US2480124A - Manufacture of selenium elements such as rectifiers - Google Patents

Description

5 1949 D. DRIVE 2,480,124

MANUFACTURE O ELENIUM EMENTS SUCH AS RECTIFIERS 7 Filed April 6, 1946 F/Gl. F/GZ.

I, f 5 \A/ fi 4 8 4 7 2 v x k? v \4 v In Mentor Ado/wig Patented Aug. 30, 1949 MANUFACTURE OF SELENIUM ELEMENTS SUCH AS RECTIFIERS Douglas Louis Ashton Driver, London, England, assignor to Standard Telephones and Cables Limited, London, England, a British company Application April 6, 1946, Serial No. 660,292 In Great Britain April 7, 1945 1 Claim.

This invention relates to dry contact rectifiers and photo-electric cells comprising a metal baseplate having thereon a layer of semi-conducting material to which is also applied a cunterelectrode.

In order to make satisfactory contact with the counter-electrode, more particularly when a number of rectifiers are to be assembled in series as a unit, it is necessary to apply a certain amount of pressure. Such pressure is also advisable when the rectifier is to be protected against ingress of moisture by a coating of varnish as explained in United States Patent No. 2,314,104, granted March 16, 1943, upon an application filed by E. A. Richards and L. J. Ellison entitled Selenium rectifier. As pointed out in the said patent such pressure causes in the case of some rectifiers, such as those using selenium as the semi-conductor material, reverse current to be increased. Accordingly it was proposed in said patent to insulate part of the semi-conductor from the counter-electrode in order to provide a part of the latter upon which pressure could be exercised without deleterious effect on the rectifier. This could be done by attaching a thin Washer of insulating material to the semi-conductor before applying the counter-electrode thereto.

It has been found that where the counter-electrode passes over the edge of the thin insulating washer it tends to develop cracks or to become unduly thin so that the resistance in the circuit of the rectifier is unduly increased.

This difficulty is overcome in accordance with the present invention by applying a thin insulating washer with its upper surface flush with the surface of the semi-conductor. This may conveniently be done by placing the insulating washer upon the surface of the semi-conductor when it is in a plastic condition and applying pressure.

The invention will be described as applied to a selenium rectifier. In known processes for manufacturing such a rectifier a base plate coated with selenium is subjected to heat and pressure as part of the treatment necessary to convert the selenium from the vitreous condition to the rectiiying allotropic modification. In carrying out the present invention a thin paper washer is placed on the surface of the selenium of such a selenium coated base plate before the heat and pressure is applied. At the conclusion of the normal heat pressure treatment the paper washer is found to have its surface flush with the surface of the selenium. A counter-electrode is then applied over the whole of the flush surface.

The rectifier may then be assembled with other rectifiers by means of pressure exerted on the area of the paper washer.

The invention is applicable also to photo-electric cells, since as pointed out in the copending application, Serial No. 639,469, filed January 5, 1946, by E. A. Richards, entitled Centre contact photo-cell, an insulating washer or layer may be used therein for the same purpose as in a rectifier.

One embodiment of the invention is illustrated in the accompanying drawings in which:

Fig. 1 shows'in cross section a base plate coated with selenium and an insulating washer placed thereon.

Fig. 2 is a cross-section of the base plate of Fig. 1 after having been treated to produce a rectifier which is assembled with other rectifiers in a unit.

Referring to the drawing a base plate I having a central aperture 2 is coated with selenium 3,-

as for example by applying selenium to the base plate I when it is at a temperature well above the melting point of selenium, and spreading the selenium over the surface in known manner. The base plate thus coated is then cooled rapidly.

The coated base plate is then in known manner to be placed in a press and heat applied, it may be, as described in United States Patent No. 2,413,013, issued December 24, 1946, upon an application by Arthur von Hippel entitled Method of making selenium rectifiers, after a preliminary heating without pressure. Immediately before inserting the selenium coated base plate in the press a paper washer 4 having an aperture therein corresponding to the aperture 2 in the base plate I! is placed on the surface of the selenium 3 as shown in Fig. 1 with the apertures in alignment. The paper washer t may be dished in the centre as shown to facilitate location, the aperture in the washer i being less than that in the base plate.

' The excess material of the washer is removed application, Serial No. 476,074, filed February 16, 1943, now Patent No. 2,434,960, issued January 27, 1948, by E. A. Richards, entitled "Cover plate for rectifier discs," may then be applied against the counter-electrode to complete the rectifier, which may then be placed on a central spindle I, and assembled with other rectifiers on the spindle into a complete unit, a conducting washer 8 being placed to make contact with the contact plate 6 and the base plate of the next rectifier in the assembly. The assembly is completed by end pressure which, since the washer 8 isnot greater in diameter than the paper washer 4', is exerted in the selenium 3 only over the area covered by th paper washer 4.

It is to be understood that the invention is also applicable to those rectifiers or photo-cells, in which pressure is applied around the periphery of the disc, the paper washer in this case covering a strip round the periphery. The washer 4 may obviously be made of other solid insulating material than paper.

Paper washers 4 after they have been applied as described above flush with the surface of the selenium on a selenium coated base plate, serve also as a protection for the edges of the central aperture 2 in the selenium when the central aperture 2 in the base plate I is formed by punching out portions of a plate already coated with selenium.

The term selenium cell as used in the following claim, is to be understood as embracing both selenium photo-cells and selenium rectifiers.

What is claimed is:

In a process for the manufacture of a stratified selenium cell having a localized mass of solid electrically insulative material in the selenium layer wherein a base element is provided with an overlying selenium layer which is hot-pressed to convert the selenium to the desired semiconductive allotroplc modification, the improvement that comprises placing the solid electrically insulative mass upon the selenium layer prior to the hotpressing, and thereafter hot-pressing against a fiat platen whereby the insulative mass is pressed into the selenium layer flush with the surface thereof and rigidly consolidated therewith, simultaneously with conversion of the selenium to the desired allotropic modification.

DOUGLAS LOUIS ASHTON DRIVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,314,104 Richards Mar. 16, 1943 2,345,122 Herrmann Mar. 28, 1944

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