A CMOS smart temperature and humidity sensor with combined readout

Clemens Eder, Virgilio Valente, Nick Donaldson, Andreas Demosthenous

Research output: Contribution to journalArticleScientificpeer-review

13 Citations (Scopus)


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 mm2or 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.

Original languageEnglish
Pages (from-to)17192-17211
Number of pages20
JournalSensors (Switzerland)
Issue number9
Publication statusPublished - 16 Sep 2014
Externally publishedYes


  • Capacitive sensor
  • Humidity measurement
  • Microelectronic implants
  • On-chip sensor
  • Oscillator
  • Temperature sensor

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