US2976426A - Self-powered semiconductive device - Google Patents

Description

March 2l, 1961 P. RAPPAPQRT 2,976,426

SELF-POWERED SEMICONDUCTIVE DEVICE Filed Aug. 3, 1955 /s/-n/Pf za/vf It (L 'ly ffy/ZZ? 5v j ZZ; 5 9

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PAUL RHPPHPURT 2Q fw TTORNEY United States Patent O SELF-POWERED SEMICONDUCTIVE DEVICE Paul Rappaport, Princeton, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Aug. 3, 1953, Ser. No. 371,823

19 Claims. (Cl. 307-885) This invention relates generally to the use of radioactive isotopes for supplying power to solid semiconductive devices. Particularly the invention relates to novel apparatus wherein a semiconductive device such as a transistor and a power source therefor are combined to form a single or self-powered unit.

ln my copending application Serial No. 365,207, iiled June 30, 1953, methods and means are disclosed and claimed whereby a solid semiconductive device is irradi- `ated with nuclear emissions so that the device becomes a primary source of electrical energy and provides useful electrical power. The high energy nuclear emissions penetrate the semiconductive device and interact with the valence bonds of the crystal to liberate charge carriers (electrons and holes). These charge carriers ow within the device and in elfect are collected to provide an electric potential at its output terminals. The energy of this output potential is utilized to supply current and power to some desired load such a circuit having low power requirements.

An object of the instant invention is to provide a selfpowered" semiconductive device.

Another object of the invention is to provide a semiconductive device having incorporated therein a radioactive power supply.

Another object of the invention is to provide a selfpowered semiconductive device including a power source of the above type.

Another object of the invention is to provide a radioactive power supply cable of generating both positive and negative voltages.

A further object of the invention is to provide a selfpowered transistor in which the power source is of the type hereinbefore described and in which a single semiconducting `body is common to both the power source and transistor structure. A further object of the invention is to provide a self-powered semiconductive device powered by radioactive means, the self-powered device being characterized by long life, ruggedness, and small size.

The foregoing objects and advantages are achieved in accordance with the invention by providing a single body of semiconducting material which is common both to a semiconductive device (which may be a transistor connected in a circuit as an amplifier, oscillator, detector, or the like) and to a power supply therefor. The semiconductive device may be either of the point contact, alloy junction, or grown junction types and includes one portion of the semiconducting body. The power supply for the semiconductive device includes another portion of the semiconducting body and has zones or regions 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 zones or regions included therein to generate suitable voltages for powering the amplifier or oscillator device comprising the other portion of the body.

2,916,426 Patented Mar. 21, 1961 "ice The invention will be described in detail with reference to the accompanying drawing in which:

Figure 1 is a schematic sectional diagram of a selfpowered semiconductive device, according to the invention, wherein the device is of the grown junction type;

Figure 2 is a schematic sectional diagram of a second embodiment of the invention in which alloy type junction structure is employed; and

Figure 3 is another embodiment of the invention employing a point-contact type of semiconductive device.

Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figure 1, a body of semiconducting material having a number of grown junctions has adjacent zones of opposite types of electrical conductivity. For example, one zone 11 may be of p-type conductivity, a zone 13 adjacent thereto of n-type conductivity, and zones l5 and 17 p-type and n-type conductivities, respectively.

One method of fabricating a semiconducting body in which p and n zones occur alternately with rectifying junctions therebetween is described in U. S. Patent No. 2,631,356 granted to M. Sparks and G. K. Teal on March I7, 1953. Briey this method involves dipping a seed of germanium into a molten mass of germanium. The seed is withdrawn from the molten mass at a rate which is suiicicnt to draw some of the molten mass therewith. As the seed is withdrawn the impurity balance in the melt is altered to effect inversion in the conductivity of the melt and of the withdrawn material. For example, if the melt initially is n-type, it may be converted to p-type by adding an acceptor material such as gallium. Reconversion to n-type is attainable by adding a donor material such as antimony.

Zones 11, 13, and 15 of the semiconducting body described above comprise the collector electrode, the base electrode, and the emitter electrode, respectively of a transistor. Zones 15 and 17 and a radioactive emitter material 19 disposed thereabout comprise a radioactive power supply for the transistor. The emitter material 19 may comprise one or a combination of radioactive isotopes which emit charged particles and/or neutral radiations. Such emitters may include, by way of example, polonium and uranium (both emitters of positively charged alpha particles), strontiumg or tritium (emitters of negatively charged beta particles), cobalt6u (an emitter of neutral gamma rays), and numerous other radioactive isotopes.

