Electrical trimming of diffused single crystal silicon resistors using aluminum/silicon alloying

Abstract

Electrical trim techniques for reducing the value of a trimmable single crystal silicon resistor (trimistor) are presented. Computer-controlled current pulses are used to incrementally decrease the value of the trimistor through metal/silicon alloying. Variations of both single and multipulse current pulses are investigated. Physical mechanisms, based on electron microscopy of trimistors trimmed under various conditions, are hypothesized to explain the observed trim behavior. Threshold currents are dependent on the initial value of the resistor, the applied current density and the trim method. The electrical trim technique for a single trimmable resistor element is optimized. The final resistance values of the trimmed trimistors are shown to be stable provided that a current at or above the threshold current is not applied thereafter. The performance of both N+ and P trim resistors is evaluated over temperature and accelerated operating life.