The design and fabrication of wideband mid-infrared metamaterial absorbers are presented. The emphasis is put on the shape-tolerant design for using masked UV (i-line) lithography and CMOS-compatible fabrication to enable on-chip co-integration with detector and readout circuits in a MEMS foundry while maintaining wafer throughput. The CMOScompatibility implies the use of aluminum rather than the commonly used high conductivity metals. The use of masked lithography rather than e-beam lithography in the fabrication of metamaterial absorbers for the mid-infrared range between 3 and 4 μm introduces the challenge of the shape-tolerant design of the unit cell. Moreover, the sensitivity of the fabricated metamaterials to the surface roughness and exposure dose were investigated in this paper. The throughput advantage of masked lithography has been exploited in the fabrication of mid-infrared absorbers over an area of several mm². The measurements confirm the theoretical spectral response and a 98% peak absorption at an angle close to perpendicular incidence. Measurements at different angles show that the absorption spectrum only deviates marginally from normal incidence for angles up to 30°. The combined CMOS-compatibility and masked lithography enable batch fabrication and the on-chip integration of the metamaterial absorbers with MEMS devices and sensors.

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This paper discusses the use of the along-track interferometric coherence as a radar observable with geophysical information rather than as a mere quality indicator. The use of dual co-polarized data to estimate the temporal decorrelation factor is explained, and preliminary results using TanDEM-X data are shown.@en

Metamaterial absorbers are photonic structures composed of an array of sub-wavelength metallic patterns. Results in literature are usually based on structures of nominal dimensions, despite the significant effect of fabrication tolerances on performance. This research aims to identify the main sources of uncertainty and to investigate their effect, notably that of an irregular surface quality (i.e., roughness) of the thin metallic layer and the lithography related variations in size and shape. The effect of the shape and positioning of the resonance peak was investigated and validated using mid-infrared metamaterial absorbers. This sensitivity analysis is essential to the batch fabrication of metamaterial absorbers for MEMS applications.@en

The preliminary results of a study on the effect of the membrane deformation on the optical response of the distributed Bragg reflector, that is based on a stack of such membranes, are presented. The analysis is applied to airgap-based optical filters, which offer an enhanced refractive index contrast and hence are highly promising for optical MEMS devices. The available methods and materials in MEMS technology would make fabrication of such devices feasible, but the optical requirements impose strict geometrical implications on the membrane structure. Although (an overall) tensile stress in membrane is expected to result in a flat structure after the release, a stress gradient results in a deformed structure. A combined finite element and finite-difference time- domain method has been utilized in this work to study the effects of a stress gradient in a distributed Bragg reflector. The results on the effects of both a linear and a non-linear stress gradient are presented. It is shown that a non-linear stress profile results in twice the deformation and a further reduction of optical performance. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.@en

A CMOS-compatible approach is presented for the fabrication of a wideband mid-IR metamaterial-based absorber on top of a Si3N4 membrane, which contains poly-Si thermopiles. The application is in IR microspectrometers that are intended for implementation in portable microsystem for use in absorption spectroscopy. Although Au is the conventional material of choice, we demonstrate by simulation that near-perfect absorption can be achieved over a wider band when using the more CMOS-compatible Al. The absorber design is based on Al disk resonators and an Al backplane, which are separated by a SiO2 layer. The fabrication process involves the deposition of Al and SiO2 layers on top of a Si3N4 membrane, lithography and a lift-off process for patterning of the top Al layer.@en

The design of a metamaterial-based absorber for use in a MEMS-based mid-IR microspectrometer is reported. The microspectrometer consists of a LVOF that is aligned with an array of thermopile detectors, which is fabricated on a SiN membrane and coated with the absorber. Special emphasis is put on the CMOS compatible fabrication, which results in an absorber design based on Al disc resonators and an Al background plane that are separated by an SiO2 layer. Wideband operation over the 3-4 μm spectral range is achieved by staggered tuning of four Al disk resonators in one 1.5 x 1.5 μm2 unit cell, using four different values of the radius of the Al disk between 0.50 μm and 0.63 μm and an SiO2 layer thickness of 150 nm. Simulations reveal an average absorption of about 95% with a ±4% ripple at normal incidence, which reduces to about 80% absorption at a 20° incidence angle. The influence of material choice and dimensions on a single absorption peak was studied and the magnetic polariton was identified as the underlying mechanism of absorption. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.@en

The design of a metamaterial-based absorber for use in a mid-IR microspectrometer-based gas sensor is reported.The microspectrometer consists of a linear variable optical filter (LVOF) that is aligned with an array of thermopiledetectors, which is fabricated on a SiN membrane and covered with the absorber. Special emphasis was put on theCMOS compatible fabrication, which resulted in an absorber design based on aluminium disk resonators and analuminium background plane that are separated by a SiO2 layer. The fabrication process is described, and thechallenges are discussed. @en