DE112017006974T5 - Converter for ionizing radiation with a network structure and method for its production - Google Patents

Abstract

The invention relates to energy converters for the conversion of ionizing radiation from isotopes to electricity (EMF). These sources differ from capacitors and batteries by a much higher energy per unit volume but have a low emitted power per unit time. These sources allow direct charging of high power batteries or capacitors in the absence of solar radiation, while being light in weight and small in size. The lifetime of the isotope converters is determined by the half-life decay time of the irradiation material. For Ni, the life is about 100 years. The objects of the invention are to increase the specific output power of ionizing radiation converters and to simplify and reduce the cost of their manufacturing technology. These goals are achieved through the use of a specific beta-radiation converter design and its fabrication technology that ensure maximum size of the isotope emission surface with a minimum size of the planar horizontal high-quality p-n junction.

Description

Field of the invention

This invention relates to ionizing radiation energy in electricity (EMF) converters and can be used in drone flight operations, in high explosive areas, such as in shafts, in nighttime displays located in difficult to access areas, in medicine (pacemakers), etc ,

• - In der Medizin, für implantierte Sensoren und Schrittmacher, die direkt in das Herz eines Patienten implantiert werden sollen (kardiale Schrittmacher). Die dauerhafte Energiequelle mit einer langen Gebrauchs-Lebensdauer (die unabhängige Lebensdauer beträgt nicht weniger als 25 Jahre) beseitigte die Notwendigkeit, die Energiequellen von Herzschrittmachern durch wiederholte chirurgische Eingriffe auszutauschen.
• - Für Sensoren, die in die Baukonstruktion eingebettet sind, z.B. als Energieversorgung für meteorologische Stationen, die in schwer zugänglichen Bereichen angeordnet sind, die eine unabhängige Messung von Temperatur, Atmosphärendruck und Windgeschwindigkeit durch Selbstaufzeichnung ermöglichen.
• - In der Raumfahrttechnik, genauer als Hilfsenergiequellen von Navigationssatelliten, weil im Raum die Energiequellen Elektrizität über eine lange Zeit unter Bedingungen einer plötzlichen und sehr starken Temperaturänderung liefern sollen.
• - In der Militärindustrie, beispielsweise für Mikroroboter als Energiequellen für bodengestützte Vorrichtungen und den Drohnen-Flugbetrieb, bei dem es um Aufklärung oder andere taktische Zwecke geht.

The interest in such energy sources is dictated to a large extent by the high energy density of radioisotopes of chemical elements, which is comparable to the energy density of lithium batteries, as well as the ability to incorporate radioisotope batteries into microelectromechanical systems, the technology of which has developed intensely these days. Independent energy sources based on betavoltaic batteries are needed in a variety of areas:

• - In medicine, for implanted sensors and pacemakers that are to be implanted directly into the heart of a patient (cardiac pacemaker). The durable power source with a long service life (the independent lifetime is no less than 25 years) eliminated the need to replace the energy sources of cardiac pacemakers with repeated surgical procedures.
• - For sensors that are embedded in the building structure, eg as energy supply for meteorological stations, which are arranged in hard to reach areas, which allow an independent measurement of temperature, atmospheric pressure and wind speed by self-recording.
• - In space technology, more specifically as auxiliary power sources of navigation satellites, because in space the energy sources should supply electricity for a long time under conditions of sudden and very strong temperature change.
• In the military industry, for example for micro-robots as power sources for ground-based devices and drone flight operations, which is about reconnaissance or other tactical purposes.

State of the art

A device structure is known ( US 20140225472 , published August 14, 2014) comprising a low-doped n (p) -line semiconductor wafer containing a highly doped semiconductor wafer n ⁺ ( p ⁺ ) Region, on the surface of which a conductive electrode is arranged, ie, a cathode (anode) on the upper side of the wafer is a highly doped one p ⁺ ( n ⁺ ) Portion forming a pn junction with the semiconductor wafer, and on the surface of the p ⁺ ( n ⁺ ) Region is an insulating dielectric and a conductive anode electrode, ie, cathode (anode), the latter being a radioactive isotope.

Disadvantages of the structure are a relatively small volume of the irradiated semiconducting material due to the small irradiated surface portion and the low penetration depth of the ionizing beta radiation (less than 25 microns) and the low lifetime of the minority carriers, which is caused by structural defects in the doping of the working surface with vanadium ,

There is known a semiconductor converter which converts beta radiation into electricity (RU 2452060, published Jun. 27, 2014), wherein a semiconductor wafer has a textured surface in the form of multiple passage microchannels, the microchannels having a round, oval, rectangular or other arbitrary shape and the wall thickness h between the microchannels is comparable to the width of the microchannels. The surface of the microchannel walls as well as the front and back sides of the semiconductor wafer have a microrelief, practically the entire surface of the semiconductor wafer, except for the side surfaces, contains an alloyed layer forming a pn junction and a diode structure, the doped layer having a electroconductive radioactive layer which fulfills the role of a current-receiving contact to the diode structure and constitutes a source of beta radiation, wherein the doped layer and the bottom layer repeat the profile of the textured surface, the contact with the base region of the semiconductor wafer being on the side surface.

