Nested Pixel Image Sensor Isolation for CMOS Crosstalk Reduction
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Solution Overview
Problem
The decreasing distance between complementary metal oxide semiconductor (CMOS) image sensor pixels leads to significant crosstalk issues, affecting image quality due to increased interference between adjacent pixels.
Innovation Solution
The implementation of deep trench isolation (DTI) structures and a pixel configuration with concentric oval-shaped perimeters for photoelectric sensors, along with a method of forming and calibrating pixels to reduce crosstalk, including the use of a pinning layer, high-K dielectric layer, and passivation layer, and a pixel readout circuit with transistors connected to both external and internal photoelectric sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the distance between CIS pixels is decreased to increase pixel density, then the pixel density and resolution are improved, but the crosstalk between adjacent pixels increases significantly
Solution Approach 1:
The patent introduces deep trench isolation (DTI) structures filled with high-K dielectric materials as intermediary elements between adjacent photoelectric sensors. These DTI structures act as physical barriers and electrical isolators, preventing charge carrier diffusion and signal leakage between neighboring pixels, thereby eliminating crosstalk while maintaining high pixel density
Solution Approach 2:
The patent applies different structural characteristics to different regions: the photoelectric sensors maintain high sensitivity for light detection, while the regions between them are filled with DTI structures having high dielectric constants and low charge carrier generation properties. This local differentiation allows each region to perform its specific function optimally without interfering with adjacent regions
2Object-affected harmful factors
If deep trench isolation structures are introduced to reduce crosstalk, then the crosstalk between adjacent pixels is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent addresses the crosstalk problem by transitioning from a two-dimensional planar isolation approach to a three-dimensional deep trench structure. The DTI structures extend vertically through multiple layers, providing isolation in the depth dimension rather than relying solely on lateral separation, thereby reducing crosstalk without significantly increasing lateral device complexity
3Productivity
If the pixel size is decreased to increase the number of pixels, then the pixel density is improved, but the crosstalk between adjacent pixels increases
Solution Approach 1:
The patent implements a nested structure where the second photoelectric sensor is positioned inside the first photoelectric sensor, with the DTI structure nested between them. This nested arrangement allows for compact pixel design with reduced pitch while maintaining effective isolation, enabling high pixel density without proportionally increasing crosstalk
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 crosstalk between adjacent pixels, enhancing image quality by isolating sensors and compensating for interference through calibration, thereby improving quantum efficiency and reducing dark current.
Implementation Method 1
a plurality of deep trench isolation (DTI) structures, each DTI structure of the plurality of DTI structures configured to isolate the first photoelectric sensor and the second photoelectric sensor
Implementation Method 2
each pixel of the plurality of pixels configured to convert light into a corresponding electric signal
Implementation Method 3
a high-K dielectric layer on the pinning layer
Data Source
AI summary
Various example embodiments are directed to an image sensor, a method of forming a pixel, a pixel readout circuit, and a calibration method. The image sensor includes a substrate including a plurality of pixels, each pixel of the plurality of pixels configured to convert light into a corresponding electric signal, each pixel including a first photoelectric sensor and a second photoelectric sensor, a plurality of deep trench isolation (DTI) structures, each DTI structure of the plurality of DTI structures configured to isolate the first photoelectric sensor and the second photoelectric sensor of a corresponding pixel of the plurality of pixels, each DTI structure in the corresponding pixel in the substrate, a plurality of metal gates (MGs) on the plurality of DTI structures, and in each pixel of the plurality of pixels, the second photoelectric sensor is included inside the first photoelectric sensor.