CMOS Image Sensor Charge Discharge Layer for Dark Current Reduction
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Solution Overview
Problem
The challenge is to reduce dark current generated at the bottom of the element isolation region in CMOS image sensors, where increasing the junction area to handle more charge leads to increased dark current, and strengthening the electric field results in higher white spot defects.
Innovation Solution
An imaging device with a charge discharge layer of the same conductivity type as the charge storage region, arranged between the element isolation region and the charge storage region, helps to reduce dark current by discharging electrons generated at the isolation region bottoms, thereby preventing them from flowing into the charge storage region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the junction area is increased to handle more charge, then the charge-handling capacity is improved, but dark current increases proportionally with area
Solution Approach 1:
A charge discharge layer of the same conductivity type as the charge storage region is introduced as an intermediary between the element isolation region and the charge storage region. This charge discharge layer acts as a mediator to redirect and discharge dark current electrons generated at the isolation region bottoms away from the charge storage region, thereby reducing dark current while preserving the benefits of a large junction area for charge handling.
2Productivity
If the electric field is strengthened to improve charge collection, then charge collection efficiency is improved, but white spot defects increase exponentially
Solution Approach 1:
The invention changes the electrical parameters in the region between the element isolation region and the charge storage region by introducing a charge discharge layer with the same conductivity type as the charge storage region. This parameter change creates a favorable electric field distribution that improves charge collection efficiency while preventing the exponential increase in white spot defects that would otherwise occur with stronger electric fields.
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 effectively suppresses dark current at the element isolation region bottoms while maintaining a large charge-handling capacity, improving the dark characteristics of the image sensor.
Implementation Method 1
a charge discharge layer of the same conductivity type as the charge storage region, wherein the charge discharge layer is arranged between the element isolation region and the charge storage region
Data Source
AI summary
An imaging device includes a plurality of pixel transistors at a substrate surface of a semiconductor substrate, an element isolation region that isolates the plurality of pixel transistors from each other, a charge storage region at a deeper position in the semiconductor substrate than the substrate surface, and a charge discharge layer of the same conductivity type as the charge storage region. The charge discharge layer is arranged between the element isolation region and the charge storage region.