Characterization, evaluation, and comparison of laser-trimmed film resistors

Methods for predicting the performance of laser-trimmed film resistors taking into account the properties of the heat-affected zone (HAZ) are discussed. A figure of merit based upon a sensitivity function called HAZ sensitivity, S/SUP HAZ/, is introduced which is useful for determining aging and temperature effects of an arbitrary film-resistor geometry with an arbitrary trim strategy. S/SUP HAZ/ is also shown to be useful in predicting performance of ratio-matched resistor structures. The proposed technique is incorporated in FIRE, a FORTRAN program for analyzing arbitrary film structures with a given trim path. Examples using popular resistor geometries and trimming algorithms illustrating the use of the suggested figure of merit are presented. The performances of these structures are compared quantitatively.