This paper reports on a new type of microresonators enabled by micromachining of ion sliced X -cut LiNbO3 thin films. In operation, the device is excited into lateral vibrations, thus allowing the center frequency to be determined by the lithographically defined dimensions of the excitation electrodes. The demonstrated device has a high electromechanical coupling (kt2) of 11.5%-the highest attained for laterally vibrating microelectromechanical systems resonators. Device orientation was also varied to investigate its impact on kt2 and experimental data have shown good agreement with theoretical predictions. Several key performance parameters, including the quality factor (Q), the static capacitance, C0 , the temperature coefficient of frequency (TCF), and the power handling, are also characterized and the related experimental data are presented. The devices demonstrate Q 's up to 1800. The measured TCFs range from -55 to -69 ppm/K and can be considered sufficiently low for wideband RF filtering. The high electromechanical coupling and the high Q of this new class of devices show promise for the implementation of multifrequency wideband multiplexers and filter banks for reconfigurable RF front-ends.

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Design and Analysis of Lithium–Niobate-Based High Electromechanical Coupling RF-MEMS Resonators for Wideband Filtering

This book gives the fundamental principles and device design techniques for surface acoustic wave filters. It covers the devices in widespread use today: bandpass and pulse compression filters, correlators and non-linear convolvers and resonators. The newest technologies for low bandpass filters are fully covered such as unidirectional transducers, resonators in impedance element filters, resonators in double-mode surface acoustic wave filters and transverse-coupled resonators using waveguides.The book covers the theory of acoustic wave physics, the piezoelectric effect, electrostatics at a surface, effective permittivity, piezoelectric SAW excitation and reception, and the SAW element factor. These are the main requirements for developing quasi-static theory, which gives a basis for the non-reflective transducers in transversal bandpass filters and interdigital pulse compression filters. It is also needed for the reflective transducers used in the newer devices. It is a thorough revision of a classic on surface acoustic wave filters first published in 1985 and still in print. It uniquely combines easy-to-understand principles with practical design techniques for all the devices in widespread use today. It includes complete coverage of all the latest devices which are key to mobile phones, TVs and radar systems; and, a new foreword by Sir Eric Albert Ash.

Surface Acoustic Wave Filters: With Applications to Electronic Communications and Signal Processing

Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Acoustic Wave Filter Technology–A Review

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO/sub 3/ and LiTaO/sub 3/ single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO/sub 3/ and LiTaO/sub 3/ crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.

Accurate measurements of the acoustical physical constants of LiNbO/sub 3/ and LiTaO/sub 3/ single crystals

High-speed sorting is an essential process in a number of clinical and research applications, where single cells, droplets and particles are segregated based on their properties in a continuous flow. With recent developments in the field of microscale actuation, there is increasing interest in replicating the functions available to conventional fluorescence activated cell sorting (FACS) flow cytometry in integrated on-chip systems, which have substantial advantages in cost and portability. Surface acoustic wave (SAW) devices are ideal for many acoustofluidic applications, and have been used to perform such sorting at rates on the order of kHz. Essential to the accuracy of this sorting, however, is the dimensions of the region over which sorting occurs, where a smaller sorting region can largely avoid inaccurate sorting across a range of sample concentrations. Here we demonstrate the use of flow focusing and a highly focused SAW generated by a high-frequency (386 MHz), 10 μm wavelength set of focused interdigital transducers (FIDTs) on a piezoelectric lithium niobate substrate, yielding an effective sorting region only ~25 μm wide, with sub-millisecond pulses generated at up to kHz rates. Furthermore, because of the use of high frequencies, actuation of particles as small as 2 μm can be realized. Such devices represent a substantial step forward in the evolution of highly localized forces for lab-on-a-chip microfluidic applications.

Highly focused high-frequency travelling surface acoustic waves (SAW) for rapid single-particle sorting

Measurements of SAW (surface acoustic wave) velocities on the entire surface of free and metallized substrates of 128 degrees rotY-LiNbO/sub 3/ are reported. The influence of mechanical loading is examined. All experimental data are given as trigonometric expansions. Improved sets of material constants for LiNbO/sub 3/ and LiTaO/sub 3/ are calculated by fitting them to the experimentally determined SAW velocities. In agreement with R. Graham (1977), a significantly larger value of e/sub 33/ was found for LiNbO/sub 3/. While all material constants of LiBnO/sub 3/ and most of LiTaO/sub 3/ have reasonable error bounds, further improvements are expected from more accurately measured unclamped permittivities. >

Improved material constants for LiNbO/sub 3/ and LiTaO/sub 3/

Piezoelectric substrates used for SAW devices are characterized by their linear elastic, piezo- electric and dielectric material constants. These data can be computed from precise SAW velocity measure- ments by a non-linear least squares algorithm, if the measured crystal cut is sensitive to all those material constants. For LiNb03 such a cut is the 128' rot Y- cut. New measurements on the entire surface of that cut are presented. Results for free and metallized sur- face - including mechanical loading influence - are given as trigonometric expansions. These recent measurements as well as our previous re- sults on Y-cut are the basis for the calculation of an improved dataset of LiNbOa. The same algorithm was also applied to LiTa03, for which we used our measure- ments on X-cut, published last year. Here we present datasets for both materials. Further we include er- ror bounds for each individual constant derived from its influence on the SAW velocities and from the mea- surement accuracy.

http://ieeexplore.ieee.org/iel2/169/4424/00171403.pdf

M. Anhorn

Papers

Improved material constants for LiNbO/sub 3/ and LiTaO/sub 3/

Improved Material Constants for LiNb03 and LiTaO3