This paper presents a 0.5mm × 0.5mm tiny-sized high-temperature piezoresistive pressure sensor fabricated with a TUB (thin-film under bulk) single-sided micromachining process from the front-side of single-layer (111) SOI wafer. The (111)-device layer of the SOI wafer is specifically selected to optimize the piezoresistor performance where the SiO2 buried layer isolates the piezoresistors from the handle substrate. And the (111)-handle layer is employed to subtly construct a single-crystalline-silicon beam-island combining with a very thin but uniform poly-silicon diaphragm for realization of both low nonlinearity and high sensitivity. Without double-sided micromachining process and wafer bonding used, a tiny sensor-chip size of 0.5mm × 0.5mm is achieved, which is required in wind-tunnel systems for measuring pressure distribution at high temperature. The testing results of the fabricated sensor show high sensitivity of 0.15mV/V/kPa for 150-kPa measure range and satisfactory linearity of ±0.11%FS at ambient temperature. At 350℃, the overal accuracy is 0.17%·FS and the thermal hysteresis is 0.22%·FS. The TCO (temperature coefficient of zero-point offset) of the sensor is tested as low as 0.01%/℃·FS and the TCS (temperature coefficient of sensitivity) is -0.07%/℃·FS within the whole temperature range from -55℃ to 350℃. Featuring the advantages of high accuracy and high-yield low-cost fabrication, the tiny-sized high-temperature pressure sensors exhibit promising perspective in the field of aerospace industry including wind-tunnel application.
A silicon-chip-based 3D metal solenoidal transformer is proposed and developed to achieve AC-DC conversion for integrated power supply applications. With wafer-level micro electromechanical systems (MEMS) fabrication technique to form the metal casting mold and the following micro-casting technique to rapidly (within 6 minutes) fill molten ZnAl alloy into the pre-micromachined silicon mold, 45-turns primary solenoid and 7-turns secondary solenoid are fabricated in silicon wafers, where the two intertwining solenoids are located at inner deck and outer deck, respectively. Permalloy soft magnetic core is inserted into a pre-etched channel in the silicon chip, which is surrounded by the solenoids. The size of the chip-style transformer is as small as 8.5 mm × 6.6 mm × 2.5 mm. The internal resistance of the primary solenoid is 1.82 Ω and that of the secondary solenoid is 0.16 Ω. The working frequency of the transformer is 60 kHz. Combined with the testing circuit of the switch mode power supply, the DC voltage of 13.02 V is obtained when the input is 110 V at 50 Hz/60 Hz. Furthermore, the on-chip 3D solenoidal transformer is used for lighting four LEDs, which shows great potential for AC-DC power supply. The wafer-level fabricated chip-style solenoidal AC-DC transformer for integrated power supply is advantageous in uniform fabrication, small size and volume applications.
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