|Publication number||US2837618 A|
|Publication date||Jun 3, 1958|
|Filing date||Aug 6, 1954|
|Priority date||Aug 6, 1954|
|Publication number||US 2837618 A, US 2837618A, US-A-2837618, US2837618 A, US2837618A|
|Inventors||Gildart Lee William|
|Original Assignee||Edward Sagerman, Jack Waldman, Louis Waldman|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (1), Referenced by (8), Classifications (17)|
|External Links: USPTO, USPTO Assignment, Espacenet|
June 3, 195s L, w GILART 2,837,618
SEMI-JONDUCTOR ALLoYs 2 Sheelbs-Sheet 2 INVENTOR. Les W. GlLDAR-r United States Patent O SEMI-CONDUCTOR ALLoYs Lee William Gildart, Irvington, N. J., assignor to Jack Waldman, Louis Waldman, and Edward Sagerman, 1.- Irvington,N.'J.v
Application August 6, 1954, Serial No. 448,284
s claims.' (ci. 20L- 63) lt .is known that alloys' 'of antimony and selenium,
particularly an alloy having the atomic ratio of 2:3 (SbzSea), have substantial electrical resistivity and belong to the class of substances known as semi-'conduc-- tors. Thermistors are thermally sensitive resistors made ot' semi-conductors .whose kresistance changes markedly with small changes in the temperature. At present thermistors have wide application as .circuit elements in the radio and communications elds, and for other purposes.
Thermistors canYalso be used in thermometers of the electric resistance type, using aresistive elementof the semi-conductor material in the form vof a pro'be. The semiaconductor properties of pure antimony triselenide and of this compound containing l percent of 'arsenic impurity are knownbut this compound has not Vbeen found of practical usefulness because its thermo-resistive behavior is erratic and unpredictable and varies widely from one batch of material to the next without denitely ascertainable reason or possibility of control.
It is an object of-the instant invention to provide semiconductorv materials, the electrical properties otwhich 'are completely predictable and easily controllable. it is aA further object of the instant invention to provide processes for the production of new thermistor materials.
lt is afurther object of the instant invention Ato, provide lan improved thermometerv probe which Yis reliable and durable in use and suitable rfor a wide Yfrange of temperatures. f I p f Y, it is a furtherf object of the instant invention to provide commercially feasible processes forfthe production ,I iprobes containingnovel semi-conductor ot thermometer material. Y Y
Thesez and' othe'robjects of'the instantA invention will become more clearly understood from the following des'criptionm 1 'i v l i it has been'discoveredthatzwhen a compound selected from the grouplrconsisting-ofrthe `trisele'nides and the trisultides yof fafmetallic' elementof the'phosp'horus family is; alloyed;;in"themanner hereinafter described, withfa compoundfselected `from the vgroup consisting of arsenic triselenidek audli'arsenic.trisulde, a family'of improved semi-conducting materials are produced.' :The electrical properties-of lthese thermistor'.materialsrare predictable and;controllableg-,andthey are suitable for use' in thermometerprobesfasihe'reinafter described,v and for other purpcsesff-f -Qln ,practicing the invention, the` 'triselenide or theatrii Patented June 3, 1958 as a thermistor material because its thermo-resistive behavior was not easily reproducible. Arsenic triselenide at room temperature is a glass with Very high resistivity:
and is classed as an insulator. It is surprising thatin producing .an alloy of these two compounds, a materialwhich is thermo-resistively stable and predictable is ob-V tained. obs-cure, the fact is well established. t.
