Dual-Gate Oxide TFT Channel Layout for Threshold Voltage Stability
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Solution Overview
Problem
Thin film transistors, particularly oxide semiconductor TFTs, face issues with driving stability due to changes in threshold voltage over time, leading to reduced device lifespan and image quality, especially in long-term usage and large-sized display applications.
Innovation Solution
A thin film transistor design incorporating a channel portion with both top and bottom gate structures, featuring excess oxygen and hydrogen areas to stabilize the threshold voltage by electron and hole traps, respectively, and a manufacturing method that includes forming gate electrodes, insulating layers, and active layers with specific hydrogen and oxygen concentrations to minimize voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxide semiconductor TFT is used to reduce manufacturing cost and enable low-temperature processing, then manufacturing cost is reduced and process temperature is lowered, but driving stability deteriorates due to threshold voltage change over time
Solution Approach 1:
The channel region is divided into multiple segments with different oxygen concentrations. The first channel region has a first oxygen concentration while the second channel region has a second oxygen concentration different from the first. This segmentation allows different portions of the channel to provide complementary effects on threshold voltage stability, resolving the contradiction between low-cost oxide semiconductor material and stable driving characteristics.
Solution Approach 2:
Different regions of the channel are given different local properties through controlled oxygen concentration variations. The first channel region and second channel region have distinct oxygen concentrations created through selective gas introduction during deposition, enabling each region to contribute differently to threshold voltage behavior while maintaining overall device functionality.
2Illumination intensity
If oxide semiconductor TFT is driven in ON-state for long time to maintain image quality, then image quality is maintained, but threshold voltage changes over time leading to device degradation
Solution Approach 1:
The structure incorporates regions with different oxygen concentrations that preemptively counteract threshold voltage drift before it occurs during prolonged operation. The complementary effects of the first and second channel regions create a self-balancing mechanism that prevents threshold voltage changes during long-term ON-state operation, enabling sustained image quality without degradation.
3Productivity
If amorphous silicon TFT is used to shorten manufacturing time and reduce cost, then manufacturing process time is shortened and production cost is reduced, but electron mobility is low and threshold voltage stability is poor
Solution Approach 1:
The oxygen concentration parameter is varied across different channel regions to fundamentally change the electrical characteristics of the oxide semiconductor. By controlling oxygen concentration during deposition through selective gas introduction, the invention achieves improved threshold voltage stability while maintaining the manufacturing advantages of amorphous oxide semiconductor TFTs.
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 provides improved driving stability by counterbalancing threshold voltage shifts, ensuring stable operation even under long-term ON-state conditions and reducing manufacturing costs, making it suitable for large-sized and high-resolution displays.
Implementation Method 1
excess oxygen area and an excess hydrogen area, wherein movement of the threshold voltage in a positive direction is induced in the excess oxygen area by electron trap
Implementation Method 2
movement of the threshold voltage in a negative direction is induced in the excess hydrogen area by hole trap
Data Source
AI summary
A thin film transistor can include a first gate electrode, an active layer including a channel portion, and a second gate electrode. The active layer is between the first gate electrode and the second gate electrode, and at least a portion of the first gate electrode does not overlap with the second gate electrode. Further, at least a portion of the second gate electrode does not overlap with the first gate electrode, and the channel portion overlaps with at least one of the first gate electrode and the second gate electrode. In addition, a first portion of the channel portion can overlaps with one of the first gate electrode and the second gate electrode, and a second portion of the channel portion can overlap with a remaining one of the first gate electrode and the second gate electrode that is not overlapped by the first portion of the channel portion.