Akitsuna Yuhara

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 Frequency and High Power SAW Devices

DC magnetron sputtering and Ti addition for Al electrodes are studied to achieve higher durability of SAW devices operating at high frequency and high power. Experiments on SAW resonators as a test medium show the following: the sputtering is better than conventional e-gun evaporation for both the reproducibility of film composition and for durability; 0.6 wt% to 0.9 wt% Ti addition to the sputtered Al films leads to durability for 3 times larger power than 0.7 wt% Cu addition to evaporated Al films, while less loss is experienced if resistivity is the same in each film.

Low loss SAW matched filters with low sidelobe sequences for spread spectrum communications

A 300 MHz SAW matched filter with reduced mismatch-loss and a transducer coded by a low autocorrelation sidelobe sequence has been developed for 1 Mbps SS weak radiation-power wireless communication modem. This low autocorrelation sequence of 25 chips was found to conform to the DS spreading DPSK signal. The sequence reduced the output signal sidelobe 6 dB lower than a 31 chip m-sequence, and further obtained a higher processing gain than that of Barker sequences. Furthermore, to reduce mismatch-loss in temperature stable SAW matched filters, a localized layered structure has been developed. ZnO is deposited only on the normal transducer on a ST-cut quartz substrate, reducing the mismatch-loss by 9 dB. An SS radio modem unit using this SAW matched filter shows a rather long transmission distance of about 20 m with a low current consumption 210 mA, considering such a high data rate 1 Mbps and the strict power regulation.

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>>

Study on Power Durability of Ti-Containing Al Surface Acoustic Wave Electrodes, Using Interdigitated Interdigital Transducer Filters

The power durability of Al-0.6 wt%Ti electrodes in 900 MHz interdigitated interdigital transducer surface acoustic wave (IIDT SAW) filters was investigated through accelerated time-to-failure (TF) tests in relation to grain sizes and annealing, and was further compared with that of pure Al, Al-0.5 wt%Pd and conventional Al-1.1 wt%Cu electrodes. TF of the Al-0.6 wt%Ti electrodes in the IIDT filter is increased by reducing the average grain size and the standard deviation of the grain size. Annealing of Al-0.6 wt%Ti film, however, results in increase of the average grain size and decrease of TF. TF of Al-0.6 wt%Ti electrodes was the largest: much larger than that of Al-0.5 wt%Pd electrodes, having almost the same grain size and standard deviation as Al-0.6 wt%Ti electrodes, and nine times as large as that of Al-1.1 wt%Cu electrodes.

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>>

Study of triple transit echo for time sidelobe of SAW matched filter

Surface Acoustic Wave (SAW) matched filter is a key-device for Spread Spectrum (SS) communication. We have shown that the Triple Transit Echo (TTE) level of a matched filter for the SS signal is lower than that of an ordinary SAW transversal filter for CW signals even if the external circuit impedance is fully matched to the SAW matched filter. A time-domain analysis using a circuit network tool for various kinds of construction has been used for the matched filter with a 25-chip low autocorrelation sequence. The analysis agreed with the experiments to verify this TTE behavior.

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.

SAW Comb Filter for TV Channel Indicating System

We successfully developed a very wideband and highly accurate SAW comb filter for a new concept of TV channel indicating system. The filter haa peaks and bottoms with P constant frequency interval (2 MHz) and has following superior perfomces. (I ) mimum frequency is very high (824 HHz for Japan system) then minimum electrode width of the IDTe is 1.1 t 0.1 TV channel). (3) Peak and bottom frequencies are highly accurate (2 0.3 MIIZ).

Measurements of SAW effective velocity angular-variation under metal strip gratings and their application to ASPW analysis

Measurements of SAW effective velocity angular-variation under metal strip gratings, using a comb-filter method are described. A distinctive characteristic was newly observed at higher frequency; the minimum observed at propagation angle 0° of the above angular-variation of LiNbO3-128° rotYX single crystal. The minimum is originated by SAW dispersion considered to be mainly due to stored energy effect. Moreover, as an example to utilize the above measurement results for an analysis of SAW second order effects, the frequency response of a 480 MHz SAW filter was calculated including SAW diffraction effect using angular spectrum of plane wave (ASPW) method. The simulation result was in good agreement with the experimental one