PTAB

IPR2023-01384

Innoscience Zhuhai Technology Co Ltd v. Efficient Power Conversion Corp

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Enhancement-Mode GaN Transistor with Ledges
  • Brief Description: The ’335 patent discloses an enhancement-mode gallium nitride (GaN) high electron mobility transistor (HEMT). The technology centers on a stacked gate structure with a p-type gate material layer beneath a narrower gate metal, creating a pair of horizontal "ledges" intended to reduce gate leakage current.

3. Grounds for Unpatentability

Ground 1: Obviousness over Saxler and Yoshida - Claims 1-7 are obvious over Saxler in view of Yoshida.

  • Prior Art Relied Upon: Saxler (Application # 2006/0108606) and Yoshida (Japanese Publication # JP H11-261053).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Saxler taught all elements of the claimed GaN HEMT, including a GaN channel layer, an AlGaN barrier layer, source/drain contacts, and a stacked gate structure comprising a p-type cap layer and an overlying gate metal. Petitioner asserted that Saxler disclosed that its gate contact may be recessed or non-recessed, and that in either configuration, the gate metal is narrower than the underlying p-type cap layer, thus forming the claimed horizontal "ledges." Yoshida was introduced to further support the obviousness of a non-recessed gate structure, as it explicitly depicted a similar device with a p-type gate material that was wider than the gate metal.
    • Motivation to Combine: Petitioner contended a POSITA would combine the teachings to simplify manufacturing and reduce costs. Saxler’s disclosure of a recessed gate involves complex fabrication with small tolerances. A POSITA would have been motivated to use Saxler’s explicitly optional non-recessed gate design, as exemplified by Yoshida, to avoid these manufacturing challenges and predictably yield a functional enhancement-mode GaN HEMT.
    • Expectation of Success: The combination was presented as a simple substitution of known elements (a non-recessed gate for a recessed one) in a well-understood device architecture, leading to a high expectation of success.

Ground 2: Obviousness over Yoshida and Saxler - Claims 1-7 are obvious over Yoshida in view of Saxler.

  • Prior Art Relied Upon: Yoshida (Japanese Publication # JP H11-261053) and Saxler (Application # 2006/0108606).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued from the alternative starting point that Yoshida disclosed the core claimed structure: a GaN HEMT with a p-type gate layer (layer 5) that is wider than the overlying gate electrode, thereby teaching the key horizontal ledges. However, Yoshida depicted the p-type gate layer with vertical sidewalls. Petitioner asserted that Saxler taught a similar GaN HEMT structure with sloped sidewalls on its p-type cap layer, a feature known to reduce gate leakage currents by increasing the leakage path length.
    • Motivation to Combine: A POSITA would combine Yoshida’s transistor with Saxler’s sloped sidewalls to achieve the known benefit of reduced gate leakage. The ’335 patent itself acknowledged that leakage along the p-type gate sidewall was a known problem. Petitioner argued that incorporating Saxler's well-understood sloped sidewall design into Yoshida’s device was an obvious solution to this known problem that would predictably improve performance.
    • Expectation of Success: Because forming sloped sidewalls via conventional etching techniques (as taught by Saxler) was common practice in semiconductor fabrication, a POSITA would have had a high expectation of success in modifying Yoshida’s device.

Ground 3: Obviousness over Saxler, Yoshida, Beach, and Shenoy - Claims 2 and 5-7 are obvious over the combination.

  • Prior Art Relied Upon: Saxler (Application # 2006/0108606), Yoshida (Japanese Publication # JP H11-261053), Beach (Application # 2007/0007547), and Shenoy (a 1996 journal article).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground specifically addressed the "self-aligned" ledges required by claims 2 and 5-7. Petitioner argued the Saxler-Yoshida combination taught the final device structure. Beach taught a self-aligned fabrication method for GaN HEMTs using a single mask to pattern stacked gate layers, ensuring alignment. Shenoy taught a conventional isotropic etching technique that symmetrically undercuts a metal layer beneath a photomask, which is the process depicted in the ’335 patent for creating the ledges.
    • Motivation to Combine: A POSITA would combine these references to manufacture the Saxler-Yoshida device more efficiently and reliably. Using Beach’s single-mask, self-aligned process would reduce manufacturing steps, lower costs, and improve layer alignment and symmetry compared to multi-mask processes. A POSITA would then apply Shenoy’s well-known undercutting technique to the gate metal layer to predictably form the symmetric, self-aligned ledges.
    • Expectation of Success: The proposed combination involved applying known, conventional fabrication techniques (self-alignment from Beach, isotropic etching from Shenoy) to a known device structure, ensuring a predictable and successful outcome.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including that claims 1-7 are obvious over Yoshida alone (Ground 4) and that claims 2 and 5-7 are obvious over the combination of Yoshida, Saxler, Beach, and Shenoy (Ground 6).

4. Key Claim Construction Positions

  • “side surfaces … extending horizontally”: Petitioner proposed construing this term to mean "side surfaces of the p-type gate material such that the bottom of the p-type gate material is more than 10% wider than the top of the material, leading to sloped side surfaces that contact the barrier layer." Petitioner argued this construction was necessary to distinguish the invention from prior art, as it was based on an explicit teaching in the priority application ([Lidow](https://ai-lab.exparte.com/case/ptab/IPR2023-01384/doc/1011)) for reducing gate leakage.
  • “self-aligned ledges”: Petitioner argued this is a product-by-process limitation that describes the method of making the ledges, not their final structure. As such, Petitioner contended the term should be given no patentable weight, and the claims should be assessed based on the structure alone, which was taught by the prior art regardless of the manufacturing process used.

5. Arguments Regarding Discretionary Denial

  • §314(a) (Fintiv): Petitioner argued that discretionary denial under Fintiv was improper. It stated that per PTAB guidance, Fintiv does not apply to parallel ITC proceedings. Further, it argued that the factors weighed against denial regarding a parallel district court case because that case had minimal investment from the parties and had been stayed pending the ITC investigation.
  • §325(d): Petitioner argued that denial under §325(d) was improper because none of the asserted prior art references (Saxler, Yoshida, Beach, Shenoy) were considered during prosecution. Petitioner contended the references were not cumulative to the art of record and raised new, substantial questions of patentability.

6. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-7 of the ’335 patent as unpatentable.