Tantalum Thin-Film RC Circuit Technology for a Universal Active Filter

This paper describes the physical layout, process sequence, and component properties of a universal active filter designated the standard tantalum active resonator (STAR). This active-filter building block was realized as a hybrid integrated circuit (HIC) using tantalum thin-film technology. Several different circuit configurations are possible using only one set of process photomasks and one HIC. This can be accomplished by a wide range of precise resistor values through the use of laser trimming and various interconnecting schemes for the components on the HIC via the printed wiring board. The STAR circuit is comprised of nine laser-adjustable tantalum thin-film resistors totalling a maximum of 1 MOmega, two 5100-pF tantalum capacitors, and one operational amplifier. The capacitors are formed by anodizing tantalum to 190 V and depositing NiCr-Pd-Au as the adherent counterelectrode. The resistors are made from 300-Omega/Box$^b$tantalum oxynitride film which is preaged at 350°C for 1 h. The single-substrate RC process is amenable to batch processing and precision tuning, making it attractive for high-level production of precision filters. New thin-film design criteria and process developments permitted this circuit to be fabricated on a 16-pin dual-inline package ceramic substrate which could be packaged for machine insertion with commercially available insertion equipment.