Vidal’s Latest Director Review Decision Finds Material Differences in Prior Art References Raised at PTAB

On March 30, U.S. Patent and Trademark Office (USPTO) Director Kathi Vidal issued a decision on sua sponte Director review that vacated a decision of the Patent Trial and Appeal Board (PTAB), which had previously denied institution of inter partes review (IPR) proceedings brought by semiconductor company Wolfspeed. In her latest in a series of sua sponte decisions, Director Vidal ruled that the PTAB erred in determining that prior art asserted by Wolfspeed was essentially the same as other prior art asserted against the same Purdue University patent claims in previous IPR proceedings that were also denied institution by the PTAB.

Wolfspeed IPR Petition Asserts Prior Art on MOSFETs, Transistor Topology

The patent challenged by Wolfspeed’s IPR petition is U.S. Patent No. 7498633, High-Voltage Power Semiconductor Device, owned by Purdue University. The ‘633 patent claims a metal-oxide semiconductor field-effect transistor (MOSFET) fabricated with a current spreading semiconductor layer formed on a front side of a drift semiconductor layer. The use of the current spreading layer claimed by the ‘633 patent addresses problems in MOSFET fabrication by which the reduction of specific on-state resistance typically results in a reduction of a semiconductor device’s blocking voltage. Purdue University had previously asserted claims of the ‘633 patent against Wolfspeed in an October 2021 lawsuit filed in the Middle District of North Carolina.

Wolfspeed’s IPR petition challenged claims 9 through 11 of Purdue’s ‘633 patent for obviousness based on a pair of prior art combinations. Both of Wolfspeed’s obviousness arguments relied on U.S. Patent Application No. 20040119076 (“Ryu”) to teach a MOSFET. To show a transistor topology feature of “base contact regions being spaced apart from each other in a direction parallel to the longitudinal axis” as claimed by the ‘633 patent, Wolfspeed’s IPR petition relied on either U.S. Patent No. 6043532 (“Depetro”) or U.S. Patent No. 5171705 (“Choy”). In particular, both Depetro and Choy supported Wolfspeed’s obviousness argument by teaching a plurality of p-type base contact regions spaced at intervals that, along with Ryu’s MOSFET, accomplishes the reduced on-resistance without sacrificing the semiconductor device’s ruggedness.

PTAB Should Have Considered Material Difference Leading to Less Rugged Device

The PTAB denied institution of Wolfspeed’s IPR petition under its discretionary denial authority codified at 35 U.S.C. § 325(d). Applying the framework from Advanced Bionics v. MED-EL Elektromedizinische Geräte, a precedential PTAB decision from 2020, the PTAB determined that Deptro and Choy were both substantially the same prior art as U.S. Patent No. 6413822 (“Williams”). Williams was asserted in combination with Ryu in a previous IPR petition filed by STMicroelectronics, another defendant in patent infringement proceedings brought by Purdue University in U.S. district court. In STMicroelectronics’ IPR petition, Williams was similarly relied upon to teach a particular transistor topology designed to reduce on-resistance as claimed in Purdue’s ‘633 patent. Applying the second step of Advanced Bionics to Wolfspeed’s IPR petition, the PTAB found that Wolfspeed did not address whether the PTAB erred in denying the prior petition filed by STMicroelectronics, thus leading to the denial of institution to Wolfspeed.

In her sua sponte ruling, Vidal determined that the PTAB erred in denying institution of Wolfspeed’s petition because Williams was not substantially the same prior art as either Depetro or Choy. In particular, she faulted the PTAB for not properly considering material differences between Williams and the prior art asserted by Wolfspeed, especially the fact that the transistor topology of Williams results in a less rugged semiconductor device. That particular disclosure was a major reason why the PTAB denied institution to STMicroelectronics’ IPR petition as it undercut the reasoning for combining Williams with Ryu’s MOSFET.

Conversely, neither Deptro nor Choy included any disclosures regarding a lack of ruggedness stemming from the use of the transistor topology claimed by either prior art reference. “Indeed, Petitioner relies upon Depetro’s teachings and its expert’s testimony to assert that Depetro’s transistor topology would not compromise ruggedness, unlike Williams’s transistor topology,” Vidal wrote.

Vidal Reviews Welcomed, But Confusion Remains on ‘Compelling Merits’ Review

Although Vidal vacated the PTAB’s denial of institution, Wolfspeed’s petition was remanded for the PTAB’s proper consideration of the Section 325(d) inquiry under Advanced Bionics. While the decision on Director review established that Wolfspeed’s petition does not include substantially the same prior art, Vidal highlighted that Advanced Bionics requires the PTAB to consider whether it was presented with substantially the same legal arguments previously raised in STMicroelectronics’ IPR petition.

The recent ruling is just the latest in a series of sua sponte reviews of PTAB decisions issued from the highest office within the USPTO. Last August, Vidal granted sua sponte review to affirm a PTAB ruling finding that interference estoppel does not prevent a party from pursuing IPR proceedings to challenge the same patent-at-issue. Then, late this February, Vidal issued a decision on sua sponte Director review to clarify the impact of a previous “compelling merits” memo on the discretionary denial framework under Apple v. Fintiv. And just one day before the Wolfspeed Director Review, she vacated another decision denying institution on a petition brought by Google.

Vidal’s sua sponte reviews have been met with a fair amount of optimism, but industry insiders reviewing her February compelling merits ruling have argued that the decision does little to dispel confusion under the Fintiv analysis.

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Author: donscarpo