Masayoshi Koshino

A wide-band balanced SAW filter with longitudinal multi-mode resonator

This paper describes a new balanced SAW filter with wide fractional bandwidth over 5% in 1.8 GHz range. The developed SAW filter is utilizing 5IDT longitudinally coupled multi-mode resonator structure with inverted output IDTs. In order to obtain wide bandwidth, mode coupling conditions were studied. Fabricated SAW filter has been realized with 100 MHz bandwidth and low insertion loss of 2 dB successfully. The package size of the filter is very small such as 2.5/spl times/2.0/spl times/1.0 mm/sup 3/ with flip-chip bonding technology. This SAW filter enables one to eliminate balun coil, which contributes to reduce mobile portable phone size.

SAW Resonator and Resonator Filter on Li2B4O7 Substrate

Lithium tetraborate (Li2B4O7) single crystal has attracted attention as a piezoelectric substrate for SAW devices. This paper focuses on its application to a SAW resonator. Reflection characteristics for aluminum strips and configuration suppressing surface-to-bulk-wave conversion are discussed. Results prove that the strips on Li2B4O7 substrate reflect efficiently, compared with those on the other substrates, and that a newly developed configuration improves the resonator Q at least twice. Further, a low insertion loss of 2.5 dB is achieved for a paging receiver filter.

Mode analysis of longitudinal multi mode SAW resonator filter

This paper describes the mode analysis for a longitudinal multi mode SAW resonator filter having 5 IDTs between the grating reflectors. The mode analysis is carried out at several conditions and frequencies, focusing on trap response. At the trap canceling condition, two resonant modes coincide in frequency and degenerate. Furthermore, at the fundamental resonant mode, SAW distribution at the center of electrode is distorted to be undulatory. In order to unify the SAW distribution of the fundamental mode, electrode pitches are adjusted partially. The developed balanced DCS-Rx filter realized low insertion loss of under 2 dB successfully.

Small-sized dual-band SAW filters using flip-chip bonding technology

New small-sized dual-band SAW filters have been developed. The filter has the dimension of 3.0×3.0×1.0 mm3 and the weight of 30 mg. In order to realize such compact packaging, 62% of surface mount area and 45% of weight of the conventional dual-band SAW filters, we adopt flip-chip bonding technology with Au-bumps. The dual-band filter, for Japanese PDC (Personal Digital Cellular) mobile phones, has been realized on a single chip. Two cascaded IIDT (Interdigitated Interdigital Transducer) resonator filters with numerous electrical connections between chip and package are easily assembled. To improve mechanical reliability, Al-Cu/Ta-Al/Al-Cu multiple layer film applied to the bump bonding pads on the chip surface. The developed filter successfully achieves high rejection level of 55 dB at image frequency as well as low insertion loss of 2.3 dB in the pass-band of around 900 MHz. A two-chip dual-band SAW filter with 1.8 GHz and 940 MHz band, with low loss of 2.7 dB, is also developed for DCS (Digital Cellular System) and EGSM (Extended Global System for Mobile communication) dual-band phones.

Stress-migration analysis on SAW duplexer

A SAW antenna duplexer (DPX) consists of a TX-filter, a RX-filter and a phase-shifter. They are demanded to be durable against 1.2 W of excitation power for several ten thousands hours. The filters, consisting of several parallel and series connected one-port resonators, contain high density SAW power and tend to deteriorate by the stress-migration of the aluminum electrodes. We analyzed the absolute values of each resonator-surface strain induced by resonant SAW energy using the numerical analysis method. Several facts are found that strains of aluminum film electrodes vary 2-3 times with driving frequency and that the connected condition of TX and RX filters through phase-shifter reduces resonators surface strains in RX filter for TX frequency band. Experimental life tests are also carried out. As a result, high textured Cu-doped aluminum on Ti film of SH-mode resonators on 36 Y-cut LiTaO3 proves to withstand for the 1.2 W driving power.

A low loss CDMA-IF filter based on RSPUDT on LBO substrate

A high performance and novel SAW IF 210 MHz filter for CDMA (PCS) system is developed on LBO substrate. The filter consists of double-tracked filters which are connected in parallel on one chip. The main track-filter is RSPUDT filter having grating reflectors, and mainly performs low loss pass-band of the total filter. The sub-track filter consists of SPUDTs arranged either side of grating reflectors. It is set to be phase-inversion at the cutoff frequency region to improve the skirt slope of the main-track filter, but is suppressed at the pass-band to avoid degrading the insertion loss of main-track filter. The minimum insertion loss of 3.5 dB, the phase linearity of 3.3° rms and the stop band attenuation better than 35 dB are achieved successfully. The developed IF filter fits into small sized ceramic package (7.0×5.0×1.6 mm3) and has high performances of the frequency characteristics.

Driving Current Dependence of Aging Drift in 600MHz Band Saw Resonators

SAW resonators driven at high driving levels are known to suffer from degradation of electrical arac- characteristics caused by stress induced metal-migration in the aluminum thin film transducers and reflectors(1), (2). The migration phenomenon is similar to an electro-migration which has been observed in aluminum film conductors of semiconductor integrated circuit.

Defects in Synthetic Quartz and the Q-Values of the -18.5° X-Cut Bar

-18.5° X-cut bar crystal blanks, 25.0×1.50×1.25 mm in size, were cut from different synthetic mother quartz. Defects in the bars were observed by light scattering tomography and X-ray traverse topography, Q-values were measured in the second overtone mode of 200 kHz in the air gap type holder and the maximum Q of 5.4×106 was obtained. Infrared absorption of the mother quartz, observed defects and the measured Q-values were discussed.

Small-sized 71 MHz GSM-IF filter using SAW resonator on Li/sub 2/B/sub 4/O/sub 7/ substrate

A small package size and low loss filter for GSM-IF have been developed with SAW resonators on LBO substrate. For realizing low loss of about 43 dB and very steep slope over 50 dB at +/-700 kHz offset from center frequency, the filter is composed of 4-pole resonator filter which consists of two cascaded IDT type DMS resonator filters. Each DMS filter is a longitudinally coupled resonator and uses withdrawn electrode technique of the IDT attached to suppress the spurious response. The filter is mounted in 9.1/spl times/48 mm ceramics package even for 71 MHz.

Experimental Investigation on Frequency Accuracy of SAW Resonator on LiTaO3 Substrate

Frequency accuracy of a LiTaO3 SAW resonator was investigated experimentally in terms of temperature characteristics, reproducibility and aging drift. The test resonator has a one-port configuration consisting of an 11-finger pair transducer between two grating reflectors, and its frequency is 90 MHz band. Temperature drift is ±540 ppm in the range from 0°C to 60°C. The relative frequency changes in the fabrication process are ±150 ppm for propagation angle deviation of ±0.5deg , ±320 ppm for aluminum thickness deviation of ±0.05 µm and ±300 ppm for etching ratio of 0.5±0.05. Aging drift is less than -100 ppm after 2000 hours exposure.