Improved electromigration reliability of surface acoustic wave devices using Ti/Al-Mo/Ti/Al-Mo electrodes

In order to obtain both high electromigration （EM） reliability and free-dimensional control in high-frequency surface acoustic wave （SAW） devices, 4-layered Ti/Al-Mo/Ti/Al-Mo electrode films were investigated on 128° Y-X LiNbO3 substrates by sputtering deposition. The resuits indicated that the 4-layered films had an improved EM reliability compared to conventional Al-0.5wt.%Cu films. Their lifetime is approximately three times longer than that of the Al-0.5wt.%Cu films tested at a current density of 5 x 107 A/cm^2 and a temperature of 200℃. Moreover, the 4-layered films were easily etched in reactive ion etching and fine-dimensional control was realized during the pattern replication for high-frequency SAW devices. For the 4-layered films, an optimum Mo quantity and sputtering parameters were very significant for high EM reliability.

Precise simulation of surface acoustic wave devices using frequency-dependent coupling-of-modes parameters

Herein we extract all the frequency-dependent coupling-of-modes （COM） parameters, which will be used to the rapid simulation and optimal design of surface acoustic wave （SAW） devices. FEM/BEM is used to calculate the exact field distributions of forward and backward surface acoustic waves within a finite-length periodic grating at every frequency. The middle compo- nent of the grating, regarded as a periodic structure, is selected to be investigated which can satisfy the presupposition of the COM model. From these field distributions, the values of P-matrix elements of one cell are calculated. The COM parameters taken as functions of frequency are accurately obtained. Specifically, the frequency-dependent relationships of reflection coefficient and propagation velocity are obtained independently. Using the resultant COM parameters, a one-port resonator on the substrate of 128°YX-LiNbO3 is simulated and the admittance curve shows good agreement with the simulating results using FEM/BEM. These results verify the validity and accuracy of this method.

Test method of frequency response based on diamond surface acoustic wave devices

In order to reduce the noises affixed to the signals when testing high frequency devices,a single-port test mode(S11) is used to test frequency response of high frequency(GHz) and dual-port surface acoustic wave devices(SAWDs) in this paper.The feasibility of the test is proved by simulating the Fabry-perot model.The frequency response of the high-frequency dual-port resonant-type diamond SAWD is measured by S11 and the dual-port test mode(S21),respectively.The results show that the quality factor of the device is 51.29 and the 3 dB bandwidth is 27.8 MHz by S11-mode measurement,which is better than the S21 mode,and is consistent with the frequency response curve by simulation.

Amplitude measurement of weak sinusoidal water surface acoustic wave using laser interferometer

To determine the amplitude of weak sinusoidal water surface acoustic wave （WSAW）, a method based on the spectrum analysis of the phase-modulated interference signal is developed. Calculated from the amplitude spec- trum of the detection signal, a characteristic ratio indicates that the phase-modulation depth of a WSAW is suggested by determining the amplitude of a WSAW according to their functional relationship. Experimental investigations for a 4 kHz WSAW evaluate the measurement＇s precision with an amplitude measurement stan- dard deviation of 0.12 nm. The measurement accuracy also is demonstrated by the experimental investigations. The theory of this method is briefly described, and the experimental setup is presented.

Investigation of surface acoustic waves in laser shock peened metals

Laser shock peening is a well-known method for extending the fatigue life of metal components by introducing near-surface compressive residual stress. The surface acoustic waves （SAWs） are dispersive when the near-surface properties of materials are changed. So the near-surface properties （such as the thickness of hardened layers, elastic properties, residual stresses, etc.） can be analyzed by the phase velocity dispersion. To study the propagation of SAWs in metal samples after peening, a more reasonable experimental method of broadband excitation and reception is introduced. The ultrasonic signals are excited by laser and received by polyvinylindene fluoride （PVDF） transducer. The SAW signals in aluminum alloy materials with different impact times by laser shock peening are detected. Signal spectrum and phase velocity dispersion curves of SAWs are analyzed. Moreover, reasons for dispersion are discussed.

Impact of cooling condition on the crystal structure and surface quality of preferred c-axis-oriented AlN films for SAW devices

AlN films with preferred c-axis orientation are deposited on Si substrates using the radio frequency(RF) magnetron sputtering method.The post-processing is carried out under the cooling conditions including high vacuum,low vacuum under deposition gas ambient and low vacuum under dynamic N2 ambient.Structures and morphologies of the films are analyzed by X-ray diffraction(XRD) and atomic force microscopy(AFM).The hardness and Young's modulus are investigated by the nanoindenter.The experimental results indicate that the(100) and(110) peak intensities decrease in the XRD spectra and the root-mean-square of roughness(Rrms) of the film decreases gradually with the increase of the cooling rate.The maximum values of the hardness and Young modulus are obtained by cooling in low vacuum under deposition gas ambient.The reason for orientation variation of the films is explained from the perspective of the Al-N bond formation.

Application of ultrasonic surface waves in the detection of microcracks using the scanning heating laser source technique

This letter reports the application of the scanning heating laser source technique to detect microcracks that may be undetected by conventional methods. In the proposed approach, we monitor changes in the transmitted surface acoustic waves （SAWs） as a heating source is scanned over the crack. The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts, whether open or closed, between the crack faces. Microeracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.

SAW filter manufacture and piezoelectric materials evaluation based on printed electronics technology

In this paper, the silver nanoparticle ink and ink-jet printing technology are used to manufacture the surface acoustic wave(SAW) filters. The characteristics of three common substrate piezoelectric materials of ST-quartz, Y36°-LiTaO3 and Y128°-LiNbO3 are evaluated. The experimental results show that Y128°-LiNbO3 matches the ink much better than others. The printed SAW filter with Y128°-LiNbO3 as piezoelectric substrate is realized, and its center frequency and bandwidth are 18.4 MHz and 500 kHz, respectively.

How to reduce the Al-texture in AlN films during film preparation

The preparation of aluminum nitrogen(AlN) film without Al texture is of great significance for the manufacture of highperformance surface acoustic wave(SAW) device.We research the process factors which bring Al into AlN film due to radio frequency(RF) magnetron sputtering system,and discuss how the process parameters influence the AlN thin film containing Al.In the research,it is found that the high sputtering power,the low deposition pressures and low partial pressure of Ar can lead to growing Al-texture during AlN thin film preparation,and the experiment also shows that filling the chamber with nitrogen gas can recrystallize a small amount of Al composition into AlN film during the annealing process in the high temperature environment.

Research on the piezoelectric response of cubic and he- xagonal boron nitride films

Boron nitride （BN） films for high-frequency surface acoustic wave （SAW） devices are deposited on Ti/AI/Si（111） wafers by radio frequency （RF） magnetron sputtering. The structure of BN films is investigated by Fourier transform infrared （FrlR） spectroscopy and X-ray diffraction （XRD） spectra, and the surface morphology and piezoelectric properties of BN films are characterized by atomic force microscopy （AFM）. The results show that when the flow ratio of nitrogen and argon is 2：18, the cubic BN （c-BN） film is deposited with high purity and c-axis orientation, and when the flow ratio of nitrogen and argon is 4：20, the hexagonal BN （h-BN） film is deposited with high c-axis orientation. Both particles are uniform and compact, and the roughnesses are 1.5 nm and 2.29 nm, respectively. The h-BN films have better piezoelectric response and distribu- tion than the c-BN films.