https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Recent developments on the preparation and application of ZnO films for acoustic wave-based microfluidics and biosensors are reviewed in this paper. High quality and strongly textured ZnO thin films can be prepared using many technologies, among which RF magnetron sputtering is most commonly used. This paper reviews the deposition of ZnO film and summarizes the factors influencing the microstructure, texture and piezoelectric properties of deposited ZnO films. ZnO acoustic wave devices can be successfully used as biosensors, based on the biomolecule recognition using highly sensitive shear horizontal and Love-wave surface acoustic waves, as well as film bulk acoustic resonator devices. The acoustic wave generated on the ZnO acoustic devices can induce significant acoustic streaming, small scale fluid mixing, pumping, ejection and atomization, depending on the wave mode, amplitude and surface condition. The potential to fabricate an integrated lab-on-a-chip diagnostic system based on these ZnO acoustic wave technologies is also discussed.

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Recent developments on ZnO films for acoustic wave based bio-sensing and microfluidic applications: a review

Piezoelectric materials play a crucial role in a large number of devices and applications modern society would not like to miss. Mobile phones and ultrasonic imaging are just the most prominent ones. Since two decades, miniaturization of mechanical devices in silicon technology is a major research direction in engineering known under name of MEMS, which stands for micro-electro-mechanical systems. Piezoelectricity fits very well into this concept and was expected right from the beginning to play its role in MEMS. The breakthrough was made with RF filters in mobile phones working on the principle of standing thickness waves in AlN films. What counts here is acoustic quality and stability. The force champion among piezoelectric thin film materials, Pb(Zr,Ti)O3 gave more problems in processing, and requires more patience to meet requirements and needs for a mass applications. It seems, however, that the breakthrough is imminent. This article attempts to give an overview of the field, highlighting recent achievements, introduce operation principles, and describe some applications.

Recent Progress in Materials Issues for Piezoelectric MEMS

Acoustic wave based MEMS devices for biosensing applications

Thin film bulk acoustic resonators (FBARs) operating in shear mode have been investigated for biosensing applications. Dynamic measurements in liquid were carried out and the adsorption of an antibody–antigen system was observed. Although this is the very first FBAR biosensor system operating in liquid environment it was found that the sensor performance ruled by the smallest detectable mass attachment, is already better (2.3 ng/cm 2 ) than that of QCMs. The ability of easy integration onto wafers together with readout-circuitry as well as the possibility of making up large arrays comprising pixels with different functionalities make these devices interesting for future acoustic biosensors.

Shear mode FBARs as highly sensitive liquid biosensors

Solidly mounted film bulk acoustic resonators (FBAR) operating at 850 MHz in the shear vibration mode have been fabricated. C-axis inclined zinc oxide (ZnO) thin films realized by modified reactive magnetron sputtering were used. Coupling factors k/sup 2/ of 1.7% and Q-factors of 312 were determined in air. Q-factors of 192 were measured in water, making these devices attractive for sensing applications in liquids, e.g., biosensing.

Solidly mounted ZnO shear mode film bulk acoustic resonators for sensing applications in liquids

Film bulk acoustic resonators (FBAR) vibrating in shear mode and operating at around 830 MHz have been fabricated. They were tested in air and water–glycerol solutions. With a sensitivity of 1 kHz cm2/ng, these devices are attractive for gravimetric sensing applications. The FBARs are solidly mounted on acoustic mirrors and use 16° c-axis inclined ZnO thin films realized by reactive sputtering. An analysis of the performance in liquids with different viscosities has been done and the effect on quality factor and resonance frequency has been shown. Effective coupling coefficients K eff 2 of up to 1.7% and quality factors of up to 380 and 199 were determined in air and deionized water, respectively. The obtained characteristics are sufficient for gravimetric sensing applications in liquid environments and the FBARs can be used as high frequency viscosity sensors for liquids of viscosities up to 10 mPa s.

Sensing characteristics of high-frequency shear mode resonators in glycerol solutions

This article reports on the growth and characterization of polycrystalline ZnO films having c axis inclined up to 16° with respect to the substrate normal. These films allow the excitation of shear and longitudinal waves with comparable electromechanical coupling constants and are of significant interest for thin film bulk acoustic resonators (FBARs). The films are deposited on silicon substrates covered by Al2O3 and SiO2 buffer layers under low pressure using a modified reactive dc-pulsed magnetron sputtering system. A blind has been positioned between target and substrate, allowing oblique particle incidence without tilting the wafer. The study of structural properties of the deposited ZnO films by x-ray diffraction and scanning electron microscopy has permitted to show the presence of the inclined structure. Electromechanical coupling constants K up to 13% have been extracted for shear-mode excitation using highly overmoded FBARs.

c-axis inclined ZnO films for shear-wave transducers deposited by reactive sputtering using an additional blind

An apparatus having a device for moving a liquid comprises a piezoacoustic resonator element (11) having at least one piezoelectric layer (110) and two electrodes (111 and 112) present on the piezoelectric layer (110). The piezoacoustic resonator element (11) is designed such that, owing to a voltage being applied to the piezoelectric layer (110) by means of the electrodes (111 or 112), a volume oscillation of the piezoelectric layer (110) is excited at a resonant frequency. The piezoelectric resonator element (11) can be acoustically coupled in a suitable manner to a liquid for the purpose of transmitting the excited oscillation into the liquid for the purpose of moving the liquid. The apparatus may be in the form of a micromixer or in the form of a micropump and may comprise, in addition, sensor elements (41) for detecting the attachment of substance.

Mathias Link

Papers

Shear mode FBARs as highly sensitive liquid biosensors

Solidly mounted ZnO shear mode film bulk acoustic resonators for sensing applications in liquids

Sensing characteristics of high-frequency shear mode resonators in glycerol solutions

c-axis inclined ZnO films for shear-wave transducers deposited by reactive sputtering using an additional blind

Apparatus and Method For Moving a Liquid by Means of a Piezoelectric Transducer