title: A CMOS smart temperature and humidity sensor with combined readout.
abstract: 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%/°C 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 mm2 or 1.2 mm2 were fabricated in a commercial 0.18 μm CMOS process. The on-chip readout electronics operate from a 5 V power supply and consume a current of approximately 85 µA.
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK. c.eder@ucl.ac.uk.
authors.forename: Clemens
authors.initials: C
authors.lastname: Eder
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK. v.valente@ucl.ac.uk.
authors.forename: Virgilio
authors.initials: V
authors.lastname: Valente
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, Malet Place, WC1E 6BT, UK. n.donaldson@ucl.ac.uk.
authors.forename: Nick
authors.initials: N
authors.lastname: Donaldson
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK. a.demosthenous@ucl.ac.uk.
authors.forename: Andreas
authors.initials: A
authors.lastname: Demosthenous
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D006813:Humidity; D019064:Product Packaging / Q000145:classification*; D012666:Semiconductors; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D018511:Systems Integration; D013696:Temperature; D013817:Thermography / Q000295:instrumentation*; D014159:Transducers; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water