Intel Corp v. VLSI Technology LLC

1. Case Identification

• Case #: IPR2020-00582
• Patent #: 7,292,485
• Filed: February 27, 2020
• Petitioner(s): Intel Corporation
• Patent Owner(s): VLSI Technology LLC
• Challenged Claims: 1–3, 5–8, 12–14

2. Patent Overview

• Title: Memory Circuit with Write-Assist
• Brief Description: The ’485 patent discloses a memory circuit, such as a Static Random Access Memory (SRAM), that uses a "write-assist" technique to improve data writing reliability. The invention reduces the voltage supplied to a selected line of memory cells during a write operation via charge-sharing with a dedicated capacitance structure that includes a plurality of dummy memory cells.

3. Grounds for Unpatentability

Ground 1: Obviousness over Nii - Claims 1–3, 5–7, and 12–14 are obvious over Nii

• Prior Art Relied Upon: Nii (Application # 2007/0030741).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Nii discloses a charge-sharing write-assist circuit (the "WAAPS Circuit") that is functionally identical to the one claimed in the ’485 patent. Nii’s circuit selectively reduces the voltage on a column of memory cells by coupling its power supply line to a capacitance structure formed by "down power supply lines." While Nii's WAAPS circuit does not explicitly use dummy cells for its capacitance structure, Nii separately teaches, in another embodiment, the use of dummy cells (with the same layout as active memory cells) to form pull-down elements for adjusting wordline voltage. Petitioner contended that Nii discloses all elements of the independent claims except for the explicit coupling of these dummy cells to the charge-sharing capacitance structure.
  • Motivation to Combine (for §103 grounds): A person of ordinary skill in the art (POSITA) would have been motivated to modify Nii's WAAPS circuit to include its disclosed dummy cells as part of the capacitance structure. Nii itself recognizes that the parasitic capacitance of its "down power supply lines" may be insufficient and that additional capacitance is needed to match the capacitance of the active memory cell lines for effective charge-sharing. A POSITA would have recognized that the unused transistors within Nii's readily available dummy cells provided a natural and efficient source of this required additional capacitance, a known technique for charge-sharing in memory arrays.
  • Expectation of Success (for §103 grounds): A POSITA would have had a reasonable expectation of success, as the modification only required making a simple electrical connection between the "down power supply line" and the power supply terminals of the existing dummy cells using standard fabrication techniques, which would predictably increase the total capacitance.

Ground 2: Obviousness over Nii in view of Hamzaoglu - Claim 8 is obvious over Nii in view of Hamzaoglu

• Prior Art Relied Upon: Nii (Application # 2007/0030741) and Hamzaoglu (Application # 2006/0268626).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground addresses dependent claim 8, which specifies that the "lines" of memory cells are organized in rows. Petitioner argued that Nii’s primary embodiment applies its write-assist on a column-by-column basis. Hamzaoglu, however, explicitly teaches a write-assist technique that reduces memory cell power supply voltage during a write operation on a row-by-row basis, where cells in a row share a common power supply line. The argument is that Hamzaoglu supplies the missing teaching of a row-based write-assist architecture.
  • Motivation to Combine (for §103 grounds): A POSITA would have been motivated to implement the modified charge-sharing write-assist technique of Nii (as argued in Ground 1) within the row-powered memory array taught by Hamzaoglu. This combination would predictably achieve the benefits of Nii's reliable write-assist in a common row-based memory architecture. Hamzaoglu itself suggests its techniques are applicable to both row- and column-powered arrays, making the application of a known write-assist circuit like Nii's a simple design choice.
  • Expectation of Success (for §103 grounds): The combination would be trivial, requiring only the routing of Nii's power supply lines along rows instead of columns, which is a predictable modification with a high expectation of success.

4. Key Claim Construction Positions

• Petitioner argued for the adoption of the district court’s construction for the term "capacitance structure" (recited in independent claims 1 and 12) as "a structure that is capable of storing and discharging electrical charge."
• This construction was central to Petitioner's argument because the claims further require that this structure "includes a plurality of dummy cells." This clarifies that the "dummy cells" are a required component of the capacitance structure, but not inherent in the definition of the structure itself, focusing the obviousness inquiry on the motivation to add the disclosed dummy cells to Nii's existing charge-sharing circuit.

5. Arguments Regarding Discretionary Denial

• §314(a) (Fintiv): Petitioner argued that discretionary denial based on the parallel district court litigation would be inappropriate. The key reasons asserted were:
  • The petition was filed promptly after the district court’s Markman order, which resolved key claim construction disputes and invalidated other claims, allowing for a more focused and efficient IPR.
  • The Patent Owner had asserted a shifting set of claims in the litigation, with final infringement contentions being served only one month prior to the IPR filing.
  • At least one challenged claim (claim 7) was not asserted in the district court, meaning the PTAB was the only forum that could adjudicate its validity.
  • The trial schedule in the district court was uncertain, and a final written decision from the PTAB could issue before a final judgment in court.
• §325(d): Petitioner argued that denial would be inappropriate because the petition raised invalidity challenges based on Nii, a reference that contains materially different disclosures from the prior art considered by the Examiner during prosecution (the ’628 Publication). Specifically, Nii was alleged to disclose the very "dummy cells" and "switching circuit" details that were added as amendments to overcome the ’628 Publication, making Nii substantially more relevant than the art of record.

6. Relief Requested

• Petitioner requested the institution of an inter partes review and cancellation of claims 1–3, 5–8, and 12–14 of the ’485 patent as unpatentable.