In this work, the dielectric properties of porous Si for its use as a local substrate material for the integration on the Si wafer of millimeter-wave devices were investigated in the frequency range 140 to 210 GHz. Broadband electrical characterization of coplanar waveguide transmission lines (CPW TLines), formed on the porous Si layer, was used in this respect. It was shown that the dielectric parameters of porous Si (dielectric permittivity and loss tangent) in the above frequency range have values similar to those obtained at lower frequencies (1 to 40 GHz). More specifically, for the samples used, the obtained values were approximately 3.12 ± 0.05 and 0.023 ± 0.005, respectively. Finally, a comparison was made between the performance of the CPW TLines on a 150-μm-thick porous Si layer and on three other radiofrequency (RF) substrates, namely, on trap-rich high-resistivity Si (trap-rich HR Si), on a standard complementary metal-oxide-semiconductor (CMOS) Si wafer (p-type, resistivity 1 to 10 Ω.cm) and on quartz.PACS84.40.-x; 77.22.Ch; 81.05.Rm
An air flow meter for measuring the intake air of an automobile engine is presented. It is based on a miniaturized silicon thermal mass flow sensor using a thick porous Si (Po-Si) layer for local thermal isolation from the Si substrate, on which the sensor active elements are integrated. The sensor is mounted on one side of a printed circuit board (PCB), on the other side of which the readout and control electronics of the meter are mounted. The PCB is fixed on a housing containing a semi-cylindrical flow tube, in the middle of which the sensor is situated. An important advantage of the present air flow meter is that it detects with equal sensitivity both forward and reverse flows. Two prototypes were fabricated, a laboratory prototype for flow calibration using mass flow controllers and a final demonstrator with the housing mounted in an automobile engine inlet tube. The final demonstrator was tested in real life conditions in the engine inlet tube of a truck. It shows an almost linear response in a large flow range between –6,500 kg/h and +6,500 kg/h, which is an order of magnitude larger than the ones usually encountered in an automobile engine.
The increasing need for miniaturization, reliability, and cost efficiency in modern telecommunications has boosted the idea of system-on-chip integration, incorporating the RF front-end circuitry and the passive elements such as RF transmission lines, inductors, antennas, and filters. However, the performance of the passive elements of these circuits is highly degraded when integrated on standard CMOS Si, due to its low resistivity. Porous silicon (PSi) has emerged as a promising local substrate material for the on-chip monolithic integration of high performance passive RF and mm-wave devices, because it combines high resistivity and low permittivity along with CMOS compatibility. This review paper aims at summarizing the obtained results so far in the above area, including transmission lines, inductors, filters, and miniaturized antennas, monolithically integrated on porous Si in a CMOS-compatible environment. In this respect, we first present the requirements for a low-loss, CMOS-compatible RF substrates and we then argue on how PSi fulfills the set requirements. Then, we present the methods used so far to extract the dielectric properties of PSi, which are necessary inputs for designing RF devices. The performance of different passive RF devices such as coplanar waveguides, inductors, filters, and antennas on the local porous Si substrate is then reviewed and compared with the performance of other state-of-the-art RF passive devices based on different technologies. Finally, we discuss the progress made so far towards the industrialization of PSi local RF substrate technology and the challenges that are currently faced towards this objective.
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