AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS1+MC-ThM

Paper SS1+MC-ThM3
The Behavior of Ultrathin Al@sub 2@O@sub 3@ Films in Very High Electric Fields: STM-induced Pitting and Dielectric Breakdown

Thursday, October 5, 2000, 9:00 am, Room 208

Session: Oxide Applications and Oxidation
Presenter: J.A. Kelber, University of North Texas
Authors: N.P. Magtoto, University of North Texas
C. Niu, University of North Texas
J.A. Kelber, University of North Texas
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The behavior of ultrathin oxides under high electric fields is of critical importance to areas as diverse as microelectronics (gate oxides, magnetoresistance devices) and corrosion. We report the use of high electric fields applied via the STM to induce pits and dielectric breakdown in ultrathin @gamma@'-Al@sub 2@O@sub 3@ films (7 Å thick) grown on Ni@sub 3@Al(111) substrates in UHV. Voltage pulses (bias voltages of 1-6 V, either polarity) are applied to a specific location on the oxide surface with the feedback current loop operative to prevent tip/sample physical interaction. Subsequent imaging at 0.1 V bias voltage and 1 nA feedback current reveal the effects of high field on surface composition and topography. Results show that dielectric breakdown occurs at a field of 12.3±0.7 MV/cm. Breakdown is marked by the creation of an area ~20 nm high and 100 nm wide and the loss of the insulating nature of the oxide as deduced from I/V spectroscopy. Once the threshold breakdown voltage is reached, the STM tip retracts precipitously (~20-25nm) from the sample surface due to the onset of the leakage current. At fields ~ 60 % of breakdown, small pits in the oxide that are 0.4-0.8 nm deep can be created. Repeated application of this field within the pit will cause dielectric breakdown, even though the same field will not induce breakdown in regions away from the pit. The results provide direct evidence of the ability of localized defects to decrease the barrier to dielectric breakdown in an ordered oxide film.