The Perils of Open-Ended Claim Ranges – A Reminder Courtesy of the Federal Circuit
Posted in Litigation, Patents

Patent prosecutors drafting claims that recite open-ended ranges (e.g., at least 10%, greater than 5 units) were again warned of the perils of claiming more than has been disclosed. In a recent decision by the Federal Circuit, MagSil Corp. v. Hitachi Global Storage Tech., Inc., the Court affirmed the trial court’s determination that the asserted claims were invalid as a matter of law for lack of enablement. The Court found that the open-ended range recited in the independent claim was not enabled because the disclosure provided support for only a small portion of the claimed open-ended range, citing to the dual function of enablement for both ensuring there is adequate disclosure to support a claimed invention and preventing claims broader than the disclosed invention. Patent practitioners reciting open-ended ranges should consider taking one or more steps to better ensure validity of their claims, including reciting the structure that enables the recited range in the claim, adding dependent claims that close the open-ended range, and providing examples in the specification that support a wide spectrum of values, and in particular values that fall within the high end of the open-ended range.

The appellants, the Massachusetts Institute of Technology (“MIT”), who owned the patent at issue, and MIT’s exclusive licensee of the patent, MagSil Corporation (“MagSil”), brought a patent infringement suit against several defendants, including Hitachi Global Storage Technologies and related companies (“Hitachi”) alleging patent infringement. While a number of defendants settled the claims with MIT and MagSil (collectively, “the Plaintiffs”), Hitachi challenged the patent as being invalid for lack of enablement.

MIT’s patent, U.S. Patent No. 5,629,922 (“the ‘922 patent”), was directed to a tri-layer tunnel junction that tunnels, aka passes, an electric current between two electrodes in a computer hard disk’s read-write sensor. The independent claim at issue recited a device forming a junction having a resistance that includes two electrodes, each having a magnetization direction, and an electrical insulator between the two electrodes. Significantly, the independent claim recited that applying a small magnitude of electromagnetic energy to the junction reverses at least one of the magnetic directions and causes a change in the resistance by at least 10% at room temperature.

The Court found that the open-ended range reciting that the change in the resistance is at least 10% at room temperature was not enabled because the specification did not support the upper limits of the range without undue experimentation. The Plaintiffs, to their own ultimate peril, relied upon testimony from an expert and its own inventor to support their position that the claims covered resistive changes of 100% or more or even 1000% or more. The specification, however, only disclosed that its invention achieved a “ten percent change in the tunneling resistance with respect to magnetic field (H) variation,” and in some cases “as much as 11.8% change was seen.” While the facts showed that 12 years after the ‘922 patent was filed resistive changes between 100% and 120% were achieved, the Court found such facts supported a finding that undue experimentation was necessary to achieve even some of the upper limits covered by the Plaintiffs’ independent claim, which the Court pointed out could be infinite. The Court noted that “a patentee chooses broad claim language at the peril of losing any claim that cannot be enabled across its full scope of coverage.” The Court also noted that in addition to ensuring there is adequate disclosure to support a claimed invention, “[t]he enablement doctrine’s prevention of over broad claims ensures that the patent system preserves necessary incentives for follow-on or improvement inventions.”

The Court’s decision is in line with In re Fisher, in which the predecessor of the Court found the limitation of “at least 1 International Unit of [adrenocorticotropic hormone] ACTH per milligram” not enabled by a specification that did not demonstrate ACTH potencies much greater than 2.3 International Units. The Court, however, distinguished open-ended claim ranges from open-ended claim language, such as the term “comprising,” by distinguishing Gillette Co. v. Energizer Holdings, Inc. from the present case. In Gillette, claim language that recited “[a] safety razor blade unit comprising … a group of first, second, and third blades” was found to also encompass a razor with four blades in view of the claim language, specification, and prosecution history. The Court distinguished MagSil from Gillette by noting that that “this cases’ claim limitation extending to an open-ended range of values, which must be present for infringement, is different from a preamble recitation ‘comprising,’ which does not exclude additional features to devices otherwise within the narrower claim definition.”

There are a number of steps patent practitioners should consider to ensure their claims are adequately enabled when reciting ranges. One step to consider is reciting the structure that actually achieves the open-ended claim range. In MagSil Corp., the specification indicated that the improved performance was believed to be a result of a decrease in surface roughness and/or a result of an improved intervening insulator that helped keep the surface integrity of the electrodes. The Court noted that the asserted claims did not include any process steps for fabricating the device or recite smoother surfaces or specifics related to an improved insulator. The Plaintiffs may have had more success arguing enablement if the claims incorporated this structure, if the structure was novel and nonobvious, and if they were able to demonstrate that the recited structure helped achieve the improved ranges.

When citing open-ended ranges in a claim, patent practitioners should also consider including dependent claims that place a cap on those ranges. The cap should correspond with examples provided in the specification to ensure enablement. Reciting a cap of an open-ended claim range in a dependent claim can provide a useful fallback position should enablement become an issue.

Still further, practitioners should include examples in the specification that support a wide spectrum of values when citing an open-ended range. In the present case, the Court noted that the open-ended claim language covers resistance changes up to infinity. While showing a change of infinity may not have been possible, the Plaintiffs would have been better positioned had they been able to include examples that showed a 100% change or a 1000% change that they testified was possible. Obviously practitioners should not make-up examples to provide enablement support, but to the extent examples can be relied upon to support a broad spectrum of values, such examples should be explained in the specification. Preferably the examples will be reduced to practice, but if not, practitioners should consider the suitability of providing a description that demonstrates that values at the high end of the spectrum are at least mathematically possible in view of the teachings of the specification.

This advisory was prepared by Nutter's Intellectual Property practice. For more information, please contact your Nutter attorney at 617.439.2000.

This update is for information purposes only and should not be construed as legal advice on any specific facts or circumstances. Under the rules of the Supreme Judicial Court of Massachusetts, this material may be considered as advertising.

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