Greenthread LLC v. Cirrus Logic, Inc. et al.

This Inter Partes Review (IPR) proceeding, IPR2024-00001, involves patent owner Greenthread LLC and petitioners Cirrus Logic, Inc., Omnivision Technologies, Inc., AMS Sensors USA, Inc., OSRAM GmbH, AMS-OSRAM AG, and Globalfoundries U.S., Inc. Greenthread LLC operates as a Patent Assertion Entity (PAE), asserting patents derived from inventor G.R. Mohan Rao, primarily related to semiconductor technology. The petitioners are established operating companies in the semiconductor industry: Cirrus Logic is a fabless semiconductor company known for mixed-signal processing solutions in mobile and consumer applications, including audio codecs and amplifiers; Omnivision Technologies designs digital imaging products like CMOS image sensors for various sectors; AMS-OSRAM AG specializes in intelligent sensors and emitter components such as LEDs and CMOS ICs; and Globalfoundries is a major semiconductor contract manufacturer (foundry) providing wafer fabrication services.

The IPR challenges U.S. Patent 10,734,481, titled "Semiconductor Device with Graded Dopant Concentration." This patent generally describes a semiconductor device incorporating at least one active region with a graded dopant concentration, which is designed to create an electric field to facilitate the movement of charge carriers from one surface to another within the substrate. The underlying context for this IPR is a patent infringement lawsuit filed by Greenthread against Cirrus Logic (1:23-cv-00369, W.D. Tex.) and other companies, alleging infringement by their semiconductor products, particularly those related to memory or CMOS devices with graded dopant regions.

The case is situated at the Patent Trial and Appeal Board (PTAB), a specialized administrative court within the USPTO, and was filed on October 12, 2023. The procedural posture of IPR2024-00001 has been dynamic: initially, a Final Written Decision (FWD) was issued by the PTAB. However, on July 23, 2025, the Director of the USPTO vacated that FWD and remanded the case back to the PTAB to allow for additional discovery regarding real-party-in-interest (RPI) and privity issues, a notable development in PTAB practice. Subsequently, the PTAB issued a second Final Written Decision on October 29, 2025, finding claims 1-9, 12-27, and 30-36 of U.S. Patent 10,734,481 unpatentable. Greenthread LLC then filed a new request for Director Review by November 28, 2025, challenging this second FWD. This IPR is notable for being part of a broader campaign by Greenthread, an NPE, asserting a family of "graded dopant concentration" patents against multiple semiconductor companies. The ongoing Director Review process and the previous vacatur and remand on RPI issues underscore the strategic interplay between district court litigation and PTAB proceedings, particularly concerning procedural challenges related to standing and time-bar.

Greenthread LLC v. Cirrus Logic, Inc. et al. - Case Summary

This report details the key legal developments and outcome for the patent infringement litigation involving Greenthread LLC and a parallel Inter Partes Review (IPR) proceeding concerning U.S. Patent No. 10,734,481.

District Court Litigation: Greenthread LLC v. Cirrus Logic, Inc. (W.D. Tex., 1:23-cv-00369)

• Filing & Initial Pleadings: Greenthread LLC initiated a patent infringement lawsuit against Cirrus Logic, Inc. in the U.S. District Court for the Western District of Texas (Case No. 1:23-cv-00369) on March 31, 2023. The complaint asserted U.S. Patent No. 10,734,481, among others, alleging infringement by Cirrus Logic's semiconductor products.
• Claim Construction (Markman): The case progressed to the claim construction phase. A Markman hearing was held on January 26, 2024. Following the hearing, the Court issued a Claim Construction Order and Memorandum in Support Thereof on March 13, 2024, which informed the parties of the final constructions for the disputed terms.
• Pre-trial Motions / Stay Pending IPR: While a formal stay order was not explicitly found in the provided search results for this specific case, the existence of parallel IPR proceedings and the ongoing interaction between the district court and PTAB (as evidenced by a PTAB document referencing the district court case and the "impact of the Director Review Order" on it) suggest a potential stay or close coordination. Other related Greenthread cases against different defendants were stayed pending IPRs.
• Current Status: The district court litigation is ongoing, likely awaiting the final resolution of the parallel IPR proceeding, especially after the Director Review.

Parallel PTAB IPR Proceeding: IPR2024-00001

• Filing: An Inter Partes Review (IPR) petition, IPR2024-00001, was filed by Cirrus Logic, Inc. and other entities against patent owner Greenthread LLC on October 12, 2023, challenging the patentability of U.S. Patent No. 10,734,481.
• Institution Decision: While the specific date of the institution decision for IPR2024-00001 was not found in the provided snippets, IPRs are typically instituted within six months of the petition filing date.
• Final Written Decision (Vacated): An initial Final Written Decision was issued, though its specific date and findings were not detailed in the search results.
• Director Review: On July 23, 2025, the Director of the USPTO issued a "Decision vacating Final Written Decision, and remanding for further proceedings" for IPR2024-00001 (and IPR2024-00016), recorded as Paper 89. This means the initial outcome of the IPR has been set aside, and the proceeding has been sent back for further consideration by the PTAB. This significantly impacts the finality of the IPR.
• Current Status: The IPR proceeding is currently in a remanded status following the Director's decision to vacate the Final Written Decision, meaning a definitive outcome on the patentability of claims in U.S. Patent No. 10,734,481 is still pending.

