CMOS Image Sensor Device Isolation Structure for Pixel Isolation
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Solution Overview
Problem
The challenge in developing high-density, highly-integrated CMOS image sensors is to achieve efficient device isolation and impurity concentration control while maintaining low power consumption and integrating signal processing circuits, which existing technologies have not adequately addressed.
Innovation Solution
The proposed solution involves a CMOS image sensor design with a substrate having a device isolation structure that includes an insulating gapfill layer extending from the top to the bottom surface, a spacer between the gapfill layer and the substrate, and impurity regions of varying conductivity types and concentrations, along with a readout circuit and color filter, to enhance pixel isolation and signal processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If device isolation structure is enhanced to improve pixel isolation, then manufacturing complexity increases
Solution Approach 1:
The device isolation structure is divided into multiple functional layers: a first device isolation layer for primary isolation, a second device isolation layer for additional isolation, and a third device isolation layer for fine-tuning isolation characteristics. This segmentation allows each layer to contribute differently to the overall isolation performance, achieving high pixel isolation while maintaining manageable manufacturing complexity through modular construction.
2Productivity
If impurity concentration is increased to improve photoelectric conversion, then impurity diffusion increases
Solution Approach 1:
A third device isolation layer is introduced as an intermediary barrier between regions with different impurity concentrations. This intermediate layer prevents direct diffusion between high and low impurity regions while allowing each region to maintain its optimal impurity concentration for photoelectric conversion, thus resolving the contradiction between conversion efficiency and diffusion control.
Solution Approach 2:
Different device isolation layers are positioned at different depths and locations to create localized isolation characteristics. The first device isolation layer provides primary isolation at a deeper level, while the second and third layers provide additional isolation at shallower levels, creating a gradient isolation structure that locally controls impurity diffusion while maintaining high photoelectric conversion efficiency in active regions.
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 design improves the uniformity of electrical characteristics, increases the photodiode area, and prevents impurity diffusion, resulting in higher performance and integration density for CMOS image sensors.
Implementation Method 1
An image sensor is a device that converts optical images into electrical signals
Data Source
AI summary
An image sensor may include a device isolation structure defining a plurality of pixel regions in a substrate and a photoelectric conversion element formed in each of the pixel regions. The device isolation structure may include an insulating gapfill layer extending from an upper portion to a lower portion of the device isolation structure, a spacer provided at the upper portion of the device isolation structure and interposed between the insulating gapfill layer and the substrate, and a lower impurity region provided at the lower portion of the device isolation structure and interposed between the insulating gapfill layer and the substrate.