DCT

1:23-cv-00369

Greenthread LLC v. Cirrus Logic Inc

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I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 1:23-cv-00369, W.D. Tex., 03/31/2023
  • Venue Allegations: Venue is alleged to be proper in the Western District of Texas because Defendant Cirrus Logic maintains its principal place of business in Austin, Texas, and has allegedly committed acts of infringement within the district. The complaint further alleges that decisions to incorporate the accused technology were made by employees located in the district.
  • Core Dispute: Plaintiff alleges that Defendant’s semiconductor integrated circuits infringe six patents related to the use of graded dopant regions to control charge carrier movement and thereby improve device performance.
  • Technical Context: The technology at issue addresses fundamental semiconductor fabrication techniques, specifically the creation of non-uniform dopant concentrations within a silicon substrate to enhance the speed, efficiency, and image quality of components like transistors and sensors.
  • Key Procedural History: The complaint states that the asserted patent family has been the subject of prior litigation, including cases against Samsung and Intel, and that courts in those matters adopted the Plaintiff’s proposed claim constructions. This history suggests that claim construction proceedings in this case may be influenced by those prior rulings.

Case Timeline

Date Event
2004-09-03 Priority date for all six asserted patents
2013-04-16 U.S. Patent No. 8,421,195 issues
2015-04-27 Inventor Dr. Rao assigns then-issued patents to Greenthread
2015-11-17 U.S. Patent No. 9,190,502 issues
2019-12-17 U.S. Patent No. 10,510,842 issues
2020-08-04 U.S. Patent No. 10,734,481 issues
2021-09-14 U.S. Patent No. 11,121,222 issues
2022-04-26 U.S. Patent No. 11,316,014 issues
2023-03-31 Complaint filed

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 8,421,195 - "Semiconductor Devices with Graded Dopant Regions"

  • Issued: April 16, 2013

The Invention Explained

  • Problem Addressed: The patent describes performance limitations in conventional semiconductor devices that arise from using uniformly doped regions. For minority carrier devices like Bipolar Junction Transistors (BJTs), this limits switching speed. For majority carrier devices like those in memory (DRAM) or imaging ICs, spurious minority carriers generated during operation can corrupt stored data or degrade image quality. ('195 Patent, col. 1:21-41; col. 2:58-67).
  • The Patented Solution: The invention proposes intentionally creating a non-uniform or "graded" dopant concentration profile within the semiconductor substrate. This gradient establishes a built-in "static unidirectional electric drift field" that actively directs the flow of charge carriers. This field can be used to sweep unwanted minority carriers away from sensitive active areas on the device surface and deep into the substrate for recombination, thereby improving DRAM refresh times and sensor resolution. ('195 Patent, Abstract; col. 3:28-44).
  • Technical Importance: This technique offered a method to improve the performance and reliability of various integrated circuits by manipulating carrier physics, as an alternative or supplement to simple geometric scaling (i.e., making components smaller). ('195 Patent, Abstract).

Key Claims at a Glance

  • The complaint asserts infringement of at least one claim of the ’195 Patent (Compl. ¶38). Independent claims 1 and 8 appear to cover the core invention.
  • Independent Claim 1 recites a CMOS semiconductor device comprising: a surface layer; a substrate; an active region (with a source and drain); a "single drift layer" with a "graded concentration of dopants" creating a "first static unidirectional electric drift field" to move minority carriers from the surface to the substrate; and at least one "well region" also having a graded concentration of dopants creating a "second static unidirectional electric drift field".
  • Independent Claim 8 is similar but recites drift fields that aid the movement of minority carriers from the substrate to the surface layer.
  • The complaint reserves the right to assert additional claims, including dependent claims (Compl. ¶36).

