K. Yamanouchi

SAW propagation characteristics and fabrication technology of piezoelectric thin film/diamond structure

The authors report a theoretical analysis of the surface-acoustic wave (SAW) propagation characteristics of ZnO/diamond and AlN/diamond structures. The analysis shows about 12000 m/s and a large electromechanical coupling coefficient K/sup 2/ of 0.03 for AlN thin film. The numerical analysis for the ZnO/diamond structure shows that there exists a coupling between the Rayleigh wave and the Sezawa wave at H/ lambda =0.2 and a complex dependency of K/sup 2/ on the thickness of ZnO film. The fabrication process of synthetic-diamond thin films is described, and experimental results on the SAW propagation characteristics are presented. With the thermal filament CVD (chemical vapor deposition) method, it is possible to obtain a diamond film on a Si substrate, but the surface of it is rough, and polishing is needed to make a fine pattern on it.<<ETX>>

Analysis of the film thickness dependence of a single-phase unidirectional transducer using the coupling-of-modes theory and the finite-element method

A coupling-of-modes (COM) analysis is given for the film thickness dependence of a single-phase undirectional transducer (SPUDT), while the finite-element method (FEM) is employed for evaluating all the coefficients of COM equations. The relationship between the directivity and dispersion curves of the transducer is discussed. The theoretical analysis shows that when the electrode finger thickness increases through a threshold value, a mode conversion phenomenon occurs and the value of the reflection phase changes from the positive to the negative. This result predicts that the forward direction of a film thickness difference type SPUDT will move conversely when the electrode film thickness increases through the threshold thickness. A prototype step-type SPUDT, fabricated on 128 degrees Y-X LiNbO/sub 3/ substrate, showed a directivity of 10 dB/transducer at 481.5 MHz, and a low-loss surface acoustic wave (SAW) filter showed a minimum insertion loss of 3.8 dB.<<ETX>>

Ultrasonic micromanipulation of small particles in liquid using VHF-range leaky wave transducers

New ultrasonic micromanipulation techniques for small particles based on the radiation forces of high-frequency ultrasound are proposed, using VHF-range leaky wave transducers. A newly developed leaky wave transducer with beamwidth compression consists of a floating-electrode-type unidirectional interdigital transducer and a LiNbO3 substrate. It has many advantages: no impedance matching scheme between liquid and substrate, efficient generation of higher-frequency ultrasonic waves into a small-scale liquid system, and isolation of interdigital electrodes from liquid. The experimental leaky wave transducer with narrow beam width of 120-μm shows a conversion loss of 5.8 dB at 97.5 MHz. Transportation and trapping of 50-μm-diameter glass spheres in water are confined by preliminary experiments in the frequency range of 50 to 100 MHz

GHz-range low-loss wide band filter using new floating electrode type unidirectional transducers

K. Yamanouchi et al. (1991) reported a very low loss surface acoustic wave (SAW) filter with minimum insertion loss of 1.9 dB at 1.0 GHz using a floating electrode type unidirectional transducer (FEUDT). The dependence of directivity on the electrode thickness for the lambda /10 type FEUDT is investigated here. Experimental results show minimum insertion loss of 6.2 dB at 4.1 GHz and 2.5 dB at 2.0 GHz. The dependence of directivity on the electrode thickness at 4 GHz differs from that at 2 GHz. The resistivities of various Al films were measured, and their surfaces are observed by scanning tunneling microscopy. An increase of the resistance due to pinholes which appear after heating is noted.<<ETX>>

A chirp spread spectrum DPSK modulator and demodulator for a time shift multiple access communication system by using SAW devices

We have developed a modulator and a demodulator for DPSK modulated chirp signals using a SAW dispersive delay line and a SAW matched filter. The SAW chirp modulator spreads the 100 MHz spectrum between every 1 bit data interval of 1.5 /spl mu/sec and provides DPSK modulation, depending upon data. The SAW demodulator demodulates data using exclusive output pulses from two output ports of a newly designed SAW matched filter. By employing nonlinear chirp modulation, the modulator generates a frequency-weighted chirp signal that keeps a flat amplitude in the time domain. The demodulator has a 19 dB process gain, and it has good correlation characteristics of less than -30 dB time sidelobe. By using these modulator and demodulator, we have examined a multiple access of the chirp spread spectrum (SS) system. The multiplexity is achieved by the time shift of chirp SS signals, which are easily produced by the SAW modulator. We have confirmed 20 multiplex accesses experimentally, and have measured the bit error rate up to 9 multiplexity. In the case of one chirp signal, the bit error rate degrades 2 dB from the theoretical level, and the degradation of multiplexity up to 9 was only 1 dB.

