Oxide Semiconductor TFTs with Localized Carrier Concentration
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Solution Overview
Problem
Active matrix substrates using oxide semiconductor TFTs face challenges in forming demultiplexer circuits with intended performance due to differing characteristics required for DMX circuit TFTs compared to pixel and driving circuit TFTs, making it difficult to produce TFTs with specific characteristics using the same oxide semiconductor film.
Innovation Solution
The active matrix substrate incorporates TFTs with different carrier concentrations in their channel regions, achieved by varying the carrier concentration in the oxide semiconductor layer, allowing for the formation of TFTs with distinct characteristics suitable for DMX, driving, and pixel applications using the same oxide semiconductor film, including a higher carrier concentration for DMX circuit TFTs to enhance ON current and lower threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the same oxide semiconductor film is used for all TFTs (pixel TFTs, driving circuit TFTs, and DMX circuit TFTs), then the manufacturing process is simplified, but it becomes difficult to achieve the different characteristics required for DMX circuit TFTs (higher ON current and lower threshold voltage)
Solution Approach 1:
The patent applies local quality by introducing hydrogen selectively into specific regions of the oxide semiconductor film. A mask is used to cover regions where standard TFT characteristics are needed, while exposing regions where DMX circuit TFTs require higher carrier concentration. This allows different parts of the same oxide semiconductor film to have different electrical characteristics, enabling DMX circuit TFTs to achieve higher ON current and lower threshold voltage without complicating the overall manufacturing process
2Power
If the carrier concentration of oxide semiconductor layer is increased to enhance ON current for DMX circuits, then DMX circuit performance is improved, but the characteristics of pixel TFTs and driving circuit TFTs may be adversely affected
Solution Approach 1:
The patent uses a mask to create local quality differences in the oxide semiconductor film. The mask prevents hydrogen introduction in regions where pixel TFTs and driving circuit TFTs are formed, maintaining their original characteristics. Meanwhile, in regions where DMX circuit TFTs are formed, hydrogen is introduced to increase carrier concentration, thereby enhancing ON current and reducing threshold voltage specifically for DMX circuits without affecting other TFT types
3Reliability
If different oxide semiconductor films are used for different TFT types to achieve different characteristics, then TFT performance is optimized, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the carrier concentration of the oxide semiconductor film through selective hydrogen introduction. Instead of using different oxide semiconductor films for different TFT types, the same oxide semiconductor film is used, but its electrical parameters (carrier concentration, threshold voltage) are changed locally through controlled hydrogen plasma treatment. This approach optimizes TFT characteristics for different applications while keeping the manufacturing process relatively simple
Data Source
AI summary
An active matrix substrate includes: a substrate (1); a peripheral circuit including a plurality of first TFTs (10); and a plurality of second TFTs (20), wherein each of the first and second TFTs (10, 20) includes: a gate electrode (3A, 3B); a gate insulating layer (5); an oxide semiconductor layer (7A, 7B) including a channel region (7Ac, 7Bc), a source contact region (7As, 7Bs) and a drain contact region (7Ad, 7Bd), wherein the source contact region and the drain contact region are located on opposite sides of the channel region; a source electrode (8A, 8B) that is in contact with the source contact region and a drain electrode (9A, 9B) that is in contact with the drain contact region; the oxide semiconductor layer of the first TFTs and the second TFTs is formed from the same oxide semiconductor film; a carrier concentration in the channel regions (7Ac) of the first TETs is higher than a carrier concentration in the channel regions (7Bc) of the second TETs.