Infrared Image Sensor Type II Multi Quantum Well Noise Rejection
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Solution Overview
Problem
Infrared image sensors face a challenge in improving the signal-to-noise ratio due to the presence of noise light with wavelengths shorter than 1.7 μm, which interferes with the signal light in the 1.7 to 2.5 μm range, causing deterioration in the output signal quality.
Innovation Solution
An infrared image sensor is designed with a bias circuit generating specific bias voltages, a semiconductor light-receiving device featuring a type II multi quantum well structure with alternating compound semiconductor layers, and a signal processing circuit that distinguishes between photocurrent components using these bias voltages to isolate the signal from noise, utilizing a III-V group compound semiconductor optical absorption layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photodiode with InGaAs/GaAsSb type II multi quantum well structure is used to detect infrared light, then sensitivity to infrared light (1.7 to 2.5 μm) is improved, but sensitivity to noise light (wavelength shorter than 1.7 μm, e.g., 1.5 μm) also increases, deteriorating the signal-to-noise ratio
Solution Approach 1:
The patent applies dynamics by making the bias voltage variable rather than fixed. The bias voltage is dynamically adjusted between a first value (second wavelength region) and a second value (first wavelength region) based on timing signals. This dynamic biasing enables selective enhancement of signal photocurrent while suppressing noise photocurrent, resolving the contradiction between sensitivity to infrared light and sensitivity to noise light
Solution Approach 2:
The patent changes the electrical parameter (bias voltage) to control the optical response characteristics of the photodiode. By varying the bias voltage between two distinct values, the patent modulates the photocurrent response to different wavelength regions. This parameter change enables selective detection of signal light while rejecting noise light, improving the signal-to-noise ratio
2Quantity of substance
If the photodiode receives incident light with wide spectrum, then both signal light (1.7 to 2.5 μm) and noise light (1.5 μm) are detected, but the output signal quality deteriorates due to mixed photocurrent components
Solution Approach 1:
The patent uses dynamic bias voltage adjustment to selectively modulate different photocurrent components. By switching between first and second bias voltage values synchronized with timing signals, the system dynamically separates signal photocurrent from noise photocurrent, enabling extraction of pure signal components despite wide spectrum illumination
Solution Approach 2:
The patent employs periodic switching of the bias voltage between first and second values in response to timing signals. This periodic action creates time-separated measurement cycles where signal photocurrent and noise photocurrent can be differentially extracted through synchronous processing, improving output signal quality
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 effectively enhances the signal-to-noise ratio by modulating the photocurrent based on bias voltage, allowing for the extraction of the desired photocurrent components from the 1.7 to 2.5 μm range, thereby improving the output signal quality.
Implementation Method 1
This InGaAs/GaAsSb type II multi quantum well structure has a sensitivity to infrared light having a wavelength of 1.7 to 2.5 μm based on the type II transition in the type II quantum well structure
Implementation Method 2
the photodiode having the InGaAs/GaAsSb type II multi quantum well structure also has a sensitivity to light having a wavelength shorter than 1.7 μm, for example, light of 1.5 μm based on the interband transition of electrons in the InGaAs semiconductor layer
Data Source
AI summary
An infrared image sensor includes a bias circuit receiving a timing signal, the bias circuit generating a bias voltage having a first value and a second value in response to the timing signal; a semiconductor light-receiving device including a photodiode, the semiconductor light-receiving device receiving the bias voltage; a read-out circuit including a read-out electrode connected to the photodiode, the read-out electrode receiving an electrical signal from the photodiode; and a signal processing circuit processing a read-out signal from the read-out circuit synchronously with the timing signal. The photodiode includes an optical absorption layer made of a III-V group compound semiconductor. The optical absorption layer has a type II multi quantum well structure including first compound semiconductor layers containing antimony as a constituent element and second compound semiconductor layers that are stacked alternately.