CMOS Pixel Isolation Structure for Dark Current and Pixel Scaling
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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 or amplifying transistor from the photoelectric conversion unit, then electrical 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 with doped regions (P-type or N-type) to achieve electrical isolation without introducing insulating film interfaces that generate dark current.
Solution Approach 2:
The patent changes the isolation mechanism from dielectric-based (insulating film) to semiconductor-based (doped regions). By altering the electrical parameters of the substrate through doping, the invention achieves isolation while eliminating the harmful interface between insulator and semiconductor.
2Object-generated harmful factors
If insulating films are not used for element isolation, then dark current noise is reduced, but a wider element isolation region is needed making it difficult to miniaturize pixels
Solution Approach 1:
The patent applies local quality by creating doped regions with specific electrical properties in localized areas. The P-type or N-type doped regions provide high-contrast electrical isolation that is confined to specific zones, achieving effective isolation with minimal spatial footprint.
Solution Approach 2:
By changing the doping parameters (concentration, depth, distribution) of the semiconductor regions, the patent achieves sharp electrical isolation boundaries that do not require wide physical isolation regions, enabling pixel miniaturization.
3Reliability
If a wider element isolation region is used to electrically isolate transistors without insulating films, then electrical isolation is maintained, but the pitch of pixels increases reducing sensitivity
Solution Approach 1:
The invention uses locally doped regions with high impurity concentrations to create strong electrical isolation fields in compact spaces. This localized approach to isolation quality allows effective transistor isolation without increasing pixel pitch.
Solution Approach 2:
The patent creates a composite structure within the semiconductor substrate by combining differently doped regions (P-type and N-type) to form isolation barriers. This composite doping structure provides enhanced isolation efficiency per unit area.
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 solution effectively reduces noise from dark current and enables pixel miniaturization by using PN isolation in the element isolation portions, enhancing sensitivity 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.