Motoyuki Tajima

A low-loss and wide-band DMS filter using pitch-modulated IDT and reflector structures

This paper proposes the use of pitch-modulated IDTs and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode SAW (DMS) filters. This technique offers drastic improvement of the device performance through the introduction of a sufficient number of DoF in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional un-modulated structure, and device performances are compared both theoretically and experimentally. Then it is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

Low-Loss and Wide-Band Double-Mode Surface Acoustic Wave Filters Using Pitch-Modulated Interdigital Transducers and Reflectors

This paper proposes use of pitch-modulated interdigital transducers (IDTs) and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode surface acoustic wave (DMS) filters. This technique offers drastic improvement of the device performances through the introduction of a sufficient number of degrees of freedom in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional unmodulated structure, and device performances are compared both theoretically and experimentally. It then is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

Realization of small and low profile Duplexer using a CSSD packaging technology

This paper presents the realization of Duplexer with small size, high reliability and excellent performance. Good heat radiation, hermetic performance and small frequency drift against temperature shift are essential to achieve small size and highly reliable Duplexers. In this paper, we will report on the advantage of the Chip Size SAW Devices (CSSD) structure for miniaturization and high reliability. In addition, we will discuss the possibility of further miniaturization.

A study of optimum material for SAW bonded wafer

We have proposed the use of a lithium tantalate (LiTaO3)/sapphire bonded substrate for compensation of temperature coefficient of frequency (TCF) in surface acoustic wave (SAW) duplexers. However, in the specific use case of a Band 8 SAW duplexer on Universal Mobile Telecommunications System (UMTS), this bonded substrate has exhibited spurious response in the pass-band. In this paper, we analyzed the spurious response by Finite Element Method (FEM) simulation and found that the spurious could be suppressed effectively by optimizing the cut angle of the LiTaO3 substrate. Moreover, we fabricated a Band 8 SAW duplexer with the optimized cut angle and obtained experimentally good insertion loss without degradation by the spurious response. The measured insertion losses of the duplexer were 2 dB and 2.5 dB at Tx and Rx bands, respectively.

Surface acoustic wave device having reflectors with both open and shorted electrodes

A surface acoustic wave device for implementing an attenuation characteristic outside of the pass band and the narrow band characteristics, preferably for use as a filter. The surface acoustic wave device includes a piezoelectric substrate, interdigital transducers formed on the piezoelectric substrate, and first and second reflectors disposed on the sides of the interdigital transducers. Each of the first and second reflectors includes an open electrode block with a plurality of electrically independent electrode fingers, and a short electrode block with a plurality of electrode fingers of which both ends are electrically shorted.

Folded type SAW filters with minimised group delay deviation

Aiming at realising the frequency response with small group delay deviation and wide passband width, we propose miniaturised surface acoustic wave (SAW) filters having folded propagation path and employing a straight edge mirror reflector for SH-type SAWs. In a filter fabricated on a PZT substrate, the group delay deviation of less than /spl plusmn/15 ns and passband width of 5% were obtained at the centre frequency of 100 MHz. The experimental result and theoretical prediction were in good agreement with each other.

An SAW filter employing weighted reflectors and a multi-strip coupler

This paper deals with a miniaturised surface acoustic wave (SAW) filter employing two IDTs, two weighted reflectors and a multi-strip coupler (MSC). In the structure, the width-weighted reflectors are to be responsible for the frequency response of the filter. The reflectors are optimally designed to realise the specified frequency response by taking account of the SAW reflectivity of width-weighted electrodes. The filter having 3 dB bandwidth of 4.0 MHz was designed at the centre frequency of 200 MHz and fabricated on 128/spl deg/ YX-LiNbO/sub 3/. The total acoustic length of the filter was reduced to less than 5 mm. The experimental result obtained was in good agreement with the theoretical prediction.