State-of-the-art phase noise performance has been demonstrated for both surface acoustic wave (SAW) r e s o n a t o r a n d d e l a y l i n e s t a b i l i z e d oscillators [l -51. The same basic feedback-loop oscillator design philosophy 16, 71 was applied i n each case in order to achieve these results. This paper reviews the design, fabrication, component selection, a n d performance for a n extremely low-noise SAW resonator hybrid circuit oscillator. Finally, s e v e r a l r e c e n t r e s u l t s including t h e flicker noise of SAW resonator devices a n d the vibration sensitivity of all quartz package SAW r e s o n a t o r s a r e d i s c u s s e d i n t h e c o n t e x t of p o t e n t i a l S A W o s c i l l a t o r p e r f o r m a n c e enhancements.
Measurements of 1/f (or flicker) frequency fluctuations in SAW resonators fabricated with etched groove reflectors on single crystal quartz have shown that the observed noise levels vary inversely with device size. These measurements were made on sixteen 450 MHz resonators of four different sizes. The 1/f noise levels were also evaluated on twenty-eight other SAW resonators ranging in frequency from 401 to 915 MHz. This additional data provides valuable information on the dependence of the flicker noise levels on resonator frequency. A model based an localized, independent velocity fluctuations in the quartz is proposed which correctly fits the observed size and frequency dependence of the measured 1/f noise levels. This model suggests that the velocity fluctuations originate in small regions (much less than ~5 mum in diameter) randomly distributed throughout the quartz with an average separation of about 5 mum between independent (incoherent) sources. The magnitude of the localized fractional velocity fluctuations, Deltav/v, averaged over a 5 micron cube is on the order of 1x10 (-9).
All quartz package (AQP) Surface Acoustic Wave (SAW) hybrid circuit oscillators with low vibration sensitivity, typically 3 to 4~1 0 -'~/ g , have been routinely achieved, provided that the oscillator package is sufficiently rigid to minimize bending stresses caused by vibration loading. This has been accomplished by bonding a suitably thick ceramic stiffener to the base of the oscillator housing. However, because of size constraints, some applications cannot accommodate a sufficiently thick stiffener. One approach toward overcoming this potential limitation on performance is to use finite element analysis to determine the stresses in the base of an oscillator package that would otherwise have an insufficiently thick stiffener, and then arrange to mount the AQP SAW device in a region of minimal stress. This approach was verified experimentally by comparing the vibration sensitivity of the same oscillator with the AQP SAW device mounted in both high-and low-stress regions. The result of the experiment was a factor of two reduction in the oscillator's vibration sensitivity. An alternative approach is to apply mass loading directly to the AQP SAW device. This is accomplished by bonding two small weights, approximately 60 mg each, to the backside of the AQP SAW substrate. Under vibration loading, these weights alter the stress gradients in the active acoustic area of the SAW substrate which reduces 7 , the magnitude of the vibration sensitivity vector.The same procedure was unsuccessfully applied to AQP SAW oscillators that had sufficiently thick stiffeners. Thus, mass loading is only effective in decreasing i: for an oscillator with an insufficiently thick stiffener.
The results of an investigation to establish whether the interdigital transducer (IDT) finger metalization was the source of observed flicker (Ilf) noise levels in high performance SAW resonator devices are described. Several alterations to the basic IDT finger metal deposition technique were used in order to vary the grain size in over approximately a 3:l range (-0.25 p m to -0.09 pm) copper-doped aluminum thin-films. Grain size was varied by changing the background 0, pressure during transducer metal deposition. In addition, the influence of grain size differences through the addition of Si or Ti as dopants in was examined in conjunction with compositional the copperdoped aluminum thin-films. The electrical performance (e.g., residual flicker (U0 noise, loaded-Q, unloaded-Q, and turn-over temperature) for more than onehundred devices was characterized, and a number of samples (TEM) to examine the corresponding microstructure of the were analyzed using transmission electron microscopy transducers' finger metalization. Although a correlation hetween average grain size and residual flicker (l/D noise hasis for further investigations into the source, or sources, was not found, the experimental techniques provide the of flicker ( M j noise in SAW resonator devices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.