Electrode Effects on Aluminum Oxide Tunnel Junctions

Handy, R.M.

doi:10.1103/physrev.126.1968

Cited by 76 publications

(10 citation statements)

References 14 publications

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“…2 The Bean-London model is applicable for type II superconductors, when the surface magnetic field is in excess of the lower critical field, He!. Losses which depend linearly on frequency have been observed in other hard superconductors.…”

Section: Discussionmentioning

confidence: 99%

Alternating Current Power Losses in Superconducting Nb-Zr Alloys

Wisseman

Boatner

Low

1964

Journal of Applied Physics

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A calorimetric technique, involving measurement of the thermal conductivity, was used to measure non-Ohmic ac power losses in short, 0.25-mm-diam samples of superconducting Nb-25% Zr and Nb-33% Zr wire as a function of frequency, current amplitude and waveform, and temperature. The observed power losses at 4.2°K ranged from 6X 10-11 to 10-7 W /cm. The losses depended linearly on frequency in the range 60--40000 cps and decreased approximately as T2.6 for temperatures T in the range 2.0o-4.2°K. Peak currents from 1 to 8 A were used to determine that the power loss was a function of the peak current 1m rather than the rms current and also was proportional to Imn, where n varied from 2.6 to 4.5. These results indicate a hysteresis loss mechanism with no detectable relaxation effects for the entire frequency range covered. Models which have been proposed to account for hysteresis losses in hard superconductors are discussed. The results of this experiment are compared with earlier measurements on Nb-Zr alloys. There is considerable disagreement between the present results and the published results of Zar in magnilude and in lhe frequency and current dependences of the ac power losses.

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Section: Discussionmentioning

confidence: 99%

Alternating Current Power Losses in Superconducting Nb-Zr Alloys

Wisseman

Boatner

Low

1964

Journal of Applied Physics

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“…Handy [18] found that smaller metal atoms gave thinner effective barriers, suggesting that the smaller atoms penetrated further into the oxide. This would have the effect of reducing din our simple model, which would increase y and therefore Am.…”

Section: A W / W = -( Q 2 / 1 6 N E E O D 3 M W~) (mentioning

confidence: 99%

Thermal Conductivity of Ribbonlike Carbon Films

Matsumura¹,

Wang

Shinohara

et al. 1995

Jpn. J. Appl. Phys.

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The shift in position on bias reversal of the 450 meV OH mode in tunnel junctions comprised of aluminium/aluminium oxide/M where M is Pb, Ag and Sn is investigated using inelastic electron tunnelling spectroscopy.Measurements presented here reveal that the peak shift is independent of M within the experimental error of this work. This is consistent with a simple superposition of the three electric fields acting on the hydroxyl group due to the tunnel barrier, the image charge and the external bias respectively. The implication is that as far as the subtle effect of peak shifts on reverse bias is concerned, the tunnel junction environment of the adsorbed species is essentially benign.For certain electrode thicknesses and geometries, peak shifts can arise due to finite electrode resistance even when four-point probe conditions pertain. A simple procedure for treating these is presented.

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“…During these tests of the oxide thickness, three types of contacts were placed on the A1 2 03. Au paste contacts, evaporated Pb contacts as reported by Handy 8 and small In spheres at the end of a tungsten wire positioned with a micromanipulator, were used.…”

Section: IIImentioning

confidence: 99%

High Frequency Tunnel Device Study

Feist¹

1963

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The work reported here is aimed at achieving low noise microwave amplification -specifically: 20 db gain, 6 db noise figure at 10 kMc, and 1 kMc bandwidth -by using tunneling. The program has two phases running concurrently. The first is aimed at an all solid state device, the second, at using a thin film cathode in conjunction with a microwave structure.In accordance with the original work statement, the feasibility of the two approaches has been determined. Exploratory work has shown that the approaches taken in the first phase will not produce the required amplification without a long and expensive effort; accordingly, further work on this phase will be suspended. The results obtained in the second phase appear to be much more promising, and henceforward all of our efforts will be diverted to this approach. Phase IThe program on the solid-state amplifier during this period involved (1) an examination of the metal-base transistor, (2) growth of A1 2 0 3 films by plasma oxidation, (3) fabrication and testing of MIA structures with an evaporated CdS emitter, (4) fabrication and testing of MIA structures with an evaporated CdS collector, and (5) an exploratory effort to fabricate a thin-film analogue structure.Metal-base transistor structures have been fabricated with Ge collectors, thin-film Au bases and single crystal Ge, Si, and evaporated CdS emitters. Active device behavior has been observed and reported.Plasma oxidation of Al films deposited upon Ge has been performed. The resulting oxides are different from those grown thermally or with UV stimulation. Good tunneling characteristics have not been observed.Metal-interface amplifier structures with evaporated CdS emitters have shown no improvement and still suggest that hot electrons are not involved in the current transfer mechanism.Phase II Approximately 150 test cathode structures have been produced using the methods described in previous Technical Notes.Pulsed emission current densities of up to several amperes per square centimeter have been obtained. Lifetime remains a serious problem. It is -iiibelieved, however, that with improved uniformity of the tuneling insulator satisfactory operation of the tunnel cathode over extended periods should be possible.The requirements on cathode dimensions and performance necessary to achieve 20 db gain at 10 kMc have been theoretically established. Work was performed towards fabricating emitting structures suitable for use as the cathode in such a tube.Since the tunneling insulator appears to be one of the very critical elements in the production of a suitable tunnel cathode, a study of these layers was undertaken. Work was begun using an ellipsometer for determining the thickness of such films. Steps were taken towards forming electrically stronger insulator layers. This work was aimed primarily towards the study of different methods of oxidation of aluminum; as well as forming insulator layers different from Al 2 0y 3 Experimental evidence about the distribution of emission over the emitting surface and th...

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Electrode Effects on Aluminum Oxide Tunnel Junctions

Cited by 76 publications

References 14 publications

Alternating Current Power Losses in Superconducting Nb-Zr Alloys

Alternating Current Power Losses in Superconducting Nb-Zr Alloys

Thermal Conductivity of Ribbonlike Carbon Films

High Frequency Tunnel Device Study

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