US3465278A

US3465278A - Molybdenum disulfide electrical resistance devices

Info

Publication number: US3465278A
Application number: US515688A
Authority: US
Inventors: Edward L Kern; Orison J Cain
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 1965-12-22
Filing date: 1965-12-22
Publication date: 1969-09-02
Anticipated expiration: 1986-09-02

Description

E. l.. KERN ETAL Sept. 2, 1969 MOLYBDENUM DISULFIDE ELECTRICAL RESISTANCE DEVICES Filed Dec. 22, 1965 (um 14,1110) f/t//v//sysay :mwN \N\QQS N w m WM.N\

)lill 1 NVENTORS. dn/drol. Kern Or/'Jon J. 6'0//7 TTORNEY United States Patent Oliice 3,465,278 Patented Sept. 2, 1969 3,465,278 MOLYBDENUM DISULFIDE ELECTRICAL RESISTANCE DEVICES Edward L. Kern, Midland, and Orison J. Cain, Auburn, Mich., assignors to Dow Corning Corporation, Midland, Mich., a corporation of Michigan Filed Dec. 22, 1965, Ser. No. 515,688

Int. Cl. H01c 7/04; H01b 1/10 U.S. Cl. 338-308 5 Claims The present invention relates to electrical resistance elements and more particularly to electrical resistance elements having temperature-controllable resistauces.

In various types of electrical circuits it is common practice to use yresistance elements which have temperature controllable resistance values. Such devices are used as sensors for measuring temperature and as thermistors in control circuits or the like, among other applications. In control circuits these devices may be either externally heated or strictly self heated as desired.

While a number of materials exhibit a negative temperature-resistance coeflicient over a range of temperature it is often desirable to have the element variable over large temperature ranges or at very low temperature. By negative temperature-resistance coeflicient it is meant that for each degree rise in temperature the electrical resistance of the element becomes lower. In materials having positive temperature-resistance coefficients the converse is true. Most commonly used electrical resistors exhibit increased resistivity with temperature.

An object of the present invention is to provide an electrical resistor which exhibits a negative temperatureresistance coefficient over a wide temperature range including low temperatures, and which is economical to produce. i

A further object is the provision of an improved negative temperature coefficient electrical resistance element having resistivities in the semiconductor range. v

These and other objects of the present invention are achieved in accordance with the invention by the provision of temperature sensitive resistance elements formed of molybdenum disulfide. Molybdenum disulfide (MoS2) is found as a naturally occurring material in molybdenite. In this form it is a crystalline laminar material which delaminatcs readily to a flake form and when ground has found substantial use as a lubricant, besides being a primary raw material for production ofmolybdenum metal. It has been found, however, by the applicants that this material also lends itself to use inwspecial application thermistors, and other types of electrical resistance elements.

It has further been found that evaporated films of molybdenum disulfide exhibit a resistivity in the semiconductor range, also with a negative temperature-resistance coefficient. The films can be tailored to give different temperature-resistance coefficients as required for particular applications.

Other objects and attendant advantages of the present invention will become obvious from the following detailed description when read in connection with the accompanying drawings wherein:

FIG. 1 is a graph showing resistivity of bulk molybdenum disulfide versus the reciprocal of temperature, and

FIG. 2 is a graph showing resistivity of a thin film of molybdenum disulfide versus temperature.

Bulk molybdenum disulfide has been found to have a negative temperature coeflicient of resistance over the range between K. and 500 K. It is a laminar material which delaminatcs readily. For use in electrical resistance elements flakes may be removed from large crystalline pieces and may `be easily cut to the shape required. For example, long narrow iilaments may be cut from a lamination of a desired thickness and electrodes positioned at the ends thereof for connection in an electrical circuit. As shown in FIG. 1 wherein resistivity in ohm-cm. is plotted on a logarithmic scale as a function of the reciprocal of temperature in degrees Kelvin, the change in resistivity is typically 5% per degree over a range between about K. to about 330 K. (100G/T approximately equal to from 9 to 3). The curve shows only a portion of the over all resistivity-temperature characteristic for illustrative purposes. This characteristic extends similarly both above and below the temperature indicated. A device such as this makes an excellent thermistor in low temperature control circuits such as those used in laboratories with liquid nitrogen. It has also been found that thin lms evaporated from MoS2 and deposited on various substrates such as, for example, glass plates, may be used with suitable electrodes affixed thereto to provide resistance elements having lower temperature coeicients of resistance than that of the bulk material. This is believed to be due to the effect of surface area and grain size in controlling the mobility of charge carriers in the material. A plot of resistivity in ohmcentimeters as a function of temperature in degrees Kelvin is shown in FIG. 2 which illustrates a temperatureresistivity coeicient of about 0.2% per degree. The thin film used in this plot was deposited on a glass plate and had a thickness of about 1 micron. By increasing thickness of the lmthe resistivity and temperature-resistance coeflicient may both be increased to provide desired characteristics for particular application. Additionally, other materials may be added to the deposited M082 to change the electrical characteristics thereof. Also, the substrate may be either electrically conductive or nonconductive to provide desired characteristics. The films thus formed may be used either as ordinary resistors or as compensating resistors Where small temperature compensation is needed.

Resistance elements of molybdenum disulfide may be deposited or formed not only by evaporation-deposition techniques, but by other methods as well. Examples of other suitable methods include sintering in absence of air and dry pressing with or without binders.

For temperature compensation the resistance elements formed in accordance with the present invention may act either as self heated or externally heated elements. Thus, higher current flow, causing higher heating will cause a decrease in resistance, altering current flow in the circuit.

Obviously variations and modifications of the present invention will become obvious to those skilled in the art. It is to be understood, therefore, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

That which is claimed is:

1. An electrical resistance element comprising a body consisting substantially of molybdenum disulde and means for supplying electrical current to and conducting electrical current away from said body.

2. An electrical resistance element as defined in claim 1 wherein said body is cut from naturally occurring molybdenum disulde.

3. An electrical resistance element as dened in claim 1 wherein said body is a layer of molybdenum disulde 5 on a substrate.

4. An electrical resistance element as dened in claim 3 wherein said layer is a vacuum evaporated layer.

5. An electrical resistance element as defined in claim 4 wherein said substrate is electrically nonconductive.

4 References Cited UNITED STATES PATENTS 2,609,470 9/1952 Quinn 252-518 XR 3,111,567 11/1963 Stewart et al. 252-518 XR WILLIAM L. JARVIS, Primary Examiner U.S.Cl.X.R.

10 lll- 201, 106; 252-518g 338-308

Claims

1. AN ELECTRICAL RESISTANCE ELEMENT COMPRISING A BODY CONSISTING SUBSTANTIALLY OF MOLYBDENUM DISULFIDE AND MEANS FOR SUPPLYING ELECTRICAL CURRENT TO AND CONDUCTING ELECTRICAL CURRENT AWAY FROM SAID BODY.