Photodiode Image Sensor Isolation Structure for Dark Current Control
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Solution Overview
Problem
As the integration of image sensors increases, the size of each pixel decreases, leading to issues such as crosstalk and dark current, which degrade the quality of the image sensor.
Innovation Solution
The image sensor incorporates a semiconductor substrate with a pixel device isolation film and a device isolation structure, featuring a conductive layer and a conductive liner that are electrically connected, with a negative bias applied to both, to reduce dark currents and improve pixel isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the size of each pixel is decreased to increase integration, then the integration increases, but crosstalk and dark current increase degrading image quality
Solution Approach 1:
The patent divides the semiconductor substrate into discrete pixel regions using pixel device isolation films and device isolation structures. These isolation structures segment the continuous substrate into isolated pixel units, preventing crosstalk between adjacent pixels while maintaining high integration density.
Solution Approach 2:
The patent introduces conductive layers and conductive liners as intermediary structures between adjacent pixels. These conductive isolation structures act as mediators that actively manage charge distribution and prevent harmful charge carrier migration between pixels, thereby reducing crosstalk and dark current.
2Productivity
If the size of each pixel is decreased to increase integration, then the integration increases, but dark current increases degrading image quality
Solution Approach 1:
The pixel device isolation films and device isolation structures physically segment the substrate, isolating each pixel's photodiode region. This segmentation prevents dark current generated in one pixel from affecting adjacent pixels, allowing high integration without proportional increase in total dark current.
Solution Approach 2:
The conductive layers and conductive liners serve as intermediary charge management structures that actively suppress dark current generation and migration. These structures mediate the electrical environment between isolated pixels, preventing thermally generated carriers from contributing to dark current signals.
3Object-generated harmful factors
If conductive layer and conductive liner are electrically connected with negative bias, then dark current is reduced, but device complexity increases
Solution Approach 1:
The patent merges the pixel device isolation film structure with the device isolation structure by electrically connecting the conductive layer in the pixel isolation film to the conductive liner in the device isolation structure. This unified conductive system simultaneously provides pixel isolation and active dark current suppression, reducing overall device complexity despite the added electrical connection.
Solution Approach 2:
The conductive layer and conductive liner structure serves multiple functions: it provides physical isolation between pixels, manages charge distribution, and actively suppresses dark current through negative bias. This multi-functional design reduces the need for separate structures, thereby managing device complexity while achieving dark current reduction.
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 implementation of the conductive layer and liner with a negative bias effectively accumulates holes, reducing dark currents and enhancing the overall quality of the image sensor by minimizing crosstalk and improving pixel isolation.
Implementation Method 1
a negative bias is applied to the conductive layer and the conductive liner
Data Source
AI summary
An image sensor including: a semiconductor substrate having a first surface and a second surface; a pixel device isolation film extending from the first surface of the semiconductor substrate into the semiconductor substrate, wherein the pixel device isolation film defines pixels in the semiconductor substrate, and includes a conductive layer; and a device isolation structure located inside a device isolation trench that extends from the first surface of the semiconductor substrate into the semiconductor substrate, wherein the device isolation structure includes a conductive liner electrically connected to the conductive layer, wherein a negative bias is applied to the conductive layer and the conductive liner.