MEMS Fabry-Perot Reflector Structure for Flat Tunable Mirrors
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Solution Overview
Problem
Existing MEMS-based tunable Fabry-Perot filters face challenges in achieving optimal optical performance due to stress-induced mirror bowing and mirror warping, limited operational wavelength range, and high actuation voltage requirements, which hinder their widespread adoption in spectroscopic imaging systems.
Innovation Solution
A method of fabricating MEMS reflectors with residual tensile stress in the top layer, supported only at the periphery, and using silicon as the high refractive-index medium to overcome stress-induced deformation and extend the operational wavelength range into visible and NIR bands, while simplifying the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multilayer dielectric mirrors are used to achieve highly resonant structures with narrow FWHM, then spectral resolution is improved, but stress gradient causes mirror bowing that degrades optical performance
Solution Approach 1:
The patent changes the stress parameter by introducing a stress compensation layer with specific material properties (lower elastic modulus than the dielectric mirror layers) to counteract the stress gradient caused by multilayer deposition. This parameter change allows the mirror to maintain both high spectral resolution and flatness without compromising either performance.
2Ease of manufacture
If single-layer top mirror is used to minimize stress-induced mirror defects, then manufacturing simplicity is improved, but bandwidth is limited to 1.5 μm allowing only coarse spectral feature discrimination
Solution Approach 1:
The patent uses a composite structure combining a single-layer top mirror with a stress compensation layer. This composite approach maintains the manufacturing simplicity of single-layer mirrors while adding the stress management capability through the compensation layer, enabling both coarse and fine spectral feature discrimination across extended bandwidth.
3Adaptability or versatility
If conventional MEMS actuators are used to tune the optical cavity, then wavelength tuning is achieved, but actuation voltage is high
Solution Approach 1:
The patent employs a flexible membrane structure as the movable mirror substrate, which allows for reduced actuation voltage compared to rigid substrates. The flexible membrane can be actuated by conventional MEMS actuators with lower voltage requirements, enabling wavelength tuning across the extended spectral range while reducing energy consumption.
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 optical characteristics with increased reflectivity and spectral resolution, reduced actuation voltage, and expanded wavelength operation from SWIR to NIR, enabling cost-effective and compact tunable optical filters.
Implementation Method 1
A method of fabricating a reflector is provided. The method comprises forming a first material layer defining a bottom layer; forming a sacrificial layer on the bottom layer; forming a second material layer defining a top layer on the sacrificial layer and a supporting structure connected to the bottom layer; and removing at least part of the sacrificial layer to form a cavity between the bottom layer and the top layer such that the supporting structure supports the top layer relative to the bottom layer and no further supporting structure is provided within the cavity, wherein after the at least part of the sacrificial layer is removed, at least the top layer has residual tensile stress.
Implementation Method 2
using silicon as the high refractive-index medium to overcome stress-induced deformation and extend the operational wavelength range into visible and NIR bands
Implementation Method 3
an actuator arranged such that at least the second reflector of the membrane is moveable relative to the first reflector between at least a first tuning position and a second tuning position
Data Source
Figure 1A~1C
Figure 1D~1E
Figure 1F~1G
AI summary
The present disclosure relates to a method of fabricating a reflector, the reflector being at least partially reflective and at least partially transmissive for at least a wavelength of electromagnetic radiation; the method comprising: forming a first material layer defining a bottom layer; forming a sacrificial layer on the bottom layer; forming a second material layer defining a top layer on the sacrificial layer and a supporting structure connected to the bottom layer; and removing at least part of the sacrificial layer to form a cavity between the bottom layer and the top layer such that the supporting structure supports the top layer relative to the bottom layer and no further supporting structure is provided within the cavity, wherein after the at least part of the sacrificial layer is removed, at least the top layer has residual tensile stress.