Image Sensor Pixel Biasing for Higher Sensitivity and Lower Dark Current
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Solution Overview
Problem
The non-synchronous solid-state image pickup element faces challenges with signal quality due to reduced photodiode sensitivity and increased dark current caused by voltage fluctuations, which cannot be effectively addressed by increasing photodiode area or power supply voltage without compromising pixel density or power consumption.
Innovation Solution
The solid-state image pickup element is configured with a photodiode, an amplification transistor, and a potential supply section that supplies a negative potential to the photodiode anode and the amplification transistor back-gate, increasing the reverse bias of the photodiode and the threshold voltage of the amplification transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of the photodiode is increased to enhance sensitivity and reduce dark current, then the signal quality is improved, but the number of pixels per unit area decreases
Solution Approach 1:
The patent applies parameter changes by adjusting the reverse bias voltage of the photodiode through the potential supply section. By supplying a negative potential to the anode of the photodiode and back-gate of the amplification transistor, the reverse bias is increased, which enhances sensitivity and reduces dark current without requiring an increase in photodiode area, thus maintaining pixel density while improving signal quality.
2Measurement precision
If the power supply voltage is increased to enhance sensitivity and reduce dark current, then the signal quality is improved, but the power consumption increases
Solution Approach 1:
The patent changes the parameter of reverse bias voltage by supplying a negative potential through the potential supply section. This approach enhances sensitivity and reduces dark current by increasing the reverse bias of the photodiode, while avoiding the need to increase the overall power supply voltage, thus controlling power consumption while improving signal quality.
3Measurement precision
If the reverse bias of the photodiode is increased to enhance sensitivity and reduce dark current, then the signal quality is improved, but voltage fluctuations cause sensitivity reduction and dark current increase
Solution Approach 1:
The patent implements a feedback mechanism through the potential supply section that supplies a negative potential to the anode of the photodiode and back-gate of the amplification transistor. This feedback approach compensates for voltage fluctuations by maintaining a stable reverse bias condition, ensuring consistent sensitivity and dark current characteristics despite power supply variations.
Solution Approach 2:
The patent applies beforehand cushioning by pre-establishing a stable reverse bias condition through the potential supply section before voltage fluctuations occur. The negative potential supply creates a buffer that protects the photodiode from the adverse effects of voltage fluctuations, maintaining stable sensitivity and dark current 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
This configuration enhances the sensitivity of the photodiode, reduces dark current, and improves the signal quality of the detection signal, while maintaining pixel density and controlling power consumption.
Implementation Method 1
a photodiode configured to convert incident light into a photocurrent
Data Source
AI summary
There is provided a solid-state image pickup element including: a photodiode configured to convert incident light into a photocurrent; an amplification transistor configured to amplify a voltage between a gate having a potential depending on the photocurrent and a source having a predetermined reference potential and output the amplified voltage from a drain; and a potential supply section configured to supply an anode of the photodiode and a back-gate of the amplification transistor with a predetermined potential lower than the reference potential.