Slingshot Printing v. Canon — Federal Circuit Affirms PTAB Invalidity of Inkjet Printer Substrate Patent

Background

U.S. Patent No. 7,195,341 covers a semiconductor substrate for a micro-fluid ejection device — specifically, a chip layout for an inkjet printer printhead designed to deliver higher-quality images at faster printing rates while keeping the substrate small and cost-effective. The patent describes an arrangement in which micro-fluid ejection actuators, power transistors, and logic circuits are arranged in columnar arrays, with power and ground conductors routed in overlapping metal layers to minimize substrate size and maintain stable electrical properties.

Canon filed a petition for inter partes review at the PTAB in 2022, challenging claims 1–5 and 8. The PTAB found all challenged claims obvious over two prior-art patents from the inkjet printhead field: U.S. Patent No. 6,412,917 (“Torgerson”) and U.S. Patent No. 7,240,997 (“Bruce”). Slingshot appealed, raising three arguments: (1) Torgerson does not teach connecting logic circuits to power transistors through a polysilicon layer; (2) no motivation existed to combine Torgerson and Bruce; and (3) the PTAB’s reasoning for the remaining claim limitations was insufficient under the Administrative Procedure Act.

The Court’s Holding

The Federal Circuit affirmed the PTAB’s unpatentability finding on all three grounds. First, on the polysilicon layer limitation, the Board’s reading of Torgerson was supported by substantial evidence: Canon’s expert testified that a skilled artisan would understand Torgerson’s polysilicon gate fingers to extend to the logic circuits as a practical matter, and Torgerson’s specification described those fingers as “interconnected at respective ends.” Slingshot’s reading that the polysilicon layer ends at the gate fingers was not supported by the record.

Second, on motivation to combine, both Torgerson and Bruce were from the same field of inkjet printhead substrates. The Board credited Canon’s expert that Bruce’s approach of placing a ground bus in a second metal layer offered multiple advantages — including reduced substrate size, lower energy variation, and avoided die-size cost increases — and that this was one of a “finite number” of known, predictable solutions to the substrate-sizing problem. This satisfied the motivation-to-combine standard. Third, the Board’s analysis of the remaining limitations, though concise, was reasonably discernible: it identified the relevant arguments and evidence and explained why they established obviousness.

Key Takeaways

• When two prior-art references are from the same technical field and one offers known advantages over the other for a recognized design need, a PTAB motivation-to-combine finding will generally withstand substantial evidence review.
• Expert testimony that skilled artisans would understand implicit connections in prior-art diagrams is highly influential and difficult to overcome on appeal.
• Brief PTAB explanations that cite to the petitioner’s evidence and follow a discernible logical path can satisfy APA requirements — though clearer reasoning reduces appeal risk.

Why It Matters

Hardware patents on semiconductor and printhead substrate designs face a challenging environment in IPR proceedings when the technical field has a long prior-art history. This case is a reminder that in mature manufacturing technology sectors — where patents from the same field often teach similar design elements — IPR petitioners can frequently find combinations that render existing patents obvious. Patent holders in these fields should consider whether their claim language is narrowly tailored to specific innovations rather than broad structural arrangements that prior-art designs may already suggest.