Comparison between ST-cut quartz 25/spl deg/ and -60/spl deg/ NSPUDT propagation directions

This paper discusses directivity and other propagation properties of natural single phase unidirectional transducer (NSPUDT) propagation directions on ST-cut quartz. The work focuses on the comparison of surface acoustic wave (SAW) directivity and propagation properties between the ST-cut quartz -60/spl deg/, Euler angles: (0/spl deg/, 132.75/spl deg/, -60/spl deg/), and the ST-cut quartz 25/spl deg/, Euler angles: (0/spl deg/, 132.75/spl deg/, 25/spl deg/), NSPUDT propagation directions, including predicted and measured directivity responses for both propagation directions. The well-known SAW 25/spl deg/ propagation direction is used for low loss, high performance SAW filter designs for consumer products and communications applications. The ST-cut quartz -60/spl deg/ propagation direction has been predicted to have a reflection coefficient 2.5 times larger than ST-cut quartz 25/spl deg/. In addition the ST-cut quartz -60/spl deg/ satisfied the NSPUDT 90/spl deg/ reflection coefficient phase condition much more closely, resulting in an improved directivity response. For the delay line structures used in the experiments, the measured directivity is 10.1 dB for the -60/spl deg/ propagation direction. For the same structures, the measured directivity along the 25/spl deg/ propagation direction is about 5.0 dB. The experimental results given in this paper verify that indeed ST-cut quartz -60/spl deg/ has a higher directivity than ST-cut quartz 25/spl deg/, confirming the theoretical predictions. In addition, this work compares other propagation properties for both directions, namely, phase velocities, electromechanical couplings, temperature coefficients of delay, power flow angles, and metallic strip reflection coefficient amplitudes and phases.