U.S. Patent No. 9,190,502 - "Semiconductor Devices with Graded Dopant Regions"

  • Issued: November 17, 2015

The Invention Explained

  • Problem Addressed: As a continuation of the same patent family, the ’502 Patent addresses the same technical problems as the ’195 Patent: performance bottlenecks in semiconductor devices caused by using uniformly doped regions, including slow switching speeds and interference from spurious minority carriers. ('502 Patent, col. 1:40-59; col. 2:58-67).
  • The Patented Solution: The solution is functionally identical to that of the ’195 Patent, employing a "graded dopant concentration" to create a built-in electric drift field. This field is engineered to control charge carrier movement, such as sweeping unwanted carriers away from the active surface circuitry to improve performance in applications like DRAMs and image sensors. ('502 Patent, Abstract; col. 3:28-44).
  • Technical Importance: The technology provides a foundational technique for enhancing the performance of various digital, analog, and mixed-signal ICs by controlling carrier dynamics within the silicon itself. ('502 Patent, Abstract).

Key Claims at a Glance

  • The complaint asserts infringement of at least one claim of the ’502 Patent (Compl. ¶45). Independent claims 1 and 7 are representative.
  • Independent Claim 7 recites a semiconductor device comprising: a surface layer; a substrate; an active region (with a source and drain); a "single drift layer" with a "graded concentration of dopants" creating a drift field to aid movement of minority carriers from the surface layer to the substrate; and at least one "well region" with a graded concentration creating a second drift field with the same function.
  • Independent Claim 1 is similar but recites a drift field aiding carrier movement in the opposite direction (from substrate to surface).
  • The complaint reserves the right to assert additional claims (Compl. ¶43).

Multi-Patent Capsule: U.S. Patent No. 10,510,842

  • Patent Identification: U.S. Patent No. 10510842, "Semiconductor Devices with Graded Dopant Regions", issued December 17, 2019 (Compl. ¶14).
  • Technology Synopsis: This patent continues the family's teachings, describing a semiconductor device with multiple active regions and underlying graded dopant concentrations. The graded regions are designed to create a drift field that aids carrier movement between the device's surface and the substrate, improving performance in CMOS devices. ('842 Patent, Abstract; col. 3:45-53).
  • Asserted Claims: At least one claim is asserted (Compl. ¶52). Independent claims 1 and 9 are representative.
  • Accused Features: The complaint alleges that transistors within Cirrus Logic's semiconductor products, which allegedly use a limited number of manufacturing processes, incorporate the claimed graded dopant region structures (Compl. ¶¶33-34).

Multi-Patent Capsule: U.S. Patent No. 10,734,481

  • Patent Identification: U.S. Patent No. 10734481, "Semiconductor Devices with Graded Dopant Regions", issued August 4, 2020 (Compl. ¶15).
  • Technology Synopsis: This patent further describes semiconductor devices with graded dopant regions and well regions. The claims focus on the use of these graded regions to aid carrier movement away from the surface of the substrate in various devices, including DRAM, flash memory, and image sensors. ('481 Patent, Abstract; Claims 1, 14-19).
  • Asserted Claims: At least one claim is asserted (Compl. ¶59). Independent claims 1 and 20 are representative.
  • Accused Features: The accused features are the same allegedly graded dopant structures within Defendant's semiconductor products (Compl. ¶¶33-34).

Multi-Patent Capsule: U.S. Patent No. 11,121,222

  • Patent Identification: U.S. Patent No. 11121222, "Semiconductor Devices with Graded Dopant Regions", issued September 14, 2021 (Compl. ¶16).
  • Technology Synopsis: This patent focuses on a VLSI (Very Large Scale Integration) semiconductor device. It claims a structure including active regions and at least one well region, where graded dopant concentrations are used to create a drift field that moves charge carriers from the active surface towards an inactive area of the substrate. ('222 Patent, Abstract; Claim 1).
  • Asserted Claims: At least one claim is asserted (Compl. ¶66). The patent contains numerous independent claims, including 1, 21, 39, and 44.
  • Accused Features: The accused features are the same allegedly graded dopant structures within Defendant's semiconductor products (Compl. ¶¶33-34).

Multi-Patent Capsule: U.S. Patent No. 11,316,014

  • Patent Identification: U.S. Patent No. 11316014, "Semiconductor Devices with Graded Dopant Regions", issued April 26, 2022 (Compl. ¶17).
  • Technology Synopsis: This patent claims a broader "electronic system" that comprises a semiconductor device with the family's core invention. The claimed device includes active regions and well regions with graded dopant concentrations that create a drift field to move carriers from the surface towards an inactive area of the substrate. ('014 Patent, Abstract; Claim 1).
  • Asserted Claims: At least one claim is asserted (Compl. ¶73). Independent claims 1 and 21 are representative.
  • Accused Features: The accused features are the same allegedly graded dopant structures within Defendant's semiconductor products, which are components of larger electronic systems (Compl. ¶¶2b, 33-34).

