Gou Endoh

Optimum leaky-SAW cut of LiTaO/sub 3/ for minimised insertion loss devices

The paper describes how the propagation loss /spl alpha/ of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle /spl theta/ for rotated Y-X LiTaO/sub 3/. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero /spl alpha/ can be realised when the slow-shear component is decoupled. This means that the optimal /spl theta/ giving zero /spl alpha/ should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal /spl theta/ shifts to 40-42/spl deg/ from the conventional value of 36/spl deg/. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing /spl theta/ to circa 42/spl deg/ from 36/spl deg/. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42/spl deg/YX-LiTaO/sub 3/.

Optimum cut of LiTaO/sub 3/ for high performance leaky surface acoustic wave filters

The paper describes how leaky surface acoustic wave (LSAW) propagation characteristics on LiTaO/sub 3/ depend upon its rotation angle when the Al electrode thickness is increased. It is shown that the propagation loss arising from the leaky nature changes parabolically with both the film thickness and rotation angle, and becomes zero when they are properly chosen. This means that even when relatively thick electrodes are needed, zero propagation loss is always achieved by properly determining the rotation angle for LiTO/sub 3/. When the electrode thickness is 0.07/spl sim/0.1 wavelengths, for example, LSAWs on the 40/spl sim/42/spl deg/ Y-X LiTaO/sub 3/ offer zero propagation loss without deteriorating other characteristics. Ladder filters for 800 MHz range were fabricated, which essentially need thick Al electrodes. As is predicted by theoretical calculation, experimental results showed that if the rotation angle a is increased to circa 42/spl deg/ from the conventional value of 36/spl deg/, the insertion loss and shape factor are improved by 0.7 dB and 0.26, respectively. The result gives a valuable guideline for determining the optimal rotation angle of LiTaO/sub 3/ to be used for high performance LSAW filters, which are one of the key components in RF sections of mobile communication systems.

High performance balanced type SAW filters in the range of 900 MHz and 1.9 GHz

This paper describes balanced SAW filters with low insertion loss and high stopband rejection, which are applicable to 900 MHz and 1.9 GHz range portable telephone. The longitudinal coupled type double mode SAW design is suitable for balanced filter design. The 42 degree Y-X LiTaO/sub 3/ substrate is chosen to get low insertion loss and high Q factor performances. The design and evaluation method are studied and the effect of phase difference between balanced terminal signals is shown. The new filter design makes it possible to convert input/output impedance in order to match to an IC impedance.

A study of leaky SAW on piezoelectric substrate with high coupling factor

Performance of the leaky SAW on rotated Y-X LiNbO3 with a heavy electrode is presented. The characteristics of propagation loss, phase velocity, and electromechanical coupling factor of the rotated Y-X LiNbO3 substrate with several electrode thicknesses were simulated. Experimental results using a delay line confirm the theoretical calculation. The optimal rotation angle shifts from conventionally 64° to a higher angle with the heavy electrode. Performance of the SAW on rotated Y-X LiNbO3 is strongly dependent upon Al film thickness.