PTAB

IPR2025-01478

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

Log In

1. Case Identification

2. Patent Overview

  • Title: Organic Light Emitting Diode Display
  • Brief Description: The ’990 patent relates to an organic light emitting diode (OLED) display pixel circuit architecture. The patent describes using a pixel circuit with six thin-film transistors (TFTs) and one capacitor, and 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 1-7, 9, 10, and 23-30 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 a compact 6T1C (six transistor, one capacitor) OLED pixel structure aimed at reducing the area occupied by pixel components for high-resolution displays. Liu allegedly taught all elements of independent claim 1 except for a "curved" channel region in the driving transistor (T4 in Liu's circuit). Udagawa was cited to teach this missing element, as it explicitly disclosed lengthening the channel of a driving TFT in an OLED circuit, including forming it in a serpentine or "snake" shape, to improve performance.
    • Motivation to Combine (for §103 grounds): Petitioner contended that a person of ordinary skill in the art (POSITA) would have been motivated to address the well-known problem of current dispersion in the small, polysilicon TFTs of a compact pixel structure like Liu's. A POSITA would combine Liu's circuit with Udagawa's known technique of using a longer, serpentine channel to reduce this dispersion, thereby improving brightness uniformity and image quality.
    • Expectation of Success (for §103 grounds): A POSITA would have had a reasonable expectation of success because elongating a TFT channel to reduce current dispersion was a well-established and predictable solution in the art at the time.

Ground 1B: Claim 8 is obvious over 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 the combination of Liu and Udagawa to further address claim 8, which required "a periphery of the second capacitor plate completely surrounds a periphery of the first capacitor plate." Petitioner asserted that while Liu's capacitor (CS) may not explicitly show this complete surrounding structure, Nakayama taught the benefits of such a configuration. Nakayama disclosed making the upper capacitor electrode larger than the bottom electrode to suppress capacitance variations caused by mask misalignment, a design which resulted in the upper electrode surrounding the lower one.
    • Motivation to Combine (for §103 grounds): A POSITA would have been motivated to improve the stability of Liu’s drive circuit by reducing capacitance variations. Applying Nakayama's known technique of sizing the capacitor plates to achieve this goal was an obvious design choice to improve the performance and manufacturing tolerance of Liu’s compact pixel circuit.

Ground 2A: Claims 1-10 and 21-30 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 this as an alternative primary combination. Noguchi-I was argued to disclose a 6T1C OLED pixel circuit similar to the ’990 patent, including features to reduce parasitic capacitance via a shield electrode. Like Liu, Noguchi-I provided the base pixel architecture but lacked the "curved" channel limitation. Udagawa was again relied upon to supply the teaching of a serpentine-shaped channel for the driving transistor.
    • Motivation to Combine (for §103 grounds): The motivation was similar to that in Ground 1A: a POSITA would apply Udagawa's known technique for reducing dispersion to improve the image quality of the OLED display disclosed in Noguchi-I. Petitioner argued this combination was particularly compelling because Udagawa's longer channel could be implemented while maintaining a compact footprint due to the parasitic capacitance reduction already provided by Noguchi-I's shield electrode.
    • Expectation of Success (for §103 grounds): A POSITA would have expected success in combining these references to predictably reduce current dispersion while improving image quality.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combinations of Liu, Udagawa, and Chung (Application # 2008/0150846) to add a seventh TFT for preventing OLED degradation; combinations with Noguchi-II (Application # 2012/0127220) and Jeong (Application # 2012/0001893) to add an adjusting transistor; and a combination with Kim (Patent 7,626,199) to teach a contiguous semiconductor layer as an alternative to Noguchi-I's non-contiguous layout.

4. Relief Requested

  • Petitioner requested the institution of an inter partes review and the cancellation of claims 1-30 of the ’990 patent as unpatentable.