US2998550A - Apparatus for powering a plurality of semi-conducting units from a single radioactive battery - Google Patents

Description

1961 w. T. COLLINS ET AL 2,998,550

POWERIN EMI-CONDUCT G A PLURALITY O S FROM A SINGLE RADIOAC VE BATTERY Filed June 50, 1954 APPARATUS FOR ING UNIT fl777/WF/ 2,998,550 Patented Aug. 29., 1961- fire.

2,998,550 APPARATUS FOR POWERING A PLURALITY F SEMI-CONDUCTING UNITS FROM A SINGLE RADIOACTIVE BATTERY Warren T. Collins and Paul Rappaport, Princeton, N.J.,

assignors to Radio Corporation of America, a c'orporation of Delaware Filed June 30, 1954, Ser. No. 440,454 '11 Claims. (Cl. 317- 101) This invention relates generally to radioactive or atomic batteries of the type employing radioactive iso topes and semi-conducting materials. Particularly the invention relates to a device wherein a plurality of semiconducting units such as transistors and a radioactive irradiated semiconductor power supply unit therefor are combined on a single body of semi-conducting material.

An object of the instant invention is to provide a device in which a plurality of semi-conducting units, such as transistors and the like, may be supplied with power by a single radioactive power unit.

Another object of the invention is to provide an improved device of the above type having a plurality of semiconducting units which are powered solely by the energy of radioactive emissions.

Another object of the invention is to provide an improved device of the type described which is characterized by long life, ruggedness, and small size.

A further object of the invention is to provide an improved self-powered semi-conducting device which utilizes the electron-voltaic elfect.

A still further object of the invention is to provide a device of the type described in which a single semiconducting body is common both to the radioactive power unit and to each semi-conducting rectifying or amplifying unit.

The foregoing and other objects and advantages are achieved in accordance with the invention by providing a single body of semi-conducting material which is common to each of the plurality of semi-conducting units, suchas diodes or transistors, and to the power supply unit. The geometry of the body is chosen such that each semi-conducting unit effectively is isolated electrically from adjacent semi-conducting units. The transistor units may be either of the alloy junction, point contact, barrier electrode, or grown junction types and each transistor unit includes a different portion of the semi-conducting body. The power supply for the transistor units includes a stilldifierent portion of the semi-conducting body and has regions or zones of different types of conductivity separated by one or more rectifying junctions. A radioactive emitter is provided for irradiating the power supply portion of the body and the regions or zones included therein to generate suitable voltages for powering each of the semi-conducting rectifying or arm plifying units comprising the other portion of the body.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIGURE 1 is a plan view of a first embodiment of the invention including a plurality of alloy junction type semi-conducting diode or transistor units and a radioactive power supply therefor;

FIGURE 2 is an elevational sectional view of the device of FIGURE 1;

FIGURE 3 is an elevational sectional view of a second embodiment of the invention in which the semiconducting diode or transistor units are of the point contact type; and

FIGURE 4 is a perspective view of a third embodiment of the invention which employs grown-junction Structure.

Similar reference characters are applied to similar ele' ments throughout the drawing.

Referring to FIGURES 1 and 2, a body 11 of semiconducting material is shown, preferably annular in form, which has an inner portion 13 and an outer portion 15 of different thicknesses. The body 11 may comprise any one of a number of suitable semi-conducting materials such as, for example, germanium, silicon, cadmium sulfid'e, and indium antimonide, the latter being one of the intermetallic compounds. For purposes of the present description, it is assumed that n-type germanium is chosen and that the resistivity of the body 11 is of the order of one or two ohm-centimeters.

