CMOS Image Sensor Charge Holding Part Depth Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors with a charge holding part face challenges such as reduced aperture ratio, decreased photo-diode sensitivity, and potential optical noise due to the limited pixel layout and exposure timing differences, leading to image distortion.
Innovation Solution
The implementation of a CMOS image sensor with a photoelectric conversion part and a charge holding part formed in a semiconductor substrate, where the holding part is constructed with a thickness of half or less of the substrate's thickness, and a charge capturing region is added to prevent light leakage and optical noise, along with a light shielding mechanism to shield light from the charge holding area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge holding part is provided in each pixel to enable global shutter scheme, then image distortion is avoided, but aperture ratio decreases and sensitivity of the photodiode may decrease
Solution Approach 1:
The patent moves the charge holding function from the lateral plane to the vertical dimension by utilizing the depth direction of the semiconductor substrate. The charge holding part is formed as a deep region extending from the front surface toward the back surface, with its bottom positioned at a specific depth. This vertical arrangement allows the charge holding function to coexist with the photodiode's light-receiving function without lateral space conflict, thereby maintaining a large aperture ratio while enabling global shutter operation.
Solution Approach 2:
The charge holding part is nested within the pixel structure in the vertical direction, with the photodiode positioned above it. The charge holding region is formed by extending a doped region deep into the substrate, creating a nested configuration where the charge storage function is embedded within the overall pixel structure without occupying lateral space that would reduce the aperture ratio.
2Reliability
If a charge holding part is provided in each pixel to enable global shutter scheme, then image distortion is avoided, but capacity of the photodiode and charge holding part may decrease
Solution Approach 1:
The patent optimizes the charge holding capacity by controlling the depth parameter of the charge holding part. The bottom of the charge holding part is positioned at a specific depth from the front surface, which is determined based on the substrate thickness. By adjusting this depth parameter, the patent achieves an optimal balance between charge holding capacity and prevention of optical noise, ensuring sufficient capacity for global shutter operation while maintaining image quality.
3Reliability
If a charge holding part is provided in each pixel to enable global shutter scheme, then image distortion is avoided, but optical noise may be generated by light incident into the charge holding part
Solution Approach 1:
The patent applies different doping concentrations to different regions of the charge holding part to create local quality variations. The charge holding part has a first doped region with a first doping concentration and a second doped region with a second doping concentration that differs from the first. This local quality differentiation allows the upper region to effectively hold charges while the lower region prevents light penetration and optical noise generation.
Solution Approach 2:
The patent introduces a light shielding layer as an intermediary between the charge holding part and incident light. This light shielding layer is positioned to prevent light from directly reaching the charge holding region, thereby eliminating the source of optical noise while allowing the charge holding function to operate effectively. The light shielding layer acts as a mediator that blocks harmful light without interfering with the electrical charge holding capability.
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 pixel signal quality by reducing optical noise and maintaining sensitivity while preventing light leakage into the charge holding part, thus avoiding image distortion.
Implementation Method 1
a photoelectric conversion part configured to convert received light into a charge
Data Source
AI summary
The present disclosure relates to an imaging device and an electronic device that make it possible to obtain a better pixel signal. A photoelectric conversion part that converts received light into a charge, and a holding part that holds a charge transferred from the photoelectric conversion part are provided, the photoelectric conversion part and the holding part are formed in a semiconductor substrate having a predetermined thickness, and the holding part is formed with a thickness that is half or less of the predetermined thickness. A charge capturing region that captures a charge is further provided on a light incident side of a region where the holding part is formed. A light shielding part that shields light is formed between the photoelectric conversion part and the charge capturing region. The present technology is applicable to an imaging device.