in order to utilize with security and continuityV the semi-conducting qualities of the antimony Ytriselenide-Y arsenic triselenide alloy produced in accordance with the instant invention, still further physico-chemical characteiristics must be considered. Particularlyygood and` permanent Contact must'be established between ,the ther# sulfidefsalt ofvveitherantimony or bismuth is alloyed with f l mistor and other solids in order to Linsure'electrical con-I tact with the required electrodes and conductorsrand, iny many instances, also for -the'purpose of insuringgood thermal contact with the medium, the temperature iof which is to be measured. Ithas been discoveredtha't adequate contact can best be obtained in either /of two ways: (l) by inserting self-heated electrodes into ythe body of the thermistor allo-y itself, and (2) by casting and shrinking the thermistor alloy around the electrode orl other solid body to be contacted. Av secure electric contact seems to require additionally/such performance of the casting or molding `and shrinking process as Vtoicreate a surface chemical reaction between the ,probe material and the electrode. f
ln practicing the instant invention, an improved probe material, an alloy of yantimony triselenide andarse'nic triselenide is produced, and in this embodimentdtis important that the individual compounds should be un. contaminated by any other elements ortracesoflelernents exceeding 0.1 percent by weight of the alloy. In Vaddi-V tion, in order to insure the benets of the stability and reproducibility of the alloy as 'previously mentioned, the
4actual weight ratios must Ibe kept uniform between sucdeviation from theoretical uniformity. y n
For example, each of the elements,y antimony andselenium, which comprise the compound, antimonyy tri-1 selenide, should be at least about 99.9 percentpureby weight, and each of the elements, arsenic :and/selenium, which comprise the compound, arsenic triselenide, should be at least about 99.9 percent pure by weight.' Further, when the two compounds are weighed out for alloying one with the other, the proportionsV should `be heldwithin limits of better than about 0.1 percent by weight in order to produce a semi-conductor alloy of predictable and reproducible electrical properties., v
The relation between the electrical resistivity and the temperature coeicient of electrical resistivity of an alloy on the one han'd and the proportionsrin weight percentages of its components on the other are clearly established in the following table:
' v Electrical Temperature SbiSea `AsiSe Resistivty Ooetlcient at Y (Weight v(Weight (Ohm-Cm. at Y 25 C..(Per Percent) Percent) 25o Centicent per grade) Degree) Although the reason for this Vresult is largely lt will be noted that the electrical resistivity increases geometrically with the increasing As2Se3 content, and that the temperature coefl'lcient of resistivity also increases, but much more slowly. It is impractical to set limits as to the range of percentages of Sb2Se3 and As2Se3 in the alloy which might be of the greatest use for semiconductor or thermistor materials. Whether the thermistor is to be made with low or high percentages of Sb2Se3 is a matter of choice, the factors of which are well known to those skilled in the art, and depends entirely on the particular application to which the material is to be put.
In other embodiments of the invention, the compounds, antimony selenide and arsenic trisulde, antimony trisulde and arsenic trisulfde, or antimony trisullide and arsenic triselenide are alloyed together in the manner described herein, and the resulting alloys have electrical resistivities and thermal coefficients similar to the alloys of antimony triselenide and arsenic triselenide. However,
these alloys have slightly lower mechanical strength than the antimony triselenide-arsenic triselenide alloys which are the preferred thermistor materials. 1
In the process of preparing the instant alloys, it is a feature of paramount importance that the constituents should be pure and their weights accurate as stated above. In practicing the invention, it is further important that in the melting and alloying step, excessively high temperatures and prolonged periods of heating be avoided in order to prevent changes in the weight proportion by evaporation or sublimation. and arsenic triselenide become fluid at temperatures slightly above about 600 C., but inasmuch as the elements Selenium and arsenic both have a tendency to sublime out of the mixture at this temperature, it is essential that the alloying and casting or molding be performed rapidly in orderto avoid substantial loss of these elements. it is almost impossible to avoid loss of some of these elements, but loss is insignificant when the process is carried out at a temperature between about 630 and about 670 C., as hereindescribed.
On the other hand, it is less important in the instant process than it was in prior attempts to prepare thermistors of antimony-selenium alloys that the exact conditions of heating and cooling be precisely duplicated between diterent batches for the same use. For instance, the antimony-selenium alloys exhibited majo-r irregularity of resistivity, depending on whether the cooling down, after solidification, was rapid or slow, and on other factors. In this respect the instant alloys are considerably steadier. Of course, major divergencies should be avoided to insure the greatest possible uniformity of results; for instance, it is not advisable to cool one part of a batch abruptly and to slowly anneal another. However, the antimony triselenide-arsenic triselenide alloys as described herein are substantially free from the irregularities mentioned as long as the alloy preparation ishandled in accordance with the instant process and in the manner obvious to persons skilled in the art.
It has also been found possible to formulate and prepare a pro-beof thermistor material so as Yto simplify the calibration of a thermometer containing the probe: this possibility arises from the fact that, subject to the precautions which have been stated, different mixtures or different batches of the alloys, such as the antimony triselenide-arsenic triselenide alloys, can Vbe rehreated and again mixed to produce intermediate alloys having desired electrical properties and without resulting irregularity in therrnoresistive behavior. As a result,a ner adjustment of resistivity becomes possible, by-remixing two or more alloys in-which the proportions of antimony triselenide to arsenic triselenide are Vnot exactly the same. No such mixing is successfully practiced with other semiconductors or thermistor materials.
