ZNO SINGLE BARRIER VARISTOR FOR LOGIC CIRCUITS PROTECTION

A PROCESS IS DESCRIBED FOR FABRICATING ZNO VARISTORS WITH A NON-LINEARITY COEFFICIENT FROM 25 TO 50 AND A BREAKDOWN VOLTAGE IN THE RANGE OF 2 TO 5 VOLTS TO PROVIDE TRANSIENT VOLTAGE PROTECTION FOR LOGIC CIRCUITS. THE PROPOSED PROCEDURE CONSISTS OF MAKING A SINGLE BARRIER JUNCTION BY ALLOYING OR SPUTTERING A THIN LAYER OF THE ADDITIVE OXIDES OF BI, SB, CO, CR, ETC. ON ZNO POLYCRYSTALLINE SUBSTRATE. THE POLYCRYSTALLINE BODY IS USED FOR ENERGY ABSORPTION AND THE JUNCTION PROVIDES THE REQUIRED NON-LINEAR CURRENT-VOLTAGE CHARACTERISTICS. THE STRUCTURE CAN ALSO BE ACCOMPLISHED BY IONIMPLANTATION OR BY USING METALLIC CONTACTS CONTAINING OXIDES OF BI AND PB WHICH ALSO SERVE AS A DIFFUSION SOURCE FOR GRAIN AND/OR GRAIN BOUNDARY DOPING. THIS METHOD PROVIDES AN IC COMPATIBLE PROCESS AND A LOW-COST PROCESS. FABRICATION AND CHARACTERIZATION OF THESE VARISTORS AND THE ROLE OF ANNEALING TEMPERATURE AND AMBIENT AND ITS EFFECT ON THE I-V CHARACTERISTICS WILL BE EXAMINED IN DETAIL.