Thin Film PZT-Based PMUT Arrays for Deterministic Particle Manipulation

Abstract

Lead zirconate titanate (PZT) based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized and tested. The PMUTs had a diaphragm diameter of 60 µm, a resonant frequency of ~ 8 MHz and an operational bandwidth of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 Vpp. The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 µm silica beads was shown to be possible with 5 Vpp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move towards diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational bandwidth. Levitation planes were generated above 30 MHz driving frequency.

Improving PMUT Receive Sensitivity via DC Bias and Piezoelectric Composition

“…The bottom electrode was deposited by sputtering 30 nm of Ti, annealing it at 700 °C for 15 min with 10 sccm of oxygen flow, and then sputtering 100 nm of Pt at a substrate temperature of 500 °C [ 14 ]. To facilitate orientation of the piezoelectric film, a PZT seed layer (Mitsubishi Materials Corporation, Hyogo, Japan) was spun, pyrolyzed, and crystallized, as described elsewhere [ 10 , 15 , 16 , 17 ]. For the MPB composition, 14 mol% lead excess Pb(Zr 0.52 Ti 0.48 )O 3 solution doped with 2% Nb (Mitsubishi Materials Corporation, Hyogo, Japan) was spun on at 2750 RPM for 45 s. The film was pyrolyzed at 100 °C for 1 min and 300 °C for 4 min, followed by crystallization in a lead-rich rapid thermal annealer for 1 min at 700 °C.…”

“…The design, fabrication process, and characterization for circular 6–8 MHz PMUTs are described elsewhere [ 10 , 17 ]. The PMUTs were wire-bonded to a pin grid array (PGA) or a circuit board and coated with 2 µm of parylene for waterproofing.…”

“…When large electrical fields are applied to a ferroelectric, such as PZT, the permittivity decreases below the zero field value due to reduced intrinsic and extrinsic contributions to the permittivity [ 7 ]. Moreover, the piezoelectric coefficient may also increase with large DC electric fields, as domains more readily remain aligned with the applied electric field [ 8 , 9 , 10 , 11 ]. Thus, if a DC electric field is applied while the PMUT functions as a receiver, the receive sensitivity should be higher than at zero applied bias.…”

Investigation of Achieving Ultrasonic Haptic Feedback Using Piezoelectric Micromachined Ultrasonic Transducer

“…The small size and low driving voltage make it easy to integrate into wearable devices and low acoustic impedance mismatching makes higher frequency applications (>250 kHz) possible, which leads to better resolutions. Several applications of pMUT, such as levitation, photoacoustic imaging, and particle manipulation, have been developed with different fabrication approaches and achieved promising results [7][8][9][10].…”

10 MHz Thin-Film PZT-Based Flexible PMUT Array: Finite Element Design and Characterization

“…Nakazawa et al [ 5 ] fabricated eight-element, 200 µm pitch and 32-element, 20-µm pitch, 1D arrays based on a polyurea film, and experimentally measured the resonance frequencies at 30 MHz, 65 MHz, and 100 MHz. Cheng et al [ 6 ] reported a 2D PMUT array consisting of 20 diaphragms, with each diaphragm having 60 µm diameter, and showed its resonance frequency at 8 MHz with 62.5% bandwidth. 9.5 kPa of acoustic pressure was measured by a hydrophone (HGL-0085, Onda, Inc,.)…”