Geiger-Mode APD Micro-Cell Packaging for Low-Photon Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing photodetectors face challenges in achieving high sensitivity and mechanical stability for detecting low-intensity photons, particularly in lidar systems, where the signals are attenuated and require precise detection of single photons, while maintaining minimal material between the photosensitive area and incoming photons to avoid signal loss.
Innovation Solution
The development of a photodetector architecture using Geiger-mode avalanche photodiodes formed into an array of micro-cells on an indium phosphide substrate, with epitaxial layers and a resistive/capacitive structure for quenching, and flip-chip bonding to a sturdy support substrate for mechanical stability and reduced material thickness, allowing for efficient detection of low photon fluxes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrodes are attached to both sides of the device to provide bias voltage across the photodetector, then the photodetector can operate with proper electrical contact, but thicker substrates and layers are required for mechanical stability, which increases the material thickness between photosensitive cells and incoming photons, potentially attenuating weak signals
Solution Approach 1:
The photodetector is divided into multiple independent photocells arranged in an array, where each cell can be electrically contacted from the same side. This segmentation allows the device to achieve mechanical stability with thinner substrates while maintaining proper electrical contact for bias voltage application.
Solution Approach 2:
The patent transitions from a traditional two-sided electrode configuration to a single-sided electrode configuration by arranging multiple photocells in an array on one side of the substrate. This dimensional reorganization eliminates the need for thick substrates required for mechanical stability in two-sided configurations.
2Strength
If thicker substrates and layers are used to provide mechanical stability, then the structural integrity of the photodetector is improved, but the material thickness between photosensitive cells and incoming photons increases, causing attenuation of weak photon signals
Solution Approach 1:
By segmenting the photodetector into multiple photocells that can be electrically contacted from one side, the device achieves mechanical stability without requiring thick substrates. The segmented array structure allows thin substrates to maintain sufficient structural integrity while minimizing photon path length through the substrate.
Solution Approach 2:
The patent employs thin substrate and layer configurations that would traditionally be too fragile for two-sided electrode mounting. The single-sided photocell array configuration allows these thin films to maintain mechanical stability while minimizing material thickness between photosensitive cells and incoming photons.
3Measurement precision
If the photosensitive area is divided into multiple photocells, then the detection sensitivity for low-intensity photons is improved and saturation problems are avoided, but the device complexity increases due to the need for multiple cells and signal combination circuits
Solution Approach 1:
The photodetector is divided into multiple photocells, each capable of detecting low-intensity photons independently. This segmentation prevents saturation by distributing the photosensitive area across multiple cells while maintaining high detection sensitivity for weak signals.
Solution Approach 2:
Multiple photocells are combined in an array configuration where their individual signals can be summed to form a total photocurrent. This merging approach maintains high detection sensitivity while avoiding saturation that would occur in a single large photocell.
4Object-affected harmful factors
If single-sided electrical contact is implemented to reduce material thickness, then signal attenuation is minimized, but mechanical stability may be compromised without proper support structures
Solution Approach 1:
The device is segmented into multiple photocells arranged in an array on one side of the substrate. This segmentation allows electrical contact to be made from a single side, eliminating the need for thick substrates required for mechanical stability in two-sided configurations, thereby minimizing signal attenuation.
Solution Approach 2:
The single-sided electrode configuration serves multiple functions: it provides electrical contact for bias voltage application, supports the photocell array structure, and minimizes material thickness between photosensitive cells and incoming photons. This multi-functional design achieves both mechanical stability and reduced signal attenuation.
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 solution enhances the sensitivity and mechanical integrity of photodetectors, enabling accurate detection of low-intensity photons with minimal signal attenuation, improving the range and information discernment in lidar systems by reducing material between the photosensitive area and incoming photons.
Implementation Method 1
Semiconductor avalanche photodiodes allow a photoelectron produced by the absorption of a photon to be amplified, increasing a detection current from a few photoelectrons to thousands of electrons
Implementation Method 2
a photoelectron produced by the absorption of a photon
Data Source
AI summary
This Application discloses methods for fabricating and packaging avalanche photodiodes (APDs), particularly useful for high sensitivity Geiger-mode APDs formed using an array of micro-cells. The photodetector is formed on a semiconductor wafer of indium phosphide (InP) having epitaxial layers, including indium gallium arsenide (InGaAs) as the photodetecting layer, with n-doped InP to one side, and layers of InP incorporating p-doped regions on the opposite side. The p-doped regions may be used to define the array of micro-cells. The photodetector is packaged by etching a well into the epitaxial structure on the semiconductor wafer, allowing an electrode to be patterned that contacts the n-doped InP layer and another that contacts the p-doped InP regions. Flip-chip bonding techniques can then attach the semiconductor wafer to a stronger support substrate, which may additionally be configured with electronic circuitry positioned to electrically contact the electrodes on the semiconductor wafer surface.