Public defence in Micro- and nanosciences, M.Sc.(Tech.) Tapio Pernu

The title of the thesis: High Sensitivity MEMS Sensors for Air Flow Measurement

Thesis defender: Tapio Pernu
Opponent: Prof. Matti Mäntysalo, Tampere University, Finland
Custos: Prof. Ilkka Tittonen, Aalto University School of Electrical Engineering

This doctoral thesis has developed new microelectromechanical (MEMS) sensors for measuring extremely low gas flow and differential pressures. The research focuses on three innovative sensor types: a capacitive differential pressure sensor, a piezoelectric micromachined ultrasonic transducer (pMUT), and a capacitive micromachined ultrasonic transducer (cMUT). These sensors are needed, for example, in building ventilation, medical devices, and industrial processes.

The aim of the research was to develop highly sensitive and temperature-stable sensors that enable accurate measurement without expensive factory calibration. Traditional differential pressure sensors and thermal mass flow meters often require factory calibration and are sensitive to changes in environmental conditions.

The solutions of the thesis are at the forefront of MEMS sensor development, especially in applications for small pressures and flows. The developed capacitive differential pressure sensor achieves a measurement error of ±0.85% in the pressure range 0–500 Pa and temperature range 0–50 °C without temperature calibration or compensation. The pMUT-based flow sensor measures extremely low flow rates (±50 sccm) with an accuracy of 0.2% at room temperature, and the cMUT-based sensor achieves 1.1% accuracy in the 0–50 °C temperature range. In addition, a new real-time frequency matching circuit was introduced in the cMUT sensor, which reduces temperature-induced zero-flow drift.

The research provides new knowledge on the applicability of MEMS ultrasonic technology for measuring extremely low flow rates, as well as on improving the temperature stability of differential pressure sensors used in flow measurement. The new solutions enable more cost-effective and reliable sensors, for example, for building ventilation, medical devices, and industrial control.

Based on the results, MEMS ultrasonic technology and capacitive differential pressure sensors offer significant advantages compared to traditional technologies: they are accurate, temperature-stable, and have great potential to eliminate the need for factory calibration.
16. Avainsanoja suomeksi/ruotsiksi

Key words: MEMS, differential pressure sensor, cMUT, pMUT, ultrasound, air flow sensor

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact: tapio.pernu@snowbyte.fi