PTAB

IPR2020-01677

Rohm Semiconductor USA LLC v. MaxPower Semiconductor Inc

Key Events

Petition

petition

Title: Trench MOSFET with Doped Compensation Regions
Brief Description: The ’076 patent relates to trench metal-oxide-semiconductor field-effect transistors (MOSFETs). The technology aims to improve device performance by providing a doped compensated zone of a second conductivity type located at least partially beneath non-gate trenches containing recessed field plates (RFPs).

Prior Art Relied Upon: So (Patent 5,895,951).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that So, which was not considered during prosecution, discloses a trench MOSFET structure that renders all challenged claims obvious. So explicitly teaches a device with active gate trenches and separate non-gate "doping trenches" that function as the claimed recessed field plates (RFPs). Crucially, So describes forming "a deep-doping region disposed underneath the doping trench," which Petitioner contended is a direct teaching of the ’076 patent’s key limitation: a diffusion of a second conductivity type lying below the RFP trench. So’s structure, including its n-type source and p-type deep-doping region, was alleged to map to the limitations of the independent and dependent claims.
- Motivation to Combine (for §103 grounds): As a single-reference ground, the argument focused on direct disclosure. Petitioner asserted So teaches that this structure improves the body diode reverse recovery speed and enhances depletion of the drift region, providing a clear reason for its configuration.
- Expectation of Success (for §103 grounds): Petitioner argued success was expected as So provides a complete description of the structure and its benefits.

Prior Art Relied Upon: Kocon (Patent 6,534,828).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner contended Kocon describes a trench MOSFET with active gate structures and separate "inactive gate structures" located in second trenches, which correspond to the claimed RFPs. Kocon explicitly discloses a "deep well region" of a second conductivity type (p-type) positioned beneath these inactive gate trenches. Petitioner argued this structure directly reads on the core limitations of the challenged claims, including the gate, RFP, and underlying diffusion region. Dependent claims related to the diffusion region extending to a body layer were also allegedly taught by Kocon’s figures.
- Motivation to Combine (for §103 grounds): As a single-reference ground, Petitioner highlighted Kocon's stated motivations. Kocon explains its deep well structure reduces high electric fields, shields the gate oxide layer, and achieves "improved breakdown voltage characteristics" and "significantly lower resistance," providing a POSITA ample reason to use the disclosed design.
- Expectation of Success (for §103 grounds): Success was expected because Kocon describes a fully realized MOSFET structure and explains its functional advantages.

Prior Art Relied Upon: Osawa (Patent 6,501,129) and Kocon (Patent 6,534,828).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner asserted Osawa teaches a trench MOSFET with active gate trenches and non-gate "contact trenches" (RFPs) that include a p-type diffusion region formed along the bottom and sidewalls. While Osawa discloses a diffusion region, Kocon provides a more explicit teaching of a "deep well" diffusion located directly underneath the RFP trench.
- Motivation to Combine (for §103 grounds): A POSITA would combine these references to improve the performance of Osawa’s device. Petitioner argued that because both patents aim to improve breakdown voltage and on-resistance in trench MOSFETs, a POSITA would be motivated to incorporate Kocon’s teaching of a deep well diffusion beneath the RFP into Osawa’s design. This combination would achieve the known benefits described in Kocon, such as improved breakdown voltage and reduced on-resistance.
- Expectation of Success (for §103 grounds): A POSITA would have a reasonable expectation of success because both references concern analogous trench MOSFET technology, and Kocon provides a detailed description of the process for creating the doped regions.
Additional Grounds: Petitioner asserted additional obviousness challenges, including that claims 1 and 8-10 are obvious over Takahashi (Patent 5,864,159), and that claims 2-4 and 15 are obvious over Takahashi in view of Osawa.

"Capacitively coupled": Petitioner proposed this term be construed as "the two regions are configured to have a static potential difference applied between the two regions, thereby inducing a change in the carrier concentrations at the coupled semiconductor interface." This construction was argued to be critical for understanding the functional relationship between the RFPs and the adjacent semiconductor material.
"Recessed Field Plate": Petitioner proposed this term be construed as a "conducting or semi-conducting material in a trench other than an active gate." This construction was used to distinguish the non-gate RFP trenches from the active gate trenches, a distinction Petitioner argued was misunderstood by the Examiner during prosecution.

Petitioner argued against discretionary denial under §325(d). It was asserted that the petition presented new, non-cumulative references (So, Osawa) not considered by the Examiner. For references cited in an IDS during prosecution (Kocon, Takahashi), Petitioner argued the Examiner failed to appreciate their applicability due to a critical error. The Examiner was alleged to have repeatedly misunderstood the claims as requiring the diffusion region to be located under the gate trench rather than the RFP trench. Because Kocon and Takahashi teach a diffusion under the RFP trench, Petitioner contended the Examiner’s error prevented these references from being substantively evaluated, thus warranting review.

Petitioner requests institution of an inter partes review and cancellation of claims 1-4, 8-10, 14, and 15 of the ’076 patent as unpatentable.