CMOS-Compatible Carbon Dioxide Sensors
This chapter presents two cost-effective sensors that measure ambient carbon dioxide (CO2) concentration, intended for application in smart ventilation systems in buildings or in mobile devices. Both sensors employ a suspended hot-wire transducer to detect the CO2-dependent thermal conductivity (TC) of the ambient air. The resistive transducer is realized in the VIA layer of a standard CMOS process using a single etch step. The first sensor determines the transducer’s CO2-dependent thermal resistance to the surrounding air by measuring its steady-state temperature rise and power dissipation. A ratiometric measurement is realized by employing an identical but capped transducer as a reference. An incremental delta-sigma ADC digitizes the temperature and power ratios of the transducers, from which the ratio of the thermal resistances is calculated. The second sensor is based on a transient measurement of the CO2-dependent thermal time constant of the transducer. The readout circuit periodically heats up the transducer and uses a phase-domain delta-sigma modulator to digitize the CO2-dependent phase shift of the resulting temperature transients. Compared to the ratiometric steady-state measurement, this approach significantly reduces the measurement time and improves the energy efficiency, resulting in a state-of-the-art CO2 resolution of 94 ppm at an energy consumption of 12 mJ per measurement.
This work was in part supported by NXP Semiconductors, The Netherlands, and in part by ams AG, The Netherlands. The authors want to thank Lukasz Pakula and Zu-yao Chang for their technical support.
- 1.Emmerich SJ, Persily AK. Literature review on CO2-based demand-controlled ventilation. ASHRAE Trans. 1997;103:229–43.Google Scholar
- 2.SenseAir K30 datasheet, SenseAir [Online]. Available: http://www.senseair.com/.
- 3.SGX Sensortech IR11BD datasheet, SGX Sensortech [Online]. Available: http://www.sgxsensortech.com/.
- 7.Kliche K, et al. Sensor for gas analysis based on thermal conductivity, specific heat capacity and thermal diffusivity. In: Proceedings of IEEE international conference on MEMS. 2011 p. 1189–92.Google Scholar
- 8.XEN-5310 datasheet. Xensor Integration [Online]. Available: http://www.xensor.nl/.
- 12.Cai Z, et al. An integrated carbon dioxide sensor based on ratiometric thermal-conductivity measurement. In: Proceedings of IEEE international conference on solid-state sensors, actuators and microsystems (Transducers ’15). 2015. p. 622–5.Google Scholar
- 15.FIGARO TGS8100 datasheet (rev06), FIGARO [Online]. Available: http://www.figaro.co.jp/.
- 17.van Vroonhoven C, de Graaf G, Makinwa KAA. Phase readout of thermal conductivity-based gas sensors. In: Proceedings of IEEE International Workshop on Advances in Sensors and Interfaces (IWASI). 2011. p. 199–202.Google Scholar
- 18.van Vroonhoven CPL, Makinwa KAA. A thermal-diffusivity-based temperature sensor with an untrimmed inaccuracy of ±0.5°C (3σ) from –40 to 105°C. In: Digest ISSCC. 2008. p. 576–7.Google Scholar