%0 Journal Article
%T A CMOS Smart Temperature and Humidity Sensor with Combined Readout
%A Clemens Eder
%A Virgilio Valente
%A Nick Donaldson
%A Andreas Demosthenous
%J Sensors
%P 17192-17211
%D 2014
%I MDPI AG
%R 10.3390/s140917192
%X A fully-integrated complementary metal-oxide semiconductor (CMOS) sensor for combined temperature and humidity measurements is presented. The main purpose of the device is to monitor the hermeticity of micro-packages for implanted integrated circuits and to ensure their safe operation by monitoring the operating temperature and humidity on-chip. The smart sensor has two modes of operation, in which either the temperature or humidity is converted into a digital code representing a frequency ratio between two oscillators. This ratio is determined by the ratios of the timing capacitances and bias currents in both oscillators. The reference oscillator is biased by a current whose temperature dependency is complementary to the proportional to absolute temperature (PTAT) current. For the temperature measurement, this results in an exceptional normalized sensitivity of about 0.77%/¡ãC at the accepted expense of reduced linearity. The humidity sensor is a capacitor, whose value varies linearly with relative humidity (RH) with a normalized sensitivity of 0.055%/% RH. For comparison, two versions of the humidity sensor with an area of either 0.2 mm 2 or 1.2 mm 2 were fabricated in a commercial 0.18 ¦Ìm CMOS process. The on-chip readout electronics operate from a 5 V power supply and consume a current of approximately 85 ¦ÌA.
%K capacitive sensor
%K humidity measurement
%K microelectronic implants
%K oscillator
%K on-chip sensor
%K temperature sensor
%U http://www.mdpi.com/1424-8220/14/9/17192