Electrochemical adjustment of thin film Ti-Pd resistors

• Published in: Thin solid films 1987-10, Vol.153 (1), p.387-399
• Main Authors: Sharp, D.J., Norwood, D.P.
• Format: Article
• Language: English
• Subjects: Applications; Applied sciences; Cross-disciplinary physics: materials science; rheology; Engineering techniques in metallurgy. Applications. Other aspects; Exact sciences and technology; Materials science; Metals, semimetals and alloys; Metals. Metallurgy; Others aspects; Physics; Specific materials
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/0040-6090(87)90199-4

Thin multilayered films consisting of tantalum nitride (Ta 2N), titanium, palladium and gold are used at Sandia National Laboratories to fabricate hybrid microcircuits. From these stock multilayered composites, various circuits can be selectively etched and patterned to provide conductors and two levels of resistor patterns. The Ta 2N is used to form resistor structures having values ranging from about 20 to 50 000 Ω. In order to provide resistors having values of about 1–4 Ω, the palladium, with its underlying titanium and Ta 2N layers, is used; these were designated as Ti-Pd resistors. Low resistivity tuned strip lines, for example, have this need. Present hybrid microcircuit technology typically limits the fabrication precision of thin film resistors to accuracies of 20% or 30%. Laser trimming is typically used to adjust out-of-tolerance resistors; however, in the case of strip-line resistor applications this introduces undesirable variations in the impedance. We have completed a study of the use of an electrochemical probe which can be used to deposit gold selectively or, alternatively, to remove palladium from the surface of the palladium composite film resistors described above. This permits resistor adjustment to either higher or lower values and does not produce discontinuities which occur with laser trimming. The process is similar in its result to that observed in the electrochemical or anodic trimming of Ta 2N resistors and is used to achieve practical tolerances of about 5% in Ti-Pd resistors. Studies describing accelerated life aging, temperature coefficient of resistance changes and final adjustment precision are discussed.