PTAB

IPR2024-00470

Monolithic Power Systems Inc v. Greenthread LLC

Key Events

Petition

petition

Title: CMOS Semiconductor Device and Manufacturing Method
Brief Description: The ’222 patent relates to a CMOS semiconductor device featuring semiconductor layers with a graded dopant concentration. This gradient creates a static, unidirectional electric drift field designed to sweep minority carriers from the device's active region at the surface toward its substrate, purportedly improving device performance.

Prior Art Relied Upon: Onoda (Japanese Application # H8-279598).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that Onoda, which describes a CMOS flash memory device, teaches every limitation of claim 44. Onoda’s figures depict a dopant profile that gradually decreases from the device surface through an epitaxial layer to the substrate. This structure inherently creates the claimed "first static unidirectional electric drift field" to sweep minority carriers. Onoda was alleged to disclose a "surface layer" with an active region, an underlying "substrate," a "single drift layer" (epitaxial layer 102) with a graded dopant concentration, and at least one "well region" (e.g., 105a) also having a graded dopant profile, creating a "second static unidirectional electric drift field."
- Motivation to Combine (for §103 grounds): Not applicable (single reference ground).
- Expectation of Success (for §103 grounds): Not applicable (single reference ground).

Prior Art Relied Upon: Onoda (Japanese Application # H8-279598) and Nishizawa (Patent 5,384,476).
Core Argument for this Ground:
- Prior Art Mapping: This ground asserted that to the extent Onoda does not explicitly disclose certain concepts, Nishizawa supplies the missing teachings. Nishizawa explicitly describes using a graded dopant profile in a buried region of a CMOS device to create an "electric drift field" that migrates minority carriers toward the substrate to prevent device errors. Petitioner contended that Nishizawa's express teachings on using graded dopant profiles for minority carrier control would make it obvious to apply this principle to the structure disclosed in Onoda.
- Motivation to Combine (for §103 grounds): A POSITA would combine Onoda and Nishizawa because both references are directed to similar memory devices and address similar problems, such as reducing punch-through. A POSITA would have been motivated to apply Nishizawa's explicit teachings on generating electric fields for carrier diffusion to the analogous graded dopant structures shown in Onoda to achieve predictable improvements in device performance.
- Expectation of Success (for §103 grounds): A POSITA would have a high expectation of success, as the combination involves applying a well-understood principle (using graded doping to create a drift field) from Nishizawa to a compatible device structure in Onoda.

Prior Art Relied Upon: Kawagoe (Patent 6,043,114).
Core Argument for this Ground:
- Prior Art Mapping: Petitioner argued that Kawagoe teaches a CMOS device with an epitaxial layer whose impurity concentration is "gradually lowered depthwise" to attract minority carriers (electrons) to the substrate, matching the purported improvement of the ’222 patent. Kawagoe’s "diffusion layer," formed by diffusing impurities into an epitaxial layer (2E) and substrate (2S), was argued to constitute the claimed "single drift layer" with a graded dopant concentration. This layer was shown to contain well regions (e.g., p-well 6p) and to inherently create the claimed first and second static unidirectional electric drift fields to move carriers toward the substrate, which lacks active regions.
- Motivation to Combine (for §103 grounds): Not applicable (single reference ground).
- Expectation of Success (for §103 grounds): Not applicable (single reference ground).
- Key Aspects: Petitioner argued that even if Kawagoe's well region extends slightly into the substrate, it would have been an obvious modification for a POSITA to confine the well entirely within the epitaxial layer, as Kawagoe teaches other embodiments with thicker epitaxial layers where this occurs.

Petitioner argued that the Board should not exercise its discretion to deny institution under §314(a) or §325(d). The petition presented compelling evidence of unpatentability, particularly the single-reference obviousness grounds based on Onoda and Kawagoe. Further, it was argued that none of the cited prior art references were applied or considered during the prosecution of the ’222 patent. Petitioner also noted that while other petitions have been filed against the patent, none had reached an institution decision at the time of filing.

Petitioner requests institution of an inter partes review and cancellation of claim 44 of the ’222 patent as unpatentable under 35 U.S.C. §103.