A Comparative Study of Si3N4 and Al2O3 as Dielectric Materials for Pre-Charged Collapse-Mode CMUTs
Marta Saccher (TU Delft - Electronic Components, Technology and Materials)
Rob van Schaijk (Philips)
Shinnosuke Kawasaki (TNO)
Johan H. Klootwijk (Philips)
A. Rashidi (TU Delft - Bio-Electronics)
V. Giagka (TU Delft - Bio-Electronics, Fraunhofer Institute for Reliability and Microintegration IZM)
Alessandro Stuart Savoia (University of Roma Tre)
R Dekker (TU Delft - Electronic Components, Technology and Materials, Philips)
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Abstract
Capacitive Micromachined Ultrasound Transducers (CMUTs) have many advantages compared to other ultrasonic transducer technologies, especially for implantable devices. However, they require a high bias voltage for efficient operation. To eliminate the need for an external bias voltage, a charge storage layer can be embedded in the dielectric. This study aims to compare the performance of Si 3 N 4 and Al 2 O 3 when used as a charge storage layer. By measuring the shift in the C-V curve, Si 3 N 4 exhibits a larger shift than Al 2 O 3 , indicating a better charge-trapping capability. When using the pre-charged CMUTs as power receivers, the Si 3 N 4 version harvested up to 80 mW -only a few mW more than the Al 2 O 3 - with an efficiency of about 50 %. Accelerated Lifetime Tests predict a lifetime of about 7.8 and 1.2 years for Si 3 N 4 and Al 2 O 3 respectively.