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A membrane supported dual-band acoustic device for biological applications
|Alexandros K. Pantazis 1,2, Electra Gizeli 2,3, George Konstantinidis 1|
1. Microelectronics Research Group, IESL-FORTH, P.O Box 1385, Vassilika Vouton, Heraklion 71110, Greece
A variety of microfabricated devices are used in biotechnology and biomedicine, mostly for interaction studies and analysis between different biomolecules (i.e. antigen – antibody) or for the detection of specific biotargets, especially when used in human health or environmental monitoring. Such biotargets can be proteins, liposomes, DNA, bacteria etc. Consequently, it is well understood that the sensitivity of these devices is very essential. Among the acoustic devices, Lamb-wave has the greater sensitivity. The reason for this is the membrane configuration that this device has. Until now, mostly of the Lamb-type devices were based on sputtered AlN or ZnO material and a few on MOCVD AlN. No reports have been made for using GaN as the piezoelectric material in these devices, just in a couple of Surface Acoustic Wave (SAW) devices. In this paper, we present the first GaN Lamb-wave device (Fig. 1). Due to the fact that when the membrane thickness is quite smaller than the wavelength of the device, only the two fundamental modes of the acoustic wave are supported (Anti-symmetrical A0 and Symmetrical S0). Thus, two different operation frequencies exist, a low one and a high. Therefore, interaction studies and analysis can be performed simultaneously for a low and a high frequency. Additionally, the chosen material offers the potential for monolithic integration with other semiconductor devices or systems.
A variety of design considerations were taken into account before the fabrication of the device. These considerations included the application of the device, the materials to be used, the experimental set-up, as well as the geometry of device and the fabrication method.
The Lamb-wave devices were fabricated by using conventional photolithographic techniques. The procedure has 3 main steps: 1) Front etch of 2 μm, in order eventually to dice the devices, 2) The electric circuit, which consists of the pads and the Interdigital Transducers (IDTs), were formed by the deposition of 20 nm Cr followed by 200 nm Au and 3) A back-etch of ~500-650 μm (depending on the thickness of the substrate) for forming the membrane. The wavelength of the device is 40 μm, while the two acoustic modes that are produced, the A0 and S0, were measured by a Network Analyzer, with operation frequencies 10.56 MHz and 192 MHz respectively, while the amplitude in S21 parameter was -79 dB and -43 dB respectively (Fig.2).
The evaluation of the sensitivity of the Lamb-wave devices to a variety of biomolecules is currently under investigation and will be presented.
Presentation: Oral at E-MRS Fall Meeting 2009, Symposium C, by Alexandros K. Pantazis
See On-line Journal of E-MRS Fall Meeting 2009
Submitted: 2009-05-25 17:46 Revised: 2009-06-07 00:44