This week the USPTO published a notice in the Federal Register (89 FR 19817, March 20, 2024), announcing the issuance of a memorandum from the Commissioner for Patents to the examiner corps (“the Memorandum”) concerning means-plus-function claiming under 35 USC 112(f).

The Memorandum does not break any new ground, but it provides a useful brief overview of the USPTO’s approach to means-plus-function claiming (which is covered in greater detail in MPEP 2181).

Section I.C of the Memorandum (“Adequate Support for § 112(f) Limitations”) provides a good entry to a discussion of the Halliburton “dead zone,” so named after a Supreme Court case, Halliburton Oil Well Cementing Co. v. Walker, 329 US 1 (1946). Halliburton invalided device claims that recited means for performing functions, without corresponding structure in the rest of the application.

In 1952 the means-plus-function claiming provision currently in 35 USC 112(f) was added by Congress, to partly undo the effect of Halliburton, and to allow functional claiming under certain conditions. The new provision stated that a claim element “may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” Nonetheless later cases have continued to cite Halliburton as establishing a judicially-created “dead zone,” invalidating functional claims that do not qualify for construction under 35 USC 112(f). See, e.g., Sanada v. Reynolds, 67 USPQ2d 1459 (BPAI 2003) (“any claim that includes purely functional claim language and which, for whatever reason, is not subject to the limited construction under 35 U.S.C. § 112, sixth paragraph [now 112(f)], falls into a ‘dead zone’ according to the Halliburton rule as applied by the Supreme Court in 1946 and thus is unpatentable.”)

What is this dead zone? And why are claims that fall into it invalid and thus unpatentable?

Claiming structural can trigger interpretation under 112(f), but does not necessarily do so, even if the term “means” is employed in the claim. Use of common terms that connote structure even though they do so in ways that describe their functions (such as a sensor (which senses things), or a fastener) are interpreted as structural terms, rather than under 112(f). And use of structural language can rebut a presumption of the applicability of 112(f) for functional language, an example being a recitation of “knife means for cutting.” Other claim elements that use functional language will generally be interpreted under 112(f).

But what if 112(f) applies, yet the specification does not describe the “corresponding structure, material, or acts” related to the recited functions, as 112(f) requires? This is where we encounter the Halliburton dead zone. The MPEP does not use the term, but Section I.C of the Memorandum describes why such claims are invalid. First, they are indefinite under 35 USC 112(b). To quote from the Memorandum (page 3), “If there is no disclosure of structure for performing the entire recited function, the claim fails to satisfy the requirements of § 112(b) and should be found indefinite. Further, the structure disclosed in the written description must be clearly linked to or associated with the function recited in the claim, or the claim should be found indefinite.”

In addition, such claims do not meet the written description requirement of 35 USC 112(a) (as well as perhaps failing to meet the enablement requirement in that same section). As the Memorandum states at page 4, “A § 112(f) claim limitation that is found to be indefinite under § 112(b) based on failure of the specification to disclose corresponding structure that performs the entire claimed function will also lack adequate written description and may not be sufficiently enabled to support the full scope of the claim under § 112(a).”

A further consideration comes into play for computer-implemented claim features interpreted under 112(f). For such features the application must disclose more than a general-purpose computer in order to avoid being indefinite. The disclosure must include an algorithm for carrying out the recited function(s), which can be “in any understandable terms including as a mathematical formula, in prose, in a flow chart, or in any other manner that provides sufficient structure,” Memorandum, page 4. Such a finding of indefiniteness may also render the computer-implemented claim as lacking written description support and/or as not enabled.

The bottom line is that device claim features must be supported by sufficient structure, either recited in the claim itself (in which case 112(f) does not apply), or elsewhere in the application sufficient to support an interpretation under 112(f). Functional claiming fully divorced from a recitation or description of sufficient structure leaves one in the Halliburton dead zone, with the claims invalid as indefinite, lacking adequate written description support, and/or lacking enablement.

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