TFT Substrate with Segmented Bottom Gate for Dual Breakdown Voltage
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Solution Overview
Problem
Current TFT substrates face challenges in efficiently forming TFTs with both high current driving capability and high breakdown voltage capability on the same substrate, requiring separate processes for low and high voltage TFTs, which increases production costs and complexity.
Innovation Solution
A TFT substrate design featuring first and second TFTs with a bottom gate electrode and a floating top gate electrode, where the top gate electrode is either present or absent to achieve dual-gate or bottom gate characteristics, allowing for easy switching between breakdown voltage capabilities without increasing the top gate electrode formation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate processes are used to form low voltage TFT and high voltage TFT on the same substrate, then different breakdown voltage capabilities are achieved, but production cost and process complexity increase
Solution Approach 1:
The gate electrode layer is segmented into first and second areas with different configurations. The first area has a gate electrode that overlaps the semiconductor layer, while the second area has no gate electrode, allowing different breakdown voltage capabilities in different regions of the same TFT structure
Solution Approach 2:
A single TFT structure with a unified gate electrode layer configuration serves dual purposes: the first area provides high breakdown voltage capability while the second area provides low breakdown voltage capability, eliminating the need for separate TFT designs
2Reliability
If multiple gate insulating films are formed for high voltage TFT, then breakdown voltage capability is improved, but manufacturing process complexity increases
Solution Approach 1:
The gate insulating film thickness is varied locally across different areas of the semiconductor layer. The first area has a thicker gate insulating film for high breakdown voltage, while the second area has a thinner gate insulating film for low breakdown voltage, allowing tailored electrical characteristics in different regions
3Adaptability or versatility
If individual top gate electrode formation processes are used for low and high voltage TFTs, then specific voltage characteristics are achieved, but production efficiency decreases
Solution Approach 1:
The gate electrode layer is formed as a single continuous structure that serves both low voltage and high voltage TFT functions simultaneously, merging what would traditionally be separate formation processes into one unified process step
Data Source
AI summary
A thin film transistor (TFT) substrate includes first and second TFTs on the same substrate. The first TFT has a feature that a lower conductive layer or a bottom gate electrode layer is provided between the substrate and a first insulating layer while an upper conductive layer or a top gate electrode layer is disposed on a second insulating layer formed on a semiconductor layer which is formed on the first insulating layer. The first conductive layer has first and second areas such that the first area overlaps with the first conductive layer without overlapping with the semiconductor layer while the second area overlaps with the semiconductor layer, and the first area is larger than the second area while the second insulating layer is thinner than the first insulating layer. The second TFT has the same configuration as the first TFT except that the gate electrode layer is eliminated.