US2984589A

US2984589A - Electrical resistors

Info

Publication number: US2984589A
Application number: US781983A
Authority: US
Inventors: Feldman Charles
Original assignee: Centre National de la Recherche Scientifique CNRS
Current assignee: Centre National de la Recherche Scientifique CNRS
Priority date: 1952-08-06
Filing date: 1958-12-22
Publication date: 1961-05-16
Anticipated expiration: 1978-05-16

Description

May 16, 1961 c. FELDMAN 2,984,589

ELECTRICAL RESISTORS Original Filed July 28, 1953 I NV EN TOR oar/F455 FEM/Vfl/V,

BY 52 kw ATTORNE St t s P e Claims. (01. 111-212 The present invention relates to a resistor and to the method for making the same wherein a resistor of high value is obtained which has a high degree of linearity. It is also possible to obtain a highly linear resistor of high value which is temperaturesensitive. This invention is a continuation of my earlier application Serial No. 370,831 filed July 28, 1953, now abandoned.

Heretofore film-like conductor deposits have been formed on insulating bases to produce high ohmic re sistors. However, the value of the resistance of such resistors is not linear with variations in applied potential and temperature. It is also known in part to protect thin film-like resistors from oxidation by covering the same with a dielectric layer. The use of a dielectric layer to alter and improve the electrical properties of a thin metal film resistor is, however, not known in the art.

According to one embodiment of the present invention there is provided an insulating base with a layer of conductor deposited thereon. One of the novel features of the invention lies in the character of this conductor deposit. It does not form a continuous layer but constitutes a lacunary film in which the conductor forms islands over the surface of the base or forms a layer having voids therein. The dimensions of these islands depend on the nature of the metal conductor and the thinness of the deposit. The islands are most prominent in extremely thin layers. Over this layer of conductor is deposited a layer of dielectric. The dielectric fills in the areas between the conducting islands and at the same time covers the conductor film to form a protective layer. The dielectric layer in combination with the lacunary conductor film provides a resistor of high ohmic value having exceptional linearity characteristics.

According to another embodiment of the present invention there is provided a base upon which is deposited a thin layer of dielectric. This dielectric layer has a highly irregular surface on an atomic scale, and there is deposited thereon a lacunary film of conductor. This particular combination provides a resistor of high ohmic value which is temperature sensitive, having temperature coefficients approaching thermistors.

According to still another embodiment of the invention a temperature sensitive resistor made according to the foregoing description is provided with a covering layer of dielectric. This produces a temperature sensi tive resistor of high ohmic value having linearity over a wide range of applied potentials.

An object of the present invention is to provide a high value resistor with a high degree of linearity.

Another object of the present invention is to provide a resistor of large ohmic value with a high degree of temperature sensitivity.

Other objects and many of the attendant advantages of the present invention will become apparent upon consideration of the following detailed specification in connection with the accompanying drawings wherein:

Fig. 1 is a sectional view of one embodiment of the present invention,

2,984,589 Patented May 16, 1961 the present invention, and

Fig. 3 is a sectional view of still another embodiment ofv aresistor according to the present invention.

According to the Fig. 1 embodimentof the present in vention an insulating support 1 is used as a'base for the resistor. A layer of conductive material 2 is applied to this insulating support by any well-known'technique. Most suitably the conductive material is applied by evaporation in a vacuum. One suitable apparatus for evaporating the conductive material onto the insulating support is disclosed in my prior application Serial No. 370,831, filed July 28, 1953. It is most important that this layer of conductive material be so thin that it forms a lacunary structure. By lacunary structure is meant a layer so thin that it is not continuous and constitutes, in effect, islands of conductive material. It is best to form the conducting layer from a hard and refractory metal. As will be more fully apparent hereinafter, it

is this structure of the conductive layer which produces the novel effects of the instant invention.

Subsequent to the application of the conductive layer 2 there is applied a layer of dielectric material as shown at 3. This dielectric layer serves as a protective coating and prevents oxidation of the conductive layer. The dielectric layer may also be applied by evaporation under vacuum. By utilizing a protective layer of dielectric over the conductive layer it is possible to obtain resistors made of refractory metals which are not inert, such as molybdenum by the method of evaporation in a vacuum, and subsequent sealing or coating.

