TFT Gate Electrode Sloping Surface for Vg-Id Inflection
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Solution Overview
Problem
The variation in threshold voltage across the channel of thin-film transistors (TFTs) due to different impurity influences at the center and sides, leading to inflection points in Vg-Id characteristics, which affects the reliability and quality of display devices.
Innovation Solution
The TFT structure is modified by forming a semiconductor layer with a specific taper angle on a sloping surface of the gate electrode, ensuring uniform impurity influence and maintaining good step coverage of insulating films, thereby eliminating or reducing inflection points in Vg-Id characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the channel width is widened to increase ON current, then the ON current increases, but the area occupied by the TFT increases which conflicts with high resolution requirements
Solution Approach 1:
The channel is extended from a planar structure to a three-dimensional structure by forming it on the projection and inclining side wall of the gate electrode. This vertical/diagonal extension allows increasing the effective channel width without proportionally increasing the planar footprint, thus maintaining high resolution while achieving higher ON current.
2Manufacturing precision
If the semiconductor layer has a tapered shape at both sides, then the side wall coverage is improved, but the impurity influence becomes non-uniform causing threshold voltage variation
Solution Approach 1:
The semiconductor layer is designed with different thickness characteristics at different locations: it has a tapered shape at the side walls for good coverage, but maintains a substantially constant thickness in the central channel region. This local differentiation ensures both manufacturing precision and electrical uniformity, eliminating threshold voltage variation while maintaining side wall coverage.
Data Source
AI summary
The purpose of the present invention is to avoid an inflection point in Vg-Id characteristics of the Thin Film transistor, and to avoid step disconnection of the insulating film formed on the semiconductor layer in the display device. The concrete structure of the present invention is: a display device including a TFT substrate having a thin film transistor (TFT) comprising; the TFT having a channel width and a channel length, a gate insulating film formed on a gate electrode, a semiconductor layer formed on the gate insulating film, wherein the gate electrode, near its edge, has a first sloping surface having a first taper angle in a cross sectional view along the direction of the channel width, an edge of the semiconductor layer in the cross sectional view along the direction of the channel width lies on the first sloping surface of the gate electrode.