Abstract:
A power source and methods thereof includes a structure comprising one or more p type layers, one or more n type layers, and one or more intrinsic layers and at least one source of radiation is disposed on at least a portion of the structure. Each of the p type layers is separated from each of the n type layers by one of the intrinsic layers.

Description:
[0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/587,364 filed Jul. 13, 2004, which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to batteries and, more particularly, to radio isotope batteries and methods thereof.  
       BACKGROUND  
       [0003]     The concept of an alpha voltaic battery was proposed in 1954 as disclosed in W. G. Pfann and W. van Roosbroeck, Journal of Applied Physics, Volume 25, No. 11, pp. 1422-1434, November 1954, which is herein incorporated by reference. A radioactive substance that emits energetic alpha particles is coupled to a semiconductor p/n junction diode. As the alpha particles penetrate into the p/n junction, they decelerate and give up their energy as electron-hole pairs. These electron-hole pairs are collected by the p/n junction and converted into useful electricity, much like a solar cell.  
         [0004]     The main reason alpha-voltaics and also beta-voltaics are not commercially successful is that the alpha or beta particles damage the semiconductor material as disclosed in G. C. Rybicki, C. V. Aburto, R. Uribe, Proceedings of the 25 th  IEEE Photovoltaic Specialists Conference, pp. 93-96, 1996, which is herein incorporated by reference. More specifically, the pn-junction in the alpha or beta voltaic device, which converts the alpha or beta particle radiation, respectively, from the radioactive isotope into electricity, rapidly degrades due to radiation damage rendering the alpha or beta voltaic device useless long before the radioisotope is depleted.  
       SUMMARY  
       [0005]     A power source in accordance with embodiments of the present invention comprises a structure comprising one or more p type layers, one or more n type layers, and one or more intrinsic layers and at least one source of radiation is disposed on at least a portion of the structure. Each of the p type layers is separated from each of the n type layers by one of the intrinsic layers.  
         [0006]     A method of making a power source in accordance with embodiments of the present invention includes depositing an intrinsic layer on one of an n type layer and a p type layer, depositing the other one of the n type layer and the p type layer on the deposited intrinsic layer, and disposing at least one source of radiation on at least the deposited one of the n type layer and the p type layer.  
         [0007]     A method of generating power in accordance with embodiments of the present invention includes emitting radiation into a structure comprising one or more p type layers, one or more n type layers, and one or more intrinsic layers and converting the emitted radiation in the structure to power. In the structure each of the p type layers is separated from each of the n type layers by one of the intrinsic layers.  
         [0008]     The present invention provides a radio isotope battery whose performance does not degrade in a matter of hours because of damage to the semiconductor material from the alpha or beta particles. The degradation is prevented in the present invention by using a structure comprising one or more p type layers, one or more n type layers, and one or more intrinsic layers, where each of the p type layers is separated from each of the n type layers by one of the intrinsic layers. The intrinsic layers prevent alpha or beta particles from the alpha or beta particle emitter from damaging the p type layers and the n type layers while successfully converting energy from the alpha or beta particles into electron-hole pairs for collection.  
         [0009]     Another advantage of the present invention is that the radio isotope battery can be made extremely small and thus is well suited for emerging micro and nano applications and technologies, such as micro electrical mechanical systems (MEMS). The radio isotope battery can produce power on the order of micro-Watts, sufficient for many MEMS applications. Additionally, the radio isotope battery is very suitable for integration directly on a semiconductor device for a “battery-on-a-chip” concept. At this time, small long lived power sources simply do not exist for these types of applications and systems.  
         [0010]     Yet another advantage of the present invention is that the radio isotope battery can be combined in parallel and series combinations to address a wide variety of higher current, voltage, and power requirements. For example, the present invention can be scaled to higher power levels on the order of hundreds of watts making it suitable for a variety of other applications, such as deep space missions. The radio isotope battery has two unique properties when compared to a conventional chemical battery that make it an outstanding candidate for deep space missions. First, the alpha or beta emitting materials have half-lives ranging from months to hundreds of years, so there is the potential for an almost “everlasting” batteries. Second, radio isotope batteries can operate over a tremendous temperature range, while an ordinary chemical batteries all fail at temperatures below −40° C. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram of a radio isotope battery in accordance with embodiments of the present invention; and  
         [0012]      FIG. 2  is a diagram of real-space energy of an n-i-p-i crystal. 
