PTAB

IPR2025-01478

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 and Driving Method Thereof
  • Brief Description: The ’990 patent describes an organic light emitting diode (OLED) display pixel circuit comprising six thin-film transistors (TFTs) and a storage capacitor. The patent purports to improve image quality by forming the channel region of the driving TFT with a plurality of bent portions (e.g., an "S" shape) to achieve a broader driving range and more precise control of gray levels.

3. Grounds for Unpatentability

Ground 1A: Obviousness over Liu and Udagawa - Claims 1-7, 9-10, and 23-30 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 disclosed a compact 6-TFT, 1-capacitor (6T1C) OLED pixel structure aimed at high-resolution displays. Liu taught nearly all structural elements of the challenged claims, including the number of transistors, their interconnections, the use of a contiguous semiconductor layer, and the overall pixel layout. However, Petitioner contended Liu did not expressly disclose the key limitation of a "curved" channel region for the driving transistor (T4 in Liu's circuit). Udagawa was cited to supply this missing element, as it explicitly taught lengthening the channel of a driving TFT in an OLED circuit, including forming it in a serpentine or "snake" shape, to reduce unwanted current dispersion effects that arise in smaller transistors.
    • Motivation to Combine: Petitioner asserted a person of ordinary skill in the art (POSITA) would combine these references to solve a known problem. Liu's goal of miniaturizing pixel circuits for high-resolution displays would lead to smaller TFTs, which, as Udagawa recognized, suffer from increased current dispersion and display irregularities. A POSITA would have been motivated to apply Udagawa's known technique of using a serpentine channel to Liu's pixel structure to mitigate these dispersion effects while still conforming to Liu's objective of maintaining a small pixel footprint.
    • Expectation of Success: A POSITA would have had a high expectation of success because elongating a TFT channel to reduce dispersion was a well-understood technique in the art by 2012, and implementing Udagawa's serpentine channel shape into Liu's polysilicon layer was a predictable design modification.

Ground 1B: Obviousness over Liu, Udagawa, and Nakayama - Claim 8 is obvious over the combination of Liu, Udagawa, and Nakayama.

  • Prior Art Relied Upon: Liu (Application # 2012/0313100), Udagawa (Application # 2003/0089905), and Nakayama (Japanese Pat. Pub. No. 2003-167533).
  • Core Argument for this Ground:
    • Prior Art Mapping: This ground built upon Ground 1A and specifically addressed claim 8, which required a "periphery of the second capacitor plate completely surrounds a periphery of the first capacitor plate." Petitioner argued that while Liu disclosed a capacitor structure, it may not have explicitly shown this complete surrounding configuration. Nakayama was introduced because it directly addressed suppressing capacitance variations due to mask misalignment by teaching that the upper capacitor electrode should be configured with a larger surface area than the bottom electrode, such that it surrounds the bottom electrode.
    • Motivation to Combine: A POSITA, seeking to improve the reliability of the Liu/Udagawa circuit, would have been motivated to incorporate Nakayama's capacitor design. Reducing capacitance variation was a known goal for improving OLED display performance. Applying Nakayama's solution to Liu's capacitor would have been an obvious way to make the circuit more robust against manufacturing tolerances, a predictable improvement.
    • Expectation of Success: The modification was a straightforward physical layout adjustment with predictable electrical benefits, and Petitioner argued it would have been well within the skill of a POSITA.

Ground 2A: Obviousness over Noguchi-I and Udagawa - Claims 1-10 and 21-30 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: As an alternative to Liu, Petitioner presented Noguchi-I as the primary reference. Petitioner asserted Noguchi-I disclosed a 6T1C OLED pixel circuit with a structure and purpose highly similar to the ’990 patent, including compensating for threshold voltage variability. Like Liu, Noguchi-I taught the core circuit layout but did not expressly disclose a "curved" driving transistor channel. Udagawa was again relied upon to teach this serpentine channel structure.
    • Motivation to Combine: The motivation was analogous to that in Ground 1A. A POSITA would have sought to improve the performance of Noguchi-I's circuit by reducing current dispersion in its driving TFT. Udagawa provided a known and predictable solution. Petitioner further argued that combining Udagawa with Noguchi-I was particularly advantageous because Noguchi-I's use of a shield electrode to reduce parasitic capacitance would allow for Udagawa's longer channel to be implemented without significantly increasing that same parasitic capacitance.
    • Expectation of Success: A POSITA would have had a reasonable expectation of success for the same reasons as in Ground 1A, as it involved applying a known solution to a known problem in a predictable manner.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including grounds that added Chung (Application # 2008/0150846) to teach a seventh TFT for preventing OLED degradation; added Noguchi-II (Application # 2012/0127220) and Jeong (Application # 2012/0001893) to teach a seventh TFT for reducing parasitic capacitance; and added Kim (Patent 7,626,199) to teach modifying Noguchi-I’s discontinuous semiconductor layer to be contiguous.

4. Relief Requested

  • Petitioner requests the Board institute an inter partes review (IPR) and cancel claims 1-30 of the ’990 patent as unpatentable.