It will be understood by persons skilled in the art that every batch should be calibrated, for precision work.
The antimony triselenide l However such calibration is greatly facilitated by the possibility of relatively accurate pre-selection of the Weight of the components in the alloying process and of mixing batches, as described. It is believed that no other material is presently known which provides such versatility together with such accuracy of pre-selection.
Actual thermometers produced in accordance with this invention can best be described in conjunction with the drawings appended hereto, wherein:
Figure l is an enlarged longitudinal section through a rst type of thermometer probe produced in accordance herewith.
Figure 2 is a section through the probe of Figure l, the section being taken along lines 2 2 in Figure 1.
Figure 3 is a View generally similar to Figure l but showing a modilied probe.
Figure 4 is a view generally similar to Figure 2 and showing a section through the probe of Figure 3 along the lines 4-4 in Figure 3.
Figure 5 is a view generally similar to Figure l but showing a second modification.
Figure 6 is a view generally similar to Figure 2, taken along the lines 6-6 in Figure 5.
Figure 7 is a view generally similar to Figure l but showing a third modification Figure 8 is a view generally similar to Figure 2, taken along lines 8-8 in Figure 7.
Figure 9 is still another view generally similar to Figure l and showing a fourth modification.
Figure l0 is a view generally similar to Figure 2 taken along lines 10--10 in Figure 9.
In all views the numeral 11 indicates the temperature sensitive probe, slug or cartridge. Preferably this element is made from the antimony triselenide-arsenic triselenide Sb2Se3-As2Se3 alloy described above, and particularly from a suitably predetermined batch, for such resistivity as may be suitable for theelectric system to be used, wherein the thermometer forms a variable resistance element. However, certain aspects of the thermometer probe design to be described presently are applicable also to other thermistor materials.
Referring first to Figures l and 2: the Sb2Se3-As2Se3 probe 11, preferably containing less than 30.00 percent `by weight of As2Se3, is disposed within a nickel-silver shell 12 at the closed tip thereof. This shell serves as one of the electrodes in the circuit containing the probe as a variable resistor; the other electrode 14 being a nickel-silver, Kovar, rodar or Nichrome wire inserted in the central upper part of the probe 11. Kovar and rodar are alloys containing nickel, cobalt, manganese and iron. In order to avoid inadvertent grounding of the outer electrode 12, this electrode may be provided with an insulating envelope or shield 15 which may consist in a plastic coating, a removable glass envelope or the like, depending upon the service to which the outer thermometer surface is subjected. l
Attention is drawn to the fact that, while the nickelsilver electrode 12 surrounds and mechanically protects the bulk of the probe 11, a central projection or finger 16, formed integrally or otherwise in or on the inside of the tip 13, is surrounded by the probe material, as is the end or tip 17 of the electrode wire 14. This arrangement is important for the production and maintenance of contact. v
In the process of producing the thermometer probe, the suitably selected material for the probe, for example, an antimony triselenide-arsenic triselenide alloy, is filled into the tip 13, in powdered or granulated condition, the wire 14 being'held in position in well known manner. The tip is then heated in order to remelt and re-fuse the probe material, subject to substantially the same precautions as have been mentioned above in connection with the original fusion process. Thereupon the casting or molding of the probe is completed by cooling it down to normal temperatures, incident to which the differential shrinkage vofthe pobeniaterial co'r'npared* with the metal of the electrodes causes' tight-'engagementand'lsqueezing ofthetips16and17. Y Y .y
More particularly,l it has beenA found preferable to provide some little time delay in one ofthe later stages of this cooling process, although the melting temperature, for reasons stated above, should be maintained-onlyfor the shortest possible time, required for-completemelting. At some suitable temperatures below 600 C., for nstance at approximately 550 C., it vis desirable to provide a stabilization period, lfor example between about 5 and about 60 minutes, preferablyI of `about. 5- minutes. A more durable contact is thus provided-probably due to the formation of metal selenides on Vthe 'electrode instance for clinical purposes, in which event the probe material, desirably, is prepared 4for high sensitivity in the usual clinical temperature range, that is, in the vicinity of about 100 F. In this connection it will beunderstood by persons skilled in the art that semi-conductors of different formulations have maximum temperature c'oecient and sensitivity in one particular part oftheir basic temperature range. Furthermore, this thermometer probe will'best be formulated for such resistance-'as allows the use of weak, clinically inoiensive electric currents, so that in'suitableY cases the metal shell 12, 13
can Ibe contacted with the body of the patientv direct, without any electric insulation andV therefore without heat insulation. The use of av stainlessV steelvshell is also desirable, from the clinical viewpoint, because the outside of such a shell can be sterilized in an autoclave. This cannot be done Ywith an ordinary fever thermometer. Themnew` VprbefmaterialV isfnot injured and not over expanded by autoclave steam temperatures ranging suitably upwards of 220 F. g
lFor other applications, itmay, be preferable ,to use higher voltages and to formulate the probe 11 accordingly, in order to simplify the circuit system or for other reasons. In such cases it is usually desirable to utilize an insulating sheath of glass or the like, in place of the stainless steel shell 15, in the actual use of the thermometer.
