Oxide Semiconductor Thin Film Transistor Crystallization Control
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Solution Overview
Problem
Existing thin film transistors using indium oxide crystals as channel layers often exhibit normally-on properties, increased carrier concentration, and decreased mobility due to crystallization steps, limiting their performance in display applications.
Innovation Solution
A stacked layer structure comprising an oxide layer with controlled crystal orientation and diameter, formed by creating a homogeneous amorphous oxide thin film and annealing it to achieve a crystalline state with specific dopant ratios and sputtering conditions, resulting in improved field-effect mobility and S-factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If indium oxide is crystallized through heat treatment to form a thin film transistor, then the crystal structure is improved, but carrier concentration increases and mobility decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the annealing temperature (150-500°C), atmosphere composition (rare gas with water/nitrous oxide), and pressure conditions during heat treatment. These parameter optimizations enable crystallization while suppressing excessive carrier generation, resolving the contradiction between crystal structure improvement and mobility maintenance.
Solution Approach 2:
The patent uses an inert atmosphere containing rare gas atoms combined with controlled amounts of water or nitrous oxide molecules during annealing. This specialized atmosphere prevents unwanted chemical reactions and controls oxygen content, allowing crystal formation without excessive carrier concentration increase, thus maintaining mobility while improving crystal structure.
2Length of stationary object
If the oxide thin film is annealed at high temperature to achieve crystallization, then the crystal diameter increases, but the transistor exhibits normally-on properties
Solution Approach 1:
The patent optimizes annealing parameters including temperature (150-500°C), time, and atmosphere composition to achieve moderate crystal growth with diameter of 1 μm or more while suppressing carrier concentration. This controlled parameter regime enables large crystal formation without normally-on properties, resolving the contradiction between crystal size and switching characteristics.
Solution Approach 2:
The patent introduces local quality variations by controlling the distribution of water or nitrous oxide molecules in the annealing atmosphere, creating localized conditions that promote crystal growth in specific regions while maintaining low carrier concentration overall. This enables selective crystal diameter increase without compromising transistor switching properties.
3Stability of the object's composition
If the amorphous oxide film is formed with high homogeneity, then the crystal orientation after annealing is controlled, but the manufacturing process complexity increases
Solution Approach 1:
The patent simplifies the manufacturing process by optimizing deposition parameters (sputtering power, gas flow ratios, substrate temperature) to directly achieve homogeneous amorphous films with controlled nucleation sites. This reduces the need for complex post-processing while ensuring controlled crystal orientation after annealing, resolving the contradiction between composition stability and process complexity.
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 approach enables the formation of high-quality thin film transistors with enhanced field-effect mobility and S-factor, reducing carrier concentration and oxygen defects, thereby improving transistor performance and reproducibility.
Implementation Method 1
annealing the amorphous thin film has a uniform crystal orientation and crystal diameter
Implementation Method 2
a crystalline semiconductor thin film obtained by forming a homogeneous amorphous oxide thin film, and annealing the amorphous thin film
Implementation Method 3
forming on the insulating layer an oxide thin film
Data Source
AI summary
A stacked layer structure including an oxide layer and an insulating layer, the oxide layer having a carrier concentration of 1018/cm3 or less and an average crystal diameter of 1 μm or more; and the crystals of the oxide layer being arranged in a columnar shape on the surface of the insulating layer.