Thin-Film Transistor Gate Structure with Segmented Materials
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Solution Overview
Problem
In thin-film transistor array devices for electroluminescence display panels, high heat-resistance metals used for gate electrodes result in high line resistance, leading to signal delays and display unevenness, and the reduction of gate insulating film thickness increases parasitic capacitance, while metal oxidation deteriorates transistor performance.
Innovation Solution
A thin-film transistor array device is designed with a gate electrode and gate line formed using different materials, where the gate electrode has high heat-resistance and the gate line has low resistance, and a conductive oxide film is used to prevent oxidation and reduce parasitic capacitance by forming a relay electrode between the gate line and the electroluminescence layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high heat-resistance metals are used for gate electrodes, then heat-resistance is improved, but line resistance increases causing signal delays and display unevenness
Solution Approach 1:
The gate electrode structure is divided into two separate components: a gate electrode made of high heat-resistance metal (Mo, W, Ta, Ti, or Ni) and a gate line made of low resistance metal (Al, Cu, or Ag). This segmentation allows each component to be optimized for its specific function - the gate electrode for heat-resistance during laser crystallization and the gate line for low resistance signal transmission.
Solution Approach 2:
Different regions of the gate structure are assigned different material properties. The gate electrode region uses high heat-resistance material to withstand laser crystallization temperatures, while the gate line region uses low resistance material for optimal signal transmission. This local differentiation of material quality resolves the contradiction between heat-resistance and conductivity requirements.
2Reliability
If gate insulating film thickness is reduced, then transistor performance is improved, but parasitic capacitance increases
Solution Approach 1:
A conductive oxide film (such as ITO, IZO, or ZnO) is introduced as an intermediary layer between the gate line and the electroluminescence layer. This intermediary conductive oxide film serves as a relay electrode that reduces parasitic capacitance between the gate line and the EL layer, while allowing the gate insulating film to be sufficiently thin for optimal transistor performance.
3Ease of manufacture
If metal electrodes are exposed to air, then manufacturing is simplified, but metal oxidation occurs deteriorating transistor performance
Solution Approach 1:
The conductive oxide film acts as a protective intermediary layer that covers the metal gate line and prevents direct contact between the metal and oxidizing environments. This intermediary layer protects the metal from oxidation while maintaining electrical conductivity, thus preserving transistor performance without complicating the manufacturing process.
Solution Approach 2:
The conductive oxide film creates an inert protective environment around the metal gate line, preventing oxidation by isolating the reactive metal surface from oxygen and moisture in the air. This protective barrier maintains the electrical properties of the metal electrode throughout the device's operational life.
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 configuration achieves low resistance for the gate line while maintaining heat-resistance of the gate electrode, reduces parasitic capacitance, and prevents metal oxidation, thereby improving signal transmission and extending the lifespan of the thin-film transistor array device.
Implementation Method 1
a conductive oxide film is used to prevent oxidation
Implementation Method 2
reduces parasitic capacitance by forming a relay electrode between the gate line and the electroluminescence layer
Data Source
AI summary
A thin-film transistor array includes first and second bottom-gate transistors, a passivation film, a conductive oxide film below the passivation film, and a relay electrode between a first conductive material in a same layer as a first electrode of the first transistor and a second conductive material in an electroluminescence layer. A first line is in a layer lower than the passivation film and a second line is above the passivation film. A terminal to which an external signal is input is provided in a periphery of the substrate in the same layer as the first electrode. The conductive oxide film covers an upper surface of the terminal and is between the relay electrode and the first conductive material. The relay electrode is formed in a same layer and comprises a same material as the second line.