     
    
     DETAILED DESCRIPTION  
       [0013]     A battery  10  in accordance with embodiments of the present invention is illustrated in  FIG. 1 . The battery  10  includes a substrate  12 , a semiconductor structure  14  with n type layers “n” or  16 ( 1 )- 16 ( 3 ), p type layers “p” or  18 ( 1 )- 18 ( 2 ), and intrinsic layers “i” or  20 ( 1 )- 20 ( 4 ), a pair of openings or holes  22 ( 1 )- 22 ( 2 ), a pair of conductive contacts  24 ( 1 )- 24 ( 2 ), and an alpha particle emitter  26 , although the battery  10  can comprise other numbers and types of components, such as a beta particle or other radio isotope emitter, in other configurations. The present invention provides a number of advantages including providing a radio isotope battery  10  whose performance does not degrade in a matter of hours because of damage to the semiconductor material from the emitted alpha or beta particles.  
         [0014]     Referring to  FIG. 1 , the structure  14  is formed on the substrate  12  which is made of an amorphous silicon, although the substrate  12  can be made of other types of semi-insulating and insulating materials.  
         [0015]     The structure  14  is formed on the substrate  12  and comprises the n type layers  16 ( 1 )- 16 ( 3 ), p type layers  18 ( 1 )- 18 ( 2 ), and intrinsic layers  20 ( 1 )- 20 ( 4 ), where each of the p type layers  18 ( 1 )- 18 ( 2 ) is separated from each of the n type layers  16 ( 1 )- 16 ( 3 ) by one of the intrinsic layers  20 ( 1 )- 20 ( 4 ), although the structure  14  can comprise other numbers and types of layers in other configurations. By way of example only, semiconductor materials which could be used for the n type layers  16 (l)- 16 ( 3 ), p type layers  18 ( 1 )- 18 ( 2 ), and intrinsic layers  20 ( 1 )- 20 ( 4 ) include GaAs, GaInP, SiC, Si, or other III-V, II-VI or group IV semiconductors, although other types of materials can be used. In this example, the semiconducting materials are grown epitaxially on single crystal wafers, such as GaAs.  
         [0016]     This structure  14  is used to convert the alpha radiation from the alpha particle emitter  26  into usable electricity, although the structure could convert other types of radio isotopes into energy, such as beta particles. This configuration of the structure  14  with each of the p type layers  18 ( 1 )- 18 ( 2 ) separated from each of the n type layers  16 ( 1 )- 16 ( 3 ) by one of the intrinsic layers  20 ( 1 )- 20 ( 4 ) also substantially prevents electrical degradation of the battery  10  by minimizing the effects alpha particle damage, although the configuration of the structure  14  can also protect from damage from other types of radio isotopes, such as beta particles. In this particular embodiment, each of the intrinsic layers  20 ( 1 )- 20 ( 4 ) has thickness of about 5000 angstrom which protects the n type layers  16 ( 1 )- 16 ( 3 ) and the p type layers  18 ( 1 )- 18 ( 2 ) from degradation, although each of the intrinsic layers  20 ( 1 )- 20 ( 4 ) could have other thicknesses which are sufficient to prevent substantial degradation while allowing conversion of the collected electron-hole pairs into useful electricity. By way of example only, a diagram of the real-space energy of another structure with this alternating configuration of an n type layer, an intrinsic layer, a p type layer, and an intrinsic layer, i.e. an “n-i-p-i” configuration or crystal, in accordance with other embodiments of the present invention is illustrated in  FIG. 2 .  
         [0017]     Referring back to  FIG. 1 , each of the holes  22 ( 1 ) and  22 ( 2 ) has a cone-shape and extends in from a surface  28  of the n type layer  16 ( 1 ) of the structure  14  through all of the n type layers  16 ( 1 )- 16 ( 3 ), p type layers  18 ( 1 )- 18 ( 2 ), and intrinsic layers  20 ( 1 )- 20 ( 4 ) to the substrate  12 , although other numbers, shapes and configurations can be used for the holes  22 ( 1 ) and  22 ( 2 ) and the holes  22 ( 1 ) and  22 ( 2 ) can extend through other numbers of layers in the structure  14 .  
