Junctionless Single Photon Avalanche Diode Dark Current Reduction
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Solution Overview
Problem
Conventional silicon avalanche diodes for image sensing suffer from high dark current rates due to junction defects and require high operating voltages, which are undesirable.
Innovation Solution
A photosensor design that utilizes a semiconductor substrate with insulated gate electrodes and doped regions biased with specific voltages to create a fully depleted region, enabling photon-induced avalanche multiplication without a P-N junction, thus eliminating dark current issues and reducing operating voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional silicon avalanche diodes with P-N junctions are used for image sensing, then photon detection capability is achieved, but dark current rate becomes unacceptably high due to junction defects
Solution Approach 1:
The patent extracts and removes the P-N junction structure from the avalanche diode, eliminating the source of junction defects that cause high dark current. The invention uses a fully depleted semiconductor substrate without any P-N junction, thereby taking out the harmful element while preserving photon detection capability through avalanche multiplication in the bulk material.
Solution Approach 2:
The patent changes the fundamental structural parameter from a junction-based design to a fully depleted bulk design. By modifying the doping profile and applying specific bias voltages to create a fully depleted region without junctions, the device achieves low dark current while maintaining avalanche gain for photon detection.
2Power
If conventional silicon avalanche diodes are designed for sufficient depletion, then breakdown voltage is achieved for avalanche multiplication, but operating voltage becomes unacceptably high (exceeding 17 Volts)
Solution Approach 1:
The patent changes the electrical parameter profile by using a fully depleted structure with controlled doping gradients. This allows achieving the necessary electric field strength for avalanche multiplication at significantly lower operating voltages compared to conventional junction-based diodes, reducing the operating voltage from exceeding 17V to acceptable levels.
3Object-generated harmful factors
If a junctionless photosensor design is implemented, then dark current is reduced and operating voltage is lowered, but device structure becomes more complex with insulated gate electrodes and multiple doped regions
Solution Approach 1:
The fully depleted region serves multiple functions simultaneously: it acts as the photon absorption volume, the avalanche multiplication region, and the charge collection volume. The insulated gate electrodes and doped regions work together to create and control the fully depleted state, combining multiple functions into an integrated structure that achieves low dark current without proportionally increasing 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
The junctionless photosensor design effectively reduces dark current and operating voltage, improving the efficiency and performance of image sensing without the drawbacks of conventional SPAD devices.
Implementation Method 1
The insulated gate electrode is configured to be biased by a gate voltage to produce an electrostatic field within the semiconductor substrate causing the formation of a fully depleted region within the semiconductor substrate
Implementation Method 2
The fully depleted region responds to absorption of a photon with an avalanche multiplication that produces charges that are collected at the first and second regions
Data Source
AI summary
A semiconductor layer is doped with a first doping type and has an upper surface. A first electrode insulated from the semiconductor layer extending through the semiconductor layer from the upper surface. A second electrode insulated from the semiconductor layer extends through the semiconductor layer from the upper surface. The first and second electrodes are biased by a voltage to produce an electrostatic field within the semiconductor layer causing the formation of a depletion region. The depletion region responds to absorption of a photon with an avalanche multiplication that produces charges that are collected at first and second oppositely doped regions within the semiconductor substrate.