SPAD Pixel Isolation Structure for Stable Drive Start Voltage
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Solution Overview
Problem
In avalanche photodiode (APD) systems, particularly single photon avalanche photodiodes (SPADs), the stopper film used for element isolation can trap charges, leading to fluctuations in the drive start voltage of pixels, affecting the operational reliability and efficiency.
Innovation Solution
An optical detection device is designed with a semiconductor substrate and insulation films where a thicker silicon oxide film is used between the avalanche amplification region and a thinner silicon nitride film, along with an aluminum oxide film to reduce charge trapping and stabilize the drive start voltage, incorporating contact plugs and diffusion layers for improved electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stopper film (silicon nitride film) is provided to form a deep element isolation portion, then pixel isolation is improved, but charge trapping occurs and drive start voltage fluctuates
Solution Approach 1:
The stopper film is segmented into two distinct layers: a first stopper film (silicon nitride) and a second stopper film (silicon oxide). This segmentation allows each layer to perform specialized functions - the silicon nitride layer provides strong pixel isolation while the silicon oxide layer prevents charge trapping and voltage fluctuation, thereby resolving the contradiction between isolation effectiveness and voltage stability.
Solution Approach 2:
The invention uses a composite structure combining silicon nitride and silicon oxide materials in the stopper film. The silicon nitride provides excellent electrical isolation properties, while the silicon oxide layer suppresses charge trapping effects. This composite material approach enables simultaneous achievement of both pixel isolation and drive start voltage stability.
2Reliability
If the element isolation portion is made deeper to improve isolation, then pixel isolation is improved, but charge trapping increases and affects detection accuracy
Solution Approach 1:
The deep element isolation structure is segmented into multiple functional layers with the second stopper film (silicon oxide) specifically positioned to prevent charge trapping at the isolation depth, thereby maintaining both isolation effectiveness and detection precision.
Solution Approach 2:
The second stopper film (silicon oxide) acts as an intermediary layer between the deep silicon nitride isolation structure and the avalanche amplification region. It mediates the interaction by preventing charge trapping while allowing the deep isolation structure to function, thus preserving both isolation quality and measurement precision.
3Device complexity
If insulation films are made thinner to reduce complexity, then device complexity is reduced, but charge trapping occurs and drive start voltage fluctuates
Solution Approach 1:
The invention optimizes the thickness parameters of the two stopper films - the first stopper film (silicon nitride) has a thickness of 50-150 nm and the second stopper film (silicon oxide) has a thickness of 10-50 nm. These specific parameter ranges achieve the optimal balance between preventing charge trapping, stabilizing drive start voltage, and maintaining reasonable device complexity.
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 suppresses fluctuations in the drive start voltage, enhancing the operational stability and efficiency of the SPADs by minimizing charge trapping and maintaining consistent pixel performance.
Implementation Method 1
a first insulation film that is provided on the second surface side and in contact with the pixel isolation portion; and a second insulation film that is provided between the first insulation film and the avalanche amplification region
Implementation Method 2
The SPAD detects one photon for each pixel by multiplying a carrier generated by photoelectric conversion in a PN junction region of a high electric field
Implementation Method 3
The Geiger mode avalanche photodiode is also referred to as a single photon avalanche photodiode (SPAD). The SPAD detects one photon for each pixel by multiplying a carrier generated by photoelectric conversion
Data Source
AI summary
Provided is an optical detection device capable of suppressing a fluctuation of a drive starting voltage in a pixel.The optical detection device according to the present disclosure includes: a semiconductor substrate that has a first surface as a light incident surface and a second surface on an opposite side to the light incident surface; a first pixel that is in the semiconductor substrate and has an avalanche amplification region including a first conductive region and a second conductive region; a pixel isolation portion that isolates the first pixel from an adjacent pixel; a first insulation film that is provided on the second surface side and in contact with the pixel isolation portion; and a second insulation film that is provided between the first insulation film and the avalanche amplification region, in which a film thickness of the second insulation film is larger than the film thickness of the first insulation film.