Probable Ion Signature in Quartz Electrodiffusion Data

Hanson, W.P.

doi:10.1109/freq.1984.200734

Cited by 4 publications

(2 citation statements)

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“…2 and 3.) These are, no doubt, the result of impurity depletion during sweeping [2]. Multiplesweeping runs using the same bar are roughly exponential in the increasing and decreasing temperature regions.…”

Section: Evaluation Of Sweeeina and Its Comeletionmentioning

confidence: 94%

“…Thefollowing,temperature-ramped [2][3][4], sweeping procedure is typical for large bars: the full DC voltage is applied at the beginning and is maintained throughoutthe run; the temperature is increased automatically 10 the maximum temperature at a rate of 20 O C h i ; the temperature is then held constant at the maximum (isothermal phase) until the current density drops to a near-constant level; the temperature is then decreayed automatically to room temperature at a rate 20 OC h i .…”

Section: Temderature-rameed Sweedinqmentioning

confidence: 99%

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Sweeping quartz crystals

Gualtieri

Proceedings., IEEE Ultrasonics Symposium

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Sweeping is a purification process that removes certain impurities and thereby improves the radiation sensitivity of quartz crystals. It is an electric field driven, high-temperature, solid-state diffusion process. The major steps of a typical sweeping process consist of: applying electrodesto the Z-surfacesof a lumberedquartz bar; applying voltage to the electrodesto produce an electricfield of approximately 1 kV/cm; heating the bar slowly either in air, vacuum, or in hydrogen containing or inert atmospheres to about 5 0 0 ' C; monitoring the current through the bar (as sweepingprogresses,the current decreases); when the current decays to some near-constant value, cooling the bar slowly to room temperature,and removing the voltage.Alkali-metal impurities, such as Li+ and Na' , are charge compensators for trivalent aluminum impurities in quartz. When sweeping is performed in air or H2, the alkalis diffuseto the cathode and are replaced by the indiffusion of hydrogen at the anode. The alkali-metal impurities are subsequently removed by lapping the Zsurfaces. The sweeping process also modifiesdislocations, reducing the tendencyfor formation of etch channels.Recent advances have involved the use of impurity characterizations, such as: electron spin resonance (ESR); acoustic loss measurements;and infrared absorption spectroscopy (IR). Future directions for technology enhancementwill probably involve: developmentof methodsto control theelectrode-quartz-gasinterface; use of H+ ion implantation techniquqand UV-stimulatedsweeping.

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Section: Evaluation Of Sweeeina and Its Comeletionmentioning

confidence: 94%

Section: Temderature-rameed Sweedinqmentioning

confidence: 99%

Sweeping quartz crystals

Gualtieri

Proceedings., IEEE Ultrasonics Symposium

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Electrodiffusion (sweeping) of ions in quartz-a review

Martin

1988

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Sweeping, a high-temperature process that selectively exchanges monovalent ions in quartz, is reviewed. Sweeping is used commercially to replace interstitial alkalis with hydrogen. Electrodiffusion improves the radiation hardness of quartz oscillator crystals and lowers the etch channel density. Sweeping affects the substitutional aluminum with its associated alkali and the extended dislocation networks with their precipitated impurities. At high temperatures the interstitials are freed and swept down the open Z-axis channels by an applied electric field. These interstitials can then be swept out at the negative electrode, provided replacement ions, usually hydrogen, are brought in at the positive electrode. Thus, the alkali associated with the aluminum is replaced by a hydrogen, and the precipitates in the dislocation networks are modified so that they are less reactive to the etchants. With the field applied at a room temperature, a peak or plateau in the sample current is observed during warm-up near 250-300 degrees C, followed by a decay at the 500 degrees C sweeping temperature. When the current becomes steady, the sweeping is thought to be complete. While infrared and high-temperature resistance measurements are useful, EPR techniques seem to provide the most reliable test for complete ion exchange at the aluminum site.

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