Oxide Semiconductor Thin Film Transistor Threshold Voltage Control
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Solution Overview
Problem
Thin film transistors with oxide semiconductor films face challenges in achieving a positive threshold voltage close to 0 V, especially with short channel lengths, leading to performance issues such as unsuitable switching functions and display unevenness due to variations in threshold voltage.
Innovation Solution
A manufacturing method involving a protective insulating layer covering the oxide semiconductor layer, with repeated temperature increases and decreases during the second heat treatment at a lower temperature than the first heat treatment, helps stabilize the oxide semiconductor layer, ensuring a positive threshold voltage and reduced variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the channel length of a thin film transistor is shortened for higher speed operation and lower power consumption, then the operating speed and power consumption are improved, but the threshold voltage shifts to the minus side due to the short channel effect
Solution Approach 1:
The patent applies parameter changes by performing multiple heat treatments at different temperature conditions (first heat treatment at a first temperature, second heat treatment at a second temperature lower than the first temperature) to modify the electrical characteristics of the oxide semiconductor layer. This enables independent control of threshold voltage without changing the channel length, thereby resolving the contradiction between short channel length and threshold voltage stability.
2Reliability
If the threshold voltage value is high or on the minus side, then the field effect mobility can be high, but the thin film transistor cannot perform the switching function properly and becomes a load when driven at low voltage
Solution Approach 1:
The patent uses parameter changes through controlled heat treatments to adjust the threshold voltage to a positive value close to 0 V while maintaining high field effect mobility. The first heat treatment at a higher temperature and second heat treatment at a lower temperature work together to optimize both switching characteristics and low-voltage operation capability.
3Reliability
If the threshold voltage value is on the minus side, then the channel can be formed and drain current can flow, but current flows between source and drain electrodes even when gate voltage is 0 V, making the transistor normally on
Solution Approach 1:
The patent applies parameter changes by performing heat treatments at different temperatures to shift the threshold voltage from negative to positive values. This eliminates the normally-on state and leakage current while preserving channel formation capability, as the positive threshold voltage close to 0 V ensures proper switching behavior.
4Ease of manufacture
If there is a large variation in threshold voltage between elements, then the manufacturing process may be simplified, but display unevenness occurs due to threshold voltage variation
Solution Approach 1:
The patent uses parameter changes through multiple heat treatments at different temperatures to reduce threshold voltage variation between elements. The first heat treatment at a higher temperature followed by second heat treatment at a lower temperature provides uniform electrical characteristics across all thin film transistors on the substrate, eliminating display unevenness.
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 method enables the production of thin film transistors with a threshold voltage close to 0 V, independent of channel length, improving switching characteristics and reducing display unevenness, while maintaining high field effect mobility and reliability.
Implementation Method 1
an oxide semiconductor layer which has been dehydrated or dehydrogenated by first heat treatment
Implementation Method 2
an oxide semiconductor layer which has been dehydrated or dehydrogenated by first heat treatment
Implementation Method 3
second heat treatment at a temperature that is lower than that of the first heat treatment, in which the increase and decrease in temperature are repeated plural times, is performed
Data Source
AI summary
It is an object to provide a manufacturing method of a structure of a thin film transistor including an oxide semiconductor film, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible. A protective insulating layer is formed to cover a thin film transistor including an oxide semiconductor layer that is dehydrated or dehydrogenated by first heat treatment, and second heat treatment at a temperature that is lower than that of the first heat treatment, in which the increase and decrease in temperature are repeated plural times, is performed, whereby a thin film transistor including an oxide semiconductor layer, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible without depending on the channel length, can be manufactured.