Hajime Kando

RF Filter using Boundary Acoustic Wave

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.

Small and Low-Loss Intermediate Frequency Surface Acoustic Wave Filters Using Zinc Oxide Film on Quartz Substrate

A ZnO/quartz substrate is expected to be applied to a intermediate frequency (IF) surface acoustic wave (SAW) filter for which a small size, a low insertion loss, and a good temperature coefficient of frequency (TCF) are necessary because it has a large ks and an excellent TCF. However it was clarified that the SAW filter consisting of a single solid electrode or single-phase unidirectional transducer (SPUDT) on ZnO/quartz substrate often has a large spurious response due to the Love wave. The new cutting angle and the propagating direction (26–27°Y-X) for quartz were developed in order to suppress the spurious response. The developed W-CDMA IF 380 MHz filter was mounted on a small package of 3.2×5.0 mm2. It had a low loss of 5.8 dB, and high adjacent channel selectivity (ACS) of 36.1 dB/35.0 dB. Then, the developed N-CDMA IF 183 MHz filter was mounted on a small package of 5×7 mm2. It had a low loss of 4.3 dB. In both cases, the frequency shift per 1°C was less than 0.37 ppm/°C.

Incredible high performance SAW resonator on novel multi-layerd substrate

High Q and low TCF are elemental characteristics for SAW resonator, in order to realize high performance filters and duplexers coping with new LTE frequency bands. Authors focus on the acoustic energy confinement in SAW propagation surface and electrical characteristics have been investigated theoretically and experimentally. A new multi-layered structure substrate have realized incredible high performances such as both three times Q and one fifth TCF compared with conventional structure. Band25 duplexer using the new structure has been developed successfully with low loss and good temperature stability.

A new tunable filter using love wave resonators for reconfigurable RF

A large number of frequency bands have been included in mobile phone handsets and in their RF front end circuit, RF paths have been increasing and the configuration has been becoming complex more and more. A new tunable filter is proposed in this paper. In order to realize a wide bandwidth SAW resonator using extension inductor, Love wave SAW resonator for the tunable filter can be obtained by the optimization of the Euler angle and Pt film thickness to avoid Rayleigh wave spurious and the bulk wave. A tunable filter is fabricated for the operation in the low frequency band of 669-960MHz which fractional bandwidth is 31.5%. This result shows promising possibility of a tunable filter for reconfigurable RF.

Piezoelectric boundary acoustic waves: Their underlying physics and applications

This paper reviews physical properties of piezoelectric boundary acoustic waves (PBAWs) and their application to miniature and high performance RF filters. First, basic properties of PBAWs are discussed. It is shown that PBAWs are supported in various structures provided that highly piezoelectric material(s) are employed as structural member(s). For example, PBAWs are trapped near the electrode region in the SiO2/heavy grating electrode/rot. YX-LN structure. This means that PBAW properties in the structure are independent of the SiO2 layer thickness. This is a significant advantage for mass production. Rot. YX-LN possesses piezoelectric coupling with the Rayleigh-type PBAW as well as the SH-type one. It is shown that the coupling can be negligible when the device structure is properly designed. The PBAW devices employing SiO2/Au electrodes/0-15degYX-LN are now being mass-produced. Because of the removed cavity from the chip surface, the packaged device size can be reduced dramatically. The minimum insertion loss achieved is comparable to that of conventional SAW filters in a relatively large device size. The SiO2 layer is effective in achieving the improved temperature coefficient of frequency.

Small and low-loss IF SAW filters with excellent temperature coefficient consisting of zinc oxide film on quartz substrate