As is pointed out hereinbefore, however, it is well known in the art to apply a protective layer to a conductor deposit. The novel feature in this embodiment of the present invention resides not in the protective character of the dielectric coating, but in the fact that it provides a high ohmic resistor having exceptional linearity characteristics. This is believed to be due to the fact that the lacunary conductor deposit has a dielectric filling the interstices between the conducting islands.

It has been found that with this type of film structure the log of the resistance is proportional to the square root of the electric field divided by the product of the square root of the dielectric constant and the temperature.

This is an extension of the well known Schottky relation for the lowering of the potential barrier at the surface of a conductor by the applied field. It is apparent that as the dielectric constant (k) is increased in the above relation the exponential term decreases and the total field effect decreases. Thus, the linearity of the lacunary film resistors is improved.

According to the modification of the invention shown in Fig. 2 the base 4 is coated with a dielectric 5. The dielectric layer has a highly irregular surface, as can readily be seen in Fig. 2. This irregular surface is a consequence of the nature of films formed by evaporation. The irregularity is of atomic size; the layers may appear smooth to the eyes or even to the optical microscope. Upon this surface is deposited a lacunary film of conductor 6. The conductor deposit forms islands on the ridges and valleys on the dielectric surface. This combination forms a resistor of high value which is temperature sensitive. At lower temperatures the electrons follow the longer path over the ridges and through the valleys of the dielectric surface. At higher temperatures when the electrons have higher energy, they tend to ump across the valleys of the dielectric surface thus shortening the path and reducing the value of the resistor.

In Fig. 3 there is shown a resistor comprising a base 7, dielectric layer 8 and conductor layer 9 made in a manner similar to that described in Fig. 2. There is applied over conductor layer 9 a dielectric layer 10. This combination provides a resistor having the characteristics tion, that is, a high value resistor having" linearity and" being temperature sensitive. v

This, embodiment may also be accomplished by evaporating simultaneously the metal and'dieleetric; The metal conductor isthus mixed with the dielectric in the While various conductive materials. anddielectrics may be used, goodgresults have'b'een achieved by usinga con-' ductive layer'of'molybdenum and a dielectric'of SiO or SiO Obviously many modifications and variations of the present invention are possiblein light of the above teachings. What is claimed as new and desired to be secured by Letters Patent is:

I claim:

1 An electricalresistor which comprises a support of an insulating material, a lacunary film-like deposit on an atomic scale ofa hard and refractory metal on said support,.the. gaps in said lacunary deposit being of submicroscopic size, and a layer of dielectric having a constant greater than 1 superimposed on said deposit and filling said. gaps.

2. An electrical resistor according to claim 1 wherein said metal deposit is molybdenum.

3. An electrical resistor according to claim 1 wherein said film-like deposit isofmolecul'ar thickness."

4. An electrical resistor according to claim 1 and further including a second dielectric layer covering said metallic deposit.

5. Method of forming'a 'resistor having high ohmic value by depositing simultaneously byevappration a metal conductor and a dielectric onto an insulating base to form a lacunary metallic film intermixed with a dielectric; l

References Cited in the fileof thispatent UNITED STATES PATENTS.

1,291,106 Payne Jan; 14, 1919 2,179,566 Stoekle Nov. 14,1939 2,374,527 Earle Apr."24; 1945 2,586,752 Weber-ct a1. Feb. 19, 1952 2,613,302. Gurewitsch Oct. 7, 1952 2,827,536 Moore Mar. 1 s, 1958 2,906,648 Kohl Sept: 29; 1959 FOREIGN PATENTS 606,894 Great Britain" Aug. 23, 1948"

Claims

1. AN ELECTRICAL RESISTOR WHICH COMPRISES A SUPPORT OF AN INSULATING MATERIAL, A LACUNARY FILM-LIKE DEPOSIT ON AN ATOMIC SCALE OF A HARD AND REFRACTORY METAL ON SAID SUPPORT, THE GAPS IN SAID LACUNARY DEPOSIT BEING OF SUBMICROSCOPIC SIZE, AND A LAYER OF DIELECTRIC HAVING A CONSTANT GREATER THAN 1 SUPERIMPOSED ON SAID DEPOSIT AND FILLING SAID GAPS.