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Open AccessArticle

A LN/Si-Based SAW Pressure Sensor

1
Carinthian Tech Research (CTR AG), Europastrasse 12, 9524 Villach, Austria
2
frec|n|sys, TEMIS Innovation, 18 Rue Alain Savary, 25000 Besançon, France
3
UNISENSOR AG, Bahnstrasse 12A, 8544 Attikon, Switzerland
*
Author to whom correspondence should be addressed.
Sensors 2018, 18(10), 3482; https://doi.org/10.3390/s18103482
Received: 20 September 2018 / Revised: 10 October 2018 / Accepted: 12 October 2018 / Published: 16 October 2018
(This article belongs to the Section Physical Sensors)
Surface Acoustic Wave (SAW) sensors are small, passive and wireless devices. We present here the latest results obtained in a project aimed at developing a SAW-based implantable pressure sensor, equipped with a well-defined, 30 μm-thick, 4.7 mm-in-diameter, Lithium Niobate (LN) membrane. A novel fabrication process was used to solve the issue of accurate membrane etching in LN. LN/Si wafers were fabricated first, using wafer-bonding techniques. Grinding/polishing operations followed, to reduce the LN thickness to 30 μm. 2.45 GHz SAW Reflective Delay-Lines (R-DL) were then deposited on LN, using a combination of e-beam and optical lithography. The R-DL was designed in such a way as to allow for easy temperature compensation. Eventually, the membranes were etched in Si. A dedicated set-up was implemented, to characterize the sensors versus pressure and temperature. The achieved pressure accuracy is satisfactory (±0.56 mbar). However, discontinuities in the response curve and residual temperature sensitivity were observed. Further experiments, modeling and simulations were used to analyze the observed phenomena. They were shown to arise essentially from the presence of growing thermo-mechanical strain and stress fields, generated in the bimorph-like LN/Si structure, when the temperature changes. In particular, buckling effects explain the discontinuities, observed around 43 °C, in the response curves. Possible solutions are suggested and discussed. View Full-Text
Keywords: SAW pressure sensor; multilayer substrate; thin LN membranes; LN/Si; wafer-bonding SAW pressure sensor; multilayer substrate; thin LN membranes; LN/Si; wafer-bonding
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Nicolay, P.; Chambon, H.; Bruckner, G.; Gruber, C.; Ballandras, S.; Courjon, E.; Stadler, M. A LN/Si-Based SAW Pressure Sensor. Sensors 2018, 18, 3482.

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