SPAD Image Sensor Isolation Structure for Crosstalk Reduction
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Solution Overview
Problem
Existing image sensing devices using single-photon avalanche diodes (SPAD) face issues with electrical and optical crosstalk, leading to reduced operational reliability and increased dark current rates.
Innovation Solution
The implementation of a multi-layer isolation structure comprising first, second, and third isolation regions around the photoelectric conversion device, including a trench-type isolation layer, to prevent electrical and optical crosstalk and reduce dark current rates, while maintaining the operational characteristics of the SPAD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a simple isolation structure is used around the photoelectric conversion device, then device complexity is reduced, but electrical and optical crosstalk increases leading to reduced operational reliability
Solution Approach 1:
The isolation structure is divided into multiple distinct regions: a first isolation region extending from the upper surface to a first depth, and a second isolation region extending from the lower surface to a second depth. These regions are electrically connected and work together to provide comprehensive isolation, preventing both electrical and optical crosstalk while maintaining manageable complexity through modular design
Solution Approach 2:
The isolation structure extends in multiple dimensions - vertically from both upper and lower surfaces of the substrate, and horizontally to surround the photoelectric conversion device. This multi-dimensional approach creates effective isolation barriers against crosstalk without requiring excessive lateral space or overly complex three-dimensional structures
2Reliability
If deeper isolation regions are implemented to reduce crosstalk, then operational reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The total isolation depth is segmented into two separate regions extending from opposite surfaces of the substrate. Each region extends to a moderate depth that is easier to control with standard manufacturing processes, while together they achieve the cumulative isolation effect that would require excessive depth in a single region
Solution Approach 2:
Instead of creating one extremely deep isolation region that would demand high manufacturing precision, the design uses two partial isolation regions extending from opposite surfaces. This partial action approach achieves sufficient total isolation depth with more relaxed precision requirements for each individual region
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
The isolation structure effectively minimizes crosstalk and dark current rates, enhancing the operational reliability and performance of the image sensing device.
Implementation Method 1
a photoelectric conversion device formed in the substrate and structured to convert incident light into an electrical signal carrying information associated with the incident light
Implementation Method 2
The isolation structure may be formed at the substrate to surround a side surface and a bottom surface of the photoelectric conversion device
Implementation Method 3
Single-photon avalanche diode (SPAD) arrays are solid-state detectors that offer imaging capabilities at the level of individual photons
Data Source
AI summary
Image sensing devices are disclosed. In some implementations, an image sensing device may include a substrate having an upper surface and a lower surface, a photoelectric conversion device formed in the substrate and structured to convert incident light into an electrical signal carrying information associated with the incident light, and an isolation structure formed in the substrate along at least a side surface and a bottom surface of the photoelectric conversion device. The isolation structure comprises a first isolation region which extends from the upper surface of the substrate to a first depth in the substrate to surround the side surface of the photoelectric conversion device, and a second isolation region which is formed in the substrate below the bottom surface of the photoelectric conversion device, the second isolation region electrically connected with the first isolation region.