In the modied 'form of Figures 3 and 4, the probe 31 is directly enclosed in a shell 32 which has electric insulating' properties and which may, for instance, consist of Pyrex glass; the thickness of the shell being suitably selected for the desired Vsensitivity of the thermometer. In this event an outer shell, stainless steel or details of lthe'fY thermometer I seal arid Y electrode construe? tion,-in the upper part remote from the probe, are not shown herein, being well known to persons' skilled in the art.
Figures 5 and 6Ashow a particularly simple or cartridge type of application, `suitable mainly for the application of relatively small thermometer elements forming permanent parts of flow systems or the like. Here the probe 51, preferably made of the `above described alloy and also preferably cast around the electrode'ends or tips 52, 53, or opposite one another,- has a generally cylin` drical formv land is suitably inserted in a protective sleeve 54 of Pyrex, ceramic material, stainless steel, or the like. In the event'that a conductor such as stainless `steel 4is used, of course it is necessary either to insulate the inside thereof or to make the radial distance from the tips 52, 53 to the shell much greater than the longitudinal distance betweenV said tips. Even then a certain shunting effect of the shell will exist, which however need-not interfere with proper thermometric measurement if the circuit system is properly designed in manners known to the ,art. The ends lof the cartridge-mayA be closed by plugs 55, 56 of wax or cement or other suitable sealing material, insulating theelectrode wires from the outsideV Vsuch current. Again the probe. is adapted to engage the electrode firmly, in the casting and cooling process. For this purpose each electrode slugin'this case has, on its probe-engaging surface, a preferably annular ridge Y or bead 74,2the-` outside of which is firmly :compressed .as
the probe material shrinks aroundV the same; A wafer or button 71, 7273 is formed of the probe and the two electrodes, whichcan be inserted Ain the working end of a thermometer 75 in a mannerbasically known to the art, providing excellent electrical as well as thermal contact. The thermometer may have, vfor instance, an
outer shell 7d of stainless steel, brass or the'like,. acting p liber, plastic or the like, 79, tosseparate the inner conthe like, not shown, may be used in order to protect the thermometer from breakage when it is not in actual use. Two parallel and similar electrodes 33 and 34 areused in this case, both being inserted in and clamped by the upper part of the probe material.
In both forms, Figures l and 2 as well as 3 and 4, the interior space 13 of the thermometer shell 12 or 32, above the probe (and 'also around the same, in View of the shrinkage of the probe material, incident to the manufacture of the thermometer) is desirably lled with an inert gas such as nitrogen or argon or the like, at such pressure or rarefaction as may be suitable for the temperature range contemplated. The life expectancy of the probe and particularly of its contact surfaces engaging the electrodes is improved by such use of neutral gases; the presence of oxygen in'this space may tend to produce chemical changes in the probe material. The
ductor 77, 78 and wafer 71,72, 73 from the outerV `terial 96, such as lead foil, may be interposed between the elements 94, 95. In this manner electric'contact may be lprovided by a press fit rather than theA casting shrinkage and selenide formation used in theother examples. Furthermore the slug and electrode canV thus be made .separable and replaceable, for instance for laboratory use and the like, wherein differently formulatedY alloy probes may be successively clamped between the same set of electrodes. v
In order to give additional understanding of the instant invention, the following examples are included; however it is to be understood that 'they are illustrative only and the'invention is not to be understood as limited thereto. l Example I A thermistor material was produced by alloying anti# mony triselenide of at least 99.9% purity with arsenic tlSelenide of 99.9%,purity by heating at 5a' temperature Here however the probe slugY 91 is connected with 7 of about 650 C. The weight ratio was aboutVV 96.00%. of the antimony triselenide to about 4.00% of the arsenic triselenide. The resulting alloy was cooled. The resulting material had a resistivity of about 140 ohm-centimeters at 25 C. and a temperature coeicient of approximately 3.5% per Ydegree centigrade.
