GB1358387A - Thin film circuits - Google Patents

Abstract

1358387 Thin film circuits HEWLETTPACKARD CO 20 July 1971 [20 July 1970] 34027/71 Heading H1R In the manufacture of a thin film circuit including capacitors and resistors, film electrodes 12 to 16 are deposited on an insulating substrate 11, the upper surfaces thereof are oxidized to form dielectric layers 19, dielectric layer 22 is applied over the substrate and oxidized electrodes, then resistive layer 23 and conductive layer 24. The substrate may be sapphire, glass or ceramic. The film electrodes may be #- tantalum, hafnium, aluminium, niobium, titanium or zirconium applied by cathode sputtering or vapour deposition using photo-etching or ion beam etching techniques. The films may initially be electrically interconnected and their surfaces may thus be oxidized by anodization in one direction (Fig. 2, not shown). The interconnections and a contact pad are subsequently removed. Dielectric coating 22 may be silicon oxide, silicon dioxide, hafnium dioxide, aluminium oxide, yttrium oxide, tantalum pentoxide or silicon nitride and may be applied by sputtering, vapour deposition or electron beam deposition. The resistive layer 23 is preferably tantalum nitride applied by reactive sputtering. It may also be nickel-chromium, hafnium nitride or rhenium. The conductive layer 24 may be chrome gold, molybdenum gold, nickel gold or copper. The thin film circuit is now fabricated from the precursor unit so formed by first etching, using a photo-resist mask, areas 25, 26, 27, 28 down to dielectric layer 22, defining the width of resistors between 25 and 26, 27 and 28, 26 and 28. Then using a mask conductive material, e.g. gold, copper is plated on to the conductive layer 24 to constitute external connection pads, interconnections and capacitor electrodes. Then, using photo-resist masking and etching, layers 23 and 24 are removed from all the areas around the various elements (Fig. 6, not shown). As shown each capacitor is effectively two capacitors in series, being constituted by one of the films 12 to 16 with external connection, and two separated electrode layers, e.g. 31, 36 or 32, 37 having external connections. The resistors are finally formed by etching the conductive layer overlying them. The resistive material may have a sheet resistivity lower than that desired, the substrate may be heated first to stabilize the resistive film, and then to increase the resistivity to that desired.