Hybrid TFT Sensor Pixel Circuit for Leakage Current Stability
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Solution Overview
Problem
Conventional sensors with oxide TFTs experience increased leakage current and threshold voltage shift after stress application, which existing technologies fail to effectively suppress, leading to reduced signal-to-noise ratio and image quality issues.
Innovation Solution
The integration of a poly-Si TFT in series with an oxide TFT in the sensor's pixel array, where the poly-Si TFT suppresses the leakage current and maintains low noise levels even after stress is applied, improving the signal-to-noise ratio by reducing leakage current and maintaining high pixel-to-pixel uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an Oxide TFT is used in the sensor, then low leakage current is achieved initially, but leakage current increases and threshold voltage shifts negatively after stress is applied
Solution Approach 1:
The patent employs a hybrid TFT structure combining poly-Si TFT and Oxide TFT materials. The poly-Si TFT provides stable threshold voltage characteristics after stress, while the Oxide TFT contributes low initial leakage current. This composite approach leverages the complementary strengths of both materials to resolve the contradiction between initial low leakage and long-term stability.
Solution Approach 2:
The sensor pixel array is segmented into multiple TFT components working in series. Specifically, the circuit includes both a poly-Si TFT and an Oxide TFT connected in series, allowing each transistor type to perform its specialized function. This segmentation enables independent optimization of each component's characteristics to address the overall system contradiction.
2Ease of manufacture
If conventional Oxide TFT technology is used, then manufacturing simplicity is maintained, but signal-to-noise ratio deteriorates due to increased leakage current after stress
Solution Approach 1:
The hybrid poly-Si/Oxide TFT structure improves signal-to-noise ratio by combining the low initial leakage of Oxide TFT with the stress-resistant characteristics of poly-Si TFT. This composite material approach maintains manufacturing feasibility while achieving superior electrical performance and lower noise levels after stress conditions.
3Duration of action of stationary object
If stress is applied to Oxide TFT, then device operation continues, but leakage current increases and uniformity across pixels deteriorates
Solution Approach 1:
The pixel circuit is segmented to include both poly-Si TFT and Oxide TFT components connected in series. This segmentation allows the poly-Si TFT to provide stable threshold voltage characteristics that maintain pixel uniformity after stress, while the Oxide TFT continues to operate with low leakage current, preserving overall device functionality and uniformity.
Data Source
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Figure 3A~3B
AI summary
A leakage current characteristic of a sensor that includes an Oxide TFT can be improved by a sensor including a plurality of electric lines including row lines and column lines, a photodiode in a pixel, a drain of a first transistor connected to the photodiode in the pixel, a drain of a second transistor connected in series with a source of the first transistor in the pixel, a source of the second transistor being connected to a column line among the plurality of electric lines, and both a gate of the first transistor and a gate of the second transistor being connected to a row line among the plurality of electric lines, wherein a channel material of the first transistor is different from a channel material of the second transistor.