Integrated multi-function sensor for flow velocity, temperature and vacuum measurements

Abstract An integrated multifunction sensor based on heat transfer at a constant chip temperature (CCT) has been fabricated by a conventional CMOS process. It consists of a temperature-sensing stage for the measurement of the chip temperature, a CMOS operational amplifier for amplification and control, and a heating branch circuit to heat the sensor chip. All three parts are integrated on one chip and connected to form a negative feedback loop for CCT operation. Using this sensor, measurements of flow velocity, temperature and vacuum have been made. The heating power of the chip is used to indicate those measurands that affect the heat transfer between the chip and the ambient. When used for flow measurements, the sensor demonstrates high sensitivity and a large output level (500 mV output at V f =50 cm/s, N 2 , and T c  T a =15°C). It can be used to measure both gas and liquid flor velocities. The sensor shows a sensitivity of −64 mV/°C when used for temperature measurements and it has the advantage of much easier design of on-chip signal processing circuits over conventional temperature sensors since the chip temperature is kept constant. When used as a vacuum sensor, experiments show that the vacuum range from atmospheric pressure to 10 −1 Torr produces an output change of about 300 mV. Lower pressures can also be measured without any problems.