Carinthian Tech Research (CTR AG), Europastrasse 12, 9524 Villach, Austria.
frec|n|sys, TEMIS Innovation, 18 Rue Alain Savary, 25000 Besançon, France.
Sensors (Basel). 2018 Oct 16;18(10):3482. doi: 10.3390/s18103482.
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.
表面声波（SAW）传感器是小型、无源和无线设备。我们在此介绍一个旨在开发基于 SAW 的植入式压力传感器的项目中获得的最新结果，该传感器配备了具有明确定义的 30μm 厚、4.7mm 直径的铌酸锂（LN）膜。使用一种新颖的制造工艺来解决 LN 中精确膜蚀刻的问题。首先使用晶圆键合技术制造 LN/Si 晶圆。然后进行研磨/抛光操作，将 LN 厚度减小到 30μm。然后使用电子束和光刻技术在 LN 上沉积 2.45GHz 的 SAW 反射延迟线（R-DL）。R-DL 的设计方式便于进行温度补偿。最终在 Si 中蚀刻膜。实施了专用的设置来对传感器进行压力和温度特性的表征。所达到的压力精度令人满意（±0.56mbar）。然而，观察到响应曲线的不连续性和残余温度灵敏度。进一步的实验、建模和模拟用于分析观察到的现象。结果表明，这些现象主要是由温度变化时在双晶-like LN/Si 结构中产生的热机械应变和应力场引起的。特别是，在响应曲线中观察到的 43°C 左右的不连续性可以用屈曲效应来解释。提出并讨论了可能的解决方案。
