The Federal Circuit Narrows IPR Estoppel

The Federal Circuit’s recent decision in Ingenico Inc. v. IOENGINE, LLC, No. 2023-1367, 2025 WL 1318188 (Fed. Cir. May 7, 2025), has clarified and limited the scope of IPR estoppel in a way that could impact IPR strategies.

Background

In 2011 Congress passed the Leahy Smith America Invents Act (AIA), which, among other things, established a post-grant review process called “inter partes review.”  The inter partes review or IPR process is typically initiated by a defendant in a patent infringement case and was intended to provide a quicker and less expensive way to challenge patent validity than district court litigation. A patent challenger initiates an IPR by filing a petition with the Patent Trial and Appeal Board (PTAB) explaining in detail why the challenger believes the challenged patent claims are invalid. If the PTAB determines that the challenger is reasonably likely to prevail with respect to at least one challenged claim, the PTAB may institute an IPR. After the IPR is instituted, the parties engage in a sort of mini trial that often involves discovery, expert witnesses and a hearing before a panel of PTAB judges. Working within statutorily dictated deadlines, the PTAB will issue a Final Written Decision providing its conclusions as to the validity of the challenged patent claims. District court litigation is often stayed during the pendency of an IPR.

One provision of the IPR statute, 35 U.S.C. § 315(e)(2), estops a patent challenger from asserting in district court litigation that a “claim is invalid on any ground that the petitioner raised or reasonably could have raised during that inter partes review.” This provision was included “to ensure that post-grant review operates fairly and is not used for purposes of harassment or delay.”

Issues with IPR Estoppel

Courts have grappled with two distinct issues in deciding whether IPR estoppel applies. The first concerns the meaning of the “reasonably could have raised” language from the statute and how it applies to particular prior art that was not raised in an IPR. The Federal Circuit resolved this issue in 2023 when it held that estoppel applies if “a skilled searcher conducting a diligent search reasonably could have been expected to discover [the prior art raised in litigation], as these are grounds that the petitioner ‘reasonably could have raised’ in its petition.”

The second issue concerns the meaning of the term “ground,” and typically arises when a patent challenger asserts in district court that a prior art system invalidates the claims and where documents exist describing that system. Section 311(b) says that an IPR can be requested “only on a ground that could be raised under section 102 or 103 and only on the basis of prior art consisting of patents or printed publications.” 35 U.S.C. § 311(b). District courts have been divided on how to interpret the term “ground,” even within the same district. In the District of Delaware, for example, Judge Stark held that the patent challenger was estopped from relying on a printed publication describing a system in combination with the system because the printed publication could have been cited in the IPR, implicitly characterizing the “ground” as the arguments based on particular disclosed features, whether disclosed in documents or a physical system.  Judge Stark characterized the system art simply as additional evidence supporting the ground for invalidity raised by the documents describing that system. In a later case, Judge Noreika held that estoppel did not apply to an invalidity challenge based on prior art considered in an IPR in combination with a system described by that prior art, characterizing a “ground” for invalidity to be “the specific pieces of prior art that are the basis or bases on which a petitioner challenges a claim” and reasoning that the printed publication and the system are different pieces of prior art.

The Federal Circuit Settles the Issue

The Federal Circuit has now settled this issue by definitively defining the term “ground.” In Ingenico, the patent challenger, Ingenico, sued IOENGINE, the patent owner, for declaratory judgment of noninfringement and invalidity and also filed an IPR challenging the asserted patents, which were directed to a portable network connection device. At trial the patent challenger argued that the claims not invalidated in the IPR were invalid as anticipated or obvious because the prior art device known as the DiskOnKey device with its Firmware Upgrader software “was either ‘on sale’ or ‘in public use’ under 35 U.S.C. § 102(b) (pre-AIA), or ‘known or used by others . . . before the date of the invention’ under 35 U.S.C. § 102(a) (pre-AIA)” Id. at *3. The jury found the claims infringed but invalid.

On appeal the patent owner argued, among other things, that the patent challenger should have been “estopped from introducing Firmware Upgrader at trial” because it “was entirely cumulative and substantively identical to” a document that could have been raised in the IPR. Id. at *11. The Federal Circuit disagreed, holding that “grounds [as used in 35 U.S.C. § 315(e)(2)] are the theories of invalidity available to challenge a claim under §§ 102 and 103.” These theories are “limited . . . to invalidity challenges based on ‘prior art consisting of patents or printed publications.’” The Court noted that “[b]y design, a petitioner has no opportunity to challenge that the claimed invention was known or used by others, on sale, or in public use at IPR.” Id. at *12, citing 35 U.S.C. § 311(b).

The Federal Circuit thus clarified that “a ground is not the prior art asserted during an IPR,” holding “that IPR estoppel applies only to a petitioner’s assertions in district court that the claimed invention is invalid under 35 U.S.C. §§ 102 or 103 because it was patented or described in a printed publication . . . . IPR estoppel does not preclude a petitioner from asserting in district court that a claimed invention was known or used by others, on sale, or in public use. These are different grounds that could not be raised during an IPR.” Id. at *12, 15-16. 

Why It Matters

By equating the “ground” for challenging invalidity with the theory of invalidity, e.g. based on a printed publication as opposed to based on prior use, and distinguishing it from the evidence used to support those theories, e.g., prior art, the Federal Circuit has clarified and arguably narrowed the scope of IPR estoppel in a way that could change the strategic thinking behind both filing an IPR and responding to one. 

Patent challengers assessing what invalidity arguments might remain for trial should they lose an IPR can take some comfort that any arguments based on prior public use, prior sale, or prior knowledge will be available regardless of whether there are documents describing the system that was the subject of such use, sale, or knowledge. Patent owners, on the other hand, must now be more wary of system art and, if it exists, can no longer hope, if they survive IPR, to use estoppel to defeat system art based on cumulative documentation.

157 Cong. Rec. S1326 (daily ed. Mar. 7, 2011) (Statement of Sen. Sessions).  A full treatment of the legislative history of the estoppel provision can be found in B. Murphy, The Many Flavors of Inter Partes Review Estoppel: A Review and Update, Haug Partners LLP 2023, available at .

Ironburg Inventions Ltd. v. Valve Corp., 64 F.4th 1274, 1298 (Fed. Cir. 2023)

See Prolitec Inc. v. ScentAir Techs., LLC, No. 20-984-WCB, 2023 WL 8697973, at *21-*23 (D. Del. Dec. 13, 2023) (collecting cases).

Wasica Fin. GmbH v. Schrader Int'l, Inc., 432 F. Supp. 3d 448, 453-54 (D. Del. 2020).

Chemours Co. FC, LLC v. Daikin Indus., Ltd., No. CV 17-1612 (MN), 2022 WL 2643517, at *1 (D. Del. July 8, 2022) (internal quotations omitted).