SWIR Sensor Stack With Resonant Cavity for Silicon Detection
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Solution Overview
Problem
Existing SWIR radiation detection technologies face limitations in efficiency and availability of suitable materials and components, particularly for area-scan sensors which are restricted products.
Innovation Solution
A SWIR detector array is developed using a CMOS process fabricated Read-Out Integrated Circuit (ROIC) with a sensor stack that includes a micro-crystalline silicon layer formed using PECVD, and a resonant cavity structure to enhance internal photoemission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional metal-semiconductor contact with internal photoemission is used, then the device structure is simple, but the detection efficiency is limited
Solution Approach 1:
The patent employs a composite sensor stack comprising multiple materials including microcrystalline silicon layer, amorphous silicon layer, and metal layers (e.g., aluminum, titanium nitride) to enhance internal photoemission efficiency. This composite structure achieves over 30% efficiency at 1000 nm wavelength while maintaining compatibility with CMOS fabrication processes.
Solution Approach 2:
The patent introduces a resonant cavity structure with specific thickness (λ/2n where λ is wavelength and n is refractive index) to create optical resonance conditions. This dimensional optimization of the sensor stack thickness enhances the internal photoemission effect by confining and amplifying the electromagnetic field within the detection region.
2Ease of manufacture
If silicon sensors are used for SWIR imaging, then the sensor is compatible with standard manufacturing, but the upper wavelength limit is approximately 1.0 μm
Solution Approach 1:
The patent changes the optical parameters of the sensor stack by introducing a resonant cavity with specific thickness matching half the wavelength of target SWIR radiation (λ/2n). This parameter optimization enables the silicon-based sensor to detect wavelengths beyond its conventional 1.0 μm limit, achieving effective detection up to and beyond 1550 nm through resonant enhancement of the internal photoemission effect.
3Adaptability or versatility
If InGaAs sensors are used for SWIR imaging, then the wavelength detection range is improved, but area-scan sensors are restricted products with limited availability
Solution Approach 1:
The patent creates a functional copy of InGaAs sensor performance using silicon-based materials with resonant cavity enhancement. By optimizing the sensor stack structure and utilizing internal photoemission at resonant conditions, the invention achieves comparable SWIR detection capability (over 30% efficiency at 1000 nm, responsive beyond 1550 nm) using readily available silicon CMOS technology, thereby replicating InGaAs performance with more accessible materials.
4Reliability
If resonant cavity structure is implemented to enhance internal photoemission, then the detection efficiency is improved, but the device complexity increases
Solution Approach 1:
The resonant cavity sensor stack structure serves multiple functions simultaneously: it acts as the detection region for internal photoemission, provides optical resonance enhancement, defines the optical path length, and interfaces with the CMOS readout circuitry. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in overall device complexity despite the enhanced efficiency.
Solution Approach 2:
The patent merges the optical resonance cavity and the photoemission detection region into a single integrated sensor stack structure. The microcrystalline silicon layer and amorphous silicon layer are combined within the resonant cavity, eliminating the need for separate optical components and reducing structural complexity while achieving enhanced detection efficiency through the unified design.
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 solution achieves improved efficiency and responsiveness to SWIR wavelengths, with efficiencies of over 30% for wavelengths of 1000 nm and continued responsiveness to wavelengths greater than 1550 nm, addressing the limitations of existing technologies.
Implementation Method 1
The principle of internal photoemission is known for some time... photoemission taking place over the Schottky barrier
Implementation Method 2
Casalino, M.; Sirleto, L.; Moretti, L.; Gioffrè, M.; Coppola, G. & Rendina, I., 'Silicon resonant cavity enhanced photodetector based on the internal photoemission effect at 1.55 μm'... resonant cavity including a bottom buried reflector and a top metal mirror surrounding a silicon layer with a thickness of λ/2
Data Source
AI summary
A short-wave infra-red, SWIR, radiation detection device comprises: a first metallic layer providing a first set of connections from a readout circuit to respective cells of a matrix, the metallic layer reflecting SWIR wavelength radiation. Each matrix cell comprises at least one stack of layers including: a first layer of doped semiconductor material formed on the first metallic layer; an at least partially microcrystalline semiconductor layer formed over the first doped layer; a second layer of semiconductor material formed on the microcrystalline semiconductor layer; at least one microcrystalline semiconductor layer; and in some embodiments a second metallic layer interfacing the microcrystalline semiconductor layer(s), the interface being responsive to incident SWIR radiation to generate carriers within the stack. The stack has a thicknessT=λ2Nbetween reflective surfaces of the first and second metallic layers.