Characterization, Evaluation, and Comparison of Laser-Trimmed Film Resistors

Methodsfor predictingthe performanceof laser-trimmed film resistors taking into account the properties of the heat-affected zone (HAZ) are discussed. A figure of merit based npon a sensitivity fnnction called HAZ sensitivity, SHA z , is introduced which is useful for determining aging and temperature effects of an arbitrary film-resistor geometry with an arbitrary trim strategy. ~H4 z is also shown to be useful in predicting performance of ratio-matched resistor structures. The proposed technique is incorporated in FIRE, a Fortran programfor analyzing arbitrary film structures with a given trim path. Examples using popular resistor geometries and trimming atgoritfnns illustrating the use of the suggested figure of merit are presented. The performances of these structures are compared quantitatively.