Solid-State Image Sensor Isolation Structure for Dark Current Noise
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in minimizing noise caused by dark current generated in element isolation regions, which affects image quality and makes it difficult to miniaturize pixels due to the need for wider element isolation regions when insulating films are not used for isolation.
Innovation Solution
A solid-state imaging device configuration where the first semiconductor substrate includes photoelectric conversion units and floating diffusion regions, and the second semiconductor substrate includes amplifying and resetting transistors, with element isolation portions that do not use insulating films, reducing dark current noise and allowing for miniaturization by eliminating the need for wide isolation regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating film is used for element isolation of the resetting transistor and photoelectric conversion unit, then element isolation is achieved, but dark current is generated at the interface between the insulating film and semiconductor substrate causing noise
Solution Approach 1:
The patent extracts and removes the insulating film from the element isolation structure. Instead of using LOCOS or STI isolation with insulating films, the invention employs a semiconductor substrate structure where the resetting transistor and photoelectric conversion unit are isolated through substrate design and doping profiles without requiring insulating films at the element isolation interfaces, thereby eliminating dark current generation at such interfaces
Solution Approach 2:
The patent changes the electrical parameters of the semiconductor substrate by introducing specific doping regions and adjusting impurity concentrations. The resetting transistor and photoelectric conversion unit are isolated through controlled doping profiles and potential barrier formation in the substrate, replacing the physical isolation method with insulating films
2Object-generated harmful factors
If no insulating film is used for element isolation, then dark current noise is reduced, but a wider element isolation region is needed making pixel miniaturization difficult
Solution Approach 1:
The patent transitions from two-dimensional planar isolation to three-dimensional substrate-level isolation. By utilizing vertical doping profiles and depth-controlled implantation, the element isolation is achieved through the thickness dimension of the substrate rather than requiring extended lateral isolation regions, enabling compact pixel design without wide isolation zones
Solution Approach 2:
The patent replaces the mechanical/physical isolation system (insulating films occupying space) with an electrical isolation system (doping-induced potential barriers). This substitution allows isolation functionality to be achieved through electrical field control rather than physical separation, reducing the spatial requirements for element isolation 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 configuration effectively reduces noise from dark current and enables pixel miniaturization by maintaining sensitivity while minimizing the impact of dark current, enhancing image quality and reducing color mixture among pixels.
Implementation Method 1
a photoelectric conversion unit configured to convert incident light into signal charge
Data Source
AI summary
A solid-state imaging device includes a first and second pixel regions. In the first pixel region, a photoelectric conversion unit, a floating diffusion region (FD), and a transferring transistor are provided. In the second pixel region, an amplifying transistor, and a resetting transistor are provided. A first element isolation portion is provided in the first pixel region, while a second element isolation portion is provided in the second pixel region. An amount of protrusion of an insulating film into a semiconductor substrate in the first element isolation portion is smaller, than that in the second element isolation portion.