Active Matrix Substrate With Segmented Oxide Semiconductor Layers
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Solution Overview
Problem
Active matrix substrates using oxide semiconductor TFTs face challenges in producing TFTs with different characteristics for various applications, as existing methods struggle to achieve the required performance and functionality for pixel and circuit TFTs, particularly in organic EL display devices where drive and selection TFTs have distinct requirements.
Innovation Solution
The active matrix substrate incorporates a top gate structure with multiple oxide semiconductor TFTs, each with distinct characteristics, utilizing different oxide semiconductor layers and gate insulating layers to achieve the necessary mobility and threshold voltage, allowing for the production of TFTs with specific characteristics suitable for different applications, such as SSD circuits and drive circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single oxide semiconductor film is used for both pixel TFTs and circuit TFTs with a common process, then manufacturing complexity is reduced, but the ability to achieve different TFT characteristics is limited
Solution Approach 1:
The substrate surface is divided into first and second regions, where different oxide semiconductor films are formed in each region. This segmentation allows pixel TFTs in the first region to use a first oxide semiconductor film with specific characteristics while circuit TFTs in the second region use a second oxide semiconductor film with different characteristics, enabling differentiated performance while maintaining a unified manufacturing process flow
Solution Approach 2:
Different oxide semiconductor films with distinct properties are applied to different spatial locations on the substrate. The first oxide semiconductor film is used where pixel TFTs are formed, while the second oxide semiconductor film is used where circuit TFTs are formed. This local differentiation of material quality enables each TFT type to achieve its required characteristics without requiring separate manufacturing processes
2Speed
If the gate insulating layer is thinned to improve current supply performance, then switching speed increases, but manufacturing precision requirements increase
Solution Approach 1:
The gate insulating layer thickness is optimized to enhance current supply performance and switching speed while maintaining manufacturing feasibility. By carefully controlling the thickness parameter within an optimal range, the invention achieves high-speed operation without imposing excessive precision requirements that would complicate the manufacturing process
Data Source
AI summary
An active matrix substrate includes a first TFT and a second TFT, in which the first TFT includes a first oxide semiconductor layer and a first gate electrode arranged on a part of the first oxide semiconductor layer with a first gate insulating layer interposed therebetween, the first gate insulating layer has a layered structure including a first insulating film and a second insulating film arranged on the first insulating film, the second TFT includes a second oxide semiconductor layer having a higher mobility than the first oxide semiconductor layer and a second gate electrode arranged on a part of the second oxide semiconductor layer with a second gate insulating layer interposed therebetween, and the second gate insulating layer includes the second insulating film and does not include the first insulating film, and the second TFT further includes a lower insulating layer including the first insulating film arranged between the second oxide semiconductor layer and a substrate.