Thin-Film Transistor Light Shielding Layer for Threshold Stability
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Solution Overview
Problem
Conventional oxide semiconductor thin-film transistors (TFTs) in liquid crystal display devices suffer from light-induced fluctuations in threshold value due to light absorption, leading to reduced reliability.
Innovation Solution
A thin-film transistor design incorporating a light shielding layer made of organic black substance or black negative photoresist, positioned between the etch stop layer and the semiconductor layer, to prevent light irradiation, combined with a method that includes photolithographic processes for forming the light shielding and etch stop layers in a single step, ensuring non-light-transmitting and non-electrically-conductive coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shielding layer is added to prevent light irradiation on the semiconductor layer, then the reliability and threshold value stability are improved, but the device complexity and manufacturing steps increase
Solution Approach 1:
The patent combines the light shielding layer formation with the existing etch stop layer formation process by using the same black negative photoresist material for both purposes. This merging of functions reduces the number of separate manufacturing steps while achieving both light shielding and etch stopping functions, thereby improving reliability without proportionally increasing device complexity
Solution Approach 2:
The black negative photoresist layer serves multiple functions simultaneously: it acts as both the etch stop layer and the light shielding layer. This multi-functionality approach allows a single layer to address both the etching process requirements and the light-induced threshold fluctuation problem, reducing overall device complexity while maintaining improved reliability
2Reliability
If a light shielding layer is added to prevent light irradiation on the semiconductor layer, then the reliability is improved, but the manufacturing time and process steps increase
Solution Approach 1:
The patent merges the light shielding layer formation with the etch stop layer formation into a single manufacturing step. By using black negative photoresist that serves both purposes, the patent eliminates the need for separate light shielding layer deposition and patterning steps, thereby reducing manufacturing time while achieving improved threshold value stability
Solution Approach 2:
The patent applies preliminary action by forming the light shielding function during the etch stop layer formation process itself. The black negative photoresist is applied and patterned to define both the etch stop and light shielding regions simultaneously, preventing light-induced threshold fluctuations from the outset without requiring additional subsequent steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively shields the semiconductor layer from light, stabilizing the threshold value and enhancing the reliability of liquid crystal display devices by preventing light-induced conductivity variations.
Implementation Method 1
The absorption of the incident light causes variation of electrical conductivity and change of the threshold value of the TFTs
Data Source
AI summary
A thin-film transistor includes a substrate, a gate electrode formed on a surface of the substrate, a gate protection layer and a semiconductor layer stacked on the gate electrode, and an etch stop layer, source terminal metal, and drain terminal metal formed on a surface of the semiconductor layer in such a way that the source terminal metal and the drain terminal metal are respectively located on two opposite sides of the etch stop layer. The thin-film transistor further includes a light shielding layer, an insulation medium layer, and a pixel electrode. The light shielding layer is stacked on the etch stop layer to prevent light from irradiating the semiconductor layer. The insulation medium layer covers the source terminal metal, the drain terminal metal, and the light shielding layer. The pixel electrode is formed on a surface of the insulation medium layer and electrically connected to the drain terminal metal.