CMOS Pixel Isolation Layout for Color Mixing and Sensitivity
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Solution Overview
Problem
The sensitivity of photoelectric conversion units in semiconductor layers, such as those used in CMOS image sensors, can be compromised by the arrangement of grooves used for element isolation, leading to decreased performance.
Innovation Solution
A photoelectric conversion apparatus is designed with a semiconductor layer featuring a first isolating portion constituted by an insulator and a second isolating portion in the form of a groove that extends closer to the second surface, allowing for improved element isolation and reduced light mixing between pixels, enhancing both optical and electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a groove is provided in the semiconductor layer for element isolation, then color mixing is suppressed and photoelectric conversion performance is improved, but sensitivity of the photoelectric conversion unit decreases
Solution Approach 1:
The isolation structure is divided into two segments: a first isolating portion (insulator) disposed on the first surface and a second isolating portion (groove) disposed closer to the second surface. This segmentation allows each portion to perform isolation functions at different depths, effectively suppressing color mixing while the strategic positioning minimizes impact on photoelectric conversion sensitivity
Solution Approach 2:
The patent applies different isolation mechanisms at different locations: the insulator-based first isolating portion is positioned where electrical isolation is critical, while the groove-based second isolating portion is positioned where optical isolation is needed. This local differentiation optimizes both color mixing suppression and sensitivity preservation
2Reliability
If an insulator is used for element isolation on the first surface, then electrical isolation is achieved, but optical isolation and sensitivity are compromised
Solution Approach 1:
The patent transitions from a single-surface isolation approach to a depth-based two-dimensional isolation strategy. By placing the groove closer to the second surface (back surface), it creates optical isolation in the depth dimension, while the insulator on the first surface maintains electrical isolation, thus resolving the contradiction between electrical and optical isolation requirements
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 enhances the sensitivity and photoelectric conversion performance by reducing light and charge mixing, while maintaining effective isolation between pixels, thus improving the overall performance of the imaging apparatus.
Implementation Method 1
As an isolating portion constituted by the groove acts as a barrier for light, an electric charge, and so on, the sensitivity improves, and color mixing is suppressed
Implementation Method 2
a first element region where a first photoelectric conversion element is provided, a second element region where a second photoelectric conversion element is provided
Data Source
AI summary
A photoelectric conversion apparatus includes an element isolating portion that is disposed on a side of a front surface of a semiconductor layer and constituted by an insulator, and a pixel isolating portion. The pixel isolating portion includes a part that overlaps an isolating region in a normal direction. The semiconductor layer is continuous across semiconductor regions in an intermediate plane. The part is located between a semiconductor region and another semiconductor region.