The thickness of the semiconducting body for maximum eiciency, is selected so that substantially all the radioactive emissions incident on the body are absorbed. With a strontium source arranged as illustrated a germanium body having a thickness of the order of a hundred mills is adequate. The thickness of a similarly irradiated silicon device is of the order of two hundred mils. When radioactive isotopes are used which produce less energetic emissions, thinner bodies of semiconducting material may be employed to advantage.

ln the power supply portion of the above unit, the radiations emitted by the radioactive material 19 interact with the valance bonds of the semiconducting body regions 1S and 17 causing charge carriers (electrons and holes) to be liberated therein. The liberation of these charge carriers corresponds to raising electrons from the lled band to the conduction band, thereby leaving behind holes in the filled band. With the incoming radiation having a minimum quantum energy which is equal to or greater than the energy gap of the empty or forbidden region. both electrons and holes are produced. The energy gaps for germanium and silicon, for example, are of the order of 0.72 electron volt and 1.12 electron volts, respectively. i

An electrostatic potential barrier exits at the junctio zlbetween zones 15 and 17. Under the inuenee of this potential barrier the liberated charge carriers flow across the junction in one direction only. Substantially all the charge carriers which get into the junction region in effect are collected and contribute to the voltage developed across a voltage divider load 23 ohmically connected between zones 15 and 17. Some of these carriers are produced in the junction region. Other charge carriers are produced outside the junction region and initially are subjected to no electrostatic potential. However, if these carriers have sufficiently great lifetimes and diffusion lengths, they also enter the junction region (solely by a diffusion process) and enhance the current output.

With fifty millicuries of strontium90 as emitter material, the open-circuit voltage derived in the manner described above may vary between thirty and several hundred millivolts, the voltage value depending on the kind and characteristics of semiconducting material employed. The power expended in a load connected to the power supply, for maximum power transfer, is of the order of several microwatts.

The terminal voltage of the power supply portion of the instant structure is used to bias or power the transistor portion in the following manner. The emitter electrode (zone I5) is common to the transistor and power supply portions. Since irradiation of the junction region between zones and 17 results in zone 15 attaining a potential which is positive with respect to the potential of zone 17, and since zone 15 is of p-type conductivity, zone 15 is biased in the forward direction, as required, with respect to the base portion (zone 13). Since the collector electrode (zone l1) must be biased in the reverse direction, i.e., negatively with respect to zone 13, the terminal of the voltage divider 23 connected to zone 17 is ohrnically connected to zone 11 by means of an isolating resistor 45. The movable tap 24 of the voltage divider 23 is ohmically connected to the base portion (zone 13) of the transistor. By varying the position of the voltage divider tap 24, any desired ratio of voltages is available for powering the junction transistor.

The self-powered semiconductive unit hereinbefore described has a number of advantages. The unit is powered solely by the energy of radioactive emissions. No external power sources or batteries are required. The unit is rugged from a physical standpoint and is not affected by vibration or mechanical shock. The size of the unit is very small, of the order of a cubic centimeter, and it has an extremely long life. The half-life of strontium 9, for example, is twenty-tive years. Other isotopes P have even longer half-lives. Furthermore, a considerable saving in materials is afforded by providing a. single semiconductive unit having incorporated therein a signal translating or oscillator device and a power supply for the device.

Figure 2 shows an embodiment of the invention in which rectitying junctions are formed in a body of semiconducting material by an alloying process. The semiconducting body portion 25 may be either of p-type or n-type conductivity. For purposes of the present description it is assumed that the material is a body of n-type germanium having a resistivity of the order of four ohmcentimeters. Pellets 27 and 29 ot a material such as indium, aluminum, gallium, or the like are alloyed into substantially opposite surfaces of one portion of the body 25 so that the pellets impart p-type conductivity to regions of the body 25. Terminal leads 3l and 33 are connected to the pellets 27 and 29, respectively, by wellknown techniques to provide means for making electrical contact thereto. The p-type conductivity regions resulting from alloying pellets 27 and 29 into the n-type germanium body 25 comprise the emitter an-d collector electrodes of a junction type transistor.

