3D Avalanche Diode Calibration Using Integrated Light Sources
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Solution Overview
Problem
Existing avalanche diode systems require lengthy calibration times due to low dark count rates, necessitating external light sources that increase device footprint and cost, and are sensitive to process variations and temperature changes.
Innovation Solution
Incorporating a local light-emitting pn-junction in a 3D integrated circuit to provide internal light sources for calibration, allowing for rapid adjustment of bias voltages using a breakdown voltage monitor circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external light sources are used for calibration, then calibration can be performed, but device footprint and cost increase
Solution Approach 1:
The patent merges the light source function with the avalanche diode sensor by integrating a light-emitting pn-junction directly into the same semiconductor substrate. This combination eliminates the need for separate external light sources, thereby reducing device footprint and cost while maintaining calibration capability. The light-emitting junction is formed in the same n-well as the avalanche diode, creating a self-contained calibration system.
Solution Approach 2:
The avalanche diode structure itself provides the light source for calibration through its integrated light-emitting pn-junction. This self-service approach eliminates dependency on external light sources, allowing the device to perform self-calibration without additional components. The light-emitting junction uses the same semiconductor material and fabrication process as the avalanche diode, making the system self-sufficient.
2Measurement precision
If external light sources are used for calibration, then calibration can be performed, but device cost increases
Solution Approach 1:
The patent merges the light source function with the avalanche diode sensor by integrating a light-emitting pn-junction directly into the same semiconductor substrate. This combination eliminates the need for separate external light sources, thereby reducing device footprint and cost while maintaining calibration capability. The light-emitting junction is formed in the same n-well as the avalanche diode, creating a self-contained calibration system.
Solution Approach 2:
The avalanche diode structure itself provides the light source for calibration through its integrated light-emitting pn-junction. This self-service approach eliminates dependency on external light sources, allowing the device to perform self-calibration without additional components. The light-emitting junction uses the same semiconductor material and fabrication process as the avalanche diode, making the system self-sufficient.
3Device complexity
If dark count monitoring is used for calibration, then no external light source is needed, but observation time must be very long
Solution Approach 1:
The patent applies preliminary action by generating light pulses from the integrated light-emitting pn-junction before performing calibration measurements. This pre-generated light provides immediate trigger events for the avalanche diode, eliminating the need for long observation periods required when relying on rare dark count events. The light-emitting junction is activated during calibration to ensure sufficient signal for rapid voltage adjustment.
Solution Approach 2:
The patent changes the operational parameters of the pn-junction by switching between reverse bias (for avalanche detection) and forward bias (for light emission during calibration). This parameter change allows the same structure to serve dual functions: detecting photons during normal operation and emitting photons during calibration, thereby reducing calibration time without requiring external light sources.
4Reliability
If avalanche diodes are operated above breakdown voltage, then sensitivity is high, but voltage regulation is required due to process variation and temperature
Solution Approach 1:
The patent implements feedback through a breakdown voltage monitor circuit that continuously monitors the breakdown voltage of the avalanche diode and adjusts the bias voltage accordingly. This feedback mechanism compensates for process variations and temperature changes, maintaining constant excess bias voltage and optimal detection sensitivity. The monitor circuit uses the integrated light source to generate calibration signals that enable precise voltage regulation.
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
Facilitates fast calibration of avalanche diodes in dark environments without increasing device footprint or cost, reducing calibration time and improving sensitivity by increasing trigger event probability.
Implementation Method 1
The bottom-tier comprises an array of integrated light sources. The light sources are operable to emit light towards the avalanche diodes.
Implementation Method 2
Single Photon Avalanche Diodes (SPAD hereinafter) are extremely fast and sensitive optical sensors
Implementation Method 3
The SPAD sensor is a reverse biased device operating at a supply voltage VHV higher than the breakdown voltage VBD
Data Source
AI summary
An avalanche diode arrangement includes a three-dimensional integrated circuit including a stack with at least a top-tier and a bottom-tier. The avalanche diode arrangement also includes a breakdown voltage monitor circuit. The top-tier includes an array of avalanche diodes. The bottom-tier includes an array of integrated light sources, located below the top-tier. In a calibration mode of operation, the light sources are operable to emit light towards the avalanche diodes. The breakdown voltage monitor circuit is operable to adjust bias voltages of the avalanche diodes depending on trigger events induced by light emitted by the light sources during the calibration mode of operation.