Electrical Conduction in Very Thin Polybutadiene Films Formed in a Glow Discharge

Abstract

Films in the thickness range 100 to 500 Å are studied. Ohmic contacts (gold electrodes) are formed only sporadically. In the best example of Ohmic contact, space-charge-limited current (SCLC) occurs at a field of 3×104 V/cm. SCLC is obtained in this and other specimens at fields great enough for field emission (3 to 5×105 V/cm) where trap densities about 1023/m3 were found, greater by a factor of ten than the lower field case. In less conclusive results and in general agreement with theory, a greater dependence on thickness as compared to voltage is found. The establishing of SCLC at fields great enough for field emission suggests a causative relation, perhaps tunneling through the blocking contact at the electrode-insulator interface. The change in the ac resistivity is lower than that using dc by about three orders of magnitude over the temperature range of 20° to 95°C. Three activation levels are found with transition points at 20° and 110°C. It is necessary to use a layer of SiO at the crossover region of the electrodes to prevent dielectric breakdown in this area. This protective layer is made sufficiently thick not to interfere significantly with the measurements on the polybutadiene.