CMOS Image Sensor Charge Storage Segmentation
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Solution Overview
Problem
Existing CMOS image sensors with global shutter function face challenges in achieving extended charge retention time and noise immunity without compromising conversion efficiency, and they are not suitable for miniaturization due to increased capacitance and component complexity.
Innovation Solution
A solid-state imaging device with a global shutter function is designed, featuring a charge storage capacitor not connected in parallel with the floating diffusion part, using a charging transistor to charge the capacitor, which allows for extended charge retention time and improved noise immunity without affecting conversion efficiency, and incorporates a minimal number of components to enable high integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large capacitance value of the charge storage capacitor is used to extend charge retention time and improve noise immunity, then charge retention time and noise immunity are improved, but the capacitance of the floating diffusion part increases, resulting in a decrease in charge-to-voltage conversion efficiency
Solution Approach 1:
The patent divides the charge storage function from the charge-to-voltage conversion function by using a separate charge storage capacitor not connected in parallel with the floating diffusion part. This segmentation allows the charge storage capacitor to have a large capacitance value for extended charge retention time and improved noise immunity without increasing the capacitance of the floating diffusion part, thereby maintaining charge-to-voltage conversion efficiency.
2Duration of action of stationary object
If a large capacitance value of the charge storage capacitor is used to extend charge retention time, then charge retention time is improved, but the capacitance of the floating diffusion part increases, resulting in a decrease in charge-to-voltage conversion efficiency
Solution Approach 1:
The patent segments the charge storage function from the charge-to-voltage conversion function by using a separate charge storage capacitor. This allows the charge storage capacitor to have a large capacitance value for extended charge retention time without increasing the capacitance of the floating diffusion part, thereby maintaining charge-to-voltage conversion efficiency.
3Reliability
If the charge storage capacitor is intended to retain the whole charge completely transferred from the photoelectric conversion part, then charge retention capability is improved, but the area of the charge storage capacitor must be as large as the photoelectric conversion part, making pixel size reduction difficult
Solution Approach 1:
The patent segments the charge storage function from the charge-to-voltage conversion function, allowing the charge storage capacitor to be optimized independently. This segmentation enables the charge storage capacitor to have sufficient capacitance for retaining the whole charge without requiring an area as large as the photoelectric conversion part, thereby enabling pixel size reduction.
4Adaptability or versatility
If two charge storage capacitors are provided per pixel to achieve global shutter function and enable signal voltage amplification, then global shutter function and amplification capability are improved, but the number of components increases, making high integration difficult
Solution Approach 1:
The patent makes the charge storage capacitor serve multiple functions: it enables the global shutter function by storing charge from the photoelectric conversion part and simultaneously serves as the basis for signal voltage amplification through the charging transistor. This multi-functionality eliminates the need for two separate charge storage capacitors, thereby reducing the number of components and enabling high integration.
5Adaptability or versatility
If the charge storage capacitor is connected in parallel with the floating diffusion part, then global shutter function is achieved, but the capacitance of the floating diffusion part increases, resulting in a decrease in charge-to-voltage conversion efficiency
Solution Approach 1:
The patent segments the charge storage function from the charge-to-voltage conversion function by using a separate charge storage capacitor not connected in parallel with the floating diffusion part. This segmentation allows the global shutter function to be achieved while maintaining the capacitance of the floating diffusion part, thereby preserving charge-to-voltage conversion efficiency.
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 achieves both extended charge retention time and improved noise immunity without decreasing conversion efficiency, enabling high integration and miniaturization of the CMOS image sensor while maintaining the global shutter function with a reduced number of components.
Implementation Method 1
a photodiode 21 for photoelectrically converting incident light to an amount of charge corresponding to an amount of the incident light
Data Source
AI summary
A solid-state imaging device comprising a plurality of unit pixels each comprising (a) a photoelectric conversion element operative to generate a charge in response to incident light, (b) a first storage element in which the charge generated by the photoelectric conversion element is stored and (c) a second storage element in which a charge based on the charge stored in the first storage element is stored, wherein, for each pixel, the second storage element is located at an opposite side of a light receiving surface of the photoelectric conversion element.