         [0018]     A region  30 ( 1 ) adjacent an inner surface of the hole  22 ( 1 ) shown by the dashed lines in  FIG. 1  is doped to form an n+ region and a region  30 ( 2 ) adjacent an inner surface of the other hole  22 ( 2 ) also shown by the dashed lines in  FIG. 1  is doped to form a p+ region, although the regions  30 ( 1 ) and  30 ( 2 ) around the inner surface of each of the holes  22 ( 1 ) and  22 ( 2 ) can have other configurations and can be doped in different manners.  
         [0019]     The conductive contact  24 ( 1 ) is located on the inner surface of the hole  22 ( 1 ) adjacent the n+ region  30 ( 1 ) and extends out from the hole  22 ( 1 ) on to a portion of the surface  28  of the n type layer  16 ( 1 ), although the conductive contact  24 ( 1 ) can be formed in other manners and in other configurations. Similarly, the conductive contact  24 ( 2 ) is located on the inner surface of the hole  22 ( 2 ) adjacent the p+ region  30 ( 2 ) and extends out from the hole  22 ( 2 ) on to a portion of the surface  28  of the n type layer  16 ( 1 ), although the conductive contact  24 ( 2 ) also can be formed in other manners and in other configurations. In this example, ordinary metallization is used for each of the conductive contacts  24 ( 1 ) and  24 ( 2 ), although other types of conductive materials can be used. A load  32  can coupled across the conductive contacts  24 ( 1 ) and  24 ( 2 ) and to ground to store or use the generated electricity, although the load  32  can be coupled in other manners.  
         [0020]     The alpha particle emitter  26  is electrochemically deposited on a portion of the n type layer  16 ( 1 ) of the structure  14  and on an inside surface of the conductive contacts  24 ( 1 ) and  24 ( 2 ) in the holes  22 ( 1 ) and  22 ( 2 ), although the alpha particle emitter  26  can be deposited or placed in other manners and configurations and other types of radio isotope emitters can be used, such as a beta particle emitter. In this particular embodiment, the alpha particle emitter  26  is Am-241 thermally diffused in silver foil and over-coated with a thin metal layer, which is the same materials found in household smoke detectors, although other types of radiation sources could be used.  
         [0021]     A method of making a battery in accordance with embodiments of the present invention will be described with reference to  FIG. 1 . The substrate  12  is made of an amorphous silicon is provided, although other types of substrates can be used. In this particular embodiment: the n type layer  16 ( 3 ) is deposited on a surface of the substrate  12 ; the intrinsic layer  20 ( 4 ) is deposited on a surface of the n type layer  16 ( 3 ); the p type layer  18 ( 2 ) is deposited on a surface of the intrinsic layer  20 ( 4 ); the intrinsic layer  20 ( 3 ) is deposited on a surface of the p type layer  18 ( 2 ); the n type layer  16 ( 2 ) is deposited on a surface of the intrinsic layer  20 ( 3 ); the intrinsic layer  20 ( 2 ) is deposited on a surface of the n type layer  16 ( 2 ); the p type layer  18 ( 1 ) is deposited on a surface of a surface of the intrinsic layer  20 ( 2 ); the intrinsic layer  20 ( 1 ) is deposited on a surface of the p type layer  18 ( 1 ); and the n type layer  16 ( 1 ) is deposited on a surface of the intrinsic layer  20 ( 1 ) to form the structure  14 , although the structure  14  can comprise other numbers and types of layers in other configurations. By way of example only, in this particular embodiment the n type layers  16 (l)- 16 ( 3 ) are each about 500 angstroms thick, each of the p type layers  18 ( 1 )- 18 ( 2 ) is about 500 angstroms thick, and each of the intrinsic layers  20 ( 1 )- 20 ( 4 ) is about 5000 angstroms thick, although these thicknesses can vary based on the particular application.  
         [0022]     In this particular embodiment, conventional photolithography is used to etch the cone-shaped holes  22 ( 1 ) and  22 ( 2 ) into the structure  14  through all of the n type layers  16 ( 1 )- 16 ( 3 ), p type layers  18 ( 1 )- 18 ( 2 ), and intrinsic layers  20 ( 1 )- 20 ( 4 ) to the substrate  12 , although other numbers, shapes and configurations can be used for the holes  22 ( 1 ) and  22 ( 2 ) and the holes  22 ( 1 ) and  22 ( 2 ) can extend through other numbers of layers in the structure  14 . The region  30 ( 1 ) adjacent the inner surface of the hole  22 ( 1 ) is doped to form an n+ region and the region  30 ( 2 ) adjacent the inner surface of the other hole  22 ( 2 ) is doped to form a p+ region, although the regions  30 ( 1 ) and  30 ( 2 ) around the inner surface of each of the holes  22 ( 1 ) and  22 ( 2 ) can have other configurations and can be doped in different manners.  
