Thermistor-like pn diode temperature-sensor and a new method to measure the absolute humidity using these temperature-sensors combined with a microheater

摘要

We have developed a temperature-sensor of pn junction diode and a microheater combined with this temperature-sensor. This pn junction diode temperature sensor can cover very wide temperature-range of about -200 /spl deg/C to 500 /spl deg/C with very high sensitivity and accuracy like a NTC thermistor. We have also developed a new absolute humidity sensor using this pn diode temperature sensor combined with a microheater formed by MEMS technique. We have found from simulation of the thermal conductivity /spl lambda/ of humid air at different temperatures that thermal conductivity difference /spl Delta/ /spl lambda/ at different humid-air temperatures has a linear dependence on molar fraction of H/sub 2/O vapor. /spl Delta/ /spl lambda/ is determined from experimental data on temperatures Ta, Tb and Tc at point A (microheater point) and B (displaced point from A) on the micro-air-bridge, and at humid air, respectively. In the measurement Ta on the micro-air-bridge is periodically kept at T/sub h/ and T/sub i/ above Tc by feedback control.