A glass/silicon technology for low-power robust gas sensors

Semiconductor gas sensors are devices based on metallic oxides that operate at high temperatures for achieving good sensitivities to the gases of interest. Silicon micromachined structures are often used as platforms for obtaining both high temperatures and low-power consumption at the same time. In this paper, a microstructure based on the combination of micromachined silicon substrates and glass wafers is presented. The device incorporates an array of four different thin-film gas sensors that, depending on the design, can operate at the same or at different temperatures. The designs have been optimized by the finite element method (FEM) and the geometrical parameters of the structure have been selected in order to reduce the power consumption. The full process fabrication is presented. It is based on the combination of bulk micromachining, glass structuring, anodic bonding, and sensitive material deposition. Electrical, thermal, and mechanical tests have been done to demonstrate that the devices show high robustness and can reach high temperatures with low-power consumption.     

New thermoelectric components using microsystem technologies

This paper describes the first thermoelectric devices based on the V-VI-compounds Bi/sub 2/Te/sub 3/ and (Bi,Sb)/sub 2/Te/sub 3/ which can be manufactured by means of regular thin film technology in combination with microsystem technology. Fabrication concept, material deposition for some 10-/spl mu/m-thick layers and the properties of the deposited thermoelectric materials will be reported. First device properties for Peltier-coolers and thermogenerators will be shown as well as investigations on long term and cycling stability. Data on metal/semiconductor contact resistance were extracted form device data. Device characteristics like response time for a Peltier-cooler and power output for a thermogenerator will be compared to commercial devices.     

Preparation, morphology, and gas-sensing behavior of Cr/sub 2-x/Ti/sub x/O/sub 3+z/ thin films on standard silicon wafers

The effect of humidity on chromium titanium oxide (Cr/sub 2-x/Ti/sub x/O/sub 3+z/, CTO), on both baseline resistance and sensitivity, is small compared to SnO/sub 2/. This has been the key to development of thick-film sensors based on CTO, for detection of carbon monoxide and ammonia in synthetic air. Thin-film structures on silicon substrates offer the possibility to use fabricating, bonding and housing equipment and, hence, a low cost gas sensor production is possible. CTO thin-film sensors on silicon substrates use conventional photolithography, sputtering and evaporation techniques. A Ta/Pt resistance layer (25/200-nm thick) for heating the device to its operating temperature and interdigital electrodes are evaporated and structured on a silicon substrate which is covered by a 1-/spl mu/m SiO/sub 2/ insulating layer. The polycrystalline p-type CTO is deposited onto the electrodes by oxidizing reactive sputtering or evaporation of Cr/Ti-sandwich structures. The resulting sensors were characterized by means of energy dispersive X-ray analysis, secondary electron microscopy, and X-ray diffraction pattern. Also, gas responses toward NO/sub 2/, NH/sub 3/, CO and CH/sub 4/, and different humidity, were investigated.     

Observation of higher subband emission from PbSe two-dimensionallayers

Energy relaxation of an optically excited two-dimensional electron-hole gas has been investigated in PbSe as an example for dimensional quantization in a semiconductor with nearly symmetric valence and conduction band extrema. As compared with bulk-like reference samples the interband emission exhibits broadening and splitting into up to 5 clearly resolved lines. A systematic variation of the spectra with excitation density was observed: With increasing pump intensity the width of the total spectrum and the number of subbands increase due to both carrier heating and band filling. The emission bands are attributed to transitions between conduction and valence subbands with equal quantum number. Above a threshold well pronounced for each subband transition, the emission becomes stimulated. That indicates a potential for laser applications     

Embossed-grating lead chalcogenide buried-waveguidedistributed-feedback lasers

The successful preparation and mode behavior analysis of buried double-heterostructure distributed-feedback (DFB) PbEuSe lasers using an embossing technique for the DFB submicrometer grating is reported here for the first time. The submicrometer grating was embossed with a silicon master grating. By our analysis of the mode spectra using a transfer matrix method, it was possible to distinguish precisely different positions of the laser facets due to the accidental cleaving relatively to the submicrometer grating