Multiband FPA Layout Using CQD SWIR and Microbolometer Integration
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Solution Overview
Problem
The integration of short wave infrared (SWIR) and long wave infrared (LWIR) detection capabilities into a single focal plane array (FPA) is challenging due to the high cost and low yield of traditional InGaAs detector hybridization processes, particularly the indium bump bonding and through vias processes, which result in electrical connection issues and thermal expansion mismatches.
Innovation Solution
A multiband FPA is developed using a single silicon CMOS readout integrated circuit (ROIC) substrate with SWIR and LWIR pixels, incorporating a colloidal quantum dot photodiode between the pixels and microbolometer, eliminating the need for indium bumps and through vias, and utilizing metal contacts for coupling, thereby simplifying the fabrication process and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional InGaAs detectors are hybridized with silicon ROIC using indium bump bonding and through vias, then SWIR and LWIR detection capabilities are achieved, but fabrication cost increases and manufacturing yield decreases
Solution Approach 1:
The patent merges SWIR and LWIR detection onto a single silicon ROIC substrate by integrating colloidal quantum dot photodiodes for SWIR and microbolometers for LWIR directly on the same substrate, eliminating the need for separate InGaAs detector hybridization and reducing fabrication complexity
Solution Approach 2:
The patent uses colloidal quantum dot photodiodes as a simplified alternative copy of traditional InGaAs detectors, achieving SWIR detection functionality through a material system (colloidal quantum dots) that can be processed on silicon substrates using standard semiconductor fabrication techniques
2Manufacturing precision
If InGaAs detectors are hybridized at small pitch to provide sufficient resolution, then SWIR and LWIR resolution is improved, but electrical connection reliability deteriorates due to short and open-circuit connections
Solution Approach 1:
The patent extracts the problematic indium bump bonding and through via processes from the fabrication workflow by directly integrating detector elements onto the silicon ROIC substrate, eliminating the source of electrical connection failures while maintaining small pixel pitch
Solution Approach 2:
The patent introduces a direct epitaxial growth process as an intermediary method to form detector elements on the silicon substrate, creating reliable electrical connections through a unified semiconductor process rather than through heterogeneous bonding interfaces
3Reliability
If through vias and indium bump bonding processes are used to interconnect microbolometer MEMS structure to silicon ROIC, then electrical connection is achieved, but fabrication cost and complexity increase
Solution Approach 1:
The patent merges the formation of electrical interconnections into the single epitaxial growth process used to create the detector elements themselves, eliminating separate via formation and bump bonding steps while achieving reliable electrical connections
4Adaptability or versatility
If heterogeneous substrates (Si to InP) are used for InGaAs detectors, then SWIR detection is enabled, but thermal expansion mismatch causes fabrication difficulties
Solution Approach 1:
The patent uses a universal silicon substrate for both SWIR and LWIR detector integration, eliminating thermal expansion mismatch issues by using the same substrate material throughout, while still achieving both SWIR and LWIR detection capabilities through different detector technologies
Solution Approach 2:
The patent achieves homogeneity by using identical silicon substrate material for both SWIR photodiodes and LWIR microbolometers, eliminating the heterogeneity and thermal expansion mismatches that occur with InP/InGaAs/ silicon hybridization
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 approach enables a low-cost, scalable, and flexible multiband FPA with broadband sensitivity from 200 to 2400 nm, reducing fabrication complexity and increasing thermal compatibility, thus overcoming the limitations of traditional methods.
Implementation Method 1
a colloidal quantum dot photodiode on the SWIR pixels between the SWIR pixels and the microbolometer
Implementation Method 2
a microbolometer on the plurality of SWIR and LWIR pixels
Data Source
AI summary
A multiband focal plane array (FPA) is provided including a readout integrated circuit (ROIC) substrate; a plurality of short wave infrared (SWIR) and long wave infrared (LWIR) pixels on the ROIC substrate; a microbolometer on the plurality of SWIR and LWIR pixels; and a colloidal quantum dot photodiode on the SWIR pixels between the SWIR pixels and the microbolometer. The microbolometer is coupled to the LWIR pixels through metal contacts on the LWIR pixels.