CMOS Image Sensor Isolation Pattern With Reflective Dark Current Control
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Solution Overview
Problem
Current CMOS image sensors face challenges with dark current occurrence, light reflection efficiency, and sensitivity, as well as integration complexity.
Innovation Solution
The proposed image sensor design includes a substrate with pixel areas, an isolation pattern extending into the substrate, and an antireflection layer on the isolation pattern, featuring a conductive reflection layer on a dielectric layer, which enhances light reflection efficiency and sensitivity by minimizing dark current through specific layer configurations and structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional isolation pattern is used in CMOS image sensors, then device isolation is achieved, but dark current occurs and light reflection efficiency is reduced
Solution Approach 1:
The isolation pattern is constructed as a composite structure comprising multiple layers: a first dielectric layer, a conductive reflection layer, and a second dielectric layer. This composite material approach enables the isolation pattern to simultaneously provide electrical isolation and optical reflection functions, resolving the contradiction between dark current suppression and light reflection efficiency.
Solution Approach 2:
The conductive reflection layer, which could potentially cause electrical interference, is instead utilized to reflect incident light back into the pixel area. This converts a potential harmful effect into a beneficial one, simultaneously achieving dark current isolation and enhancing light reflection efficiency to improve sensor sensitivity.
2Object-affected harmful factors
If the isolation pattern is positioned closer to the pixel area, then dark current is reduced, but light reflection efficiency decreases
Solution Approach 1:
By incorporating the conductive reflection layer within the multi-layer isolation pattern, the structure can be positioned close to the pixel area for effective dark current isolation while the reflection layer simultaneously reflects light back into the pixel, maintaining or even enhancing sensitivity despite the close positioning.
Solution Approach 2:
The close positioning of the isolation pattern, which would normally reduce light reflection efficiency, is compensated by the conductive reflection layer that actively reflects light back into the pixel area. This converts the potential disadvantage of close positioning into a benefit for both dark current isolation and light reflection.
3Measurement precision
If additional layers are added to the isolation pattern to improve light reflection, then sensitivity increases, but device complexity increases
Solution Approach 1:
The conductive reflection layer serves multiple functions simultaneously: it provides optical reflection to enhance sensitivity, acts as an electrical isolation layer to suppress dark current, and can serve as a structural support layer. This multi-functionality reduces the need for separate dedicated layers, thereby limiting the increase in device complexity while achieving improved sensitivity.
Solution Approach 2:
The isolation pattern is designed as an integrated composite structure where the first dielectric layer, conductive reflection layer, and second dielectric layer work together as a unified system. This composite approach achieves multiple functions (isolation and reflection) within a single integrated structure rather than requiring separate independent components, thus limiting complexity increase.
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 reduces dark current, increases light reflection efficiency, and improves sensitivity, resulting in a highly integrated and efficient image sensor.
Implementation Method 1
a conductive reflection layer on the first dielectric layer... increases light reflection efficiency
Implementation Method 2
Each of the pixels includes a photodiode (PD). The photodiode transforms an incident light into an electrical signal.
Data Source
AI summary
An image sensor includes a substrate that includes a first surface and a second surface that are opposite to each other, where the substrate includes a plurality of pixel areas; an isolation pattern that extends from the first surface and into the substrate, where the isolation pattern is between the plurality of pixel areas; and an antireflection layer on the isolation pattern, where the isolation pattern includes: a first device isolation pattern that contacts the antireflection layer; and a second device isolation pattern that is spaced apart from the antireflection layer, where the first device isolation pattern includes: a first dielectric layer; and a conductive reflection layer on the first dielectric layer, and where a top surface of the conductive reflection layer and a top surface of the first dielectric layer extend from the second surface of the substrate by a same distance.