Amorphous Silicon Photosensor Forward Bias Sensitivity
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Solution Overview
Problem
The high cost and reduced sensitivity of photosensor devices using amorphous silicon or microcrystal silicon, particularly for large-area applications such as biometric authentication, due to the inferior performance of these materials compared to single-crystal silicon, necessitate a solution to enhance sensitivity while maintaining low production costs.
Innovation Solution
A photosensor device with a photodiode array using amorphous silicon or microcrystal silicon photodiodes, driven by a scanning circuit and signal processing circuit that applies forward bias voltage and adjusts voltage levels to optimize sensitivity, allowing for low-voltage operation and improved performance on glass or single-crystal silicon substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-crystal silicon is used for photo area sensors, then sensitivity and resolution are improved, but manufacturing cost increases and large-area production becomes difficult
Solution Approach 1:
The patent replaces expensive single-crystal silicon with amorphous silicon or microcrystal silicon deposited on glass substrates. These cheaper materials can be manufactured at lower cost while still achieving functional photo sensor arrays, directly addressing the cost barrier for large-area sensors
Solution Approach 2:
The patent changes the material parameter from single-crystal silicon to amorphous/microcrystal silicon and modifies the operational parameters by applying forward bias voltage and utilizing channel resistance changes. This enables cost-effective large-area sensors while maintaining sensitivity through alternative physical mechanisms
2Ease of manufacture
If amorphous silicon or microcrystal silicon is used on glass substrates, then manufacturing cost decreases, but sensitivity deteriorates due to poor transistor performance
Solution Approach 1:
The patent extracts the amplifier from each pixel location, removing the component that causes sensitivity deterioration. Instead of using transistors for signal amplification at each pixel, the invention reads signals directly from the photodiode voltage fluctuations, eliminating the transistor performance limitation
Solution Approach 2:
The patent substitutes the transistor-based amplification mechanism with a direct voltage fluctuation reading mechanism. By measuring the voltage changes across the photodiode under forward bias, the system replaces the mechanical/electrical amplification process with a direct electrical measurement approach
3Measurement precision
If amplifiers are formed in each pixel to improve sensitivity, then signal detection capability increases, but transistor variations cause fixed noise and performance deterioration
Solution Approach 1:
The patent removes the amplifier component from each pixel, eliminating the source of transistor variation-induced fixed noise. The signal detection is achieved directly through voltage fluctuation measurement without active amplification at the pixel level
Solution Approach 2:
The patent uses the inherent voltage fluctuation signal from the photodiode as a direct copy of the light signal, avoiding the need for amplification. This direct signal copying approach preserves signal integrity without introducing transistor-related noise
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 enables a low-cost, high-sensitivity photosensor device that can be driven with low voltage, suitable for large-area applications, offering improved performance and dynamic range compared to existing CCD and CMOS sensors.
Implementation Method 1
a photodiode array in which a plurality of photodiodes are arranged in an array shape... each of the photodiodes is made of amorphous silicon or microcrystal silicon
Implementation Method 2
It has been found, by the study of the characteristics of photodiodes produced using amorphous silicon or microcrystal silicon, that each channel resistance of the photodiodes is changed by incident light.
Data Source
AI summary
The present invention provides a photosensor device including: a photodiode array in which photodiodes are arranged in an array shape; scanning lines which are coupled to first electrodes of the photodiodes in respective lines of the photodiode array; read lines which are coupled to second electrodes of the photodiodes in respective columns of the photodiode array; a scanning circuit which is coupled to the scanning lines and sequentially supplies a selected scanning signal to the respective scanning lines in each horizontal scanning period; and a signal processing circuit which is coupled to the read lines and loads each voltage fluctuation of the read lines in one horizontal scanning period as signal voltage when reading a signal, wherein each of the photodiodes is made of amorphous silicon or microcrystal silicon, and forward bias voltage is applied to each of the photodiodes when reading a signal.