PZT acoustic wave force sensor made in LTCC technology

In the paper technology and properties of the simple acoustic wave force sensor are presented. The sensor consists of LTCC (Low Temperature Co-fired Ceramic) cantilever with an active layer made of PZT (Lead Zirconate Titanate) tape with two IDTs (Inter-Digital Transducers). The cantilever dimensions of test samples are set to 25×8×0.5 mm³. The interdigital electrodes with designed line/space width of 125/125 μπι are made using screen printing technique. The distance between centers of IDTs is equal to 10 mm. Two configurations of cantilever fixture are manufactured and tested. One is completely made of LTCC and the other of FR4 laminate. In case of the LTCC fixture with rigid glass bond between beam and support there is impossible to make any measurements because of very high attenuation of the signal. In case of the FR4 laminate and epoxy glue joints the attenuation is at acceptable level and it´s possible to record transition spectrum of the device. For prepared samples, the minimum attenuation of the signal is observed at frequency of about 15 MHz and differs for various samples. The impact of force applied to free end of the cantilever beam as well as temperature on acoustic wave frequency is measured. The IDTs are mechanically coupled through the ceramic beam, hence the frequency shift is observed due to beam bending. Determined force sensitivity and temperature coefficient of frequency are equal to -11 kHz/N ±1 kHz/N and -110 ppm/K ±10 ppm/K, respectively.