STMicroelectronics Inc v. Trustees Of Purdue University

1. Case Identification

• Case #: IPR2022-00723
• Patent #: 7,498,633
• Filed: March 25, 2022
• Petitioner(s): STMicroelectronics, Inc.
• Patent Owner(s): The Trustees of Purdue University
• Challenged Claims: 1–8 and 12–15

2. Patent Overview

• Title: Silicon Carbide Vertical Metal Oxide Semiconductor Field Effect Transistor with Current Spreading Layer
• Brief Description: The ’633 patent discloses a vertical double-implanted metal-oxide semiconductor field-effect transistor (MOSFET) for high-voltage power applications. The device is formed on a silicon-carbide (SiC) substrate and includes specific structural features, such as a current spreading layer and defined topological configurations for its source and base contact regions, intended to reduce on-resistance.

3. Grounds for Unpatentability

Ground 1: Claims 1–8 and 12–15 are obvious over Ryu in view of Williams.

• Prior Art Relied Upon: Ryu (Application # 2004/0119076) and Williams (Patent 6,413,822).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Ryu, which is directed to SiC MOSFETs, discloses a vertical transistor structure strikingly similar to that claimed in the ’633 patent. Ryu was asserted to teach the core structural limitations of independent claims 1 and 12, including a SiC substrate, a drift layer, a current spreading semiconductor layer, a JFET region with specific doping concentrations, source regions, and base contact regions. However, Ryu only illustrates this structure in a cross-sectional view and does not explicitly disclose a top-down layout with a plurality of alternating source and base regions. To remedy this, Petitioner asserted that Williams, which relates to vertical MOSFETs, explicitly teaches various plan-view source-body designs, including a “bamboo ladder structure” of alternating N+ source regions and P+ body contact regions arranged as linear strips. Petitioner contended that applying the alternating strip layout from Williams to the cross-sectional structure of Ryu renders the topological configurations of claims 1 and 12 obvious. Dependent claims were argued to be obvious as they recite specific, narrow JFET widths or doping concentration ratios that were disclosed or suggested within the ranges taught by Ryu.
  • Motivation to Combine: Petitioner asserted a person of ordinary skill in the art (POSITA) would combine Ryu and Williams because both references are in the same field of endeavor (vertical MOSFETs) and share the common goal of reducing on-resistance. Williams explicitly teaches its alternating strip source-body configurations as a design choice to balance low on-resistance with device ruggedness. Petitioner argued it was well-known in the art to apply design principles from silicon MOSFETs (like Williams) to SiC MOSFETs (like Ryu). Therefore, a POSITA seeking to optimize the on-resistance and layout of Ryu’s device would have been motivated to implement the known, predictable linear cellular geometry taught by Williams.
  • Expectation of Success: A POSITA would have had a reasonable expectation of success because implementing Williams's well-known linear cellular geometry on Ryu's planar MOSFET structure was a straightforward modification using standard semiconductor fabrication techniques. The result—a device with a specific trade-off between on-resistance and ruggedness—was predictable. The petition noted that Williams presents several such layouts as known design choices, indicating that their implementation was routine and their effects were well understood.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under §314(a) based on the Fintiv factors would be inappropriate. The petition asserted that the co-pending district court litigation was in a very early stage with minimal investment, and the trial date was uncertain and likely to occur after a Final Written Decision (FWD) in the IPR. Petitioner also stated that it would seek a stay of the litigation if the IPR was instituted and that the grounds presented were unique and meritorious.

5. Relief Requested

• Petitioner requests institution of an inter partes review (IPR) and cancellation of claims 1–8 and 12–15 of the ’633 patent as unpatentable.