Potential Distribution and Negative Resistance in Thin Oxide Films

Abstract

Al–SiO–Al–SiO–Au triodes with SiO thicknesses between 150 and 500 Å have been used to measure the potential distribution in thin oxide films before, during, and after the development of voltage-controlled negative resistance (VCNR) in the current-voltage characteristics. Development of VCNR in the triode is accompanied by the establishment of a high-field region about 120 Å in thickness near the negative electrode. If triode potentials are reversed after developing conductivity, VCNR is still found in the current-voltage (I-V) characteristic of the triode but the potential distribution in the triode is only slightly changed. VCNR in the I-V characteristic is a high-field phenomenon but it does not depend on field emission of electrons from the metal electrodes. Conductivity in the bulk of the insulator is Ohmic with electron mobilities ∼10−3−10−2 cm2/V-sec. The behavior of Al–SiO–Au diodes is identical to that of triodes. Electroluminescence of Al–SiO–Au diodes, which appears when conductivity is developed, is characterized by a steep rise in intensity at 1.8 V, the voltage at which electron emission into vacuum from such diodes is first detected. Both electroluminescence and electron emission provide evidence for high-energy processes in the oxide film. A phenomenological model of conductivity and voltage-controlled negative resistance in thin oxide films is developed in which impurity conduction is the most important conduction mechanism.