III. The Accused Instrumentality

Product Identification

  • The complaint broadly identifies the "Cirrus Logic Accused Products" as a wide range of semiconductor devices, including amplifiers, converters, and signal processor ICs (Compl. ¶31). It names one exemplary product: the Cirrus Logic CLI1793B1 power management integrated circuit (“PIMIC”) (Compl. ¶33).

Functionality and Market Context

  • The accused products are described as semiconductor devices for mixed-signal and analog processing, used in end-products like laptops and computers (Compl. ¶¶2b, 32). The core accused functionality is the alleged use of "regions with graded dopant concentrations" in the transistors and other structures within these ICs (Compl. ¶34). The complaint alleges these structures are designed according to a "limited number of processes" and provide benefits such as improved switching time (Compl. ¶34). The complaint highlights the historical significance of this type of technology by including a photograph of a Smithsonian Institution exhibit crediting the named inventor, Dr. Rao, with the development of an experimental 1-megabit CMOS DRAM (Compl. p. 9).

IV. Analysis of Infringement Allegations

The complaint alleges that the Accused Products, exemplified by the CLI1793B1 PIMIC, meet every limitation of at least one claim of each asserted patent. The specific, element-by-element mapping is said to be detailed in Exhibit 8 to the complaint, which was not publicly available for this analysis (Compl. ¶¶11, 33, 38). The tables below summarize the infringement allegations for a representative claim from the two lead patents based on the narrative theory provided in the complaint.

'195 Patent Infringement Allegations

Claim Element (from Independent Claim 1) Alleged Infringing Functionality Complaint Citation Patent Citation
A CMOS Semiconductor device... The Accused Products, including the exemplary CLI1793B1 PIMIC, are alleged to be semiconductor devices containing transistors and other structures. ¶10, ¶33 col. 2:17-19
a substrate... The Accused Products are built on a semiconductor substrate. This structural element is detailed for the exemplary PIMIC in Exhibit 8. ¶33, ¶34 col. 4:46
an active region including a source and a drain... The Accused Products contain transistors, which inherently include active regions with sources and drains. This is detailed for the exemplary PIMIC in Exhibit 8. ¶10, ¶33 col. 4:49-54
a single drift layer disposed between the other surface of said surface layer and said substrate, said drift layer having a graded concentration of dopants... The complaint alleges the Accused Products utilize regions with "graded dopant concentrations" that meet this limitation, as detailed for the exemplary PIMIC in Exhibit 8. ¶33, ¶34 col. 3:28-35
at least one well region... having a graded concentration of dopants... The Accused Products are alleged to include well regions with graded dopant concentrations, as detailed for the exemplary PIMIC in Exhibit 8. ¶33, ¶34 col. 3:45-53

'502 Patent Infringement Allegations

Claim Element (from Independent Claim 7) Alleged Infringing Functionality Complaint Citation Patent Citation
A semiconductor device... The Accused Products, including the exemplary CLI1793B1 PIMIC, are alleged to be semiconductor devices. ¶10, ¶33 col. 1:31
a substrate... The Accused Products are built on a semiconductor substrate. This structural element is detailed for the exemplary PIMIC in Exhibit 8. ¶33, ¶34 col. 4:46
an active region including a source and a drain... The Accused Products contain transistors with active regions, sources, and drains, as detailed for the exemplary PIMIC in Exhibit 8. ¶10, ¶33 col. 4:49-54
a single drift layer... having a graded concentration of dopants generating a first static unidirectional electric drift field to aid the movement of minority carriers from said surface layer to said substrate... The Accused Products allegedly include regions with graded dopant concentrations that create a drift field to move carriers away from the surface, as detailed in Exhibit 8. ¶33, ¶34 col. 3:28-44
  • Identified Points of Contention:
    • Evidentiary Question: The central factual dispute will be whether reverse engineering of the Accused Products confirms the structural allegations made in the complaint and its missing Exhibit 8. Does the CLI1793B1 PIMIC, or any other accused device, actually contain regions with a "graded dopant concentration"?
    • Scope Question: A key legal dispute may arise over the definition of "graded." The patents provide examples such as linear or exponential gradients ('195 Patent, col. 3:1-3). The question for the court will be whether the specific dopant profiles in the accused devices, if any are found, fall within the patent's definition of "graded," or if they represent a different, non-infringing type of dopant variation.
    • Functional Question: Does any dopant gradient found in the accused devices actually perform the claimed function of creating a "static unidirectional electric drift field" that "aid[s] the movement of... carriers"? Defendant may argue that any observed variations are incidental to manufacturing and do not produce the functional result required by the claims.

