CMOS Image Sensor Honeycomb Pixel Architecture
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in reducing size while maintaining resolution, as the decrease in active pixel sensor size leads to increased parasitic resistance and capacitance, and a honeycomb structure is desired to address these issues.
Innovation Solution
A CMOS image sensor design featuring a shared floating diffusion circuit among unit pixels, forming a honeycomb structure with hexagonal photodiodes, which includes two unit pixels per block, each with a shared floating diffusion, transfer transistors, a reset transistor, a drive transistor, and overflow transistors for overflow drainage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of active pixel sensor is decreased to reduce overall sensor size, then the sensor compactness is improved, but parasitic resistance and capacitance increase
Solution Approach 1:
Adjacent unit pixels share a common floating diffusion region, merging previously separate circuit elements. This sharing approach reduces the total number of floating diffusion regions needed, thereby reducing overall parasitic capacitance while maintaining compact pixel dimensions
Solution Approach 2:
The shared floating diffusion region serves multiple unit pixels simultaneously, functioning as the charge collection node for multiple photodiodes. This multi-functional design reduces redundant circuit elements and minimizes parasitic effects
2Manufacturing precision
If unit pixels are arranged in square shape with increased integration, then resolution is improved, but pixel pitch increases leading to increased parasitic resistance
Solution Approach 1:
The patent employs a hexagonal photodiode geometry instead of traditional square pixels, creating an asymmetric honeycomb arrangement. This asymmetric tiling achieves more efficient space utilization, reducing dead space and minimizing pixel pitch while maintaining high integration density
Solution Approach 2:
The honeycomb structure introduces a new spatial arrangement dimension, organizing pixels in a hexagonal grid pattern rather than conventional square lattices. This dimensional reorganization optimizes space utilization and reduces the distance between adjacent pixel centers
3Reliability
If a honeycomb structure with shared floating diffusion is implemented, then parasitic resistance and capacitance are reduced, but device complexity increases
Solution Approach 1:
The sensor is divided into repeating unit blocks, each containing a standardized configuration of photodiodes and shared floating diffusion regions. This modular segmentation makes the complex honeycomb structure manufacturable and easier to design while maintaining the parasitic reduction benefits
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 design reduces pixel pitch, decreases dead space, and enhances image clarity by allowing for pixel summation mode and effective overflow drainage, particularly at high illumination levels, thereby improving the integration and resolution of the image sensor.
Implementation Method 1
a photodiode (PD) may convert incident light into an electric signal based on the light's wavelength
Data Source
AI summary
Example embodiments may provide a CMOS image sensor. The CMOS image sensor may include a plurality of unit blocks each including two unit pixels. Each unit block may include two photodiodes having a hexagonal shape, a floating diffusion shared by the two unit pixels, a first transfer transistor and a second transfer transistor between the floating diffusion and the two photodiodes, respectively, a reset transistor connected with the floating diffusion, a drive transistor with a gate connected with the floating diffusion, and/or a selection transistor connected to the drive transistor in series. Example embodiment CMOS image sensors may be used in digital cameras, mobile devices, computer cameras, or the like.