Demodulation Pixel Buried Channel High-Low Junction Charge Transport
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Solution Overview
Problem
Current demodulation pixel architectures face limitations in charge transport speed and photo-sensitivity due to non-perfect linear potential distribution in semiconductor substrates, leading to reduced accuracy and increased power consumption in 3-D imaging applications.
Innovation Solution
A new pixel structure combining enhanced charge transport and photo-sensitivity through a buried channel, majority carrier current, and high-low junctions or graded doping, enabling faster and more accurate charge transfer and detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional demodulation pixel architectures are used, then device complexity is maintained at acceptable levels, but charge transport speed is limited due to non-perfect linear potential distribution
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photo-sensitive detection region with specific doping profiles, a drift region for charge transport, and a storage region. This segmentation allows optimization of charge transport speed in each region while maintaining overall device manageability. The detection region uses high-low junctions or graded doping to create favorable potential conditions, while the drift region implements linear potential distribution through controlled doping, and the storage region provides charge accumulation - each segment performing its specific function efficiently.
Solution Approach 2:
Different regions of the pixel are given different local properties to optimize specific functions. The detection region has high-low junctions or graded doping for enhanced photo-sensitivity and charge generation. The drift region has linearly graded doping specifically designed to create uniform electric field for fast charge transport. The storage region has different doping characteristics for charge accumulation. This local differentiation of properties allows simultaneous optimization of multiple parameters without requiring complete structural redesign.
2Measurement precision
If conventional pixel structures with non-perfect linear potential distribution are used, then manufacturing processes remain standard, but measurement precision decreases due to slower charge transport
Solution Approach 1:
The doping concentration parameters are systematically changed across different regions to achieve the desired linear potential distribution. The drift region employs linearly graded doping where the doping concentration varies linearly with depth, creating a uniform electric field that accelerates charge transport. The detection region uses high-low junctions or graded doping profiles with specific parameter ranges to enhance photo-sensitivity. These parameter changes are implemented through standard semiconductor fabrication techniques such as ion implantation and diffusion processes, maintaining ease of manufacture while dramatically improving measurement precision through faster and more accurate charge transport.
3Use of energy by moving object
If faster charge transport is implemented through improved potential distribution, then optical sensitivity increases, but power consumption increases due to enhanced electric fields
Solution Approach 1:
The drift region is designed with linearly graded doping that creates a uniform electric field, establishing equipotential conditions that optimize charge transport efficiency. This uniform field distribution ensures that charges experience consistent acceleration throughout the drift region, maximizing transport speed and photo-sensitivity. The equipotential design in the drift region, combined with the specific doping profiles in adjacent regions, enables fast charge collection while minimizing the voltage requirements and associated power consumption compared to non-uniform field designs.
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 new pixel structure achieves high-speed charge transport and enhanced photo-sensitivity, allowing for precise optical time signal resolution with nanosecond accuracy and improved optical sensitivity beyond prior-art demodulation pixels.
Implementation Method 1
the n-type buried channel 210 generates a lateral drift field 108 that transports the photo-generated electrons 110b through the semiconductor substrate 101 in lateral direction
Implementation Method 2
deeply generated electrons 110d are transported toward the surface by the vertical drift field components 109 around the high-low junction 105 or graded doping
Implementation Method 3
after receiving a light pulse by the buried charge-generation region, in the semiconductor layer just under the buried charge-generation region, an optical signal is converted into signal charges
Data Source
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AI summary
A demodulation pixel improves the charge transport speed and sensitivity by exploiting two effects of charge transport in silicon in order to achieve the before-mentioned optimization. The first one is a transport method based on the CCD gate principle. However, this is not limited to CCD technology, but can be realized also in CMOS technology. The charge transport in a surface or even a buried channel close to the surface is highly efficient in terms of speed, sensitivity and low trapping noise. In addition, by activating a majority carrier current flowing through the substrate, another drift field is generated below the depleted CCD channel. This drift field is located deeply in the substrate, acting as an efficient separator for deeply photo-generated electron-hole pairs. Thus, another large amount of minority carriers is transported to the diffusion nodes at high speed and detected.