What is a means-plus-function claim?

What is a means-plus-function claim?

By Ameera Haider, law clerk, and Jay Moldovanyi, partner, Fay Sharpe LLP

Inventors occasionally create complex, technical devices that can be better described by the function they perform, as opposed to their structure. This is particularly true of inventions in the electronic and computer arts but can also be true of mechanical inventions.

Traditional patent claims describe the specific structure of an invention. In contrast, “means-plus-function” claims express a technical feature in functional terms. This offers patent writers more flexibility in how they describe the function a device performs. For example, an inventor could claim an electronic or electromechanical device by describing circuits performing specific functions, as opposed to the circuitry of the actual device.

Statutory support for means-plus-function claims is found in 35 U.S.C. 112(f), which states, “An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure.”

Previous standard: strong ‘means’ presumption

The rule for means-plus-function claim drafting has changed multiple times in the past two decades. In the early 2000s, the Federal Circuit held that using any word other than “means” in a claim was usually not sufficient for the claim to be considered a means-plus-function claim. More recently, a “strong presumption” added that means-plus-function was not indicated in the absence of the word “means.”

For example, in Flo Healthcare Solutions, LLC v. Kappos (2012), the Court was unwilling to allow other words (besides “means”) to be considered as means-plus-function wording in a claim if the limitation had any structural connotation. Relying on this standard, a three-judge panel of the Federal Circuit in the Williamson v. Citrix case in 2014 found the word “module” to have several dictionary meanings with structural connotations, disqualifying it as a means-plus-function claim.

En banc holding reverses presumption

On reconsideration in 2015, the Federal Circuit en banc (all the judges together) reversed the decision of the panel as to what happens when the word “means” is replaced with another nonstructural term, such as “module.” The implications of the Williamson case will affect the way in which claims for future inventions are drafted and how these claims are construed during litigation.

Williamson v. Citrix background

Williamson owns U.S. Patent No. 6,155,840, which describes methods and systems for distributed learning to connect presenters with remote audiences. Claim 8 of this patent describes a distributed learning control module that executes three functions. While claim 8 describes three functions, it lacks the important trigger word “means.” Instead, the claim uses the word “module.”

Williamson v. Citrix en banc analysis

The Federal Circuit en banc reversed the “strong presumption” precedent tied to the word “means,” finding that the inquiry is not merely the presence or absence of the word “means.” Rather, the new standard is whether the words of the claim are understood by a Person Having Ordinary Skill in the Art (PHOSITA) to have a sufficiently definite meaning as the name for structure.

Section 112(f) now applies when a claim “fails to recite sufficiently definite structure” or the claim recites “function without reciting sufficient structure for performing that function.” But use of the word “means” does create a presumption that 112(f) applies.

Applying this new standard, the en banc court found that using the word “module” in claim 8 was sufficient for the claim to be interpreted as a means-plus-function claim. The court found the term “module” to be a nonce word, acting as a substitute for “means” in the context of the claim.

The court also found claim 8 to be indefinite because the specification did not disclose adequate structure corresponding to the term “module.”

What are nonce words?

Nonce words are generic, verbal constructs that do not connote definite structure. Examples of nonce words include module, component, apparatus, element, system, device and member. However, patent practitioners may not know which words are considered nonce words until litigating their cases.

Long-term impacts for patent claims

Inventors need to think carefully about how to best conceptualize their inventions, especially if the invention is executing a function. Patent applicants should also draft claims and prosecute applications cautiously to avoid unintended means-plus-function treatment, including considering whether a limitation could be characterized as a nonce word subject to Section 112(f). Using “means” as a triggering word when writing a means-plus-function claim is always advisable to eliminate ambiguity.

Changes in means-plus-function rules also affect defendants in patent litigation cases. For example, it may now be easier to demonstrate that claim limitations with nonce words – such as module – should be construed as means-plus-function claims under Section 112(f). On that basis, defendants can argue non-infringement or invalidity.

Ultimately, there is still uncertainty around how Williamson will apply in practice. What are considered nonce words and understanding what a PHOSITA considers structure are fact-specific questions that the court will need to answer in each case. And judging by the shifting standards of the court over the last two decades, there is no guarantee that it will stick to the new standard outlined in Williamson.

Ameera Haider is a law clerk at Fay Sharpe LLP. Reach her at ahaider@faysharpe.com or (216) 363-9133.

Jay Moldovanyi is a partner with Fay Sharpe LLP. If you have questions about patent preparation or prosecution, reach him at jmoldovanyi@faysharpe.com or (216) 363-9127.