PTAB

IPR2025-01479

BOE Technology Group Co., Ltd. v. Samsung Display Co., Ltd.

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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 with a pixel circuit comprising multiple thin-film transistors (TFTs) and a storage capacitor. The invention aims to achieve a large number of gray levels and improve image quality by forming the channel region of the driving TFT to include at least one bent portion.

3. Grounds for Unpatentability

Ground 1: Claims 1-6, 8-13, 15-20, 22-26, and 28-30 are obvious over Liu in view of 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 discloses an OLED pixel structure with six TFTs and one capacitor (6T1C), meeting most limitations of independent claim 1. Liu's focus is on reducing the pixel area for high-resolution displays. However, Petitioner contended Liu does not expressly disclose the claimed limitation of a "bent portion" in the semiconductor layer of the second TFT (the driving transistor). This limitation is allegedly taught by Udagawa, which discloses lengthening a driving TFT's channel by forming it in a serpentine or "snake-like" shape to reduce dispersion in current values, thereby improving display uniformity.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) would combine Udagawa’s serpentine channel with Liu’s compact pixel structure to solve the known problem of increased current dispersion that arises from the miniaturization of TFTs in high-resolution displays like Liu's. The combination would predictably improve the image uniformity of Liu’s design without significantly increasing pixel size, thus achieving the benefits of both references.
    • Expectation of Success: A POSITA would have a reasonable expectation of success because elongating a TFT channel to reduce dispersion was a well-known technique, and implementing it as a serpentine shape was a known design choice for conserving space.

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

  • Prior Art Relied Upon: Noguchi-I (Application # 2012/0199854) and Udagawa (Application # 2003/0089905).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner asserted Noguchi-I as an alternative primary reference that discloses a 6T1C OLED pixel structure aimed at improving image quality by reducing parasitic capacitance via a shield electrode. Like Liu, Noguchi-I allegedly provides the foundational pixel circuit but lacks the "bent portion" of the driving transistor's channel. Udagawa is again relied upon to teach this serpentine channel structure.
    • Motivation to Combine: A POSITA would be motivated to incorporate Udagawa’s teaching into Noguchi-I for the same reasons as with Liu: to improve image quality further by addressing the known issue of current dispersion. Udagawa's solution is complementary to Noguchi-I’s, as both aim to enhance display performance. Combining them would achieve reduced parasitic capacitance (from Noguchi-I) and improved current uniformity (from Udagawa).
    • Expectation of Success: The combination was a predictable application of a known solution (Udagawa's channel shape) to a known problem (dispersion) in a similar OLED circuit (Noguchi-I), well within the skill of a POSITA.

Ground 3: 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 builds upon the combination of Liu and Udagawa to address claims requiring a seventh TFT. Petitioner argued that the base combination of Liu and Udagawa discloses a six-transistor pixel circuit. Chung is introduced because it explicitly teaches adding a seventh switching transistor to an OLED pixel circuit to apply a reverse bias to the OLED during non-emission periods, thereby preventing degradation and improving the device's lifespan.
    • Motivation to Combine: After improving the pixel's electrical performance by combining Liu and Udagawa, a POSITA would be motivated to improve its long-term reliability. Chung provides a known solution for preventing OLED degradation. Adding this feature from Chung to the Liu/Udagawa circuit is a logical next step to create a more robust and durable display.
    • Expectation of Success: Incorporating a single, well-understood transistor for a specific, known purpose (preventing degradation) into an existing 6T1C circuit was presented as a routine and predictable modification for a POSITA.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combinations based on Liu/Udagawa with Nakayama or Murade to address capacitor structure and layout; combinations based on Noguchi-I/Udagawa with Kim to address contiguous semiconductor layers; and combinations based on Noguchi-I/Udagawa with Noguchi-II and Jeong to address further circuit modifications.

4. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-30 of the ’991 patent as unpatentable.