GB1180928A - Improvements in or relating to Thin Film Circuit Devices. - Google Patents

Abstract

1,180,928. Capacitors. PLESSEY CO. Ltd. 25 April, 1967 [28 April, 1966], No. 18584/66. Heading H1M. A thin film capacitor having a required capacitance is made by forming a capacitor of nominal size an electrode 2 of which is so shaped that it comprises a main area 4 connected in parallel with smaller areas 5, 6, 7, 8 and 9 such that the sum of the capacitances of the smaller areas and the main area is at least equal to the required capacitance, and taking as many of the smaller areas out of circuit as will bring the capacitance of the remaining combination to the required value. Aluminium electrode 2 deposited on glass substrate 1 is covered with a dielectric layer, e.g. silicon monoxide and a rectangular second aluminium electrode. The areas 5 to 9, are preferably in geometric progression, e.g. 16, 8, 4, 2 and 1% of area 4. To adjust the capacitance value, the capacitor is passed through a series of machines the first of which determines whether or not is value greater than 116% of the required value. If it is, a mechanical diamond-headed scriber cuts out capacitor 5 and the capacitor passes to the second machine which determines whether or not its value is greater than 108% of the required value and so on, the value eventually achieved being within 1% of the required value. For ease in masking the electrode may be deposited as a main area separated from the smaller areas, and then electrically connected thereto by deposited thin films of e.g. gold (Fig. 2, not shown). The counter-electrode may be deposited so that there is an unmetallized strip where one section will pass (Fig. 3, not shown).