High Stability Cosputtered Ta-50 At. %Al Alloy Film Resistors

The potential of sputtered Ta-50 at. % Al alloy films for tantalum integrated circuit resistor applications was evaluated. Test resistors covering a range of 25 to 1000Ω/o were fabricated from 900 to 1500 alloy films (on ceramic substrates) using two different anodic thinning-stabilization heat treatment process sequences. The effect of initial thickness and process sequence on stability was determined by accelerated aging, thermally at 250 and 15O°C, and under DC power at 2 watts (6.2 watts/cm2). It was found that the Ta-50 at. % Al alloys offer outstanding potential for circuit and R-C network applications requiring highly stable 25 to 1000Ω/o film resistors. For such applications, the alloys exhibit a combination of attractive characteristics which include: 1) the ability to readily adjust the sheet resistance by anodization; 2) the maintenance of a relatively constant temperature coefficient of resistance; 3) excellent stability during both thermal and power aging tests.