In recent years, the degree to which a patent claim may be extended beyond its literal scope has been one of the most controversial and rapidly developing areas in patent law. In patent speak, this is referred to as claiming infringement under the "doctrine of equivalents." Under this doctrine, a product or process that is missing an element required by a patent claim can still be found to infringe if it contains a corresponding element that is no more than "insubstantially different."
The doctrine of "prosecution history estoppel" can limit the scope of the doctrine of equivalents. If the patent applicant amends the stated scope of his or her application after it is filed, he or she may be barred from relying on the doctrine of equivalents to embrace an element in an accused product or process that is different from what the amendment specified, even if the difference is only insubstantial.
In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., Case No. 95-1066 (Fed. Cir. Sept. 26, 2003) – the ninth judicial decision in a lawsuit that was originally filed about 15 years ago –the Federal Circuit, sitting en banc and after sifting through no less than 15 amicus briefs, laid down a new set of new rules for determining the scope of a prosecution history estoppel.
The Law Before Festo IX
The amendment to the application had to first be analyzed to determine whether it narrowed the scope of the patent. If it did not, there would be no estoppel against arguing infringement under the doctrine of equivalents.
However, if the amendment did narrow the scope, the patent owner had to demonstrate that the amendment was not made for a reason "relating to patentability." He or she could only establish this by pointing to information in the file that the U.S. Patent and Trademark Office maintains on the patent application (commonly referred to as the "prosecution history record" or "file wrapper"). If the patent owner succeeded in this effort, there would again be no estoppel. If, on the other hand, the patent owner was unable to demonstrate that the amendment was made for a reason other than patentability, the doctrine of prosecution history estoppel would apply.
The application of the doctrine of prosecution history estoppel could prevent the scope of a patent claim from being expanded under the doctrine of equivalents to embrace a product or process that is only insubstantially different from the element that was amended. Once an estoppel is determined to apply, the insubstantially different element in the accused product or process could only have been embraced if the patent owner could prove that "one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent." Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 535 U.S 722, 741 (2002) (Festo VIII). This test could be met, the U.S. Supreme Court said in Festo VIII, if:
- "[T]he equivalent [was] unforeseeable at the time of the [amendment]";
- "[T]he rationale underlying the amendment [bore] no more than a tangential relation to the equivalent in question"; or
- "[T]here [was] some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question."
Festo IX – The New Rules
The Federal Circuit in Festo IX reaffirmed these principals as stated by the U.S. Supreme Court and went on to set forth guidelines as to when each of these three tests could be met. The Federal Circuit first said that it is up the court, not the jury, to decide whether the evidence is sufficient to overcome an estoppel: "Questions relating to the application and scope of prosecution history estoppel . . . fall within the exclusive province of the court."
The court next directed its attention to explaining the first test – when the equivalent would have been unforeseeable at the time of the amendment. The Federal Circuit said that the demarcation of such evidence "is best left to development on a case-by-case basis." Nevertheless, the court set forth "general guidance." The court said that unforseability must be determined from the perspective of a hypothetical person of ordinary skill in the art. An allegedly equivalent element that was not known at the time of the amendment, the court said, "would not have been foreseeable." An allegedly equivalent element that was known at the time of the amendment "would more likely have been foreseeable." If the element was also known in the field of the invention at the time of the amendment, the court said that the equivalent "certainly should have been foreseeable."
The Federal Circuit pointed out that the second test – the "tangential relation" test - examines "whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent." While the court did not define the scope of this test any more precisely, it did state that an amendment made to avoid prior art that contains the equivalent is not tangential. The court said that the tangential relation test must be determined solely based on the prosecution history record. Still, the court left the door open to testimony from those skilled in the art "when necessary" to explain the meaning of the record.
The Federal Circuit observed that the third test- the "some other reason" inquiry- "while vague, must be a narrow one." The court said that the test may be satisfied by proof that there was "some reason, such as the shortcomings of language, why the patentee was prevented from describing the alleged equivalent when it narrowed the claim." Proof that the equivalent was an "inferior and unacceptable design," however, is insufficient to meet this requirement. The court also said that the proof should be limited to the prosecution history record "[w]hen at all possible," but did not explain when extrinsic proof would be permitted.
Proof that an element urged to be an equivalent was not known at the time of the amendment appears to be almost certain to overcome an estoppel. Even if the element was known, proving that it was not known in the field of the invention may be sufficient.
On the other hand, proof that the equivalent was known in the field of the invention means that the equivalent "certainly should have been foreseeable." Curiously, however, when it came time for the Federal Circuit to apply this test to the facts in Festo IX, the court appeared to apply a different and more lenient test.
One of the patent claims at issue in Festo had been amended to require a motor sleeve that was magnetizable. The accused product, however, used an aluminum sleeve that was not magnetizable. Aluminum was undoubtedly a known material in the art of motor design. Yet, the Federal Circuit remanded the case to the district court to determine "whether an ordinary skilled artisan would have thought an aluminum sleeve to be an unforeseeable equivalent to a magnetizable sleeve in the context of the invention (emphasis added)." Thus, the question appears to be whether it was foreseeable to substitute the insubstantially different element in the invention, not merely whether the element was known to those in the field of the invention.
The new tests announced in Festo IX, coupled with the determination that they must be resolved by the judge, may lead to a whole new breed of court hearings in patent cases. Soon, there may be "Festo hearings," much like the 1996 Supreme Court decision in Markman v. Westview Instruments, Inc led to "Markman hearings" to determine the meaning of the patent claims.
The technical issues of "equivalents" and "estoppel" will continue to have a real effect on many patent cases. The determination of whether an element is only insubstantially different from what is required by the patent has always been regarded as a determination of fact for the jury to decide. Thus, once a party is given the right to assert infringement under the doctrine of equivalents, he is assured of having his infringement case decided by a jury that can often be swayed by other types of evidence.
Festo IX will require that a high level of effort to be made by patent prosecutors to obtain the broadest possible patent claims. Under Festo IX, it may be difficult to avoid the bar of an estoppel. Thus, obtaining claims of the correct scope in the original application may be of paramount importance.
Undoubtedly, many patent owners will be unhappy with this new decision. In his concurring opinion in Festo IX, Judge Rader expressed concern about "the difficulty of preserving expectations when frequently revising standards affect the scope of patent coverage." In her dissent, Judge Newman was more blunt: "By adopting a generous interpretation of the scope of surrender, and stinginess towards its rebuttal, the ensuing framework is one that few patentees can survive."