Oxide Semiconductor Transistor Threshold Voltage Stability
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Solution Overview
Problem
Conventional oxide semiconductor transistors have low on/off ratios and normally-on characteristics due to negative threshold voltages, which are unsuitable for display device applications.
Innovation Solution
The formation of an oxide insulating film with desorbed oxygen, followed by heat treatment to remove hydrogen and diffuse oxygen into the oxide semiconductor film, reducing oxygen vacancies and hydrogen concentration, thereby improving electric characteristics and threshold voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is conducted to remove hydrogen from the oxide semiconductor film, then the threshold voltage becomes more stable and positive, but the oxygen in the oxide insulating film may be desorbed causing oxygen vacancies
Solution Approach 1:
The oxide insulating film is pre-formed with excess oxygen content before the heat treatment step. This preliminary preparation ensures that when hydrogen is removed from the oxide semiconductor film during subsequent heat treatment, the oxygen needed to fill any potential vacancies is already available in the oxide insulating film, preventing oxygen deficiency without requiring additional oxygen introduction steps
Solution Approach 2:
The heat treatment parameters are optimized to conduct the process at temperatures and durations that preferentially remove hydrogen from the oxide semiconductor film while maintaining conditions that prevent excessive oxygen desorption from the oxide insulating film. This selective parameter control allows hydrogen removal without creating oxygen vacancies
2Ease of manufacture
If conventional oxide semiconductor transistors are used, then the manufacturing process is simple, but the on/off ratio is low and threshold voltage is negative
Solution Approach 1:
The oxide insulating film is pre-formed with excess oxygen content before the heat treatment step. This preliminary preparation ensures that when hydrogen is removed from the oxide semiconductor film during subsequent heat treatment, the oxygen needed to fill any potential vacancies is already available in the oxide insulating film, preventing oxygen vacancies without requiring additional oxygen introduction steps
Solution Approach 2:
The heat treatment parameters are optimized to conduct the process at temperatures and durations that preferentially remove hydrogen from the oxide semiconductor film while maintaining conditions that prevent excessive oxygen desorption from the oxide insulating film. This selective parameter control allows hydrogen removal without creating oxygen vacancies
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 approach enhances the electric performance of transistors by reducing defects and carrier sources, shifting the threshold voltage to a positive range, making them suitable for use as normally-off transistors in display devices.
Implementation Method 1
heat treatment is then conducted at a temperature at which hydrogen contained in the oxide semiconductor film is desorbed and part of oxygen contained in the oxide insulating film is desorbed
Implementation Method 2
heat treatment is then conducted at a temperature at which hydrogen contained in the oxide semiconductor film is desorbed
Data Source
AI summary
A transistor with superior electric characteristics is manufactured. An oxide insulating film is formed over a substrate, an oxide semiconductor film is formed over the oxide insulating film, heat treatment is then conducted at a temperature at which hydrogen contained in the oxide semiconductor film is desorbed and part of oxygen contained in the oxide insulating film is desorbed, then the heated oxide semiconductor film is etched into a predetermined shape to form an island-shaped oxide semiconductor film, a pair of electrodes is formed over the island-shaped oxide semiconductor film, a gate insulating film is formed over the pair of electrodes and the island-shaped oxide semiconductor film, and a gate electrode is formed over the gate insulating film.