Disadvantages of the semiconductor converter are the complex technology of its production and filling of the through-channels with solid-state radioisotopes. A low quality surface of the textured channels and a correspondingly high leakage current level do not allow to obtain a high specific power of the converter.

The closest prior art for the first subject of the invention is a 3D structure of a betavoltaic semiconductor converter which converts radiation into electricity ( US 20080199736 , published on 21.08.2008), in which channels are arranged on the top surface of a low-doped semiconductor wafer of the n (p) conduction type, whose surfaces are highly doped n ⁺ (p ⁺ ) Have regions which form vertical pn junctions with the semiconductor wafer, the channels being filled with a conductive radioisotope material forming the electrode, ie an anode ( Cathode) of the converter diode, and wherein on the bottom surface of the wafer, a horizontal highly doped layer of n ⁺ ( p ⁺ ) Contact type is arranged on the surface of a metallic cathode electrode (anode) is arranged.

Disadvantage of the above construction is the low quality of the surface and, accordingly, the high level of backflow of a p-n junction in the microchannels, which does not allow to obtain a high specific power of the converter.

The closest prior art to the second subject of this invention is the method of fabricating a 3D structure of a semiconductor diode used as a betavoltaic converter for beta radiation of a ⁶³ Ni isotope into electricity ( US 20080199736 , published on 21.08.2008), which is the formation of a horizontal highly doped layer of the n ⁺ ( p ⁺ ) Conduction type on the bottom surface of a low-doped n (p) conductivity type wafer, formation of vertical channels by etching the top surface of the semiconductor wafer, doping the channel wall surfaces, deposition of a radioisotope metal as an electrode, ie, anode (cathode), on the top surface of the wafer and in the channels, and the deposition of a metal layer as an electrode, ie, anode (cathode), on the bottom surface of the wafer.

worin U_id = Φt × L_n (I_SC / I_s + 1), wobei Φt das thermische Potential ist und I_sc der Kurzschlussstrom ist, der durch die radioaktive Strahlung erzeugt wird.Disadvantages of the known method are the complex and inadequately reproducible technology of generating pn transitions in the channels, which reduces the efficiency of the converter, and particularly important a high level of dark current ( I _D ) of the mass pn junction, which is the open circuit voltage ( U _id ) of the converter and thus also the maximum output power ( P _max ), as is true $${\text{P}}_{\text{Max}}={\text{U}}_{\text{id}}\times {\text{I}}_{\text{sc}}\times \text{FF}$$

where U _id = Φt × L _n (I _SC / I _s + 1), where .phi.T the thermal potential is and I _sc is the short-circuit current generated by the radioactive radiation.

Disclosure of the invention

The technical result of the first subject of this invention is an increase in energy e _u per unit volume of the converter due to the large emission surface of the radioactive isotope ( S _em ) and thus the surface of the mass pn junction ( S _{pn, b} ).

The technical result of the first subject of the invention is achieved as follows.

The design of the ionizing radiation converter having a network structure comprises a lightly doped semiconductor n (p) conductivity type semiconductor wafer whose mass includes vertical channels, one end of which is connected to the wafer surface, the channel wall surfaces having highly doped regions of the p ⁺ ( n ⁺ ) Comprise conduction type which form vertical pn junctions with the semiconductor wafer.

The channels are filled with the conductive radio-biotope material forming the electrode, ie, anode (cathode), the converter diode, and the bottom surface of the wafer comprises a horizontally highly doped layer of n ⁺ ( p ⁺ ) Conductivity type whose surface has a metallic electrode, ie anode (cathode), of the converter.

The top surface of the wafer comprises a horizontal highly doped area of the wafer p ⁺ ( n ⁺ ) Line type that forms a horizontal pn junction. The surfaces of the vertical channels are low-doped and have the n (p) conduction type, with one end of each of the vertical channels connected to the bottom surface of the wafer and the other end, ie, the bottom of each of the vertical channels spaced apart the cover surface of the wafer, wherein the distance is greater than the entire depth of the horizontal pn junction in the space charge region, which is formed by it.

The technical result of the second subject of this invention involves a simplification of the converter manufacturing technology.

The technical result of the second subject of the invention is achieved as follows.

The manufacturing process involves the formation of a highly doped layer of n ⁺ ( p ⁺ ) Conduction type on the bottom surface of a low-doped n (p) -line type wafer, formation of vertical channels by etching the top surface of the semiconductor wafer, doping of the channel wall surfaces, deposition of a radioactive isotopic metal as an electrode, ie, anode (cathode), on the top surface of the wafer and in the channels, and the deposition of a metal layer as an electrode, ie, anode (cathode) on the bottom surface of the wafer.

