This paper reports on the IC-compatible fabrication of vertically tapered optical layers for use in linear variable optical filters (LVOF). The taper angle is fully defined by a mask design. Only one masked lithography step is required for defining strips in a photoresist with trenches etched therein of a density varying along the length of the strip. In a subsequent reflow, this patterned photoresist is planarized, resulting in a strip with a local thickness defined by the initial layer thickness and the trench density at that position before reflow. Hence a taper can be flexibly programmed by the mask design to be from 0.001• to 0.1 • , which enables the simultaneous fabrication of tapered layers of different taper angles. The 3D pattern of resist structures is subsequently transferred into Si or SiO 2 by appropriate etching. Complete LVOF fabrication involves CMOS-compatible deposition of a lower dielectric mirror using a stack of dielectrics on the wafer, tapered layer formation and deposition of the top dielectric mirror. Design principle, processing and simulation results plus experimental validation of the technique on the profile in the resist and after transfer of the taper into Si and SiO 2 are presented.
Future cosmology space missions will concentrate on measuring the polarization of the Cosmic Microwave Background , which potentially carries invaluable information about the earliest phases of the evolution of our universe. Such ambitious projects will ultimately be limited by the sensitivity of the instrument and by the accuracy at which polarized foreground emission from our own Galaxy can be subtracted out. We present the PILOT balloon project which will aim at characterizing one of these foreground sources, the polarization of the dust continuum emission in the diffuse interstellar medium. The PILOT experiment will also constitute a test-bed for using multiplexed bolometer arrays for polarization measurements. We present the results of ground tests obtained just before the first flight of the instrument.
The spectral resolution of a MEMS-based IR microspectrometer critically depends on the thermal cross-talk between adjacent TE elements in the detector array. Thermal isolation between elements is realized by using bulk micromachining directly following CMOS processing. This paper reports on the characterization results of bridge-shaped TE detector elements that are cut out of a membrane. Elements with dimensions of 650 × 36 μm 2 are separated by 10 μm wide gaps in order to minimize the thermal cross-talk by heat conduction through the support structure. The static and dynamic aspects of thermal cross-talk have been evaluated with an emphasis on the effect of the thermal conductivity of air as a function of the package pressure.
The design and fabrication of a thermopile detector array for use in a fully integrated infrared optical spectrometer are described. IC-compatible MEMS technologies are used for fabrication of the spectrometer components, such as the slit, planar imaging diffraction grating and detector array. The IR micro-spectrometer was designed for operation in the 1.5-3 µm wavelength range with the size of the largest dimension about 8 mm. The imaging properties of the diffraction grating result in non-uniform dispersion, which imposes special requirements on the dimensions of each single detector in the array. The result is an array of unequally sized elements. The design considers technological constraints, sensitivity and cross-talk between elements. Simulation results, final design, fabrication technique and fabricated devices are presented.
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