One of the authors reported that a surface acoustic wave (SAW) substrate with an excellent temperature coefficient of frequency (TCF) and a large electromechanical coupling factor could be realized by a combination of a specific quartz (cut-angle and propagation-direction) substrate having a positive TCF and a ZnO film having a negative TCF from theoretical and experimental investigations. The authors have tried to apply this ZnO/quartz substrate to various SAW filters at an intermediate frequency stage (IF). But, it was clarified that the SAW filter consisting of a single electrode (strip) or single-phase unidirectional transducer (SPUDT) on these substrates often had a large spurious response due to the Love wave which was a higher-order-mode of the Rayleigh wave. The new cut angle of quartz was developed in order to suppress its response. The IF filters for wide-band code division multiple access (W-CDMA: 380 MHz) and narrow-band CDMA (N-CDMA: 183 MHz) were developed by combining the new cut angle quartz and the ZnO film. As a result, small-sized IF filters without a spurious response due to the Love wave and with excellent TCF, low insertion loss, and cost advantages in the applications were obtained. Their frequency shift per 1/spl deg/C from -20/spl deg/C to 80/spl deg/C was less than 0.37 ppm//spl deg/C. Their insertion losses were 3.6 to 4.4 dB lower than, those of conventional SAW filters consisting of the ST-X quartz substrate. Adjacent channel sensitivities (ACSs) of the W-CDMA filter were always larger than 36.1 dB/35 dB in the temperature range of -20 to 80/spl deg/C.

Improvement in temperature characteristics of plate wave resonator using rotated Y-cut LiTaO 3 / sin structure

Realization of a high frequency resonator for 3.6 GHz-band filter in the International Mobile Telecommunication Advanced (IMT-Advanced) system is desired. It is difficult to accomplish such a high frequency resonator using conventional surface acoustic wave (SAW) technology, because the strip width of the inter-digital transducers (IDT) becomes too narrow. Although anti-symmetry 1st (A1) mode Lamb type plate wave is known to have a high propagation velocity, however it has a problem such as large temperature coefficient of frequency (TCF). This paper reports an improved technique for TCF in A1 mode Lamb type plate wave resonator with air-gap type membrane by using rotated Y-cut single crystal LiTaO3 thin plate. The fabricated plate wave resonator has excellent characteristics such as a zero TCF, a large electromechanical coupling coefficient (k2) of 7 % and a high acoustic wave velocity of 12,142 m/s.

Improvement of Temperature Characteristics of Boundary Acoustic Wave Resonators Using Multilayered Electrodes

In this paper, we describe a new boundary acoustic wave structure employing multilayered metal electrodes with a high-density metal and a low-density metal. By using this structure, such as Pt/Al/Pt, the electromechanical coupling coefficient (k2) and temperature coefficient of frequency (TCF) of the boundary acoustic wave can be changed. We theoretically studied the dependence of the energy distribution of the boundary wave on the position of the total electrode gravity center when the electrode layer structure is changed. It was experimentally confirmed that k2 and TCF can be changed simultaneously. By using this structure, we developed a novel filter with good electrical characteristics, and a very small variation of the filter characteristic with temperature (almost zero TCF) was successfully realized.

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

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.

IF SAW filters without Love wave's spurious consisting of ZnO film and specific cut angle quartz substrate

The substrate with large electromechanical coupling factor and excellent temperature coefficient of frequency (TCF) is required to realize surface acoustic wave filters for the first intermediate frequency stage (1st IF). One of the authors (M. Kadota) realized a Rayleigh wave substrate with an excellent TCF and a large electromechanical coupling factor by a combination of a specific quartz substrate (ST-cut 35/spl deg/X propagation: ST- 35/spl deg/X) having a positive TCF with a ZnO film having a negative TCF. But, it has been clarified that the SAW filter having of a single electrode (strip) or single-phase unidirectional transducer (SPUDT) on the ZnO/ST-35/spl deg/X-quartz substrates, often had a large spurious response due to the Love wave which was a higher-order-mode of the Rayleigh wave. The new cutting angle and the propagating direction (26-27/spl deg/Y-X) on quartz has been developed in order to suppress the spurious response. The IF SAW filters for the wide-band and the narrow-band code division multiple access (W-CDMA: 380 MHz and N-CDMA: 183.6 MHz) have been developed by combining this 26-27/spl deg/YX quartz with the ZnO film. The IF filters which have a small-size, an excellent TCF, a low insertion loss, a cost advantage in their applications, and no spurious responses due to the Love wave have been realized. Their frequency shift per 1/spl deg/C from -20/spl deg/C to 80/spl deg/C was less than 0.37 ppm//spl deg/C, which was better than a Rayleigh SAW on an ST-cut X propagation quartz.