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Optimization of electrode size for aluminum-nitride matrix ultrasonic transducers in the frequency range above 200 MHz

: Wei, Y.; Herzog, T.; Heuer, H.


Ultrasonics 53 (2013), Nr.3, S.739-744
ISSN: 0041-624X
Fraunhofer IZFP, Institutsteil Dresden ( IKTS-MD) ()

This paper describes an optimization method of the top electrode size for a thin film matrix ultrasonic transducer (M-UT) in the frequency range above 200 MHz. The goal of this work is to design an optimal top electrode size for an M-UT providing the maximal output peak-peak voltage (V-PP) and the maximal signal-to-noise ratio (SNR) without additional electrical impedance matching. In order to reduce the complexity of the M-UT with more than 1000 elements, an intrinsic matching by electrode size variation is necessary. However, the size of a single element top electrode for an M-UT is related to the number of elements within a targeted sensor area, V-PP and SNR of the transducer. In this paper, varying the active area of the top electrode from 0.09 to 25 mm(2) shows that for an Al-AlN-Al on silicon wafer configuration connected with a JSR Ultrasonics pulser/receiver (50 ohms), the optimal electrode size is 1 mm2. With the optimal size electrode, the maximum output V-PP of 0.08 V and the SNR of 42.93 dB are achieved at the resonance frequency of 225 MHz, and the bandwidth is 16.21 MHz.