Discrete microfluidics based on aluminum nitride surface acoustic wave devices

Abstract

To date, most surface acoustic wave (SAW) devices have been made from bulk piezoelectric materials, such as quartz, lithium niobate or lithium tantalite. These bulk materials are brittle, less easily integrated with electronics for control and signal processing, and difficult to realize multiple wave modes or apply complex electrode designs. Using thin film SAWs makes it convenient to integrate microelectronics and multiple sensing or microfluidics techniques into a lab-on-a-chip with low cost and multi-functions on various substrates (silicon, glass or polymer). In the work, aluminum nitride (AlN)-based SAW devices were fabricated and characterized for discrete microfluidic (or droplet based) applications. AlN films with a highly c-axis texture were deposited on silicon substrates using a magnetron sputtering system. The fabricated AlN/ Si SAW devices had a Rayleigh wave mode at a frequency of 80.3 MHz (with an electromechanical coupling coefficient k 2 of 0.24 % and phase velocity v p of 5,139 m/s) and a higher-frequency-guided wave mode at 157.3 MHz (with a k 2 value of 0.22 % and v p of 10,067 m/s). Both modes present a large out of band rejection of *15 dB and were successfully applied for microfluidic manipulation of liquid droplets, including internal streaming, pumping and jetting/ nebulization, and their performance differences for microfluidic functions were discussed. A detailed investigation of the influences of droplet size (ranging from 3 to 15 lL) and RF input power (0.25-68 W) on microdroplet behavior has been conducted. Results showed that pumping and jetting velocities were increased with an increase of RF power or a decrease in droplet size.

On‐Chip Generation of Vortical Flows for Microfluidic Centrifugation

“…SAWs, as well as thickness‐mode bulk waves, can also be generated on thin piezoelectric films (the latter being known as thin film bulk acoustic resonators, and has the advantage of overcoming challenges associated with fabricating interdigitated transducers with micron or submicron widths and thicknesses necessary to generate SAWs at higher (e.g., GHz) frequencies), on which similar azimuthal microfluidic centrifugation flows can be effected. In addition to demonstrating the microvortical flow arising from these devices for various applications, including hydrodynamic particle trapping, biomolecular concentration and the shearing of polyelectrolyte films for drug release, the piezoelectric films can be overlaid onto regular substrates so as to circumvent the need for the piezoelectric substrate as well as to facilitate microfluidic operations on flexible substrates . To however separate the actuator from the microfluidic components, so as to enable reuse of the actuator (i.e., the piezoelectric chip) while facilitating a disposable option for the microfluidic chip, it is necessary to transmit the SAW vibration through a liquid couplant into a superstrate (e.g., a low‐cost and hence disposable chip on which the microfluidic operations are to be carried out as opposed to the reusable higher‐cost piezoelectric substrate to drive the microfluidic actuation), as first shown by Hodgson et al, or even a capillary tube .…”

Ring-Shaped Sensitive Element Design for Acceleration Measurements: Overcoming the Limitations of Angular-Shaped Sensors

“…where σ 1 is a tensile stress (Pa), σ 2 is a maximum bending stress (Pa), ψ 1 (u) were obtained graphically for the stress-strain curve. The maximum stress values obtained were σ max = 141.8 MPa and 106.8 MPa for the quartz ST-cut and the lithium niobate YX-128 • -cut, accordingly [8,9,13]. These values were used in further mathematical models and computer simulations.…”

“…In the current literature, various aspects of SAW sensor design and its manufacturing technology have been investigated thoroughly. Issues considered in recent literature include the choice of the sensitive element material [6,8,9], and the possibility of passive implementation with a wireless interface [10][11][12]. Acceleration measurements represent a prominent application possibility [13], where the proposed class of solutions has the potential to develop serial devices characterized by enhanced robustness and the implementation of high-G values, as indicated by a series of recent publications [14][15][16][17], including some developments by our research team [18,19].…”

Study on the Influencing Factors of the Atomization Rate in a Piezoceramic Vibrating Mesh Atomizer

“…Specifically, the micron-sized droplet technique, with the characteristics of stable injection and full dispersion, constitutes an important development direction in these fields [10]. To realize the above-mentioned objectives, surface acoustic wave atomizer [11] and static mesh atomizer [12] can suffer high pressure across the whole system, which inevitably results in high-energy consumption, high cost, and high loss. Furthermore, structures of this type have a low energy utilization rate in which their atomization process is random and uncontrollable, and are also extremely inconvenient to carry and practical use [13].…”