The outer portion 15 of the body 11 is dimensioned to have a thickness suitable for transistor operation. For such operation the thickness of this portion 15 of the device is of the order of five to ten mils. The geometry of the device preferably is made such that the outer portion of the body 11 comprises a plurality of radial toothshaped members 31. This type of geometry may be achieved by grinding or cutting away sections of the outer body portion 15 with a diamond saw or other means. After such cutting or grinding, pellets 2.7 and 2-9 of a material such as indium, gallium, aluminum, or the like are alloyed into opposing surfaces of each tooth-shaped member 31 to form therein p-type conductivity regions. Terminal leads 33 and 35 are then connected to the pellets 27 and 29, respectively, to make electrical contact thereto. The p-type conductivity regions resulting from alloying. pellets27 and 29 into the n-type germanium body of each member 31 comprise the emitter and collector electrodes, respectively, of a junction type transistor. Each such transistor effectively is isolated electrically from adjacent transistors by the impedance of the semi-conducting body material intermediate the transistors. In the event still greater electrical isolation is desired each member 31 may include a slot 32 which further increases the impedance between adjacent units. In the embodiment illustrated in FIGURE 1 ten such semiconducting units are shown spaced about the periphery of the device, each of which effectively is isolated electrically from adjacent units. It will be appreciated, however, that any number of semi-conducting units may be formed in the manner described and that the number ten. is merely illustrative. Also, it is pointed out that the semi-conducting units need not all be transistor type units, but may include two element semi-conducting units such as rectifiers.

The power supply portion of the device includes as one element thereof the inner portion 13 of the body 11. Impurity pellets 17 and 19 are alloyed into opposing surfaces of the inner body portion 13 at points substantially opposite each other. Since the emitter and collector electrodes of each semiconducting or transistor unit of each member 31. are to be biased in the forward and reverse directions, respectively, it is essential that the power supply portion of the device generate terminal voltages having different polarities. One of the voltages is for biasing the transistor emitter circuit in the forward direction and must be positive with respect to the body 11. The other voltage is for biasing the collector circuit in the reverse direction and must be negative with respect to the body 11. To achieve the desired positive and negative voltages, the pellet 17 (indium, aluminum, gallium, for example) is selected to impart p-type conductivity to the region of the inner body portion 13 wherein it is alloyed. The pellet 19 is selected to impart n-type conductivity to the region of the body portion 13 wherein it is alloyed which is different in degree or higher than the normal n-type conductivity of the body. Materials having a higher impurity concentration capable of imparting higher n-type conductivity to an n-type semiconducting body are; for example, lead antimony and lead arsenic. Leads 21 and Bare provided. for makingin the power supplyportionof the devices The emitter material 25 may comprise one-or a combination. of: radio active isotopes which emit' charged particles and7'or neutral emissions; Such emittere' may: include,- by" way of example, polonium and uranium- (both emitters of positively charged alpha particles), strontiuxnQOl or: triif' ium (emitters of negatively charged beta particlesf), cobalt 60 (an emitter of neutral gamma rays), and numerous other radioactive isotopes;

Thethickness of the inner portion: 13 of the sem-ia conducting body 11, for maximum efliciency, isrse'l'ected so that substantially all the radioactiveemissions incident on the body are absorbed. With a'strontium 90 source arranged as illustrated a germanium body having a; thickness of the order of'a hundred milsis adequate. The thickness of a similarly irradiated silicon deviceisl of; the order of two hundred mils. When radioactive isotopes are used which produce less energetic emissions, thinner bodies of semi-conducting material maybe employed to advantage.

The theory of operation of the-power supply portion ofthe instant device is believed to be as follows. The radiations emitted by the radioactive-material. interact with the valence bonds of the semi-conducting; body 11 causing charge carriers (electrons and holes) to; be liberated therein. The liberation of these charge carriers corresponds to raising electrons from the-filled band to the conduction band, thereby leaving behind holes in; the filled band. With the incident radiation having aminimum quantum energy which is equal to or greater than the energy gap of the empty or-torbidden region, both electrons and holes are-produced. The energy gaps'for germanium and silicon, for-example, areoftheorder of 0.72 electron volts and 1.12 electron volts, respectively;

