Measurement of Flicker Noise in High-Q, Lithium Tantalate, Bulk Wave Resonators

High-Q, LiTa03, bulk wave resonators have been fabricated for use in low insertion loss, bandpass ladder filters 111. The high-Q (80.000 at 2 MHz) large acoustic coupling (7: 1 capacitance ratio) and low temperature coefficient (1 5°C turnover temperature) make the resonators attractive candidates for low noise voltage controlled oscillators capable of large percentage tuning range. Measurements of resonator device short-term frequency stability have been made and indicate device self-noise levels are characterized by Sy (f = 1 Hz) in the range 1 x These levels are typically much higher than that exhibited by HF quartz resonators. The relatively high levels of device selfnoise, as well as noted noise level improvement versus time achieved under conditions of continuous RF drive, are consistent with similar results observed for LiNb03 SAW resonators by R.L. Baer at Hewlett Packard [2]. VHF, overtone mode resonators are currently being fabricated, and results of comparative evaluation of these devices should provide added insight into the influence of drive level, overtone mode, acoustic coupling, unloaded Q, etc, on resultant resonator noise level. Lateral field device excitation may provide a means for obtaining significant increase in obtainable resonator unloaded Q. In addition, LiTAO3 resonator stabilized oscillators have been fabricated, and measurement of oscillator output signal phase noise sideband spectra confirm that near-carrier (flicker-of-frequency) noise is due to short-term frequency instability in the resonators themselves. to 5 x