The power supply for the above transistor comprises the semiconductive body 25 (also incorporated as a part 4 of the transistor structure) and impurity pellets 35' and 37. Pellets 35 and 37 are spaced from pellets 27 and 29 and are alloyed into opposite surfaces of the gennanium body at points substantially opposite cach other. Since the cmitter and collector electrodes of the transistor' portion ot the unit are to be biased in the forward and reverse directions, respectively, it is essential that the power supply portion 0i the unit generate terminal volt-- ages 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 25. The other voltage is for biasing the collector circuit in the reverse direction and must be negative with respect to the body 2S. To achieve the desired positive and negative voltages, the pellet 35 (indium, for example) is selected to impart p-type conductivity to a region of the semiconducting body 25. The pellet 37 is selected to impart n-type conductivity to the body 25 which is diierent in degree or higher than the normal n-type conductivity of the body. Materials having a higher impurity concentration and capable of imparting higher n-type conductivity to an n-type semiconducting body are, for example, lead antimony and lead arsenic. Leads 39 and 41 are provided for making electrical contact to the pellets 35 and 37 and to the p and n regions formed thereby.

The radioactive emitter material 19 is coated or is otherwise applied to the power supply portion of the semiconducting body 25 and pellets 35 and 37. The theory of voltage generation for the instant device is much the same as heretofore explained with reference to the description of the operation of the device of Figure l. The high energy radioactive emissions emitted by the material 19 liberate charge carriers within the device which take part in a conduction process. In one instance carriers produced in and carriers which diffuse into the junction region between the body 25 and the indium pellet 35 are collected so that the potential of the pelle-t 3S is positive with respect to the potential of the body 25. In the other instance charge carriers produced in and carriers which diffuse into the junction region between the body 25 and the pellet 37 result in the pellet 37 attaining a potential which is negative with respect to the potential of the semiconducting body. The value of the positive and negative potential with respect to the base is determined by the impurity concentration in the recrystallized r1 and p regions formed b-y the alloying of the pellets into the body 25 and may be controlled by varying the impurity concentrations. The highest voltage is obtained when using high impurity concentrations. The positive and negative potentials dcveloped in the above described manner are applied to the emitter and collector circuits, respectively, of the transistor portion of the unit via isolating resistors 43 and 45. A blocking capacitor 47 is provided for applying desired signals between the emitter circuit and the semiconducting body 25 and for isolating the input circuit from the radioactive power supply.

The amount of power generated by the power supply portion of the instant unit is determined by the amount of radioactive emitter material employed and by the area of the junctions between the pellets and the semiconducting body. If greater power is required of the device for the emitter and/ or collector circuits of the transistor, the

' junction areas should be made large enough so that the i device generates the required levels of power.

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p and n type conductivities to the portions of the body wherein they are alloyed, the impurity concentration of the p region being greater than that of the p-type semiconducting body. Pellet 37 may comprise lead antimony or lead arsenic and pellet 39 may comprise indium, gallium, aluminum, etc.

Figure 3 shows an embodiment of the invention which is similar in part to the apparatus described with reference to Figure 2. The power supply portion of the self-powered unit is substantially identical to that shown in Figure 2. However, the transistor portion of the unit is a point-contact device rather than a junction device as heretofore shown. The point-contact structure comprises a base connection 49 which makes electrical contact to a portion of the semiconducting body. Spaced point electrodes 51 and 53 make contact with the semiconducting body on a surface opposite that to which the base connection is made. Point electrode 51 is connected to one terminal the power supply via isolating resistor 43 and electrode 53 is connected to the oppositely poled terminal of the power supply via resistor 45.

What is claimed is:

l. A self-powered electrical unit comprising, a body of semiconductor material, a semiconductive device, and a primary power supply for said semiconductive device, said device and said power supply being integral with said body of semiconducting material.

2. A self-powered electrical unit comprising, a semiconductive device, and a power supply for semiconductive device, said device and said power supply having in cornmon `a body of semiconducting material, the power supply portion of said body being partially surrounded by a radioactive emitter.

3. Electrical apparatus comprising, a body of semiconducting material having a rst portion including emitter and collector electrodes, a second portion of said y body comprising a power supply for said first portion, said second portion including two zones of opposite type conductivity, and a radioactive emitter positioned to irradiate said second portion.

4. Electrical apparatus comprising, a body of semiconducting material having a first zone of one type conductivity, an adjacent second zone of conductivity type opposite to said one type conductivity, a third zone adjacent said second zone and having said one type conductivity, a fourth zone adjacent said third zone and having said opposite type conductivity, and a radioactive emitter for irradiating portions of said third and fourth zones.

5. Apparatus as claimed in claim 4 including means coupled to said third and fourth zones for deriving different electric potentials, and means for applying said different potentials to said first and second zones.

6. Electrical apparatus comprising, a body of semiconducting material of one conductivity type, a material alloyed into said body to impart to rst and second regions of said body a conductivity type opposite to said one type, materials alloyed into regions of said body spaced from said first and second regions to impart a third region of said body a conductivity type opposite to said one type and to a fourth region of said body a conductivity of the same type as but diiferent in degree from said one type conductivity, and a radioactive emitter for irradiating said third and fourth regions.

