IPR Estoppel

IPR estoppel is a statutory bar under 35 U.S.C. § 315(e) that prevents an IPR petitioner from raising certain invalidity arguments in subsequent proceedings after the PTAB issues a final written decision (FWD) in the IPR. WHAT TRIGGERS ESTOPPEL: the FWD must be a 'final written decision' — it must be reached on the merits; if the IPR is instituted and PTAB issues a FWD, estoppel attaches. ESTOPPEL DOES NOT ATTACH IF: (1) the IPR petition was denied institution — no FWD on the merits; (2) the IPR was settled before a FWD was issued — parties can terminate the IPR by joint motion, and estoppel does not apply; (3) the IPR was instituted but the petitioner's claims were not challenged — only grounds that were instituted (actually tried) create estoppel. SCOPE OF § 315(e): § 315(e)(1) — estoppel applies in subsequent USPTO proceedings (ex parte reexam, supplemental examination, etc.): petitioner estopped from raising ANY ground raised or reasonably could have been raised in the IPR; § 315(e)(2) — estoppel applies in civil actions (district court) and ITC proceedings: petitioner estopped from asserting as invalid any claim 'on any ground that the petitioner raised or reasonably could have raised' during the IPR. IPR ESTOPPEL IS ONE OF THE MOST SIGNIFICANT STRATEGIC RISKS of filing an IPR — a failed IPR can eliminate many of the petitioner's strongest invalidity arguments in subsequent litigation.

The 'reasonably could have raised' language in § 315(e) is one of the most contested and consequential aspects of IPR estoppel. TWO COMPETING INTERPRETATIONS: (1) BROAD INTERPRETATION (minority of courts): estoppel applies to any ground based on any prior art that a 'skilled searcher' could have found using reasonable diligence — i.e., any patents or printed publications that existed and were publicly accessible; some courts have applied this broadly to bar petitioners from raising even prior art that wasn't cited in the IPR; (2) NARROW INTERPRETATION (majority view): estoppel only applies to grounds that were actually raised or that the petitioner ACTUALLY KNEW about or reasonably should have discovered based on the prior art search conducted for the IPR; prior art discovered after the IPR through additional investigation is not necessarily estopped. KEY CASES: California Institute of Technology v. Broadcom (Fed. Cir. 2022) — the Federal Circuit confirmed that § 315(e)(2) estoppel applies to grounds the petitioner 'raised or reasonably could have raised' in the IPR petition, including grounds based on prior art that was available but not cited in the petition; this is an objective standard; Ironburg Inventions v. Valve Corp. (Fed. Cir. 2023) — elaborated on the standard. STRATEGIC IMPLICATION: petitioners should conduct a thorough prior art search BEFORE filing the IPR and cite ALL relevant prior art in the petition, even if they don't plan to use every reference — failure to cite known prior art may later be used to argue that the petitioner 'could have raised' that ground, creating estoppel.

IPR is limited to prior art challenges under § 102 and § 103. Estoppel under § 315(e) applies to grounds that were 'raised or reasonably could have raised' — and courts have generally interpreted this to mean only § 102 and § 103 grounds based on patents or printed publications, since those are the ONLY grounds available in IPR. THEREFORE: § 101 (patent eligibility / Alice) invalidity defenses are NOT subject to IPR estoppel — they cannot be raised in IPR, so they could not 'reasonably have been raised' in IPR, and estoppel does not bar them in subsequent litigation. § 112 (written description, enablement, indefiniteness) invalidity defenses are similarly NOT subject to IPR estoppel — these grounds cannot be raised in IPR; they remain available in district court and ITC proceedings regardless of an IPR result. § 102 and § 103 grounds based on PUBLIC USE, PRIOR SALE, or prior KNOWLEDGE (not documented in a printed publication) are also NOT subject to IPR estoppel — IPR is limited to patents and printed publications; non-documentary prior art cannot be raised in IPR and is thus not estopped by § 315(e). PRACTICAL SIGNIFICANCE: a petitioner whose IPR fails on prior art grounds should pivot to § 101 and § 112 challenges in district court, which remain fully available; this is why comprehensive invalidity analyses always include § 101 and § 112 arguments alongside prior art.

The Sotera waiver is a strategic tool that petitioners use to avoid discretionary denial of IPR institution under the Apple v. Fintiv framework — in exchange for a broader estoppel commitment. BACKGROUND: under the Apple v. Fintiv precedent (PTAB, 2020), PTAB may exercise discretion to DENY IPR institution when a parallel district court litigation is advanced (close trial date) because instituting the IPR would not serve judicial efficiency. SOTERA WAIVER: in Sotera Wireless v. Masimo Corp. (PTAB, 2021), PTAB held that if the petitioner VOLUNTARILY agrees to be estopped under § 315(e)(2) as if a FWD had been entered for ALL grounds in the petition (not just the instituted grounds), PTAB weighs that voluntary commitment as a factor militating AGAINST discretionary Fintiv denial; the expanded estoppel commitment (covering grounds the petitioner 'raised or reasonably could have raised' across the entire petition) makes the IPR more valuable to the district court and is a meaningful concession. WHAT THE PETITIONER GIVES UP: by filing a Sotera waiver, the petitioner is estopped from raising in any civil action or ITC proceeding any invalidity ground based on patents or printed publications that was raised or reasonably could have been raised in the petition — even if the IPR is ultimately not instituted; this is broader than standard § 315(e) estoppel, which only attaches after a FWD. STRATEGIC CALCULUS: file a Sotera waiver if: the Fintiv factors weigh heavily against institution; the value of institution is high; and the petitioner is comfortable accepting full estoppel consequences.

IPR estoppel creates a complex coordination problem for defendants who are both IPR petitioners and district court defendants: RISK OF FAILED IPR: if the IPR is instituted and results in a FWD confirming the challenged claims, the defendant is estopped from raising those same prior art grounds in district court — potentially with fewer invalidity defenses just when the infringement trial begins; RISK OF OVER-CITATION: citing too many prior art references in the IPR means more references are potentially estopped after the FWD — petitioners should be selective about which references to cite; GROUNDS NOT IN IPR: retain § 101, § 112, and non-documentary prior art invalidity arguments in district court parallel to the IPR; TIMING COORDINATION: ideally, the IPR timeline should be coordinated with the district court trial date so that the FWD issues before trial — if the IPR succeeds, the patent owner's case is significantly weakened; if the FWD confirms claims, the defendant knows what defenses remain; PATENT OWNER PERSPECTIVE: a patent owner who survives IPR has a 'confirmed validity' argument for the prior art that was tried — juries may view PTAB-confirmed claims as stronger; but the defendant retains § 101 and § 112 defenses that were not available in IPR. THE BOTTOM LINE: IPR estoppel is a significant and irreversible cost of filing an IPR — it should be analyzed carefully before filing, with full consideration of the district court invalidity strategy.