Laser-trimmed resistor

Abstract

A laser-trimmed film resistor wherein the laser kerf terminates in an area outside the electrical current path across the resistor. FIELD OF THE INVENTION This invention relates to film resistors. More particularly, this invention relates to laser-trimmed thin and thick film resistors containing a laser kerf which terminates outside the electrical current path across the resistor. BACKGROUND OF THE INVENTION Film resistors are commonly used in hybrid circuits and include thick film resistors which are conventionally formed by screen-printing a resistive material on an insulating substrate and then firing the material, and thin film resistors which are conventionally formed by sputtering or vacuum-depositing a resistive material on an insulating substrate. In hybrid circuits it is often necessary to adjust the resistance of the film resistors in the circuit. To increase the resistance of a film resistor the resistor is "trimmed" by forming a kerf, i.e., a cut or ditch, across the electrical current path in the resistor to make the effective width of the resistor smaller and thereby increase the resistance. The kerf may be formed by mechanical abrasion, chemical etching, or laser vaporization of the resistor material. The advantages of laser-trimming over mechanical- or chemical-trimming include very high production rates, greater flexibility in functional trimming, and tighter tolerances. The greatest disadvantage of laser-trimmed resistors with conventional kerf configurations (which will be described hereinafter) is that they exhibit appreciably greater drift, i.e., change in resistance per unit time or temperature, than mechanically- or chemically-trimmed resistors. Consequently, the inherent advantages of laser-trimming can be outweighed by the undesirable drift characteristics of the laser-trimmed resistor. Therefore, it is important to develop laser-trimmed resistors with low resistor drift. SUMMARY OF THE INVENTION I have discovered that directing the terminus of a laser kerf in a laser-trimmed film resistor into an area outside the electrical current path across the resistor results in less resistor drift.

Dependencies are inferred from the claim text.