Silicon Back-Gate Shielding Oxide TFT Photovoltaic Leakage
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Solution Overview
Problem
Oxide TFTs in display devices experience increased off-leakage current due to photovoltaic effects when irradiated with light, leading to reduced voltage holding and abnormal compensation processes, which degrade display quality.
Innovation Solution
A display device with pixel circuits that utilize a threshold voltage compensation transistor with a back-gate electrode made of silicon connected to the second conductive electrode of a drive transistor, effectively shielding short-wavelength light and preventing off-leakage current, while also eliminating the need for additional manufacturing steps by extending the silicon channel region of the drive transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide TFT is used in pixel circuit, then off-leakage current is reduced, but display quality degrades due to photovoltaic effect under light irradiation
Solution Approach 1:
A back-gate electrode is introduced as an intermediary component between the substrate and the oxide TFT channel. This back-gate electrode applies a negative potential to suppress the photovoltaic effect-induced off-leakage current, thereby maintaining the low off-leakage current advantage of oxide TFTs while counteracting the harmful photovoltaic effect under light irradiation.
Solution Approach 2:
The invention changes the electrical parameter (potential) of the back-gate electrode to dynamically suppress the photovoltaic effect. By applying a negative potential to the back-gate electrode during light irradiation, the threshold voltage of the oxide TFT is shifted, preventing the increase in off-leakage current caused by the photovoltaic effect.
2Object-affected harmful factors
If back-gate electrode is added to suppress photovoltaic effect, then display quality is maintained, but device complexity increases
Solution Approach 1:
The back-gate electrode is designed to serve multiple functions: it acts as a light shielding layer to block photons from reaching the oxide TFT channel, and simultaneously functions as a back-gate to apply electrical potential for suppressing the photovoltaic effect. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The back-gate electrode is constructed using a composite structure combining a light-shielding material layer and a conductive material layer. This composite design enables the single component to provide both optical shielding and electrical potential control, effectively suppressing the photovoltaic effect while minimizing structural complexity.
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 configuration effectively suppresses off-leakage current and maintains display quality by shielding short-wavelength light, preventing degradation caused by light irradiation and reducing manufacturing complexity and yield loss.
Implementation Method 1
when the oxide TFT is irradiated with light, off-leakage current increases due to the photovoltaic effect
Implementation Method 2
silicon connected to the second conductive electrode of the drive transistor is used as the back-gate electrode of the threshold voltage compensation transistor... Since the silicon can effectively shield, particularly short-wavelength light
Data Source
AI summary
In a display device including pixel circuits including oxide TFTs, degradation in display quality caused by light irradiation onto the oxide TFTs is suppressed. A TFT having a channel region formed of silicon is adopted as a drive transistor. A TFT having a gate electrode; a first conductive electrode and a second conductive electrode that function as a drain electrode and a source electrode; a back-gate electrode; and a channel region formed of an oxide semiconductor is adopted as a threshold voltage compensation transistor. A second conductive electrode of the drive transistor is connected to the first conductive electrode of the threshold voltage compensation transistor, and a gate electrode of the drive transistor is connected to the second conductive electrode of the threshold voltage compensation transistor. Silicon connected to the second conductive electrode of the drive transistor is used as the back-gate electrode of the threshold voltage compensation transistor.