Abstract
In this paper, we describe the design and characterization of a CMOS micromachined suspended structure with a PMOS transistor operated in the subthreshold region for thermal sensing. The sensor has an area of 70 νm by 70 νm and the sensing transistor is placed inside a suspended plate of 50 νm by 50 νm. The device is fabricated by successive dry etching steps on a CMOS die. For device characterization, each sensor has an embedded polysilicon heater capable of providing a heating efficiency of 0.84 °C mW -1 . The measured MOS output resistance changes from 108.3 MΩ to 90.4 MΩ for a temperature rise of 5.5 °C, which is equivalent to a measured temperature coefficient of resistance -3% °C -1 , much better than the value of transistors operated in saturation. The measured input-referred noise voltage from the pre-amp is 7 νV Hz -1/2 , equivalent to an input-referred noise temperature of 14.9 mK Hz -1/2 . © 2006 IOP Publishing Ltd.