Image Sensor Dummy Region for Crosstalk Reduction
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Solution Overview
Problem
Image sensors face challenges in maintaining uniformity of transistors at the edges of the active pixel region, leading to image quality deterioration due to deep trench isolation (DTI) differences compared to those in the middle, causing crosstalk and reduced signal-to-noise ratio.
Innovation Solution
Incorporating a dummy region between the active pixel region and the guard ring region, with a first pixel having a photoelectric conversion element and a second pixel without one, both equipped with transistors and deep trench isolations (DTIs), where the second pixel's gate terminal is floated and connected to a guard ring for ground or constant voltage, enhancing transistor uniformity and reducing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If deep trench isolation (DTI) is formed to reduce crosstalk between pixels, then crosstalk is reduced, but transistor uniformity deteriorates at the edges of the active pixel region
Solution Approach 1:
A dummy region is formed between the active pixel region and the guard ring region, containing dummy pixels with transistors and DTIs. This preliminary structure compensates for the non-uniformity that would otherwise occur at the edges of the active pixel region, ensuring that transistors in the active region maintain uniform characteristics by providing a reference environment for the DTI formation process.
Solution Approach 2:
The dummy region is specifically designed with different characteristics from the active pixel region. The dummy pixels contain transistors and DTIs but are configured to provide isolation and uniformity reference rather than active sensing. This local differentiation allows the DTI structure to be optimized for uniformity in the active region while maintaining effective crosstalk reduction.
2Object-affected harmful factors
If DTI is formed between pixels, then electrical crosstalk is reduced, but optical crosstalk and image quality deterioration persist
Solution Approach 1:
The dummy region with dummy pixels is formed in advance between the active pixel region and guard ring region. These dummy pixels contain complete transistor structures and DTIs that create a preliminary isolation barrier, preventing both electrical and optical interference from reaching the active pixels. This preliminary structure ensures that when actual imaging occurs, the active pixels are protected from residual crosstalk that would otherwise degrade image quality.
Solution Approach 2:
The dummy region acts as an intermediary buffer zone between the active pixel region and the guard ring region. This intermediate structure absorbs and isolates electromagnetic and optical interference, preventing it from directly affecting the active pixels. The dummy pixels with their transistor structures and DTIs serve as a mediating layer that protects the sensitive active region while maintaining the protective function of the guard ring.
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 improves the uniformity of transistors and DTIs, leading to enhanced image sensor performance by reducing electrical and optical crosstalk, thereby improving image quality and signal-to-noise ratio.
Implementation Method 1
Each of the pixels includes a photoelectric conversion element which generates an electrical signal that changes as a function of the amount of incident light
Data Source
AI summary
An image sensor includes a first pixel that is in an active pixel region, a second pixel that is in a dummy region adjacent the active pixel region, and a first deep trench isolation (DTI) formed between the first pixel and the second pixel.