Surrender of Claim Scope by Prosecution Statements Must Be "Clear and Unmistakable"

The U.S. Court of Appeals for the Federal Circuit has held that the doctrine of prosecution disclaimer may not be used to narrow the ordinary meaning of a patent claim based on statements during prosecution, unless the allegedly disavowing statements or actions are "clear and unmistakable." Omega Engineering, Inc. v. Raytek Corp., Case No. 02-1478 (Fed. Cir. July 7, 2003).

Omega Engineering involved three patents that disclosed a laser sighting system used to target infrared thermometer scans. The district court’s claim construction analysis focused on language in the patents describing the use of lasers to outline a target energy zone. The district court read the means-plus-function claim language directed to this feature to exclude targeting that involved a laser beam that strikes inside the target energy zone. The district court’s claim construction rested heavily on the application of the doctrine of prosecution disclaimer. It found that the plaintiff had made numerous statements during the prosecution of the patents in suit that narrowed the scope of the disputed claims. Based on its claim construction, the district court granted summary judgment of non-infringement and, in the alternative, granted summary judgment invalidating two of the disputed claims.

The Federal Circuit reversed and remanded. In a panel decision authored by Judge Clevinger, the court noted the general rule that where "the patentee had unequivocally disavowed a certain meaning to obtain his patent, the doctrine of prosecution disclaimer attaches and narrows the ordinary meaning of the claim congruent with the scope of the surrender." However, the Court admonished that the doctrine of prosecution disclaimer does not apply "where the alleged disavowal of claim scope is ambiguous."

Rather, the Court explained that the doctrine of prosecution disclaimer requires that the defendant demonstrate a "clear and unmistakable disclaimer," reasoning that such a clear and unmistakable disclaimer is required in order to maintain the balance between the need for adequate public notice and the right to seek broad patent coverage. The Court noted in a footnote that "this is the same standard applicable, in the context of the doctrine of equivalents, to the doctrine of argument-based estoppel. ..."

The Federal Circuit then found that the district court had mistakenly used a number of ambiguous statements in the prosecution history to narrow the scope of the patents in suit. The Court also held that triable issues of material fact existed after the erroneous claims construction had been corrected and reversed and remanded for further proceedings.