Patent GB-809901-A (GB)
Title: Improvements in film resistors and in methods of manufacturing such resistors
IPC: C23C14/24
Filed: 1955-05-31
Abstract: 809,901. Coating by vapour deposition. CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE. May 31, 1955 [June 1, 1954; March 11, 1955(2)], No. 15581/55. Class 82(2) .[Also in Group XXXVI] A process for depositing a film-like layer of a conductive material on an insulating support the layer being in the form of a narrow long and meandering strip comprises the deposition of the material by evaporating in a vacuum through a mask of the desired shape from a single evaporator which is given a relative movement to the insulating support. A diaphragm reduces the width of the beam of evaporated atoms to ensure a sharp limitation of the edges. In the process shown in Figs. 2 and 3 for forming an electric resistor the mask a is formed by two metal sheets which have intermeshing teeth, Fig. 1 (not shown), the space between the teeth forming a Greek fret. The deposit is obtained by evaporation of the conductor substance from the heating element b on to the insulating support c the whole being placed in a container with a high vacuum. The evaporator b is movable along a slideway g where it is supported by a carriage h and is given a reciprocating movement through means not shown. The width of the beam is limited by a shield k. The supports may be initially cleaned by removal of the mask a and a discharge being set up between electrodes c and f. The insulating support c is preferably made of glass. When the deposit required on the resistor is of noble metal such for example as iridium the heating element is a tungsten strip and the metal is deposited in the form of a powder. A number of resistors may be made simultaneously, Fig. 4 (not shown), by use of a single movable evaporator with several insulating supports each protected by a mask. Where, as shown in Fig. 5, a getter is placed in the evacuated bulb containing the resistor it is placed at one end and as shown at n in the Figure the side on which it evaporates being towards the end wall of the bulb. Surfaces and m are metallized by incrustation of silver or platinum under the action of heat and formed into electrodes. The resistor may be protected against the effects of evaporation of the getter by a suitable shield placed between the getter and the resistor, Figs. 7 and 8 (not shown) and to prevent the getter deposit on the envelope of the bulb from being subjected to the voltage applied to the resistor the input terminals are separated from the getter deposit over a sufficient length, Fig. 6 (not shown). When the bulb containing the resistors is very small a non-volatile getter is preferably used such as zirconium or one consisting chiefly of cerium and thorium, the getter which is in powdered form is heated by means of high frequency current, the within the main resistor enclosing the bulb getter powder being contained in a bulb within the main resistor enclosing the bulb Fig. 14 (not shown). If a higher ohmic value of resistor is required thin layers may be deposited in the forms of narrow sinuous strips on a cylindrical tube. A uniform evaporation without a mask may then be obtained over the whole area of the support and the layer engraved to form a long narrow and sinuous line. An element having a helical path Fig. 15 (not shown) may be obtained. In the case of flat deposits Figs. 19 and 20 (not shown) photographic engraving of the coating is preferably used. A considerable number of resistors may be formed at the same time, Figs. 18 and 19 (not shown), and then separated from one another. In a modification, Fig. 20 (not shown) a resistor of circular shape in the form of a Greek fret is produced by photographic engraving and constitutes a potentiometer plate for high value of resistance. A resistor constituting a thin ribbon forming a spiral on a flat disc may be formed, Fig. 24 (not shown), or an inverted double spiral, Fig. 25 (not shown), may be formed. In a further modification, Fig. 27 (not shown), two spirals are formed one on either side of the insulated support thus providing a resistor of very low self inductance since the spirals are run in opposite directions. Specification 809,902 is referred to.