Pulse trimming of thin-film resistors

Resistivity decreases can be induced in Cr-SiO films by current pulses of short duration. Precision resistance measurements between pulses permit trimming of film resistors to 0.1 percent in less than one second, provided pulse power, duration, and frequency are adjusted properly. A trimmer system that contacts several resistors through multiple probes and controls the process through a paper-tape reader is described. Pulse trimming has been applied to film resistors ranging from pure Cr up to Cr-40 mole % SiO. After annealing at 400°C, additional resistance decreases of at least 20 percent are possible with all compositions containing SiO. The interval between 15 and 30 mole % SiO is most suitable because substantial resistance changes are obtained at pulse powers well below the limits at which resistors burn out.