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(Fed Cir 2/11/08)

IR sued IXYS for patent infringement, with IR prevailing at trial; the Federal Circuit reversed the judgment of infringement and dismissed the cross-appeal as moot.

IR holds the '699, '725, and '767 patents, all of which disclose metal oxide semiconductor field effect transistors. A prior appeal in this matter was taken from summary judgment opinions in which the trial court held that the accused devices infringed the claims at issue. The Federal Circuit articulated revised interpretations of each term. As to the "adjoining" limitation, the Federal Circuit previously held that there could be no infringement. Regarding the remaining disputed claims, the Federal Circuit found that fact issues existed as to both the "polygonal" and "annular" limitations. On remand, the trial court concluded that the Federal Circuit's mandate with respect to the term "adjoining" pertained only to literal infringement. As a result, the issue of infringement under the doctrine of equivalents was tried to a jury, which found that the accused devices infringed the "adjoining" claims by equivalents. The jury also found that the accused devices met the "polygonal" limitation under the doctrine of equivalents, but that they did not possess any "annular" source regions.

IXYS argued that IR was foreclosed by prosecution history estoppel from resorting to the doctrine of equivalents as to the "adjoining" limitation. During prosecution of the '699 patent, IR chose to introduce the term "adjoining." This term excluded structure that might have been covered by the original claim language because the "support body" of the old claim was only required to "support said lightly doped major body portion," not necessarily to touch it. The amendment therefore narrowed the scope of the claim. IR's decision to claim structure using the limiting term "adjoining" could not be described as only tangentially related to the equivalency of a structure with non-adjoining regions. Accordingly, prosecution history estoppel barred IR from asserting infringement of the "adjoining" limitation under the doctrine of equivalents. IR also argued that IXYS was precluded from contesting the presence of annular source regions in the accused devices because it failed to contest that limitation in the submissions required under the local rules. However, this argument was raised and rejected by the Federal Circuit in the prior appeal. The Federal Circuit's mandate in the prior appeal required the trial court to treat the "annular" limitation the same way in all three patents. The combination of the Federal Circuit's mandate in the prior appeal and the jury verdict of non-infringement as to the "annular" limitation compelled a judgment of non-infringement regarding the remaining asserted claims.