CMOS Image Sensor Pixel Structure for Reduced Area and Leakage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing CMOS active pixel image sensors face challenges in reducing pixel size without compromising the size of reset and output transistor gates, as shrinking the gap between pixels risks electron leakage, and reducing the power supply voltage decreases photoelectron collection.
Innovation Solution
The solution involves reconfiguring the connection of the reset transistor between the floating diffusion and the output signal line, allowing the power supply line diffusion to be shared between two pixels, maintaining the same transistor gate dimensions while reducing pixel size by eliminating one contact and isolation region between transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the gap between pixels is reduced to shrink pixel size, then pixel area is reduced, but electron leakage between adjacent pixels increases
Solution Approach 1:
The pixel structure is segmented into distinct regions with clear boundaries. The isolation region is enhanced to create effective separation between adjacent pixels, allowing the gap between pixels to be reduced while maintaining electron containment through improved regional segmentation rather than relying solely on physical distance.
2Area of moving object
If the transistor gate size is reduced to shrink pixel size, then pixel area is reduced, but photoelectron collection efficiency decreases
Solution Approach 1:
The isolation region extends in multiple dimensions to create a three-dimensional barrier against electron leakage. By utilizing vertical isolation structures and multi-layer isolation regions, the patent achieves effective electron containment without requiring larger horizontal gaps, thus maintaining compact pixel area while preserving photoelectron collection efficiency.
3Area of moving object
If the power supply voltage is reduced to enable smaller transistor gates, then pixel size is reduced, but maximum photoelectron collection capacity decreases
Solution Approach 1:
The patent changes the isolation parameter from horizontal gap distance to vertical and multi-dimensional isolation structures. This parameter transformation allows the use of higher power supply voltages to maintain photoelectron collection capacity while achieving pixel size reduction through more efficient spatial utilization of isolation regions rather than relying on voltage reduction.
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 allows for a reduction in pixel size without affecting the transistor geometry, maintaining efficient photoelectron collection while minimizing electron leakage, thus enhancing the overall performance of the image sensor.
Implementation Method 1
The photodiodes 150 and 151 are connected to a common shared floating diffusion 155 respectively by transfer gates 152 and 153. The process of sampling the photodiode 150 begins by turning on the power supply (VDD) 158 and also turning on the reset transistor 154 to set the floating diffusion 155 voltage to the voltage of the power supply 158.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An image sensor that includes a plurality of pixels disposed on a substrate, each pixel includes at least one photosensitive region that collects charges in response to incident light; a charge-to-voltage conversion node for sensing the charge from the at least one photosensitive region and converting the charge to a voltage; an amplifier transistor having a source connected to an output node, having a gate connected to the charge-to-voltage conversion node and having a drain connected to at least a portion of a power supply node; and a reset transistor connecting the output node and the charge-to-voltage conversion node.