CMOS Image Sensor Substrate Bias Segmentation
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Solution Overview
Problem
CMOS image sensors experience a blooming effect due to excessive photocharges generated from strong light, leading to screen distortion and reduced image quality, as the photodiode's storage capacity is overwhelmed, causing charges to overflow to adjacent pixels.
Innovation Solution
Implementing different substrate bias voltages on a CMOS image sensor, where the pixel region is biased to a negative voltage to increase the photodiode's full-well capacity, thereby reducing the blooming effect by enhancing the storage capacity and preventing charge overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single substrate bias voltage is applied to the entire semiconductor substrate, then the device complexity is low and ease of manufacture is high, but the photodiode storage capacity is limited causing blooming effect
Solution Approach 1:
The semiconductor substrate is divided into multiple regions (first region for pixels, second region for logic circuits) with different substrate bias voltages applied to each region. This segmentation allows the pixel region to have a higher storage capacity while keeping the logic circuit region separate, resolving the contradiction between increased storage capacity and device complexity.
Solution Approach 2:
Different regions of the substrate are assigned different bias voltage characteristics - the first region receives a first substrate bias voltage optimized for photodiode storage capacity, while the second region receives a second substrate bias voltage optimized for logic circuit operation. This local differentiation resolves the contradiction by allowing each region to have optimal electrical properties for its specific function.
2Reliability
If the photodiode storage capacity is increased to prevent blooming effect, then image quality is improved, but the device structure becomes more complex requiring different bias voltages
Solution Approach 1:
The substrate is segmented into distinct voltage regions that can be independently controlled. The first region containing pixels is biased to maximize storage capacity and prevent blooming, while the second region containing logic circuits is biased separately. This segmentation maintains high image quality without requiring complex modifications to the overall device structure.
Solution Approach 2:
The substrate bias voltage parameter is changed spatially across different regions of the semiconductor substrate. By applying different voltage levels to different regions, the photodiode storage capacity is increased in the pixel region to prevent blooming effect, while maintaining proper operation of logic circuits in the second region, thus improving reliability without excessive complexity.
3Object-affected harmful factors
If different substrate bias voltages are applied to different regions, then the photodiode capacity is increased to reduce blooming effect, but the manufacturing process becomes more complex
Solution Approach 1:
The substrate is divided into manufacturable regions with distinct bias voltage applications. The first region for pixels and second region for logic circuits are structured to allow separate bias voltage application through dedicated electrical paths. This segmentation reduces the blooming effect while maintaining ease of manufacture by organizing the device into manageable, functionally-distinct regions that can be manufactured using standard CMOS processes with additional biasing infrastructure.
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 approach effectively reduces the blooming effect, maintaining image quality by increasing the photodiode's capacity to store charges, thereby preventing charge overflow and improving the overall performance of the image sensor.
Implementation Method 1
The photodiode is a device that generates photocharges in proportion to the amount of light applied thereto
Implementation Method 2
the first region is substrate biased to a first voltage and the second region is substrate biased to a second voltage different from the first voltage
Data Source
AI summary
An image sensor having different bias voltages is provided. The image sensor may include a plurality of pixels configured to output pixel signals based on a received optical signal, and logic circuits configured to output the pixels signals as image data. The pixels may be formed on a first region of a semiconductor substrate, the first region being substrate biased to a first voltage. The logic circuits may be formed on a second region of the semiconductor substrate different from the first region, the second region being substrate biased to a second voltage different from the first voltage. A full-well capacitance (FWC) of the photodiode may be increased by applying the first voltage, which is a negative (−) voltage, to a photodiode of a pixel to reduce (or, alternatively prevent) a blooming effect.