Active Matrix Substrate With Localized Gate Insulator Thickness
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Solution Overview
Problem
Active matrix substrates face challenges in balancing the film thickness of gate electrodes and insulating films to enhance on-current and withstand voltage, as increasing film thickness can lead to electrostatic breakdown and reduced on-current.
Innovation Solution
The active matrix substrate design includes a thin film transistor with a gate electrode covered by a first inorganic insulating film, a second inorganic insulating film with openings overlapping the gate electrode, and source and drain electrodes that cover part of the second insulating film, with the surface of the first insulating film in one region lower than in another, optimizing film thickness to increase on-current and withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the film thickness of the gate electrode is increased to reduce the resistance of the gate wiring line, then the resistance is reduced, but the distance between the gate electrode and the source electrode/drain electrode is reduced, causing electrostatic breakdown of the gate insulating film
Solution Approach 1:
The gate insulating film is designed with different thicknesses in different regions: a first thickness in the channel region and a second thickness (greater than the first) in the region overlapping the source/drain electrodes. This local variation in thickness provides different electrical characteristics in different areas, allowing the film to withstand higher voltages where needed while maintaining proper transistor operation in the channel region.
2Reliability
If the film thickness of the gate insulating film is increased to increase the withstand voltage, then the withstand voltage is increased, but the on-current of the TFT is decreased
Solution Approach 1:
The gate insulating film thickness is optimized locally: thinner in the channel region to allow higher on-current and stronger electric field for charge carrier modulation, and thicker in the source/drain overlapping regions to provide enhanced insulation and prevent electrostatic breakdown. This resolves the contradiction by providing different thicknesses for different functional requirements.
Data Source
AI summary
An active matrix substrate includes a thin film transistor that includes a gate electrode, a first inorganic insulating film that covers the gate electrode, a second inorganic insulating film that is disposed on the first inorganic insulating film and that has an opening overlapping the gate electrode, a source electrode and a drain electrode disposed on the second inorganic insulating film, and a semiconductor layer that overlaps the gate electrode in an opening of the first inorganic insulating film and that covers the source electrode and the drain electrode. Regarding a surface of the first inorganic insulating film in a first region overlapping the opening of the first inorganic insulating film and a surface in a second region other than the first region, the surfaces being arranged nearer to the second inorganic insulating film, the surface in the first region is lower than the surface in the second region.