Field analysis o SAW single-phase unidirectional transducers using internal floating electrodes

A coupled-mode analysis is presented of the performance of a single-phase unidirectional transducer utilizing the internal reflections of floating electrodes of electrically open circuited and shorted metal strips within an interdigital electrode. All four independent parameters (self- and mutual-coupling coefficients, transduction coefficient, and static capacitance) governing the coupled-mode equation with an electrical transduction term are analytically derived using extended Legendre polynomial expansions of electrical fields and a perturbation analysis. The frequency response of the radiation admittance and the insertion loss, and the growing surface acoustic wave (SAW) field distributions are calculated from simple closed-form solutions of the coupled-mode equation. The shift effect of reflection and transduction centers due to the asymmetric electrode structure is clarified. Experimental results are given for test devices fabricated on a 128 degrees YX LiNbO/sub 3/ substrate, and compared with the theory. The theoretical results are in good agreement with experiments.<<ETX>>

Super high electromechanical coupling and zero temperature coefficient surface acoustic wave substrates in KNbO/sub 3/ single crystal

The propagation characteristics of surface acoustic waves (SAW) and piezoelectric leaky surface waves in KNbO/sub 3/ single crystal have been investigated theoretically and experimentally. The results show that the electromechanical coupling coefficient k/sup 2/ of the surface wave propagating along the X-axis of the rotated Y-cut plate is very large with k/sup 2/=0.53. This is about 10 times as large as that of LiNbO/sub 3/ in the surface wave branch. Experimental results for wideband SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20%, and insertion losses are less than 2 to 6 dB. Simulation results for a ladder type filter using Y-cut KNbO/sub 3/ indicate that a bandwidth of 40% should be possible. The KNbO/sub 3/ substrates exhibit zero temperature coefficient of frequency (TCF) around 20/spl deg/C in rotated Y-cut substrates.

SHF-range surface acoustic wave interdigital transducers using electron beam exposure

Nanometer electrodes of 0.085- mu m width have been fabricated using direct electron beam lithography, normal lift-off techniques, and an I/sub 2/-plasma cleaning system. These techniques have been applied to interdigital transducers used as surface acoustic wave (SAW) transducers in the SHF range. SAW filters experiments were performed in the SHF-range. Filters with minimum insertion loss of 15.0 dB at the center frequency of 5 GHz and 24 dB at 11 GHz were obtained.<<ETX>>

New electrode separation technology using anodic oxidation and application to SAW interdigital transducers

By anodic oxidation of the edges of the portions of the Al film under photoresist, controllable gaps between electrodes with good insulation can be obtained. These techniques are applied to realize a surface-acoustic-wave (SAW) narrow gap interdigital transducer (NG-IDT) and narrow gap unidirectional transducer (NG-UDT). The experimental result shows 7.2 dB insertion loss with amplitude ripples of +or-1.2 dB for a conventional NG-IDT. Directives of 3-dB/transducer at 440 MHz (fundamental) and 13-dB transducer at 870 MHz (second-harmonic operation) for a new floating electrode type unidirectional transducer (NG-FEUDT) are demonstrated. Also a three transducer low loss filter using a combination of NG-IDT and NG-FEUDT exhibits 3.46 dB insertion loss at 894 MHz (second-harmonic operation, electrode width of 1.7 mu m) with sidelobe suppression greater than 35 dB.<<ETX>>

High efficient electro-acoustic convolvers

Elastic convolvers are very important for signal-processing devices of the spread spectrum communication systems. The more efficient convolvers are required for the application in the spread spectrum and next stage communication systems. The efficiency of electro-acoustic convolvers depends on the sheet conductivity and thickness of the thin film semiconductor. Generally, the sheet conductivity is larger and the thickness of the film is thinner for optimum efficiency. In this paper, monolithic planner type of the convolver utilizing a strip coupler to couple a piezoelectric material and semiconductor is described. The 128/spl deg/Y-X LiNbO/sub 3/ and InSb thin film semiconductor are put together using the MBE. The strip electrodes are fabricated on the LiNbO/sub 3/ and InSb substrates using lithography process. The gaps between the coupler electrodes and InSb are very small. Therefore the high efficient and high frequency convolvers by using a longitudinal coupling are obtained. The experimental result shows the F-value of about -35 dB at 100 MHz.