Stability Analysis of Laser Trimmed Thin Film Resistors

Laser trimmed tantalum nitride thin film resistors age at a greater rate than untrimmed films. The high energy required to vaporize material in the cut, or' kerf, modifies the aging characteristics of film contiguous to the kerf. This undesirable feature could be mitigated if a design procedure were available to assure that end of life tolerances were manageable. In this paper a r. model is developed that relates end of life drift to the extent of laser machining. Experimental! data are used to obtain an aging model for material near the kerf and that parallel portion which is. more remote. It is found that precise definition for the boundary between these areas is not essential to complete characterization of the composite. The result is a graphical design procedure 'that assures laser trimmed resistors will meet end of life tolerance specifications. The analysis was extended to determine the position of "L' cuts in bar resistors yielding optimum lifetime stability. It was found that trimming with an 'L' cut at the mid point of the resistor results in acceptably small deviations from maximum stability.