Silicon Gate Electrode for Stable TFT Crystallization
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Solution Overview
Problem
During the crystallization of the active layer in thin film transistors (TFTs) used in flat panel display devices, heat flow to the gate electrode can prevent stable crystallization due to the high heat conductivity of metal gate electrodes, leading to poor quality products.
Innovation Solution
A TFT structure is developed with a gate electrode formed of silicon doped with impurities, which has lower heat conductivity, and a double-layered gate wiring with a metal layer on top, preventing heat flow from the active layer during crystallization, and including an etching stop layer and passivation layers for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal gate electrode is used, then high electrical conductivity is achieved, but heat flows to the gate electrode during active layer crystallization, preventing stable crystallization
Solution Approach 1:
A silicon layer is introduced as an intermediary between the metal gate electrode and the active layer. This silicon layer has lower thermal conductivity than metal, thereby blocking heat flow from the active layer to the gate electrode during crystallization, while still allowing electrical field penetration for gate control functionality.
Solution Approach 2:
The gate electrode structure is made composite by combining metal (for electrical conductivity) with silicon (for thermal insulation). The metal gate electrode is covered with a silicon layer, creating a composite structure that simultaneously achieves electrical conductivity and thermal insulation properties.
2Reliability
If the gate electrode is formed with metal, then electrical conductivity is improved, but heat conductivity causes heat to flow during crystallization
Solution Approach 1:
The silicon layer serves as a thermal barrier intermediary that prevents heat from reaching the metal gate electrode during the crystallization process, while maintaining the electrical conductivity function of the metal gate through field penetration.
Solution Approach 2:
Different parts of the gate structure have different properties: the metal layer provides local electrical conductivity, while the silicon layer provides local thermal insulation. This local differentiation of material properties resolves the contradiction between electrical and thermal requirements.
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
This solution ensures stable crystallization of the active layer, reducing the risk of poor quality products and maintaining high electron mobility in the gate wiring, thereby improving the overall performance of the TFT and flat panel display devices.
Implementation Method 1
a gate wiring connected to the gate electrode... The gate wiring may include a silicon layer doped with the same impurities as the silicon forming the gate electrode and on the same layer as the gate electrode
Implementation Method 2
The active layer may be formed of amorphous silicon crystallized by heating
Data Source
AI summary
A thin film transistor (TFT) and a flat panel display device including the same. The TFT includes a substrate, a gate electrode formed over the substrate, the gate electrode formed with silicon doped with impurities, a gate wiring connected to the gate electrode, an active layer formed over the gate electrode, and source and drain electrodes connected to the active layer. According to such a structure, since heat flow to the gate electrode during crystallization of the active layer may be prevented, stable crystallization of the active layer may be performed, and thus an error rate of a product may be decreased.