A small form factor microsensor system with optical MEMS devices is discussed in this paper. The key components in
the microsensor system include a temperature and humidity sensor for environmental monitoring, a microprocessor for
signal processing, and an optical MEMS device (active corner cube retroreflector or CCR) for remote free space optical
communication. A flexible circuit design and a folded packaging scheme have been utilized to minimize the overall form
factor. Flat, flexible polymer batteries are incorporated to minimize the vertical profile to a few millimeters. The entire
fully packaged sensor system is about 30mmx30mmx6 mm. MEMS design of the CCR, fabrication, hermetic packaging
of CCR, flexible circuit design and fabrication, flip chip bonding of die form microprocessor, and a battery replacement
scheme for extended operation lifetime are crucial elements for the development of a real product for the microsensor
system. Optical MEMS CCR is a torsion mirror design and was fabricated using surface micromachining with Si<sub>3</sub>N<sub>4</sub> as a
structural layer. A finite element analysis (FEA) model was developed to optimize design and performance of the
MEMS structures. The sensor system has a miniature mechanical switch for local actuation and an optical switch for
remote actuation. The applications of such a microsensor system include both tracking, tagging, locating (TTL) and
This paper reports modeling, simulation, design and fabrication results for an uncooled MEMS capacitive thermal detector for IR focal plane array (FPA) imaging. Finite element analysis (FEA) was used to simulate the thermal and thermal-structural behaviors of the device. Sensitivity and thermal response time were simulated, as well as noise equivalent temperature difference (NETD).
The detector structure consists of a suspended IR absorption/capacitive plate (100μm×100μm) made of Si<sub>3</sub>N<sub>4</sub>/Pt. The first section of each supporting arm has a bilayer structure, which consists of a SiO<sub>2</sub> layer and a thick Al layer. The arm and the plate exhibit an out of plane movement due to a bilayer effect caused by temperature rise under IR radiation. This results in a capacitive sensing signal. The second section of each arm has a SiO<sub>2</sub> layer and a very thin Al layer to serve as thermal isolation, as well as an electrical connection for capacitive sensing signal.
A FEA parametric model was created and several key dimensions of the structure were simulated for better performance. Especially, the thicknesses of Al thermal isolation layer and bilayer were evaluated regarding sensitivity and thermal time constant. For a 0.8μm bilayer Al thickness and a 30nm isolation layer Al thickness, a simulated displacement sensitivity of 0.83nm/(pW⋅μm<sup>-2</sup>) was achieved. Subsequent NETD calculations predicted a temperature fluctuation NETD of 3.4mK, a background fluctuation NETD of 1.0mK, a thermal-mechanical NETD of 9.2mK, a capacitive readout NETD of 7.4mK, and a total NETD of 12.3mK, with a 18.6ms thermal time constant.
Following the design for the photomasks, fabrication processes were developed and the detectors were fabricated successfully.