Norio Hosaka

A Study of Al-Alloy Electrodes for High Power SAW Filters

Durability of aluminum-alloy electrodes for high power SAW filters which are used for antenna duplexers in cellular portable telephones is experimentally investigated. Titanium added aluminum is deposited by DC magnetron sputtering. The new alloy expands the limitation on the driving power of the filters. Temperature, particularly, accelerates the degradation of the high power filters, the film resistance causes an even greater increase in temperature. Thus, optimum value for titanium of 0.4 wt.% can be achieved for high durability filters.

Sputtered Al-Ti electrodes for high power durable SAW devices

DC magnetron sputtering and Ti addition for Al electrodes are studied to achieve higher durability of SAW (surface acoustic wave) devices operating at high frequency and high power. Experiments on SAW resonators and ladder-type SAW filters were conducted. The sputtering is shown to be better than conventional electron-gun evaporation for both the reproducibility of the film composition and durability. The sputtered Al films with 0.4-wt.%-to-0.8-wt.% Ti addition lead to a durability for three-times-larger power than for 0.7-wt.% Cu addition to evaporated Al films.<<ETX>>

Al electrodes fabrication technology for high-frequency and high-power durable SAW devices

Addition of Ti, Ge, and Zn to sputtered Al electrodes in order to obtain both high power durability and fine dimensional control in high-frequency SAW (surface acoustic wave) devices is investigated. Ti is shown to be more effective than Ge, Zn, and conventional Cu. Improvement of electrode durability to SAW power is related to the grain refinement and static stress incorporated by addition of Ti, Ge, Cu and by the sputter deposition. Investigation of fine dimensional control revealed that the electrodes with Ti addition resulted in smaller width deviation brought about by reactive ion etching a dyed UV-posi-type resist of the vertical wall; the deviation is 40% of that brought about with conventional wet etching.<<ETX>>

High isolation SAW antenna duplexer modules

Optimized phase shifter conditions for SAW antenna duplexer modules at not 50 ohm cases have been analytically provided to achieve desired isolation performances. In order to confirm the prediction, obtained optimum condition are applied to two cases. In the EGSM/DCS dual band SAW antenna duplexer modules case, impedances of low noise amplifier connecting the Rx ports are not 50 ohm when the amplifier are off state at transmitter period. We propose a optimized phase shifter circuit for EGSM and DCS Rx output ports using the equation. In Japanese cdmaOne duplexer case, we also propose an optimized phase shifter circuit for the transmitter circuit between Rx band trap and transmitter top filter block. The predictions are verified by the experiments.

Computer aided design of low-loss SAW filters employing IIDT for high performance mobile radio duplexer

The authors describe a computer-aided design method to optimize all the design parameters of the IIDT (interdigitated interdigital transducer)-type SAW (surface acoustic wave) filter so that it satisfies the required frequency and electrical characteristics. By connecting the admittance matrices of each IDT, each SAW propagation path, and each IIDT-track, a dual IIDT-track configuration is represented by a six-port admittance matrix in an equivalent circuit model. A merit function, which is defined as the sum of squared of deviations from the target specifications, is introduced to evaluate filter characteristics. By iterating calculations of the equivalent circuit model, the design parameters are determined so as to minimize the merit function. A high-performance filter which satisfies the requirement is thus achieved. Some design examples are given, and they are verified by experimental results.<<ETX>>

Study of high isolation techniques for surface acoustic wave duplexer modules

The isolation characteristics between transmitter and receiver ports for surface acoustic wave (SAW) antenna duplexer modules are studied. Three new techniques are developed to achieve the desired isolation performances in this study. Optimized phase shifter conditions are solved analytically. An improved switching circuit is proposed for cancellation of the inductive element of a pin-diode. A design rule of distance between two lines for SAW antenna duplexer modules is also proposed. The obtained condition and circuit are applied to an extended global system for mobile communication/digital cellular system (EGSM/DCS) dual-band and an extended global system for mobile communication/digital cellular system/personal communication system (EGSM/DCS/PCS) triple-band SAW antenna duplexer modules. Sufficiently high isolation characteristics are obtained.

Ti-Added Al Electrodes on LiTaO3 36° Y-X Substrates for High Power Surface Acoustic Wave Devices I

The influences of the internal stress of the film, annealing treatment and a sputtered Ti-added Al electrode on 36° rotated Y-X LiTaO3 substrates were investigated. Higher activation energy of the time to failure (TF) was obtained when the amount of internal stress was decreased. The annealing temperature is limited to below 400°C because of discoloration and phase change of the substrate. TF with Al-0.6 wt%Ti electrodes in IIDT filters became ten times that obtained with Al-0.2 wt%Ti electrodes. By the increase of the amount of Ti, the grain size and the standard deviation were decreased.

Miniature SAW duplexers with high power capability

Miniature SAW duplexers with high power capability corresponding to future GSM power regulation have been reported. We applied an improved cascade resonator structure to the duplexer in order to equalize power density on substrate. Power durability of the developed duplexers is verified by an experiment under the condition of 3/8 duty mode operation corresponding to future regulation. Furthermore, we reduce the coplanarity of the duplexer using a partial metalized patterning on the back of the base board. A 14.8/spl times/8.0/spl times/1.8 mm dimension structure and a 80 micron (80 micron improvement as compared with conventional structure) typical coplanarity is obtained for the duplexer.

Automatic design procedure using circuit composition technique for SAW devices

A fully comprehensive electrical admittance matrix composition technique including the effects of residual electrical elements (capacitance, inductance and resistance) will be reported corresponding the various kind of the devices. An automatic design technique based on the optimization method is applied using the above composition routine. The automatic design procedure determines the parameters for SAW Filter elements and the external circuit element. It is possible that the procedure perform using measured admittance matrix elements. In order to verify the technique dual band filters and duplexers for digital mobile terminals were designed using the above procedure. The performance of these devices was found to be in good agreement with the design predictions.

Sputter Deposition for High Power Durable SAW Electrodes

DC magnetron sputtering of Al and Al alloy is studied to fabricate high power durable SAW electrodes. Experiments on SAW resonators as a test medium show that the time to failure is inversely proportional to the cube of SAW power in the sputtered Al films. Structure analyses and measurements on static stress reveal the following: the reduced static stress has a significant effect on higher durability to SAW power in the sputtered Al electrodes, and in addition, reduction of grain size in the films results in higher resistance to mechanical migration.