Amorphous Germanium Waveguides for LWIR Sensing
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Solution Overview
Problem
Chemical sensors operating in the Mid-Wave Infrared (MWIR) and Long-Wave Infrared (LWIR) wavelength range are incompatible with CMOS materials, leading to expensive and complex sensing systems, and current silicon-on-insulator platforms for data communication are costly due to large bending radii, while amorphous germanium faces issues with high free carrier absorption and non-ohmicity.
Innovation Solution
Amorphous germanium waveguides are deposited on substrates at room temperature, utilizing E-beam evaporation to achieve low hole concentration, high mobility, and low absorption loss, compatible with CMOS technology, suitable for MWIR and LWIR applications, and used in chemical sensing and data communication systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If amorphous germanium is used as waveguide material, then low absorption loss is achieved, but high free carrier absorption and non-ohmicity problems occur
Solution Approach 1:
The patent changes the carrier concentration parameter of amorphous germanium from high to low (10^16 to 10^18 cm^-3) through controlled deposition processes, transforming the material's optical and electronic properties to simultaneously achieve low absorption loss and improved reliability
Solution Approach 2:
The patent creates a composite waveguide structure using amorphous germanium layer deposited on silicon substrate, combining the low absorption loss property of amorphous Ge with the mechanical stability and CMOS compatibility of silicon, while controlling the overall carrier concentration to minimize free carrier absorption
2Device complexity
If CMOS-compatible materials are used for MWIR/LWIR chemical sensors, then integration with IC chips is enabled, but material incompatibility with current sensor designs occurs
Solution Approach 1:
The patent modifies the optical properties of amorphous germanium by controlling deposition parameters to achieve low carrier concentration, enabling the material to be transparent in MWIR/LWIR ranges while maintaining CMOS process compatibility, thus resolving the material incompatibility issue
Solution Approach 2:
The patent uses amorphous germanium as an intermediary material layer that bridges CMOS technology and MWIR/LWIR sensing requirements, allowing integration of infrared-sensitive waveguides with standard silicon-based integrated circuits through compatible fabrication processes
3Ease of operation
If silicon-on-insulator platform is used for data communication, then waveguide functionality is achieved, but large bending radius increases device size
Solution Approach 1:
The patent creates a composite waveguide structure with amorphous germanium on silicon substrate that enables tight bending radii, allowing compact device layouts while maintaining waveguide functionality through the optimized optical properties of the amorphous Ge layer
4Quantity of substance
If amorphous germanium is deposited using conventional methods, then material deposition is achieved, but high contamination and structural non-uniformity occur
Solution Approach 1:
The patent replaces conventional thermal evaporation or sputtering methods with molecular beam epitaxy (MBE) deposition, using precise beam-controlled material transport to achieve atomic-layer precision, ultra-high purity amorphous germanium films with controlled stoichiometry and minimal contamination
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 amorphous germanium waveguides provide low loss and wide transparency, enabling efficient sensing of organic molecules and effective data communication with reduced size, weight, and power consumption, while maintaining CMOS compatibility.
Implementation Method 1
E-beam yielded the purest material, with 96% Ge and 4% carbon contamination
Implementation Method 2
Thin films of amorphous Ge can be obtained using various processing approaches: sputter deposition, electron beam evaporation (E-beam), and physical vapor deposition (or thermal evaporation)
Implementation Method 3
The amorphous Ge is used as a waveguide for use in evanescent sensing and data communication applications in the MWIR and LWIR
Implementation Method 4
In terms of optical properties, ellipsometry shows an absorption coefficient of 0.1 cm−1 at a wavelength of 8 μm. A waveguide made of amorphous Ge shows a low absorption loss of 2 dB/cm at a wide wavelength range including 8 μm
Data Source
AI summary
A layer of amorphous Ge is formed on a substrate using electron-beam evaporation. The evaporation is performed at room temperature. The layer of amorphous Ge has a thickness of at least 50 nm and a purity of at least 90% Ge. The substrate is complementary metal-oxide-semiconductor (CMOS) compatible and is transparent at Long-Wave Infrared (LWIR) wavelengths. The layer of amorphous Ge can be used as a waveguide in chemical sensing and data communication applications. The amorphous Ge waveguide has a transmission loss in the LWIR of 11 dB/cm or less at 8 μm.