Overall Outcome / Present Posture

The patent infringement litigation (1:23-cv-00369) remains active in the Western District of Texas. While claim construction has occurred, the ultimate disposition of the district court case is likely contingent on the final outcome of the remanded IPR proceeding (IPR2024-00001) at the PTAB. The Director's decision to vacate the Final Written Decision for IPR2024-00001 means the patentability of U.S. Patent No. 10,734,481 is still under review at the PTAB.

Press coverage specifically detailing the IPR2024-00001 case, its Director Review, and the subsequent second Final Written Decision is limited. However, several legal news and IP-focused platforms have reported on related IPRs involving Greenthread LLC and the broader implications of its patent assertion campaign, particularly concerning the Director Review process.

IIPLA reported on November 16, 2025, that Greenthread had "asked the head of the U.S. Patent and Trademark Office to review decisions made by the Patent Trial and Appeal Board" in a broader context of challenging patent invalidations. This aligns with the known request for Director Review in IPR2024-00001 following the second Final Written Decision. The significance of this particular IPR (IPR2024-00001) is underscored by its inclusion in a series of IPRs where the USPTO Director vacated initial Final Written Decisions and remanded for further discovery on real-party-in-interest (RPI) and privity issues. This procedural aspect has been noted by legal analysis sites, highlighting the importance of thorough discovery in PTAB proceedings. For instance, Irwin IP discussed on May 13, 2025, the USPTO Director's decision to vacate and remand three Final Written Decisions in IPRs filed by Semiconductor Components Industries, LLC (onsemi) against Greenthread, specifically instructing the PTAB to allow "narrowly tailored discovery" on the privity issue. This ruling emphasized that denying discovery and then faulting a patent owner for failing to provide evidence of privity was an error, setting a precedent for related Greenthread IPRs, including IPR2024-00001.

The underlying district court litigation between Greenthread LLC and Cirrus Logic, Inc. (1:23-cv-00369, W.D. Tex.) has been mentioned in a broader context of Greenthread's enforcement efforts. PatSnap Eureka, on April 25, 2024, analyzed a related case, Greenthread LLC v. Monolithic Power Systems, which involved several patents from the same family, including U.S. Patent 10,734,481, and discussed the stay of district court proceedings pending IPR outcomes. This article noted that Greenthread's patents, directed toward "semiconductor devices with graded dopant regions," cover "foundational technology in semiconductor device architecture." While the specific financial impact or damages sought in Greenthread v. Cirrus Logic were not readily available in the searched press, the fact that Greenthread is a Patent Assertion Entity (PAE) suggests its primary goal is to secure licensing fees or damages from alleged infringers. Earlier, in 2003, EDN Magazine reported on a separate patent litigation where Cirrus Logic received a $9 million payment as part of a cross-license agreement and settlement, demonstrating the potential for significant financial outcomes in semiconductor patent disputes. Another article from EE Times in 2000 reported Cirrus Logic being awarded $3.8 million in attorney fees in a patent suit against Opti Inc. and TriTech Microelectronics. These past cases, while not directly related to Greenthread, illustrate the financial stakes involved in patent litigation within the semiconductor industry for a company like Cirrus Logic.

The Director Review process itself, and specifically the vacatur and remand in the Greenthread IPRs, represents a significant development in PTAB practice, highlighting increased scrutiny of procedural fairness, particularly regarding discovery into real parties-in-interest and potential time-bar issues under 35 U.S.C. § 315(b). The USPTO's status page on Director Review requests confirms that the requests in IPR2024-00001 and IPR2024-00016 were granted, and the Final Written Decisions vacated and remanded for further proceedings. This ongoing review process for Greenthread's patents is important for both patent owners and petitioners, as it shapes the strategic landscape for challenging and defending patent validity at the PTAB.

Sources

• irwinip.com
• ptablitigationblog.com
• patsnap.com
• ipwatchdog.com
• eetimes.com
• uspto.gov
• uspto.gov

Greenthread LLC, the patent owner in IPR2024-00001, is represented by attorneys from McKool Smith, P.C. and Duane Morris LLP in related district court litigation.

Counsel of record for Greenthread LLC in the underlying district court cases, which inform the IPR proceeding, include:

• Alan L. Whitehurst (Lead Counsel)

  • Firm: McKool Smith, P.C.
  • Office Location: Washington, DC
  • Note: Whitehurst is listed as counsel for Greenthread in the Western District of Texas case against Cirrus Logic, Inc.. He has been involved in other Greenthread patent litigation, including a case against ON Semiconductor in Delaware.

• Arvind Jairam (Counsel)

  • Firm: McKool Smith, P.C.
  • Office Location: Washington, DC
  • Note: Jairam is also listed as counsel for Greenthread in the Western District of Texas case against Cirrus Logic, Inc.. He was part of the litigation team representing Greenthread in the case against ON Semiconductor.

