PTAB

IPR2025-01479

BOE Technology Group Co Ltd v. Samsung Display Co Ltd

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Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Organic Light Emitting Diode Display
  • Brief Description: The ’991 patent describes an organic light emitting diode (OLED) display pixel circuit comprising multiple thin-film transistors (TFTs) and a storage capacitor. The patent purports to achieve a large number of gray levels by forming the channel region of the driving TFT to include a plurality of bent portions.

3. Grounds for Unpatentability

Ground 1A: Claims 1-6, 8-13, 15-20, 22-26, and 28-30 are obvious over Liu and Udagawa.

  • Prior Art Relied Upon: Liu (Application # 2012/0313100) and Udagawa (Application # 2003/0089905).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Liu disclosed all elements of a baseline OLED pixel structure as required by independent claim 1, including a six-transistor, one-capacitor (6T1C) driving circuit on a non-conductive substrate. However, Liu did not expressly disclose the key limitation of the driving transistor’s semiconductor layer having "at least one bent portion." Petitioner asserted that Udagawa remedied this deficiency by explicitly teaching the use of a serpentine ("snake-like" or bent) channel for a driving TFT in an OLED display to increase the channel length.
    • Motivation to Combine: Petitioner contended that both references sought to improve OLED display design and operation. A person of ordinary skill in the art (POSITA) would have recognized that the miniaturized TFTs in Liu's design would suffer from electric current dispersion, a known problem that degrades image uniformity. Udagawa taught that lengthening the channel via a serpentine shape reduces this dispersion. A POSITA would combine Udagawa's bent channel with Liu’s compact pixel circuit to achieve the dual benefits of a small footprint and improved electrical performance, resulting in more uniform brightness.
    • Expectation of Success: Petitioner argued that a POSITA would have had a reasonable expectation of success because elongating a TFT channel to reduce current dispersion was a well-known and predictable technique in the art by 2012.

Ground 2A: Claims 1-6 and 17-20 are obvious over Noguchi-I and Udagawa.

  • Prior Art Relied Upon: Noguchi-I (Application # 2012/0199854) and Udagawa (Application # 2003/0089905).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner presented Noguchi-I as an alternative primary reference that disclosed a 6T1C OLED pixel structure with a storage capacitor utilizing a shield electrode to reduce parasitic capacitance. Similar to Liu, Noguchi-I taught the fundamental circuit elements of claim 1 but lacked the "bent portion" for the driving TFT's channel. Udagawa was again relied upon to teach this bent, serpentine channel structure.
    • Motivation to Combine: The motivation was analogous to that in Ground 1A. A POSITA would have been motivated to improve the performance of Noguchi-I's driving TFT by reducing current dispersion. Udagawa's teaching of a serpentine channel offered a known solution. Petitioner also noted that Udagawa taught that a longer channel increases oxide film capacitance, which could be used as retention capacitance to further improve the OLED's image quality, providing additional motivation to combine the references.
    • Expectation of Success: As with the previous ground, the technique of using a longer, serpentine channel to reduce dispersion was well-established and would have yielded predictable results.

Ground 1C: Claims 7, 14, 21, and 27 are obvious over Liu, Udagawa, and Chung.

  • Prior Art Relied Upon: Liu (Application # 2012/0313100), Udagawa (Application # 2003/0089905), and Chung (Application # 2008/0150846).

  • Core Argument for this Ground:

    • Prior Art Mapping: This ground built upon the combination of Liu and Udagawa to address dependent claims requiring a seventh thin-film transistor. Petitioner asserted that Chung disclosed an OLED pixel circuit, similar to Liu's, that explicitly included a seventh transistor (SW_TR6). This seventh transistor was used to apply a reverse bias to the OLED during non-emission periods, thereby preventing its degradation.
    • Motivation to Combine: Petitioner argued that a POSITA, having created the improved circuit of Liu and Udagawa, would be further motivated to enhance its operational lifespan and reliability. Chung provided a known technique for preventing OLED degradation by adding a seventh transistor. A POSITA would combine Chung's teaching with the Liu/Udagawa circuit to create a display that was not only compact and uniform but also more durable.
    • Expectation of Success: Petitioner asserted a high expectation of success, as adding a single, well-understood transistor to an existing 6T1C circuit was a routine and predictable modification for a POSITA in 2012.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combinations relying on Nakayama (Japanese Pat. Pub. No. 2003-167533) for capacitor plate sizing to reduce capacitance variations, Murade (Japanese Pat. Pub. No. 2008-008942) for using a contact hole through a capacitor plate for routing, and Kim (Patent 7,626,199) for implementing a contiguous semiconductor layer across all TFTs.

4. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-30 of Patent 11,574,991 as unpatentable.