Electrostatic potential barriers exist in the junction regions between the p-type region and the-body portion 13 and between thebody portion 1'3 and the higher concentration n-type region. Under the influence of these potential barriers the liberated charge carriers flow across the junctions. A hole which approaches azp-type junction region sees an electrostatic held of the properpolarity for the hole to be collected. However, an electron'appreaching the p-type region is repelled. In a like manner electrons which approach the n-typeregion are-collected and holes are repelled. The difiusion' length. of the charge carriers for improved operation should, be at least twice the distance between the p-type and n type regions in order that the carriers repell'edata given junction may becollected at the junctiomhavihgthe opposite type conductivity. Since electrons and" holes arecollected in the manner described above, a positive. voltage isdeveloped (for po'weringthe transistor emitter circuits) between the p-type region and'thebodyll and-anegative voltage (for powering the; transistor collector circuits) is developed between the n-type region- 'and -the'body 11.

These voltages are attributable to anelectron volta'ic ef feet and may be utilized to powereach-of th'e-serni-con ducting units included in the outer portion lief" the device. r

The amount of power generated" the radioactive power supply described above is determined bythe amount of radioactive emitter employedandbythe area of the junctions between the-pellets I'Tand I9and the semi conducting body portion 13; *Piefrablythe area of the junction regions formed bythe alloying of pellets 4 17 and 19 is at least twice the junction area of any one semi-conducting unit. If greater power is required of the device by the circuits to be powered, the junction areas should be made large enough so that the power supply portion generates the required levels of power.

FIGURE 3 shows a second embodiment of the invention which is similar in part to the structure described with reference to FIGURES l and 2. The radioactive power supply portion of the device is substantially as shown and described in these figures. However, the outer portion of the device, in the present instance, comprises point contact semi-conducting units. Each. tooth-shaped member 31, all of which comprise the outer portion 15 of the semi-conducting body 11, has connected thereto a metal tab 37 such as antimony platedindium which makes'ohmic-connection to the'body. Spaced point'elec trodes 39 and 41 make contact with the body 1 1 on a surface'of member 31. opposite that to which the tab is connected. Point electrode 39 may be connected to' one terminal of the power supplyportion of. the device and point electrode 41 may be connected to the remaining power supply terminal.

In FIGURE 4 a third embodiment of the invention is shown in which grown junction: structure is employed. The semi-conducting body 12 may be formed according to thefollowing method; A. seed of germanium is dipped into. a molten mass of germanium. The seed. is withdrawn from the molten mass at a. rate which is sufficient to draw some of the molten mass'therewith. As the seed is. withdrawn. the impurity balance in the melt is altered to eflfect inversion inthe type. of conductivity of the melt and of the withdrawn material. For example, ifthemelt initially isn-type,,it may be converted to p-type by adding 1 an acceptor material such, as gallium. Reconversion to n-type is achieved by adding a donor material. such as antimony.

The body 12 thus comprises: alternate p-type and n-type conductivity zones. In the device of the invention four 1 zoues-are-required, the first and third zones beingof one type conductivity, for example, p-type, and the second and fourth. zones being; of the opposite or. n-type. conductivity. The body- 12 is cut or ground so that the third and fourth zones and a portion of: the second zone. are subdivided into a plurality of electrically isolated. semi-. conducting units 42. Each semi-conducting unit 42. has a zone 43 of n-type conductivity, an adjacent zone 45 0f p-type conductivity, and a zone 47 of n-type conductivity adjacent the-p-type zone 45. These zones 43, 45' and.47 comprise, respectively, thecollector, base, and emitter electrodes. of a transistor. The first zone 49, the remaining portioni51 of the second zone, andiat radioactive emitter 25- comprise the-powersupply portionof the device; Theradioactiv'e-emitter. 25 preferablyis coated on the zone 49' and the zone portion 51.