7. Apparatus as claimed in claim 6 wherein the areas of said third and fourth regions is substantially greater than the areas of said lirst and second regions.

8. Apparatus as claimed in claim 6 wherein said iii-st region is substantially opposite said second region and said third region is substantially opposite said fourth region.

9. Apparatus as claimed in claim 6 including means for coupling said third and fourth regions to said first and second regions.

l0. Electrical apparatus comprising, a body of n-type semiconducting material, a material alloyed into said body to impart p-type conductivity to rst and second regions of said body, materials alloyed into regions of said body spaced from said rst and second regions to impart ptype conductivity to a third region of said body and n-type conductivity to a fourth region of said body, the conductivity of said fourth region being different from the conductivity of said body, and a radioactive emitter surrounding a portion of said body for irradiating said third and fourth regions.

1l. Electrical apparatus comprising, a body of p-type semiconducting material, a material alloyed into said body to impart n-type conductivity to first and second regions of said body, materials alloyed into regions of said body spaced from said rst and second regions to impart ntype conductivity to a third region of said body and p-type conductivity to a fourth region of said body, the conductivity of said fourth region being different from the conductivity of said body, and a radioactive emitter surrounding a portion of said body for irradiating said third and fourth regions.

12. Electrical apparatus comprising. a body of semiconducting material of one conductivity type, a conductive base connection for a portion of said body, a point electrode in contact with said body and positioned substantially opposite said base connection, materials spaced from said point electrode and base connection alloyed into regions of said body to impart to one region of said body a conductivity type opposite to said one type and to another region of said body a conductivity of the same type as but different in degree from said one conductivity, and a radioactive emitter surrounding a portion of said body for irradiating said one and another regions.

i3. Electrica] apparatus comprising, a body of semiconducting material of one conductivity type, a conductive base connection for a portion of said body, a plurality of point electrodes in contact with said body and positioned substantially opposite said base connection, materials spaced from said point electrodes and base connection alloyed into regions of said body to impart to one region of said body a conductivity type opposite to said one type and to another region ot' said body a conductivity of the same type as but diiierent in degree from said one conductivity. and a radioactive emitter surrounding a portion of said body for irradiating said one and another regions.

14. Electrical apparatus comprising, a body of semiconducting material of one conductivity type, a conductive base connection for a portion of said body, a pair of spaced emitter and collector point electrodes in contact with said body and positioned substantially opposite said base connection, materials spaced from said point electrodes and base connection alloyed into regions of said body to impart to one region of said body a conductivity opposite to said one type and to another region of said body a conductivity of the same type as but different in degree from said one conductivity, and a radioactive emitter surrounding a portion of said body for irradiating said one and another regions.

l5. Apparatus as claimed in claim 14 for coupling said one and another irradiated regions to said emitter and collector electrodes.

16. Electrical apparatus comprising, a body of semiconducting material of one conductivity type, a rst pair of junction regions formed in opposing surfaces of said body each having a conductivity type opposite to said one type, a second pair of junction regions formed in said body spaced from said first pair of junction regions. one of the regions of said second pair having a conductvity type opposite to said one type and the other region of said second pair having said one type conductivity but different in degree and a radioactive emitter positioned to irradiate said second pair of junction regions.

17. Electrical apparatus comprising, a body of semiconducting material of one conductivity type, a pair of rectifyiug contacts in contact with one surface of said body, an electrode in contact with a portion of the opposing surface of said body, and a pair of junction regions formed in said body spaced from said rectifying contacts, one of said junction regions having a conductivity type opposite to said one type and the other junction region having said one type conductivity but different in degree.

18. Electrical apparatus as claimed in claim 17 including a radioactive emitter positioned to irradiate said junction regions.

I9. A self-powered electrical unit comprising, a semiconductive device and a power sup-ply including a radioactive emitter for said semiconductive device, said device and said power supply having in common a body of semiconducting material.

ReferencesV Cited in the file` of this patent UNITED STATES PATENTS Kannenberg May 30, 1939 Wallhausen et al Aug. 23, 1949 Pfann July 24, 1951 Pfann May 20, 1952 Pantchechnikof Feb. 24, 1953 Ebers Oct. 13, 1953 Baldwin Apr. 20, 1954 Rappaport July 19, 1955 Sziklai Feb. 21, 1956 Johnson July l0, 1956 Dacey et al. Jan. 22, 1957 OTHER REFERENCES The New Electrical Encyclopedia, vol. I page 260, Mar.

The Electrician, Oct. 31, 1924, p. 497.

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