Transistor heater for microhotplate-based metal-oxide microsensors

A transistor-type heater is presented, which has been developed to regulate the temperature of microhotplates in industrial CMOS technology. The heating transistor preserves its transistor characteristics up to 350/spl deg/C and shows almost linear heating characteristics at temperatures higher than 100/spl deg/C. The temperature can be controlled by adjusting the transistor source/gate voltage. Sensor measurements for CO are presented in two different sensing modes: chemoresistive readout and calorimetric readout by means of monitoring changes in the source/gate voltage which is required to keep the microhotplate temperature at the preset value. The device is part of an approach to monolithically integrate metal-oxide chemical sensors with circuitry.