BlueHouse Global Ltd v. Semiconductor Energy Laboratory Co Ltd

1. Case Identification

• Case #: IPR2018-01362
• Patent #: 8,492,840
• Filed: July 9, 2018
• Petitioner(s): BlueHouse Global Ltd.
• Patent Owner(s): Semiconductor Energy Laboratory Co., Ltd.
• Challenged Claims: 1, 2, 4, 14, 16, 17, and 19

2. Patent Overview

• Title: Semiconductor Device
• Brief Description: The ’840 patent relates to semiconductor devices, particularly top-gate thin-film transistors (TFTs). The disclosed technology involves a structure with an oxide semiconductor layer, a gate electrode, and multi-layer source and drain electrodes that are in contact with the semiconductor layer.

3. Grounds for Unpatentability

Ground 1: Anticipation of Claims 1, 4, 14, 16, and 19 under 35 U.S.C. §102(b) over Toyota

• Prior Art Relied Upon: Toyota (Application # 2008/0299693).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that Toyota, specifically its FIG. 3B, discloses a top-gate TFT that meets every limitation of independent claims 1 and 14. This disclosed structure includes an oxide semiconductor layer, a two-layer source electrode, a two-layer drain electrode, a gate electrode overlapping the semiconductor layer, and a gate insulating layer positioned between them. Petitioner asserted that Toyota teaches the claimed structural arrangements, including the lower conductive layer of the electrodes protruding beyond the upper layer and the end portions of the upper conductive layers being "opposed to" each other. For dependent claims 4 and 19, Petitioner contended Toyota’s disclosure of using TiN (titanium nitride) as a possible material for the lower conductive layer satisfies the "nitride of a metal" limitation.

Ground 2: Obviousness of Claims 2 and 17 under 35 U.S.C. §103 over Toyota in view of Chung

• Prior Art Relied Upon: Toyota (Application # 2008/0299693), Chung (Application # 2005/0173752).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that while Toyota teaches the base structure of claims 2 and 17 (which depend from claims 1 and 14), it does not expressly disclose that the four conductive layers of the source and drain electrodes each have a "tapered shape." Chung allegedly remedies this deficiency by teaching that multi-layer electrodes in a TFT should have tapered lateral sides to improve the adhesion of an overlying layer.
  • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine Chung's teaching of tapered electrodes with Toyota's TFT structure. The motivation was to solve a known problem by improving the adhesion of the passivation layer (identified as PAS in Toyota's FIG. 3B) to the underlying source and drain electrodes, a specific benefit disclosed in Chung.
  • Expectation of Success: A POSITA would have a reasonable expectation of success because tapering was a well-known technique in semiconductor fabrication for improving interlayer adhesion, and applying it to the Toyota device was a straightforward implementation of a known solution to a predictable problem.

Ground 3: Obviousness of Claims 4 and 19 under §103 over Toyota in view of Miyazaki

• Prior Art Relied Upon: Toyota (Application # 2008/0299693), Miyazaki (Patent 6,784,453).
• Core Argument for this Ground:
  • Prior Art Mapping: This ground presented an alternative argument for claims 4 and 19, which require the second and fourth conductive layers (the lower layers of the electrodes) to be a "nitride of a metal." If the Board determined that Toyota did not inherently disclose this feature, Petitioner argued that Miyazaki supplies the missing element. Miyazaki discloses using a metal nitride layer (specifically titanium nitride) stacked under an aluminum layer in a two-layer gate electrode.
  • Motivation to Combine: Miyazaki teaches that its stacked metal/metal nitride structure reduces defects during etching processes and improves overall device reliability. A POSITA would be motivated to apply this known manufacturing benefit from Miyazaki’s gate electrode to the similarly structured multi-layer source and drain electrodes of Toyota's device to achieve the same advantages of reduced manufacturing defects and enhanced reliability.
  • Expectation of Success: The combination involved applying a known technique for improving reliability in one type of electrode (gate) to other electrodes (source and drain) with a similar layered structure. This application of a known solution to a similar problem would provide a POSITA with a high expectation of success.
• Additional Grounds: Petitioner asserted an additional obviousness challenge for claims 4 and 19 based on Toyota in view of Akimoto (Application # 2007/0072439), which also taught the use of metal nitrides in conductive films for semiconductor devices, providing a similar motivation and rationale.

4. Key Claim Construction Positions

• "in contact with": Petitioner proposed this term be construed to mean "physically touching." This construction was argued as critical for demonstrating that the lower layer of the electrodes in Toyota, which passes through a contact hole to touch the semiconductor layer, meets the claim limitation.
• "opposed to": Petitioner proposed this term be construed to mean "located directly across from." This construction supports the argument that the source and drain electrodes in Toyota, which are formed simultaneously from the same metal layers, have end portions arranged opposite one another in the channel region, as required by the claims.

5. Relief Requested

• Petitioner requests institution of an inter partes review and cancellation of claims 1, 2, 4, 14, 16, 17, and 19 of the ’840 patent as unpatentable.