         [0023]     A conductive material is deposited on the surface  28  of the n type layer  16  and on the inner surfaces of the holes  22 ( 1 ) and  22 ( 2 ) and portions of the conductive material on the surface  28  of the n type layer  16  are etched away to form the conductive contacts  24 ( 1 ) and  24 ( 2 ), although other numbers and types of conductive contacts and other manners for forming the conductive contacts can be used. In this particular embodiment, ordinary metallizations are used for form the conductive contacts  24 ( 1 ) and  24 ( 2 ). A load  32  can be coupled to each of the conductive contacts  24 ( 1 ) and  24 ( 2 ) and to ground, although the load  32  can be coupled in other manners.  
         [0024]     The alpha particle emitter  26  deposited on a portion of the surface  28  of the n type layer  16 ( 1 ) of the structure  14  and on an inside surface of the conductive contacts  24 ( 1 ) and  24 ( 2 ) in the holes  22 ( 1 ) and  22 ( 2 ), although the alpha particle emitter  26  can be deposited in other manners and configurations and other types of radio isotope emitters, such as a beta particle emitter can be used. In this particular embodiment, the alpha particle emitting isotopes for the alpha particle emitter  26  are electrochemically deposited, although other manners for forming the alpha particle emitter  26  or other radio isotope emitter can be used, such as by physically placing the alpha particle emitter  26  on the structure  14 .  
         [0025]     The operation of the battery  10  in accordance with embodiments of the present invention will now be described with reference to  FIG. 1 . Alpha particles are emitted from the alpha particle emitter  26  into the structure  14 , although other types of radio isotopes could be emitted, such as beta particles. As the alpha particles from the alpha particle emitter penetrate into the “p-i-n” junctions formed by each of the p type layers  18 ( 1 )- 18 ( 2 ) separated from each of the n type layers  16 ( 1 )- 16 ( 3 ) by one of the intrinsic layers  20 ( 1 )- 20 ( 4 ), they decelerate and give up their energy by creating electron-hole pairs in the structure  14 . These electron-hole pairs at each of the “p-i-n” junctions formed by each of the p type layers  18 ( 1 )- 18 ( 2 ) separated from each of the n type layers  16 ( 1 )- 16 ( 3 ) by one of the intrinsic layers  20 ( 1 )- 20 ( 4 ) are converted into useful electricity much like a solar cell.  
         [0026]     The electron and holes are collected in the spatially separated n type layers  16 ( 1 )- 16 ( 3 ) and p type layers  18 ( 1 )- 18 ( 2 ) of the structure  12  and are transported in a parallel direction to the conductive contacts  24 ( 1 ) and  24 ( 2 ). The n+ region  30 ( 1 ) and the p+ region  30 ( 2 ) provide a lateral field or extraction voltage within the collection layers. As a result, charge separation and transport occur within two separate orthogonal planes so that there is a reduction in the overlap of the electron and hole wave functions and hence longer recombination lifetimes. The battery  10  is not diffusion limited, but instead is drift dominated. Therefore, the battery  10  has a high radiation tolerance because of the “p-i-n” junctions formed by each of the p type layers  18 ( 1 )- 18 ( 2 ) separated from each of the n type layers  16 ( 1 )- 16 ( 3 ) by one of the intrinsic layers  20 (l)- 20 ( 4 ), but still recovers energy from the alpha particle radiation from the alpha particle emitter  26  or the energy from other types of emitted radio isotopes. This generated electricity or power is transferred to a load  32  which is coupled to the conductive contacts  24 ( 1 ) and  24 ( 2 ) and is also coupled to ground.  
         [0027]     Accordingly, the present invention provides a radio isotope battery whose performance does not degrade in a matter of hours because of damage to the semiconductor material from the alpha particles. Additionally, the present invention provides a radio isotope battery that can be made extremely small and thus is well suited for emerging micro and nano applications and technologies, such as MEMS. Further, the present invention is very suitable for integration directly on a semiconductor device for a “battery-on-a-chip” concept. The present invention also can be combined in parallel and series combinations to address a wide variety of higher current, voltage, and power requirements.  
         [0028]     Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.