Example II i A thermistor material was prepared in the manner described in Example l, except that the weight ratio was about 92.00% antimony triselenide to about 8.00% oi arsenic triselenide. At 25 C. the resistivity or this thermistor was about 370 ohm-centimeters, and the temperature coefficient was approximately 3.8% per degree centigrade.
Example HI A thermistor alloy was produced by remelting a portion of the alloys obtained in Example I and in Example II and mixing them in a ratio by weight of 1:1. The resulting semi-conductor had a resistivity of about 225 ohm-centimeters at 25 C., and the temperature coefcient was approximately 3.65% per degree-Vcentigrade.
Example` IV A thermistor alloyfwas prepared in the manner described in Example I in which about 75.00% by Weight of antimony and about 25.00% by weight of arsenic triselenide were alloyed and cooled. The resulting material had an electrical resistivity of about 12,000 ohmcentimeters at 25 C., and `hada temperature coefficient of approximately 4.6%V per degree centigrade.
Having thus fully described andillustrated the character of the instant invention, what is desired to be protected and secured by Letters Patent is:
1. A semi-conductor alloy suitable for use in thermistors consisting of a compound selected from the group consisting of the triselenides and the trisuldes of the group consisting of antimony and bismuth, -alloyed with at least 'about` 2% by weight of a compound selected from the group consisting of arsenic triselenide and arsenic trisulfide.
2. A semi-conductor alloy suitable for use in thermometer probes consisting of a major amount of acompound selected from the group consisting vof the triselenides and the trisuldes of the group consisting of antimony tft and bismuth, and at least 2% by weight ofa compound selected from the group consisting of arsenic triselenide and arsenic trisulde. j
3. A `semi-conductor alloy suitable for use in thermistcrs kconsisting of anV alloy of antimony triselenide and atleast aboutY 2%Y by weight'of arsenic triselenide.
, 4. A thermometer probe material comprising an alloy containing between about 70% jand about 95% by weight of antimony triselenide and betweenabout 30% and aboutSZ/o by Weight ofarsenic triselenide.
5. In a process for the production of thermistors including production of semi-conductor material and form-- ingV a `v resistance element therefrom, the improvement comprising alloying substantially pure arsenic triselenide and substantially pure antimony triselenide at a temperature between 630 and about 670 C., and cooling Vthe resultingthermistor material.. Y
6. A method `offproducing a 4thermometerprobe comprising melting ,a bodyof an alloy containing between about;;70% and about 95% by weight of antimony triselenide and between about 30% and about 5% by weight of arsenic triselenide around a pair of electrode tips at a temperature'between about 630 and about 670 C., cooling the body to a temperature between about 550 and about 600 C., allowing the partially cooled material to stand Yat such temperature for between about 5 and about'60 minutes, and then cooling theA resulting material to about atmospheric temperature.
7. A thermometer probe comprisingA a solid body of,
an antimony selenium arsenic alloy cast around and thereby shrunk upon a pair of electrodes, wherein one. of ,the electrodes castvinto the probe body substantially. consists in an inward projection of a metallic body also forming an outer shell for the probe.
8. A thermometer probe as described in claim 7, wherein the outer Vshell'rand inward projection thereofv substantially consists of stainless steel.
' OTHER REFERENCES Cullity et al., Trans. A. L. M. E. V. 188, JanuaryV 1950, Journal of Metals-pages 47-52.
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|US3047780 *||Jul 21, 1958||Jul 31, 1962||Pacific Semiconductors Inc||Packaging technique for fabrication of very small semiconductor devices|
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|U.S. Classification||338/22.00R, 136/228, 338/331, 428/2, 438/54, 252/519.4, 420/579, 252/62.30T, 136/233, 338/28, 148/33|
|International Classification||H01C7/04, H01B1/00|
|Cooperative Classification||H01B1/00, H01C7/04|
|European Classification||H01B1/00, H01C7/04|