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

Abstract

The paper describes how leaky surface acoustic wave (LSAW) propagation characteristics on LiTaOi depend upon its rotation angle when the AI electrode thickness is increased.It is shown that the propagation loss arising from 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 the relatively thick electrodes are needed, zero propagation loss is always achieved by properly determining the rotation angle for LiTOl When the electrode thickness is 0.07 -0.1 wavelengths, for example, LSAWs on the 40-42" Y-X LiTaOi offer zero propagation loss without deteriorating other characteristics.Ladder filters for 800MHz range were fabricated, which essentially need thick AI electrodes. As is predicted by theoretical calculation, experimental results showed that if the rotation angle B is increased to circa 42" from the conventional value of 36' , the insertion loss and shape factor are improved by 0.7dB and 0.26, respectively. The result gives a valuable guideline for determining the optimal rotation angle of LiTaOi to be used for high performance LSAW filters, which are one of the key components in RF sections of mobile communication systems 1. INTRODUCTlON Because of their attractive features such as compactness, light weight and low price, surface acoustic wave (SAW) filters are widely used in both RF and IF sections of mobile communications hand set units. For RF filter applications, adding to high stop-band rejection, ultimately low insertion loss is required for reduced power consumption or to realize better reception sensitivity in these terminals. For this purpose, leaky SAWS (LSAU's) on 36" Y-X LiTaO? [ l ] and 64' Y-X LiNb03 [ 2 ] have extensively been usedI3-61 because of their very large electromechanical coupling factor K' and low propagation loss. In modem mobile communication systems, their operation frequencies are becoming higher and higher: 800-900MHz range is employed in AMPS and GSM, while I~5GHz range in PDC1500, 1.8-I.9GHz range in PHs, PCS and PCN, and 2.4Gl-I~ range in wireless LAN When designing LSAW 0-7803-3615-1/96/$5.00 0 1996 IEEE 19% IEEE ULTRASONICS SYMPOSIUM -71

On the theory of the elastic wave propagation in a crystal coated with a solid layer. I. Two-component surface waves and simple reflection

“…However, it remains unclear whether H j determined from equations (3.28) will be positive so that numerical computations are needed to check the possibility of the transformation of the leaky solution into the surface wave in multilayered structures. That in fact a lm allows the suppression of radiative loss is con rmed by numerical computations for Y {X LiTaO 3 cuts coated with Al (Kawachi et al 1996). The piezoe¬ect in LiTaO 3 is of no signi cance in this case.…”

Clinton Sylvester Hartmann: His achievements and our unwritten stories

“…The stories tell how deeply Clinton contributed to my career up and early achievements including FEMSDA [2] and 42 o YX-LiTaO 3 (42-LT) [3]. They also show how Clinton motivated, trained, and directed one young engineer.…”

“…He was interested in this topic, however, I did not receive a response on this from the company. A few year later, I proposed the same idea to Fujitsu, which succeeded in finding the optimal orientation (42-LT) [3] and got certain profit.…”

Ladder Type Saw Filter and Its Application to High Power Saw Devices

“…18 shows a comparison of S21 between a ladder type filter and a DMS filter. The substrate used for both filters is 42Y-X LiTaO3, which is rotated Y cut further than 36 degrees and is found to have lower loss for thick Al films as reported by Kawachi et al 19. The advantages of the ladder type SAW filter when compared with the DMS filter are, a) Wider band-widthb) Higher power durability.…”