Oxide Semiconductor Thin Film Transistor Threshold Voltage Stability
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Solution Overview
Problem
Thin film transistors with high threshold voltage values face challenges in controlling circuits, especially at low voltages, leading to instability and malfunction due to high or negative threshold voltages, which affects the performance of semiconductor devices across various temperature ranges.
Innovation Solution
A method for manufacturing a semiconductor device involving the formation of a gate electrode layer, gate insulating layer, oxide semiconductor layer, source and drain electrode layers, and an insulating layer, with specific heat treatment steps in nitrogen or rare gas atmospheres to achieve stable electric characteristics, including a threshold voltage that remains relatively constant across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is performed at high temperature to improve semiconductor characteristics, then field effect mobility increases, but threshold voltage becomes high or negative causing circuit control difficulties
Solution Approach 1:
The heat treatment process is divided into multiple sequential steps with different temperature ranges and atmospheric conditions. First heat treatment (350-750°C in nitrogen or rare gas) removes hydrogen and improves mobility, while second heat treatment (100-750°C in oxygen-containing atmosphere) adjusts threshold voltage. This segmentation allows independent optimization of mobility and threshold voltage without compromise.
Solution Approach 2:
The invention changes multiple parameters systematically: temperature (350-750°C range), atmosphere (nitrogen/rare gas then oxygen-containing), and timing (first before source/drain formation, second after insulating layer formation). These parameter changes enable precise control over both field effect mobility and threshold voltage to achieve stable electric characteristics across temperature ranges.
2Reliability
If threshold voltage is increased to prevent leakage current, then device stability improves, but switching function is lost at low voltage
Solution Approach 1:
The threshold voltage is made dynamically adjustable through the two-stage heat treatment process. The first heat treatment establishes a base threshold voltage, while the second heat treatment fine-tunes it after source/drain and insulating layers are formed. This dynamic adjustment capability allows the device to maintain appropriate threshold voltage for both stability and low-voltage switching across different operating conditions.
3Reliability
If multiple heat treatment steps are added to control threshold voltage, then electric characteristic stability improves, but manufacturing complexity increases
Solution Approach 1:
The first heat treatment step serves multiple functions: removing hydrogen from the oxide semiconductor layer, improving field effect mobility, and providing a foundation for subsequent threshold voltage adjustment. The second heat treatment step similarly serves dual purposes of adjusting threshold voltage and stabilizing electric characteristics. This multi-functionality reduces the need for additional dedicated process steps.
Solution Approach 2:
The first heat treatment is performed preliminarily before source/drain electrode and insulating layer formation to remove hydrogen and establish good semiconductor characteristics. This preliminary action prevents hydrogen-related issues in subsequent processing and creates a stable base for the final device characteristics, reducing the need for corrective steps later.
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 method results in a thin film transistor with stable electric characteristics and reliable performance, ensuring the semiconductor device operates effectively even at varying temperatures without significant changes in threshold voltage, enhancing the overall stability and functionality of the device.
Implementation Method 1
performing first heat treatment after forming the oxide semiconductor layer
Implementation Method 2
hydrogen is removed from the oxide semiconductor layer
Implementation Method 3
performing second heat treatment after forming the insulating layer
Implementation Method 4
heat treatment in an oxygen-containing atmosphere
Data Source
Figure 1A~1E
Figure 2A~2C
Figure 3A~3B
AI summary
It is an object to provide a highly reliable thin film transistor with stable electric characteristics, which includes an oxide semiconductor film. The channel length of the thin film transistor including the oxide semiconductor film is in the range of 1.5 µm to 100 µm inclusive, preferably 3 µm to 10 µm inclusive; when the amount of change in threshold voltage is less than or equal to 3 V, preferably less than or equal to 1.5 V in an operation temperature range of room temperature to 180 ? inclusive or -25 ? to -150 ? inclusive, a semiconductor device with stable electric characteristics can be manufactured. In particular, in a display device which is an embodiment of the semiconductor device, display unevenness due to variation in threshold voltage can be reduced.