloses the specific shape and location of the claimed rectangular and round openings."¹⁶³

Infab's accused stretcher did not literally infringe the patent because its handhold openings were all rectangular, not a mixture of rectangular and rounded openings. Because of the patent's prosecution history, a district court also held that prosecution history estoppel precluded the patentee's reliance on the doctrine of equivalents. The court granted the accused infringer's motion for summary judgment of no infringement.

The Federal Circuit affirmed the district court in Dixie USA. Whether or not the accused stretcher performed the same function as the claimed invention, in substantially the same way, to achieve substantially the same result (i.e., was technologically equivalent as a factual matter), the patentee was estopped from relying on the doctrine of equivalents to establish infringement liability. The Federal Circuit concluded that "when a patentee, during the prosecution of his application, adds a limitation to rectangular and round openings in response to a rejection based on prior art references describing rectangular openings in an effort to overcome that rejection, the patentee cannot later successfully argue that an accused device that lacks the rectangular and round limitation infringes the patent."¹⁶⁴

Prosecution history estoppel resulted in Dixie USA from the combined effect of the patent applicant's amendment of his claims as well as his written arguments made to the USPTO accompanying the amendment. However, a patentee's claims need not be amended at all in order to trigger prosecution history estoppel. In some cases, the applicant's arguments alone, generally made in the form of the applicant's written "remarks" filed in response to the examiner's rejections, can create "argument-based prosecution history estoppel." These arguments may involve characterizations of the claimed invention and/or the prior art, and will typically assert differences between the two that support patentability. Because argument-based prosecution history estoppel is not founded on any explicit changes being made to the claims, a "clear and unmistakable surrender of subject matter" is necessary to invoke it.¹⁶⁵

Prosecution history estoppel can also arise without an applicant amending her claims, but rather through the arguments she makes to obtain allowance. As the Circuit observed in its 2006 decision Conoco, Inc. v. Energy & Envtl. Int'l, L.C.,¹⁶⁶

[P]rosecution history estoppel limits the broad application of the doctrine of equivalents by barring an equivalents argument for subject matter relinquished when a patent claim is narrowed during prosecution. We have recognized that prosecution history estoppel can occur during prosecution in one of two ways, either (1) by making a narrowing amendment to the claim ("amendment-based estoppel") or (2) by surrendering claim scope through argument to the patent examiner ("argument-based estoppel"). ¹⁶⁷

The second variety of prosecution history estoppel, less common than the amendment-based estoppel exemplified by Dixie USA, is referred to as "argument-based estoppel" and further detailed in a separate subsection of this chapter.¹⁶⁸

[2] Scope of Estoppel

Assuming that a patentee's actions during prosecution (in the form of claim amendments and/or arguments) triggered prosecution history estoppel, the next step of the analysis is to determine the proper scope of that estoppel. In other words, may the patentee narrow its claim via amendment in response to USPTO rejections and yet still retain some scope of equivalents beyond the literal scope of the amended claim?

Consider, for example, a claim reciting "a composition of matter comprising less than 50 percent X by weight." In response to a USPTO rejection based on prior art that taught a composition having 40 percent X, assume that the patent applicant narrowed its claim to recite that the patented composition must comprise "less than 20 percent X by weight."¹⁶⁹ If an accused infringer manufactures and sells a composition having 25 percent X, there is no literal infringement.¹⁷⁰ Nevertheless, could the accused...