Four-Way-Shared Pixel Architecture with Straight Gate Transfer
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Solution Overview
Problem
As pixels in imaging devices become smaller, the space taken up by transistors responsible for reading out the pixel signal increases, reducing the photosensitive area and fill factor, and metal routing layers obstruct light reaching the photosensor, necessitating a design that enhances fill factor and light sensitivity.
Innovation Solution
The implementation of a four-way-shared pixel architecture where multiple pixels share a readout circuit, including a single floating diffusion region and straight gate transfer gates, reduces the space used by readout circuits and increases the overlap between transfer gates and photosensors, enhancing charge transfer efficiency and reducing metal routing above the photosensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If pixels are made smaller to increase image sensor density, then the number of pixels per unit area increases, but the photosensor area and fill factor decrease as transistors take up more space
Solution Approach 1:
Multiple pixels share common readout circuitry including floating diffusion regions and transistors. Specifically, four pixels share two floating diffusion regions and associated readout transistors, reducing the per-pixel transistor count and freeing up photosensor area while maintaining the required number of pixels.
Solution Approach 2:
The shared readout circuitry serves multiple pixels simultaneously. The floating diffusion regions and associated transistors perform readout functions for multiple pixels, eliminating the need for dedicated readout circuitry in each pixel and increasing fill factor.
2Quantity of substance
If pixels are made smaller to maintain small image sensor size, then pixel density increases, but metal routing layers become more obstructive to light reaching the photosensor
Solution Approach 1:
The readout circuitry including floating diffusion regions and associated transistors is extracted from within each pixel and placed in shared locations between pixels. This removes metal routing layers that would otherwise be present above each photosensor, reducing light obstruction while maintaining high pixel density.
3Reliability
If more transistors are included in each pixel for signal readout, then signal reading capability is maintained, but the fill factor and photosensitive area are reduced
Solution Approach 1:
Readout transistors and floating diffusion regions are merged into shared structures that serve multiple pixels. Four pixels share two floating diffusion regions and associated readout transistors, maintaining signal readout capability while reducing the total transistor count per pixel area and increasing fill factor.
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 increases the fill factor and sensitivity of each pixel by reducing the space used by readout circuits, allowing more light to reach the photosensors, thereby improving image resolution and frame rate while maintaining a small image sensor size.
Implementation Method 1
The photosensor 102 is connected to the floating diffusion region FD by the transfer gate 104 when the transfer gate 104 is activated by a transfer control signal TX
Data Source
AI summary
Methods and apparatuses using four-way-shared readout circuits to increase pixel fill factor. Embodiments consolidate circuits from several pixels, reducing the number of components in each pixel and this increasing the fill factor of each pixel. Additionally, embodiments use “straight gate” transfer gates to increase the readout speed and symmetry of the smaller pixels.