Frequency instabilities in SAW resonators and oscillators

SAW (surface acoustic wave) oscillator stability is limited by intrinsic instabilities of the oscillating loop and by instabilities due to external causes translated into phase noise. Thus, frequency and phase fluctuations are due to noise in the SAW resonator and its electronics and to temperature effects and mechanical stresses acting on the SAW device. Results concerning both aspects of the problem are described. An analytic method is used to choose a quartz cut which minimizes simultaneously the sensitivities to static thermal effects and to mechanical stresses which induce frequency shifts through the support deformations of the propagation substrate. Experimental curves on an STC cut and a new low-sensitivity cut are presented. Stability measurements are reported for several SAW oscillators built from SAW resonators fabricated according to different processes. Short-term stability and aging are compared, and their relation to the details of fabrication is discussed