Coplanar Thin Film Transistor Light Shielding
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Solution Overview
Problem
Oxide semiconductor-based thin film transistors, particularly those with an inverted-staggered structure, face challenges due to high parasitic capacitance and light-induced hysteresis, making them unsuitable for large-scale display devices and affecting their reliability and performance.
Innovation Solution
A thin film transistor with a coplanar structure is developed, utilizing a flexible substrate, an oxide semiconductor active layer, and a buffer layer with a reflective metal layer and insulating layers to shield the active layer from external light, reducing parasitic capacitance and light-induced threshold voltage shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inverted-staggered structure is used, then the transistor can be fabricated, but high parasitic capacitance between gate electrode and active layer occurs, making it unsuitable for large-scale display devices
Solution Approach 1:
A buffer layer is introduced as an intermediary between the substrate and the active layer. This buffer layer serves as a light-shielding barrier that prevents incident light from reaching the active layer, thereby eliminating light-induced hysteresis while maintaining the inverted-staggered structure's fabrication advantages
Solution Approach 2:
The device is segmented into distinct functional layers with the buffer layer positioned between the substrate and active layer. This segmentation allows the buffer layer to specifically address light shielding without interfering with the electrical characteristics of the active layer or gate electrode
2Ease of operation
If oxide semiconductor material is exposed to incident light, then the transistor can operate, but hysteresis (threshold voltage shift) occurs, affecting reliability
Solution Approach 1:
The buffer layer is positioned to preemptively block incident light from reaching the active layer before light exposure can occur. This preliminary protective action prevents the generation of carriers in the active layer that would cause threshold voltage shifts and hysteresis during operation
Solution Approach 2:
The buffer layer, while adding structural complexity, converts the harmful effect of incident light into a beneficial protective function. By absorbing or reflecting light, the buffer layer protects the active layer from degradation and maintains stable threshold voltage characteristics
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 enhances the optical reliability and stability of thin film transistors, improving their performance and operational stability by effectively blocking external light and minimizing threshold voltage fluctuations, making them suitable for large-scale display devices.
Implementation Method 1
a buffer layer with a reflective metal layer and insulating layers to shield the active layer from external light
Data Source
Figure 1a~2a
Figure 2b~3a
Figure 3b~4b
AI summary
A thin film transistor, a method of manufacturing the thin film transistor, and a display device including the thin film transistor are provided. The thin film transistor comprises a gate electrode formed on the oxide semiconductor layer such that a first surface of the oxide semiconductor layer faces the gate electrode. A source electrode and a drain electrode are electrically connected to the oxide semiconductor layer, respectively. The oxide semiconductor layer, gate electrode, source electrode and drain electrode are arranged in a coplanar transistor configuration. A light-blocking element is also arranged to shield a second surface of the oxide semiconductor layer from external light.