Inverted Staggered TFT Structure for Oxidation-Resistant LCDs
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Solution Overview
Problem
Thin film transistors using polycrystalline semiconductor films for channel formation in liquid crystal display devices are complex, leading to decreased yield and increased costs, and microcrystalline semiconductor films are prone to oxidation, affecting electric characteristics.
Innovation Solution
A liquid crystal display device with an inverted staggered thin film transistor structure, where a microcrystalline semiconductor film serves as the channel formation region, and a buffer layer made of amorphous semiconductor film with nitrogen, hydrogen, or halogen is used to prevent oxidation and improve field-effect mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polycrystalline semiconductor film is used for channel formation, then field-effect mobility is improved (two or more orders of magnitude greater than amorphous), but process complexity increases and yield decreases
Solution Approach 1:
The patent changes the crystalline state parameter of the semiconductor film from amorphous to microcrystalline, achieving high field-effect mobility without requiring the complex crystallization processes needed for polycrystalline films. The microcrystalline structure provides sufficient mobility while simplifying manufacturing.
Solution Approach 2:
The patent applies local quality by creating a buffer layer with specific composition (amorphous semiconductor with nitrogen, hydrogen, or halogen) at the interface between the gate insulating film and microcrystalline semiconductor film. This localized treatment improves carrier transfer at the critical interface without affecting the entire film structure.
2Productivity
If a microcrystalline semiconductor film is used for channel formation, then mass productivity is improved, but oxidation of crystal grains occurs causing electric characteristics to deteriorate
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the gate insulating film and the microcrystalline semiconductor film. This buffer layer, composed of amorphous semiconductor containing nitrogen, hydrogen, or halogen, acts as a protective barrier that prevents oxidation of the crystal grains while maintaining good electric characteristics and mass productivity.
Solution Approach 2:
The buffer layer creates a chemically inert environment at the interface between the gate insulating film and microcrystalline semiconductor film. By incorporating nitrogen, hydrogen, or halogen atoms in the buffer layer, the patent effectively shields the crystal grains from oxidation without requiring external inert atmosphere processing.
3Ease of operation
If source and drain electrodes are aligned with end portions of source and drain regions, then connection is improved, but leakage current and short circuit occur
Solution Approach 1:
The patent applies asymmetry by intentionally misaligning the source and drain electrodes with respect to the source and drain regions. The electrodes are positioned to overlap with the central portions of the regions but are deliberately offset from the end portions, creating an asymmetric configuration that prevents leakage current while maintaining adequate electrical connection through the overlapping regions.
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 results in highly reliable thin film transistors with improved electric characteristics and increased mass productivity, reducing leakage current and oxidation of crystal grains, thus enhancing the overall performance and efficiency of the liquid crystal display devices.
Implementation Method 1
surfaces of crystal grains of a microcrystalline semiconductor film are easily oxidized. Therefore, when crystal grains in a channel formation region are oxidized, oxide films are formed on the surfaces of the crystal grains and the oxide films become obstacles to carrier transfer
Implementation Method 2
a buffer layer made of amorphous semiconductor film with nitrogen, hydrogen, or halogen is used to prevent oxidation and improve field-effect mobility
Data Source
AI summary
A method of manufacturing, with high mass productivity, liquid crystal display devices having highly reliable thin film transistors with excellent electric characteristics is provided. In a liquid crystal display device having an inverted staggered thin film transistor, the inverted staggered thin film transistor is formed as follows: a gate insulating film is formed over a gate electrode; a microcrystalline semiconductor film which functions as a channel formation region is formed over the gate insulating film; a buffer layer is formed over the microcrystalline semiconductor film; a pair of source and drain regions are formed over the buffer layer; and a pair of source and drain electrodes are formed in contact with the source and drain regions so as to expose a part of the source and drain regions.