Ge-on-Si SPAD Array Integration for Low-DCR Infrared Detection
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Solution Overview
Problem
Existing photo detection devices using InGaAs and Ge for infrared light detection face high substrate costs, afterpulsing, high dark count rates (DCR), and difficulty in integrating multiple SPADs in an array with a driving circuit on the same chip.
Innovation Solution
A photo detection device comprising a P-type silicon substrate with a P-type germanium layer formed by epitaxial growth, where multiple SPADs are arranged in an array and a CMOS transistor circuit is integrated on the same substrate, using ion implantation and smart-cut techniques to reduce DCR and afterpulsing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If InGaAs is used to detect infrared photons, then detection capability for wavelengths ≥1 μm is improved, but substrate cost increases and afterpulsing occurs
Solution Approach 1:
The device is divided into distinct functional layers: a Ge layer for infrared photon absorption and a Si layer for avalanche multiplication. This segmentation allows each material to perform its optimal function while avoiding the harmful effects of using InGaAs alone.
Solution Approach 2:
The invention uses a composite Ge-Si structure where germanium and silicon are combined in a specific configuration. The Ge layer detects infrared photons while the Si layer provides avalanche multiplication, creating a material composite that achieves both detection capability and low afterpulsing.
2Adaptability or versatility
If Ge is used to detect infrared photons, then detection capability is improved, but dark count rate increases due to thermal excitation
Solution Approach 1:
The detection function is segmented from the multiplication function. The Ge layer is responsible only for photon absorption while the Si layer handles avalanche multiplication, allowing optimization of each layer to minimize dark count rate.
Solution Approach 2:
The p-type Si layer acts as an intermediary between the Ge absorption layer and the readout circuit. It separates the thermal excitation issues of Ge from the avalanche multiplication process, reducing dark count rate while maintaining detection capability.
3Productivity
If multiple SPADs are arranged in an array on the same chip, then two-dimensional range information capability is improved, but integration with driving circuit becomes difficult
Solution Approach 1:
The Ge-Si structure merges the detection and signal processing functions into a single integrated device. The avalanche multiplication occurs within the same chip structure as the SPAD array, enabling both two-dimensional detection and circuit integration.
Solution Approach 2:
The P-type Si layer serves multiple functions: it provides avalanche multiplication for signal amplification, acts as a charge collection layer, and enables integration with standard Si-based driving circuits. This multi-functionality simplifies the overall device architecture.
4Adaptability or versatility
If InGaAs is formed on Inp substrate by MOCVD, then infrared detection is achieved, but substrate manufacturing cost becomes expensive
Solution Approach 1:
The invention replaces expensive Inp substrates with standard Si substrates. The Ge layer is deposited on inexpensive Si using established techniques, making the device much more cost-effective while maintaining infrared detection capability.
Solution Approach 2:
The invention changes the substrate material parameter from Inp to Si, and changes the deposition method from MOCVD to ion implantation and epitaxial growth. These parameter changes dramatically reduce manufacturing cost while achieving the same functional outcome.
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 device achieves reduced substrate costs, lower DCR, and enables a two-dimensional image sensor in one chip with integrated signal amplification and processing capabilities.
Implementation Method 1
detects a single photon of incident light, in particular, infrared light whose wavelength is about 0.9 to 1.6 μm
Implementation Method 2
an avalanche region is formed in a P-type silicon (Si) layer
Data Source
AI summary
To provide a photo detection device and a manufacturing method thereof, the photo detection device comprising a SPAD in which a substrate-manufacturing cost is kept sufficiently low compared to InGaAs, afterpulsing is less and DCR is also reduced.A photo detection device detecting an incident light from an object, comprising: (i) a P-type silicon (Si) substrate; (ii) a P-type germanium (Ge) layer formed by epitaxial growth on a first surface serving as a front surface of the P-type silicon (Si) substrate; and (iii) a P-type thin film silicon (Si) layer formed on the P-type germanium (Ge) layer, (iv) wherein the P-type thin film silicon (Si) layer is divided into a first region and a second region by a Shallow Trench Isolation (STI), multiple single photon avalanche diodes (SPADs) arranged in an array are formed in the first region, and a CMOS transistor circuit driving the SPADs is formed in the second region.