SPAD Light Detection Apparatus Dynamic Bias Control
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Solution Overview
Problem
Existing light detection apparatuses using single photon avalanche diodes (SPADs) face increased noise due to unwanted charge avalanche multiplication, which occurs when a high reverse bias voltage is applied for extended periods, leading to increased leak current and noise generation from crystal defects within the semiconductor substrate.
Innovation Solution
The apparatus separates the signal charge accumulation and avalanche multiplication regions, allowing for controlled potential changes to manage the depletion layer and reverse bias voltage, reducing unwanted charge multiplication by applying a lower reverse bias during signal accumulation and increasing it only during signal transfer for avalanche multiplication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high reverse bias voltage is applied to the avalanche diode for extended periods to enable avalanche multiplication, then the signal charge detection capability is improved, but the unwanted charge generation increases leading to noise
Solution Approach 1:
The patent applies dynamic control of the reverse bias voltage by switching between a first potential (lower reverse bias) during the accumulation period and a second potential (higher reverse bias) during the readout period. This dynamic voltage adjustment enables the system to maintain low noise during signal accumulation while achieving sufficient avalanche multiplication for detection during readout, thereby resolving the contradiction between detection capability and noise generation.
Solution Approach 2:
The patent implements periodic switching between accumulation mode and readout mode with distinct voltage levels. During the accumulation period, a lower reverse bias is applied to minimize unwanted charge generation, while during the readout period, a higher reverse bias is applied to enable signal detection. This periodic action pattern allows the system to achieve both low noise and high detection capability at different time intervals.
2Power
If a high reverse bias voltage is applied to the avalanche diode, then avalanche multiplication occurs enabling photon detection, but the leak current increases
Solution Approach 1:
The patent dynamically adjusts the reverse bias voltage level based on the operational phase. During accumulation, a lower voltage minimizes leak current and energy loss. During readout, the voltage is increased to enable avalanche multiplication for signal detection. This dynamic adjustment resolves the contradiction between achieving sufficient avalanche multiplication power and minimizing energy loss from leak current.
3Measurement precision
If the incident light detection period is lengthened to improve measurement accuracy, then more photons can be detected, but the noise increases due to extended high voltage application
Solution Approach 1:
The patent structures the detection process into periodic accumulation and readout phases. The accumulation period can be extended to collect more signal charges from incident photons, while the readout period uses high voltage only briefly to transfer and detect the accumulated charges. This periodic action allows extended detection time for improved accuracy without proportionally increasing noise, as the high-voltage noise-generating phase remains brief.
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 reduces noise and dark current generation, improving the signal-to-noise ratio and power consumption by minimizing the duration of high reverse bias application, thereby enhancing the accuracy and efficiency of light detection.
Implementation Method 1
Generation of a signal charge by photon incidence
Implementation Method 2
avalanche multiplication of the generated signal charge
Data Source
Figure 1A~1B
Figure 1C
Figure 2A~2C
AI summary
A light detection apparatus according to an embodiment includes a first semiconductor region having a first conductivity type, a second semiconductor region having a second conductivity type, a third semiconductor region having the first conductivity type, and circuit means configured to count the number of generation times of an avalanche current, wherein a reverse bias voltage for causing avalanche multiplication of the signal charge is applied to the second semiconductor region and the third semiconductor region, and the signal charge is accumulated in the first semiconductor region when the potential barrier is formed, wherein the control means controls the height of the potential barrier.