Ge-on-Si Pyramidal SWIR Focal Plane Array for Low-Cost Detection
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Solution Overview
Problem
Current short wave infrared (SWIR) focal plane arrays (FPAs) are costly due to their reliance on InGaAs materials, making them unsuitable for consumer market applications, while there is a need for high-performance SWIR photodetectors and FPAs based on silicon and other group IV materials at a lower cost.
Innovation Solution
The development of light detecting structures featuring a Si base with a pyramidal shape and a Ge photodiode on top, which includes a p-n or p-i-n junction, integrated with a microlens and anti-reflection layer, to detect light in the SWIR range, fabricated using a method that includes growing a Ge layer on a doped Si substrate with a growth seed to trap threading dislocations and improve crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If InGaAs material system is used for SWIR FPA, then detection performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive InGaAs photodetectors with cheaper silicon-based photodetectors that have sufficient lifetime for consumer applications. The silicon photodetectors are fabricated using standard CMOS processes, making them cost-effective while maintaining adequate detection performance for SWIR imaging in consumer devices.
Solution Approach 2:
The patent modifies the photodetector design by changing from InGaAs to silicon material system, and implements specific structural parameters including pyramidal microstructures with optimized dimensions, specific doping concentrations, and layer thicknesses to enhance SWIR detection capability of silicon photodetectors while reducing manufacturing cost.
2Ease of manufacture
If silicon based photodetectors are used, then manufacturing cost is reduced, but detection performance deteriorates
Solution Approach 1:
The patent introduces pyramidal microstructures on the silicon photodetector surface with curved facets. These pyramidal structures increase the optical path length of incident SWIR light within the silicon, enhancing absorption efficiency and detection performance while maintaining the cost advantage of silicon-based fabrication.
Solution Approach 2:
The patent creates a composite structure combining silicon photodetectors with specific microlens materials and anti-reflection coating materials. This composite design optimizes light coupling and absorption in the SWIR range, improving detection performance while utilizing standard semiconductor manufacturing processes.
3Ease of manufacture
If standard planar structure is used, then fabrication is simplified, but light collection efficiency decreases
Solution Approach 1:
The patent replaces the standard planar surface with pyramidal microstructures that have curved facets. These pyramidal structures trap incident light through multiple internal reflections, significantly increasing the optical path length and absorption probability for SWIR wavelengths, thereby improving light collection efficiency while remaining compatible with standard semiconductor fabrication techniques.
Solution Approach 2:
The patent transitions from a two-dimensional planar surface to a three-dimensional pyramidal structure array. This dimensional change increases the effective surface area and creates multiple light-trapping interfaces, enhancing light collection efficiency without complicating the fabrication process beyond standard microelectromechanical systems capabilities.
4Area of stationary object
If pyramidal structure with large base is used, then light collection area is increased, but device complexity increases
Solution Approach 1:
The patent divides the large pyramidal structure into an array of smaller pyramidal microstructures on the photodetector surface. Each pyramid has a base size of approximately 10-50 micrometers, collectively providing large light collection area while keeping individual structure fabrication within standard semiconductor process capabilities, thus managing device complexity.
Solution Approach 2:
The patent employs pyramidal microstructures with specific curved facet angles and dimensions that optimize light trapping while being fabricable using standard anisotropic etching processes. The pyramid geometry with controlled base sizes and facet angles provides large effective collection area without requiring complex fabrication steps beyond conventional semiconductor manufacturing.
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 results in low-cost, high-performance SWIR light detecting structures with reduced dark current and enhanced light collection efficiency, enabling the formation of FPAs suitable for consumer applications.
Implementation Method 1
Ge photodiode formed on the Si pyramid top, wherein the Ge photodiode is operable to detect light in the SWIR range
Implementation Method 2
a microlens placed between the pyramid bottom and the incoming light
Implementation Method 3
an anti-reflection layer positioned between the pyramid bottom and the microlens
Data Source
AI summary
Light detecting structures comprising a Si base having a pyramidal shape with a wide incoming light-facing pyramid bottom and a narrower pyramid top and a Ge photodiode formed on the Si pyramid top, wherein the Ge photodiode is operable to detect light in the short wavelength infrared range, and methods for forming such structures. A light detecting structure as above may be repeated spatially and fabricated in the form of a focal plane array of Ge photodetectors on silicon.