The evolution of SAW oscillator technology over the past 17 years is described and a review of the current state of the art for high-performance SAW oscillators is presented. This review draws heavily upon the authors' own experience and efforts, which have focused upon the development of a wide variety of SAW oscillators in response to numerous high-performance military system requirements. >

Precision surface-acoustic-wave (SAW) oscillators

Narrow Bandpass Filter Using Double-Mode SAW Resonators on Quartz

SAW delay lines and resonators are now used in a number of oscillator applications where high frequency and/or low noise are important considerations. All present applications, however, have a large frequency window which permits very loose tolerances on frequency settability and long term stability. Yet, there exists a large number of potential applications which have a much smaller frequency window, on the order of 210 ppm. For military applications additional requirements may be: (1) a noise floor approaching -180 dBc/Hz, (2) low vibration sensitivity, and (3) temperature compensation or fast warm up ovens. Significant progress in building such precision oscillators has bee:i made at Raytheon and other laboratories, and will be discussed in this paper. Particular emphasis will be given to the problems of frequency settability and long term stability. Obtaining a precise frequency setting is strongly influenced by fabrication variables and may require a frequency trimming step. A discussion of both topics will be presented along with data showing observed frequency shifts during bake-out and sealing of SAW devices. The topic of long term stability will also be discussed and data will be presented to show aging rates for trimmed devices, polyimide mounted devices, and devices with large fractional metalization .

Precision Surface Acoustic Wave (SAW) Oscillators

Narrow Bandpass Filter Using Dopuble-Mode SAW Resonators on Quartz

A method for trimming the resonant frequency of fabricated SAW devices. The resonant frequency of SAW devices of the type having a substrate with structures made of a second material, other than the substrate material, upon its surface, is decreased by removing quantities of the substrate material until the desired change in frequency is obtained. In one embodiment, the substrate material of the SAW device is removed by etching the substrate in a fluorocarbon plasma, which leaves the structure made of the second material substantially unchanged. In a second embodiment, the resonant frequency of SAW resonators is increased by heating the SAW device at a temperature in excess of 250° C. until the desired change in resonant frequency is obtained.

Method for post fabrication frequency trimming of surface acoustic wave devices

Hybrid SAW Oscillator Fabrication and Packaging

http://ieeexplore.ieee.org/iel5/10315/32748/01537442.pdf

Absolute and Differential Aging of SAW Resonator Pairs

A non-conventional acoustical type of underwater sound detector utilizing surface acoustic wave (SAW) resonator controlled oscillators is described. Unlike ceramic baseband transducers, the output variable is a frequency offset from a reference oscillator. The SAW sensor is comparable to conventional baseband sensors with a sensitivity of -180 dB re 1 V/uPa. Experimental sensors are described and characterized in terms of noise floor, signal to noise ratio, and frequency response. Using a SAW resonator controlled oscillator results in maximlm stability and hence a minimum noise floor. In addition a minimum of circuit grain required foroscillation minimizes the amount of power consumed by the sensor circuitry.

Surface Acoustic Wave Underwater Sound Sensors

The electrical characteristics of surface acoustic wave devices depend critically on the physical and chemical properties of the device surface as well as on the interaction between the propagating wave in the substrate with its surrounding gaseous medium. tions were carried out in a dual chamber vacuum apparatus with a SAW resonator isolated in each chamber. One resonator, kept continually under vacuum, acted as a reference, while the second resonator was exposed to a variety of gases under controlled conditions. The nature of the chemical changes occurring on the surface were confirmed by examining the device surface by x-ray photoelectron spectroscopy. Experiments have been performed to study the physical and chemical absorption of reactive and non-reactive gases. experiments are needed to understand and model the aging mechanisms of SAW resonators. results will be presented. The gas-surface interac

http://ieeexplore.ieee.org/iel5/10280/32713/01534325.pdf

Surface Chemistry Related to SAW Resonator Aging

A 375 MHz SAW resonator controlled oscillator is developed for application in the Transit satellite marine navigation system. The SAW oscillator, in a two-cubic-inch hybrid package, contains a heater, a voltage regulator and a divider and is a direct replacement for a bulk wave oscillator and its multiplier chain. Short term stability of 2E-10 and aging of 3E-8/day were achieved at 75 'C. Comparison tests showed that the navigation system accuracy with the SAW oscillator was equivalent to a bulk oscillator.

E.J. Staples

Papers

Hybrid SAW Oscillator Fabrication and Packaging

Absolute and Differential Aging of SAW Resonator Pairs

Surface Acoustic Wave Underwater Sound Sensors

Surface Chemistry Related to SAW Resonator Aging

Commercial Satellite Navigation Using SAW Oscillator