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

To develop the high-performance filters and duplexers required for recent long-term evolution frequency bands in mobile handsets, a surface acoustic wave (SAW) resonator is needed that has a higher quality (Q) and a lower temperature coefficient of frequency (TCF). To achieve this, the authors focused on acoustic energy confinement in the depth direction for a rotated Y-X LiTaO3 (LT) substrate. Characteristics of multilayered substrates with low-impedance and high-impedance layers under LT layer were studied numerically in terms of acoustic energy distribution, phase velocity, coupling coefficient, and temperature characteristics employing a finite-element method simulation. After several calculations, a novel multilayered structure was developed that uses SiO2 for a low-impedance layer and AlN for a high-impedance layer under the thin LT layer. A one-port resonator using the new substrate was fabricated, and its experimental results showed that the developed resonator had a Bode-Q over 4000 and TCF of −8 ppm/°C, which are four times higher than and one-fifth as small as those of a conventional 4° YX-LT SAW resonator, respectively. By applying this technology, a band 25 duplexer with very narrow duplex gap was successfully developed, which shows extremely low insertion loss, steep cutoff characteristics, and stable temperature characteristics.

High-Performance SAW Resonator on New Multilayered Substrate Using LiTaO 3 Crystal

A dielectric substance is laminated on one surface of a piezoelectric substance, and an IDT and reflectors are disposed as electrodes at a boundary between the piezoelectric substance and the dielectric substance, and the thickness of the electrodes is determined so that the acoustic velocity of the Stoneley wave is decreased less than that of a slow transverse wave propagating through the dielectric substance and that of a slow transverse wave propagating through the piezoelectric substance, thereby forming a boundary acoustic wave device.

Boundary acoustic wave device

Various characteristics for RF filters in mobile terminals are required corresponding to expansion of mobile terminals. I.H.P. SAW (Incredible High-performance SAW) with high Q and temperature stability has been developed to resolve these challenges. In this paper, its high Q mechanism of the new multi-layered structure (LiTaO 3 / SiO 2 / AlN / Si substrate) has been studied numerically in terms of acoustic energy confinement by using wave propagation analysis in real-space and wavenumber domains. One-port resonators employing I.H.P. SAW were fabricated after optimizing the multi-layered structure. Experimental results show higher Bode-Q values over 6000 at 0.9 GHz to 1900 at 3.5GHz successfully, which are over 3 times higher than those of conventional 42YX-LT SAW resonators. Very small TCF of −8 ppm/°C is also realized, and wider bandwidth and superior heat dissipation performance have been achieved. A new Wi-Fi filter with very narrow adjacent gaps and a new Band 25 / 66 / 30 hexaplexer, one of the most difficult multiplexers, have been developed using I.H.P. SAW technology, which show low insertion loss, steep cut-off, deep attenuation and extremely high isolation characteristics.

I.H.P. SAW technology and its application to microacoustic components (Invited)

This work demonstrates a group of shear horizontal (SH0) mode resonators and filters using lithium niobate (LiNbO3) thin films on silicon carbide (SiC). The single-crystalline X-cut LiNbO3 thin films on 4H-SiC substrates have been prepared by ion-slicing and wafer-bonding processes. The fabricated resonator has demonstrated a large effective electromechanical coupling (k
 2
) of 26.9% and a high-quality factor (BodeQ) of 1228, hence resulting in a high figure of merit (FoM = k
 2
 · BodeQ) of 330 at 2.28 GHz. Additionally, these fabricated resonators show scalable resonances from 1.61 to 3.05 GHz and impedance ratios between 53.2 and 74.7 dB. Filters based on demonstrated resonators have been demonstrated at 2.16 and 2.29 GHz with sharp roll-off and spurious-free responses over a wide frequency range. The filter with a center frequency of 2.29 GHz shows a 3-dB fractional bandwidth of 9.9%, an insertion loss of 1.38 dB, an out-of-band rejection of 41.6 dB, and a footprint of 0.75 mm
 2
. Besides, the fabricated filters also show a temperature coefficient of frequency of -48.2 ppm/°C and power handling of 25 dBm. Although the power handling is limited by arc discharge and migration-induced damage of the interdigital electrodes and some ripples in insertion loss and group delay responses are still present due to the transverse spurious modes, the demonstrations still show that acoustic devices on the LiNbO3-on-SiC platform have great potential for radio-frequency applications.

