Piezoelectric Micro Ultrasonic Transducer (PMUT) For Underwater Sonar Applications
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Date
2013-07
Authors
Yaacob, Mohd Ikhwan Hadi
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Typical piezoelectric micro ultrasonic transducer (pMUT) yields resonance in the very
high frequency (VHF) range, due to its thin membrane structure. Thin piezoelectric
film utilized in pMUT has reduced its receiving sensitivity and require thick
encapsulation layer to avoid damage to the membrane. Development of pMUT
specifically for underwater usage was described in this thesis. Main objective for this
study is to tune the pMUT resonance into the medium frequency (MF) range while
improving the sensitivities. This was achieved by simulating the pMUT with water
loading, utilizing CuAl10Fe4 also known as “sea bronze” alloy film as part of the
vibrating membrane and simplifying the fabrication process through polymer adhesive
wafer bonding method. Design process started with benchmarking six existing
pMUT’s architectures from various researchers. From that, total of ten pMUT designs
were proposed and analyzed using finite element modeling (FEM), with different
shapes, dimensions and materials. FEM and device’s simulation was carried out using
CoventorWare software. From the simulation, pMUT design using lead-zirconatetitanate
(PZT) with “sea bronze” film coating on Polydimethyl-Siloxane (PDMS)
membrane at 2 mm diameter and 142.3 μm of thickness was found to carry resonance
between 85.9 - 101.0 kHz. This design was then fabricated. Total of four prototypes
have been fabricated using PZT-5A and PZT-5H ceramics with and without “sea
bronze” alloy coating. Key fabrication methods include the sputtering of “sea bronze”
alloy and SiO2 as well as the spin-coating of PDMS. At the sputtering yield of 5.9732
W/cm2, deposition rate for sea bronze alloy was discovered at 16.667 nm per minute.
Extensive energy dispersive x-ray (EDX) and atomic force microscopy (AFM)
analyses were carried out on the deposited alloy to determine its composition change
and the surface roughness respectively. Finally, pMUT chips was adhered on the
printed circuit board (PCB) and sealed using epoxy. An equivalent circuit for each
pMUT including all circuit parameters was determined according to the BVD
approximation and curve fittings via impedance analysis. Throughout the fabrication
phase, material layer thickness was measured using cross sectional SEM. In the final
stage of device’s implementation, all fabricated pMUTs have undergone underwater
calibration and characterization. Underwater calibration data revealed that the pMUT
with CuAl10Fe4 coating on PZT ceramics have shown 50-100 kHz decrement in
resonant frequency compared to the original PZT, with positive gain in sensitivity
between 0.65-5.09 dB.
Description
Keywords
Piezoelectric micro ultrasonic transducer , for underwater sonar applications