Abstract
The paper deals with laser trimming of film resistors. The finite-difference solution of the electric field calculated by a digital computer gives the total resistance and the inhomogeneous current distribution within the resistor area. The current noise voltage was found to be proportional to the sum of reciprocal subareas wherein the current density is approximately constant. Resistor trimming is modelled by finite increments of cut length to obtain the resistance trim rate and the trim sensitivity.Known and new resistor geometries and cut configurations are compared (based on the same resistor area and the same initial tolerance of ± 20%) to find the optimal geometry depending on the ratio of the nominal resistance value to the sheet resistivity. Diagrams are given leading to practical design rules not only for resistance trimming but also for deterministic and functional tuning.