Oxide Semiconductor Transistor Light Deterioration Control
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Solution Overview
Problem
Oxide semiconductor transistors used in display devices suffer from light deterioration, leading to unstable electrical characteristics and potential leakage currents due to photoexcitation, especially when irradiated by backlights in liquid crystal display devices.
Innovation Solution
A transistor design incorporating an oxide semiconductor layer with a gate insulating layer and electrode structures that exhibit two distinct relaxation times for carrier photoresponse, where the longer relaxation time (τ2) is 300 seconds or less, effectively suppressing light-induced deterioration by utilizing 'safe' traps that trap holes without trapping electrons, thereby stabilizing electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an oxide semiconductor layer is used as the active layer in a transistor, then the transistor can transmit visible light and has a wide band gap, but the electrical characteristics become unstable when irradiated with visible light or ultraviolet light due to light deterioration
Solution Approach 1:
The patent applies parameter changes by carefully controlling the carrier concentration of the oxide semiconductor to be lower than 10^18/cm³ and adjusting the band gap to approximately 3 eV. These parameter optimizations enable the material to maintain both light transmission capability and reduced photoexcitation effects, resolving the contradiction between light transmission and electrical stability.
2Use of energy by moving object
If a transistor including an oxide semiconductor is irradiated with light from a backlight in a liquid crystal display device, then the display can be illuminated, but leakage current is generated due to photoexcitation even in the off state
Solution Approach 1:
The patent converts the harmful photoexcitation effect into a beneficial outcome by designing the oxide semiconductor with specific properties (carrier concentration < 10^18/cm³ and band gap ≈ 3 eV). These design choices ensure that while light transmission is maintained for display illumination, the photoexcitation-induced leakage current is minimized, effectively turning potential harm into benefit.
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 transistor maintains stable electrical characteristics and reduces light-induced deterioration, enhancing the reliability of semiconductor devices by controlling carrier relaxation times and photoresponse behavior.
Implementation Method 1
When a semiconductor is irradiated with light having an energy of greater than or equal to the band gap and absorbs the light, electrons in the valence band are transferred to the conduction band and holes are generated.
Implementation Method 2
a relaxation time of carriers in photoresponse characteristics of the oxide semiconductor layer has at least two kinds of modes: τ1 and τ2, τ12 is satisfied, and τ2 is 300 seconds or less
Data Source
AI summary
Manufactured is a transistor including an oxide semiconductor layer, a source electrode layer and a drain electrode layer overlapping with part of the oxide semiconductor layer, a gate insulating layer overlapping with the oxide semiconductor layer, the source electrode layer, and the drain electrode layer, and a gate electrode overlapping with part of the oxide semiconductor layer with the gate insulating layer provided therebetween, wherein, after the oxide semiconductor layer which is to be a channel formation region is irradiated with light and the light irradiation is stopped, a relaxation time of carriers in photoresponse characteristics of the oxide semiconductor layer has at least two kinds of modes: τ1 and τ2, τ1<τ2 is satisfied, and τ2 is 300 seconds or less. In addition, a semiconductor device including the transistor is manufactured.