The vertical channels are formed by etching the bottom surfaces of the low-doped wafer of FIG p ⁺ ( n ⁺ ) Conduction type followed by doping the channel wall surface with a donor (acceptor impurity) and forming a horizontal pn junction on the top surface of the wafer by doping with an acceptor (donor) impurity.

This invention will now be illustrated with reference to figures showing examples of the converter construction, wherein 1 shows a section of the converter structure for the first structural example, 2 shows a bottom view of a converter structure for the first structural example, 3 shows a section of the converter structure for the second structural example, and 4 shows a bottom view of the converter structure for the second structural example.

The design of the converter of the present invention comprises a low-doped semiconductor wafer ( 1 ) of the n (p) -line type, wherein the bottom surface of the wafer has a contact layer ( 2 ) from n ⁺ ( p ⁺ ) -Line type, wherein the wafer mass has vertical channels ( 3 ), wherein one end of each of the vertical channels is connected to the bottom surface of the wafer while the top surface of the wafer is a region (Fig. 4 ) from n ⁺ ( p ⁺ ) Line type of a horizontal pn junction, wherein the region comprises a space charge region ( 5 ) in the wafer, the surface area of the n ⁺ ( p ⁺ ) Conduction type comprises a metallic radioactive isotope, which is the anode ( 6 ) the diode forms, and the bottom wafer surface and the channels have a metallic radioactive isotope that is a cathode ( 7 ).

The working principle of the converter of this invention is based on the ionization of the semiconductive material, eg silicon, by the beta radiation of isotopes, eg nickel, tritium, strontium, cobalt etc. The electron / hole pairs formed due to the irradiation are dominated by the Field of pn junction in the space charge region separated and generate a difference of potentials between p ⁺ (n ⁺ ) Areas of the converter (the photovoltaic EMF). Similarly, a portion of the electrode / hole pairs may also be collected through the pn junction field in the quasi-neutral region at the diffusion distance distance.

It has been shown that efficient (optimal) operation of the converter requires high quality silicon, where the diffusion length of the minority carriers L _d is greater than the silicon wafer thickness, ie L _d > h _w ,

The distance between the channels must be greater than the penetration depth for the beta radiation of the ⁶³ Ni isotopic electrons whose mean energy E = 17.5 keV.

Embodiments of the invention

Various examples of the design of the beta converter are possible, which differ in terms of their technical parameters. For example, the converter included in the 1 and 2 is the highest unit performance, but is quite expensive due to the large amount of nickel in the channels. The converter in the 3 and 4 is shown to require a significantly lower amount of ⁶³ Ni and is therefore cheaper while having a lower unit performance.

The embodiment for a converter design, as in the 1 can be shown in phosphorous doped silicon wafers KEF quality of 5 kOhm × cm, a diameter of 100 mm, a thickness of h _w = 420 microns, a (100) orientation, a carrier lifetime t = 2 ms and a diffusion length L _d > 1.0 cm can be realized.

For example, ⁶³ Ni can be selected as the isotope source, which has a long half-life of 50 years and emits electron radiation with an average energy of 17 keV and a maximum energy of 64 keV, which is associated with almost no health risk. This electron energy is lower than the vacancy bonding energy in silicon, which is 160 keV. The absorption depth of electrons with an average energy of 17 keV in silicon is about 3.0 μm; for a 90% absorption this depth is 12 μm. These dimensions should correspond to the design of the pn junction depths as well as the size of the space charge area, and this is achievable for conventional silicon structures. It should be noted that, alternatively, materials other than radioactive isotopes could be used, eg, tritium, etc. It is also important that the radiation source is not necessarily a beta radiation source but may alternatively be an alpha radiation source, eg ^238U , with a medium energy of 6 MeV and a silicon penetration of about 20 to 25 microns, which poses no threat to the pn junction.

The manufacturing method for the converter according to the invention comprises the following sequence of method steps.

Thermal oxidation (up to 0.6 μm) of the surface of a batch of silicon wafers having a 5 kOhm.cm resistivity, a diameter of 100 mm and a (100) orientation, performing a "0" lithography on the backside of the wafers, Formation of vertical channels by reactive ion beam etching and diffusion into the surface of the protection.

A first lithograph for the n ⁺ Protective areas on the upper wafer surfaces, a phosphorus diffusion and formation of n ⁺ Protective areas on the deck (front) wafer surfaces and n ⁺ Contact layers on the bottom wafer surface.

A second lithograph and the formation of the p ⁺ Contact area by Borionendotierung with a dose of D = 600 μCl and the energy E = 30 keV, a thermal burn of the implanted impurity at T = 1050 ° C for t = 40 min, the growth of a thermal oxide on the semiconductor wafer at T = 950 ° C for t = 40 min, thickness 0.3 μm.