V. Key Claim Terms for Construction

  • The Term: "graded dopant concentration"

  • Context and Importance: This term is the technological core of all asserted patents. The entire infringement case rests on whether the accused devices possess this feature. Its construction will be dispositive; a narrow construction could place the accused devices outside the claims' scope, while a broader one could support infringement.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: The specification provides a non-exhaustive list of possible gradients ("linear, quasi linear, exponential or complimentary error function") ('195 Patent, col. 3:1-3), suggesting the term is not limited to just these examples. Plaintiff may argue that any intentionally created, non-uniform dopant profile designed to produce the claimed drift field meets the definition.
    • Evidence for a Narrower Interpretation: The specification consistently links the "graded dopant" structure to its function: creating an "aiding drift electric field" ('195 Patent, col. 3:3-5). Defendant may argue that a dopant profile is not "graded" in the claimed sense unless it is specifically engineered to and actually does produce a functionally significant drift field, as opposed to incidental variations from manufacturing.

  • The Term: "static unidirectional electric drift field"

  • Context and Importance: This functional language defines the required outcome of the "graded dopant concentration." Proving infringement will require showing not only that the accused structure exists but also that it produces this specific result.

  • Intrinsic Evidence for Interpretation:

    • Evidence for a Broader Interpretation: "Static" can be interpreted as simply being built-in to the device structure, rather than externally applied. "Unidirectional" could mean a net directional influence on carriers (e.g., generally towards the substrate), not necessarily a perfectly uniform field at every point. ('195 Patent, col. 3:31-35).
    • Evidence for a Narrower Interpretation: Defendant may argue this requires a field of a certain minimum magnitude and consistency to be functionally significant. They could contend that any minor potential variations in their devices do not rise to the level of a "unidirectional electric drift field" capable of performing the claimed function of "aid[ing] the movement of minority carriers" ('195 Patent, col. 1:11-14).

VI. Other Allegations

  • Indirect Infringement: The complaint alleges that Defendant places products into the stream of commerce with "awareness, knowledge, and intent" that they will be used by others in an infringing manner (Compl. ¶7). This language lays a foundation for a claim of induced infringement, though it does not specify the acts of inducement (e.g., providing datasheets or instructions).
  • Willful Infringement: The complaint does not contain specific allegations of willful infringement or pre-suit knowledge of the patents. The prayer for relief includes a request for a finding that the case is "exceptional" under 35 U.S.C. § 285, but the factual basis for such a finding is not developed in the body of the complaint (Compl. Prayer ¶D).

VII. Analyst’s Conclusion: Key Questions for the Case

This case appears to center on fundamental questions of semiconductor structure and claim interpretation. The key questions for the court will likely be:

  • A primary evidentiary question: Does the physical evidence obtained from reverse engineering the accused Cirrus Logic products confirm the complaint's allegation that they are manufactured with the "graded dopant concentration" regions described in the Greenthread patents?
  • A central issue of claim scope: Will the term "graded dopant concentration" be construed to cover any non-uniform dopant profile, or will it be limited to specific, engineered gradients that produce a functionally significant result, potentially excluding the accused devices?
  • A key procedural question: To what extent will the court adopt the claim construction rulings from the prior Samsung and Intel litigations involving the same patent family, and how will that precedent shape the infringement and validity disputes in this case?