Reversing (for a second time) a judgment of infringement of three International Rectifier patents by a district court, the U.S. Court of Appeals for the Federal Circuit recently handed semiconductor manufacturer IXYS an important victory in its long-running battle against competitor International Rectifier Corp. International Rectifier Corp. v. IXYS Corp., Case Nos. 07-1063, -1441, -1165 (Fed. Cir., Feb. 11, 2008) (Linn J.).
The International Rectifier patents are directed to metal-oxide-semiconductor field-effect transistors (MOSFETs). IXYS's accused devices include MOSFETs that are manufactured, in part, by doping the surface of a silicon wafer with a pattern of impurities to create multiple regions with different electrical properties. At issue in the case were three claim terms, each relating to the shape and configuration of these regions. One of the patents, U.S. Patent No. 4,959,699 (the '699 patent), requires that the semiconductor wafer include "a lightly doped" region that is "adjoining" a "region of opposite conductivity type."
The district court initially granted summary judgment of infringement of the '699 patent, which the Federal Circuit reversed after articulating a revised interpretation of the term "adjoining." Although the Court remanded and instructed the district court to enter judgment of non-infringement in favor of IXYS, the district court concluded the mandate applied only to literal infringement. It allowed the issue of infringement under the doctrine of equivalents to be tried to a jury, which found infringement. IXYS appealed.
The Federal Circuit found that besides side-stepping its mandate to enter a judgment of non-infringement, the district court apparently did not show proper deference to the prosecution history concerning the "adjoining" claim term. Specifically, the term "adjoining" was added during prosecution to overcome a rejection under 35 U.S.C. §112. The Court rejected two arguments by International Rectifier that the amendment did not preclude doctrine of equivalents. First, it did not matter that the amendment in question broadened the claim in certain respects. The Court found that the addition of the word "adjoining" narrowed the scope of the claim, at least with respect to that term and rejected International Rectifier's argument that the amendment was broadening merely because it eliminated some claim limitations." Second, the Court disagreed that the purpose of the amendment was tangential to the asserted equivalent. By adding the limitation "adjoining," International Rectifier limited the claimed structure from one that could perform as either a MOSFET or an insulated gate bipolar transistor (IGBT) to one that could perform only as a MOSFET. The Court held that International Rectifier's decision to limit its claim to only the MOSFET structure, "whether or not required to overcome the rejection, cannot be described as only tangentially related to the equivalency of a structure with non-adjoining regions." Holding that "prosecution history estoppel precludes consideration of infringement by equivalents," the Court vacated the damages award and permanent injunction.
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