/pdf/surface-acoustic-wave-devices-using-lithium-niobate-on-3u9pcpu4ma.pdf

Surface Acoustic Wave Devices Using Lithium Niobate on Silicon Carbide

In an elastic wave device, an electrode, which is formed in a comb-like shape and is made of conductive material having a prescribed thickness, is arranged on a substrate of a piezo-electric element containing lithium niobate as a main component Also, in this elastic wave device, a surface of the substrate is set to a plane which is obtained by rotating a plane perpendicular to a crystal Y-axis of the lithium niobate by an angle ranging from 55 degrees to 57 degrees around a crystal x-axis of the lithium niobate, and a duty ratio (a width w of an electrode finger/an arrangement interval p of a pair of electrode fingers) of each of a plurality of electrode fingers composing the electrode is equal to or higher than 04 and is lower than 10

Elastic wave device

In this paper, we report a new structure of a shear horizontal (SH) type boundary acoustic wave for cellular phone applications. Such a structure composed of electrodes with a low shear wave velocity between two materials, namely, the SiO2 film/Au-electrode/LiNbO3 substrate, is proposed. The ladder filter used in this paper had this structure. By changing the propagation angle of the acoustic wave, the electromechanical coupling factor k2 range from 0 to 16% was obtained, as well as a normalized bandwidth range 0.67 to 1.85 fold as large as that of a 36–46°Y–X LiTaO3 leaky surface acoustic wave (LT-LSAW) filter. In addition, an excellent temperature coefficient of delay time (TCD=25 ppm/°C) and a large mutual coupling coefficient κ12 (=0.15) were also obtained.

http://iopscience.iop.org/article/10.1143/JJAP.45.4651/pdf

RF filter using boundary acoustic wave

An acoustic wave element includes an IDT electrode in contact with a piezoelectric material and including a plurality of electrode fingers, which include first and second electrode fingers that adjoin each other in an acoustic wave propagation direction and that connect to different potentials and a first dummy electrode finger facing the first electrode finger via a gap located on an outer side in an electrode finger length direction of the first electrode finger. At an area near the gap, first protrusions are provided in at least one of the first electrode finger and the first dummy electrode finger, the first protrusion protruding in the acoustic wave propagation direction from at least one of side edges of the at least one of the first electrode finger and the first dummy electrode finger. The acoustic wave element has greatly improved resonance characteristics of a resonance frequency and prevents short-circuit failure between electrode fingers and degradation in insulation properties.

Acoustic wave element

A boundary acoustic wave device includes a first medium, a second medium, and an IDT electrode disposed at an interface between the first medium and the second medium, the IDT electrode having an Au layer defining a main electrode layer, wherein a Ni layer is laminated so as to contact at least one surface of the Au layer, and a portion of Ni defining the Ni layer is diffused from the Ni layer side surface of the Au layer toward the inside of the Au layer.

Boundary acoustic wave device comprising Ni diffused in Au and method for manufacturing the same

Disclosed is a boundary acoustic wave device wherein loss is reduced. Specifically disclosed is a boundary acoustic wave device (1) comprising a first medium (2), a second medium (3) and an IDT electrode (4) arranged on the interface between the first medium (2) and the second medium (3). The IDT electrode (4) has an Au layer (11) as a main electrode layer, and an Ni layer (12) is arranged in contact with at least one side of the Au layer. A part of Ni constituting the Ni layer (12) is diffused into the Au layer (11) from the Ni-layer-side surface of the Au layer (11).

Boundary acoustic wave device and method for manufacturing same

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