• Jennifer Truelove (Counsel)

  • Firm: McKool Smith, P.C.
  • Office Location: Marshall, TX
  • Note: Truelove is listed as counsel for Greenthread in the Western District of Texas case against Cirrus Logic, Inc..

• John B. Campbell (Counsel)

  • Firm: McKool Smith, P.C.
  • Office Location: Austin, TX
  • Note: Campbell is listed as counsel for Greenthread in the Western District of Texas case against Cirrus Logic, Inc.. He also represented Greenthread in a case against Intel Corporation in the Western District of Texas.

• Gilbert A. Greene (Counsel)

  • Firm: Duane Morris LLP
  • Office Location: Austin, TX
  • Note: Greene is listed as counsel for Greenthread in the Western District of Texas case against Cirrus Logic, Inc..

Additionally, in other related district court litigation, Greenthread LLC has been represented by:

• Brian E. Farnan (Local Counsel)

  • Firm: Farnan LLP
  • Office Location: Delaware
  • Note: Farnan served as Delaware local counsel for Greenthread in the case against ON Semiconductor Corporation.

• Michael J. Farnan (Local Counsel)

  • Firm: Farnan LLP
  • Office Location: Delaware
  • Note: Farnan also served as Delaware local counsel for Greenthread in the case against ON Semiconductor Corporation.

This section identifies the counsel of record representing the Petitioners (Cirrus Logic, Inc., Omnivision Technologies, Inc., AMS Sensors USA, Inc., OSRAM GmbH, AMS-OSRAM AG, and Globalfoundries U.S., Inc.) in IPR2024-00001.

Counsel for Petitioners

• Scott Weidenfeller - Lead Counsel

  • Firm: Covington & Burling LLP, Washington, DC
  • Experience: Mr. Weidenfeller is listed as counsel of record for the Petitioners in IPR2024-00021, a related IPR proceeding, and his email address is provided in a motion to seal document. His practice includes patent litigation.

• Anupam Sharma - Counsel

  • Firm: Covington & Burling LLP, Washington, DC
  • Experience: Mr. Sharma is also listed as counsel of record for the Petitioners in IPR2024-00021 and has an email address provided in a motion to seal document. His experience likely includes patent litigation.

While specific appearances for all named Petitioners in IPR2024-00001 could not be definitively found for each individual attorney, Covington & Burling LLP appears to be representing at least some of the Petitioners, particularly Cirrus Logic and Omnivision, given their involvement in related IPRs challenging Greenthread's patents. The Petitioners in this IPR are operating companies in the semiconductor manufacturing sector and frequently engage in patent litigation and IPR proceedings to defend against patent assertions.

Additional searches for counsel representing specific Petitioners in other patent litigation contexts provide further insight into their legal teams:

• Cirrus Logic, Inc. regularly works with Jackson Walker L.L.P. on patent prosecution matters. Attorneys like Brian K. Prewitt, Temple Keller, Andrea Thai, and Tori Emery have assisted Cirrus Logic in securing numerous U.S. and foreign patents. Cirrus Logic has also been represented by Quinn Emanuel and Morris Nichols in other patent disputes.
• Omnivision Technologies, Inc. has a firm policy of defending itself against non-practicing entity (NPE) patent assertions and has been represented by Barack Ferrazzano Kirschbaum & Nagelberg LLP and Richards Layton & Finger P.A. in past patent litigation. More recently, Omnivision secured a patent litigation victory with Stradling and Benesch Law. Robert Cleary is the General Counsel of OMNIVISION and a former patent litigator.
• AMS Sensors USA, Inc. was involved in an optical sensor patent infringement case where Munck Wilson Mandala LLP represented the plaintiff (AMS Sensors) and Siebman Burg Phillips & Smith LLP represented the defendant. This indicates their engagement with specialized patent litigation firms.
• OSRAM GmbH and AMS-OSRAM AG (ams OSRAM) are active in enforcing their intellectual property rights, particularly concerning LED technology. Gerd Pokorny is noted as the General Counsel of OSRAM GmbH and has emphasized the company's commitment to vigorously enforcing its patent rights. They have used firms like ArentFox Schiff LLP for patent prosecution.
• Globalfoundries U.S., Inc. (GF) has a dedicated Intellectual Property Law team and is involved in patent litigation and pre-litigation matters, often partnering with outside counsel. GF has filed its own patent infringement lawsuits to protect its technologies. In a case where GF was a defendant, it was represented by its patent litigation team.

It is important to note that the provided information from IPR2024-00001 (Paper 89) mentions that Cirrus Logic, Inc., Omnivision Technologies, Inc., and Texas Instruments Incorporated filed authorized responses to Greenthread's requests for Director Review. Texas Instruments Incorporated had also been joined as a petitioner to IPR2024-00001. This suggests a potentially broader group of Petitioners being represented, even if specific counsel for all parties in this particular IPR are not explicitly detailed in every search result. Due to the nature of IPRs, it is common for multiple petitioners to be represented by the same counsel, especially when the challenged patent claims and prior art arguments are similar.