A third lithography of the p-n junction p-layer formed by boron doping, thermal firing of the implanted impurity at T = 950 ° C for t = 40 min.

A fourth lithograph of the contact window to the p ⁺ -Layer.

⁶³ Ni isotope deposition on the top surface of the wafers and a fifth lithography to form the anode electrodes.

Thinning the bottom wafer by chemo-mechanical polishing, followed by electrolysis of radioactive ⁶³ Ni onto the bottom surface of the wafers, and chipping the wafers.

It should be noted that there is a simpler embodiment of the process flow, ie, by photolithography of vertical channels at the end of the process after deposition of the ⁶³ Ni isotope on the top surface of the wafer. However, this option does not include the wafer dilution step.

Experimental studies of silicon-based converters with a prototype network structure and a planar design at a ⁶³ Ni isotope radiation power and a dose rate P = 2.7 mC / cm ² showed that the horizontal planar pn junction with the surface S _pn.pl that is located on the polished top surface of the wafer, has a low dark leakage current: $${\text{I}}_{\text{d},\text{pl}}=0.5\text{n / A}/{\text{<figure-callout id="2" label="cm" filenames="DE112017006974T5\_0006.png,DE112017006974T5\_0007.png" state="{{state}}">cm</figure-callout>}}^2$$

The leakage current of a corresponding pn junction area formed in the channels is three orders of magnitude larger: $${\text{I}}_{\text{lk},\text{b}}=1\mu \text{A}$$

This corresponded to the no-load _current for the planar pn junction U _id.pl = 0.1 V and for the mass pn junction U _id.b = 4 mV: $${\text{U}}_{\text{id},\text{pl}}=\mathrm{\phi }\text{t}\times {\text{L}}_{\text{n}}\left({\text{I}}_{\text{sc}}/{\text{I}}_{\text{d}}+1\right)=0026\times {\text{L}}_{\text{n}}\left(27/0.5+1\right)=0.1\text{V}$$

Herein, Φt is the thermal potential and I _sc is the short-circuit current generated by radioactive radiation.

The converter performance is determined by the following relationship: $${\text{P}}_{\text{Max}}={\text{U}}_{\text{id}}\times {\text{I}}_{\text{sc}}\times \text{FF}$$

For a planar pn junction is P _max.pl 1, 7 nW, and for a mass pn junction is P _max.b 0.08 nW.

A technical advantage of this invention is an increase in unit performance and efficiency of the converter as well as a simplification and lower cost of its manufacturing technology.

This is achieved because of the design of the beta radiation converter and its technology, which provides the fundamental opportunity to realize the equivalent emission performance of the isotopic surface at Sis as in the prototype having a 3D structure; However, the ionization current receiver is a horizontal (non-vertical) pn junction with a relatively small area ( S _pp , _pl ) located on a polished high quality top surface of the wafer, which minimizes the dark current and increases the no-load current and hence the unit performance of the converter.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 20140225472 [0003]
• US 20080199736 [0007, 0009]

Claims (2)

An ionizing radiation converter having a mesh structure comprising a low-doped n (p) -line semiconductor wafer having in its mass vertical channels formed from the top to the wafer surface, the surfaces of the channel walls being dominated by a highly doped p ⁺ (n ⁺ ) Are conduction type and the channels are filled with a conductive radioisotope material forming the electrode, ie anode (cathode), of the converter diode and wherein the bottom surface of the wafer has a horizontal highly doped region of n ⁺ (p ⁺ ) conduction type having a horizontal pn Transition, and the top surface of the wafer has a horizontal highly doped region of the p ⁺ (n ⁺ ) conduction type forming a horizontal pn junction, the surfaces of the vertical channels being low doped and having an n (p) conduction type one end of each of the vertical channels is connected to the bottom surface of the wafer and the other end, ie, the bottom of each of the vertical channels, is spaced from the top surface of the wafer, the distance being greater than the total depth of the horizontal pn junction in the space charge region formed therefrom. A method of manufacturing comprising: forming a horizontal n + (p +) conductivity type heavily doped layer on the bottom surface of a low doped n (p) conductivity type wafer, forming vertical channels by etching the top surface of the semiconductor wafer, doping the channel wall surfaces, doping radioactive isotopic metal for an anode (cathode) electrode, on the top surface of the wafer and in the channels, and depositing a metal layer for the anode (cathode) electrode on the bottom surface of the wafer, the vertical channels being etched through the substrate Top surface of the low doped n (p) conductivity type semiconductor wafer, doping the channel wall surfaces with a donor (acceptor) impurity, and forming a horizontal pn junction on the top surface of the wafer by dopant donor (acceptor) impurity doping.

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