Theterminal voltage of the power supply portion of this embodiment of the invention isusedtor biasthe transistor units 42 in the following manner. The col-v lector electrode: 43- of each unit 42v eflectively iscommon to the transistor and powersupply'portionssince itis contiguous with the-zone portion 51; Since irradiationof the junction region between zones 49 and' 511 results in zone portion 51 attaining a potential which isnegative with respect to zone 49; the collector electrodes 43- are biased in the reverse. direction, as required, withrespect to the base electrodes 45. Since the'emitter electrodes 47 must be biased in the forward: direction, avoltage divider '(not shown) may be connected between zones 49 and 51 with an ohmic connection between: zone. 49 and the. emitter electrodes. 47.. This biases" the emitter electrodes 47-in the forward direction. The movabletap of the divider is'connected to the base electrodes. 45.. By varying the position of the tap any desired ,ratio of voltages. is available for powering the'transistor devices;

.What is claimed is: I

1. Electrical apparatus comprising a body of semiconducting material of one conductivity-type having a plurality of first portions each including a semiconducting unit having at least one rectifying electrode, said body being slotted between said first portions to eifectively electrically isolate said units from each other, and said body having a second portion integral with each of said first portions, said second portion including one region of opposite conductivity-type and another region of the same type as said one conductivity-type but greater in degree.

2. Apparatus as claimed in claim 1, each of said regions in said second portion being at least twice the area of said rectifying electrodes in said first portions.

3. Apparatus as claimed in claim 1 wherein said rectifying electrodes are junction electrodes of opposite conductivity-type than said one type.

4. Apparatus as claimed in claim 1 wherein said rectifying electrodes are point contact electrodes.

5. Electrical apparatus comprising a body of semiconducting material of one conductivity-type having a plurality of first portions each including a semiconducting unit having at least one rectifying electrode, said body being slotted between said first portions to effectively electrically isolate said units from each other, and said body having a second portion integral with each of said first portions, said second portion including one region of opposite conductivity-type and another region of the same type as said one conductivity-type but greater in degree, and a radioactive emitter positioned adjacent said second portion to irradiate said second portion and said regions.

6. Electrical apparatus comprising a plurality of semiconductor units and a power supply for said units, said units and said power supply having in common a body of semiconducting material, said body having first portions of one thickness each supporting said units and surrounding a second portion of a thickness greater than said one thickness supporting said power supply, said body being slotted between said units to effectively electrically isolate said units fiom each other.

7. Electrical apparatus comprising a plurality of semiconductor units and a power supply for said units, said 6 units and said power supply having in common a body of semiconducting material, said body having first portions Olf one thickness each supporting said units and surrounding a second portion of a thickness greater than said one thickness supporting said power supply, said body being slotted between said first and second portions to effectively electrically isolate said units from each other.

8. Electrical apparatus comprising a plurality of semiconductor units and a power supply for said units, said units and said power supply having in common a body of semiconducting material, said body having first portions of one thickness each supporting said units: and surrounding a second portion of a thickness greater than said one thickness supporting said power supply, said body being apertured between said units to efiectively electrically isolate said units firomeach other.

9. Apparatus as claimed in claim 8 including a radio active emitter for irradiating said second body portion.

10. Apparatus as claimed in claim 9 wherein the thickness of said second body portion is less than one-half the difiusion length of charge carriers produced in said second body portion as a result of said irradiation.

11. Apparatus as claimed in claim 8 wherein said body is substantially annular in form and said first body portion comprises a plurality of tooth-shaped members, each tooth-shaped member comprising an element of one of said semi-conducting devices.

References Cited in the file of this patent UNITED STATES PATENTS 2,655,625 Burton Oct. 13, 1953 2,669,635 Pfann Feb. 16, 1954 2,713,644 Rappaport July 19, 1955 2,735,948 Sziklai Feb. 21, 1956 2,745,973 Rappaport May 15, 1956 2,754,431 Johnson July 10, 1956 2,816,228 Johnson Dec. 10, 1957 2,870,344 Brattain et al Jan. 20, 1959

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