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Claims Anticipated by Inherent Features of Prior Art

September 21, 2001
Brittingham IV, Smith R.

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Last Month at the Federal Circuit - October 2001

Judges: Rader (author), Plager, and Dyk

In EMI Group North America, Inc. v. Cypress Semiconductor Corp., No. 00-1508 (Sept. 21, 2001), the Federal Circuit affirmed a district court’s decision to refuse a new trial to correct supposedly inconsistent jury verdicts, but reversed the district court’s finding that the asserted patent claims were not invalid as inherently anticipated. The Court agreed that there was sufficient evidence in the record to support the jury’s conclusion that it was scientifically impossible to implement the claimed invention. At the same time, the Court also agreed that the evidence supported an alternative finding that the invention was inherently anticipated by prior art structures and methods, assuming it was not impossible. As a result, the Court reversed the district court’s decision to grant a JMOL in favor of the patent holder and held the patents invalid.

EMI Group North America, Inc. (“EMI”) owns two related patents, U.S. Patent Nos. 4,826,785 (“the ‘785 patent”) and 4,935,801 (“the ‘801 patent”), both of which relate to semiconductor fuses. The patents cover a structure and a method for producing a fuse that can be easily severed so that redundant circuitry on a chip can be disconnected. Prior art devices had previously used fuses with polysilicon interconnects, which were easily disconnected using laser energy. However, metal fuses were preferred since they produced more efficient and reliable connections. Unfortunately, higher energy lasers were needed to disconnect metal fuses, leading to problems with other structures on the chip.

The patents described a way to melt or disconnect metal fuses using low-energy lasers. The claimed inventions used a metal interconnect layer, such as aluminum, underneath a cap of optically absorptive refractory material with a higher boiling point than the underlying metal layer, such as tungsten or titanium. One embodiment also included a glass passivation layer on top of the optically absorptive, or transition, metal layer. The patents stated that low-laser energy would be absorbed by the transition layer, which would then melt the underlying metal interconnect layer with its lower melting point. This would in turn cause a vapor pressure to develop under the transition metal layer. Ultimately the fuse material would explode, disconnecting the circuit.

This explosion mechanism was part of each asserted claim in both patents. Yet the inventors had never actually practiced or observed this mechanism. The patents merely provided a theoretical explanation for why the system worked.

EMI sued Cypress Semiconductor Corporation (“Cypress”) for infringement of both the ‘785 and ‘801 patents. Cypress’s accused products used fuses with an aluminum layer covered by a tungsten-titanium alloy layer and glass passivation layer. At the trial, Cypress’s expert testified that the explosion mechanism simply could not happen and that the patents claimed an impossible process or structure. He also stated that, assuming the explosion mechanism was not impossible, it was inherently practiced in several prior art references that disclosed the same sort of structures even if they did not describe a similar theoretical explanation.

The jury agreed with both of the expert’s conclusions. The jury found that the patents did claim an impossible process and structure, and that if the process and structure were not impossible, they were inherently anticipated by the prior art. The jury also found that the Cypress devices did not infringe the patents. EMI requested that the district court order a new trial, arguing that the jury conclusions that the claimed fuse and process were impossible and also inherently anticipated were inconsistent. EMI also sought a JMOL, arguing that the asserted claims were not invalid as impossible or anticipated and that the accused products did infringe the patents. The district court denied the motion for new trial and the JMOL with respect to infringement and invalidity due to impossibility, but granted the JMOL as to anticipation.

The Federal Circuit agreed that a new trial was not necessary. Under applicable regional circuit law, a defense on alternative theories was permitted as long as the theories were explained carefully in language capable of lay comprehension. The Court noted that the alternative nature of Cypress’s argument—that the process was impossible or, if not impossible, inherent in the prior art—was adequately supported by evidence in the record. Further, the alternative nature of the two conclusions was clearly set forth in the jury verdict form. Accordingly, the Court concluded that the district court did not abuse its discretion in harmonizing the various jury conclusions.

The Federal Circuit also affirmed the district court’s refusal to overturn the jury’s verdict that the patents were invalid because the explosion mechanism was impossible. The Court noted that, where a claim includes “incorrect science in one limitation,” the entire claim is invalid. The Court concluded that the trial testimony of Cypress’s expert regarding the impossibility of the explosion mechanism provided ample support for the jury’s verdict.

Finally, the Federal Circuit reversed the district court’s decision to grant EMI’s JMOL that the patents were not anticipated through inherency. Cypress’s expert had testified that no prior art reference actually disclosed the explosion mechanism. However, he testified that there were prior art references disclosing the same structure as that found in the patents and that whatever scientific mechanism was responsible for severance of the prior art fuses would have been an inherent feature of those structures.

The district court had found that evidence insufficient, relying on certain cases that suggested that inherency could be satisfied only if a person of ordinary skill would have actually recognized the missing feature to be described in the prior art reference itself. The Federal Circuit disagreed, concluding that where the limitations are theoretical mechanisms or rules of natural law, there is no requirement that a person of ordinary skill appreciate the existence of that mechanism before there can be anticipation.