RU2715735C1 - Method of semiconductor beta-voltaic cells manufacturing based on nickel-63 radionuclide - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to a method of making semiconductor beta-voltaic transducers based on a nickel-63 radionuclide for use in autonomous power sources. Method of producing semiconductor beta-voltaic cells based on nickel-63 radionuclide, consisting in heating metal nickel containing radionuclide ⁶³Ni, to its evaporation temperature in vacuum chamber, three-step selective photoionisation of atoms of target isotope ⁶³Ni by simultaneous pulsed irradiation of atoms with spatially aligned laser beams with wavelength 3222.566±0.001Å, 5464.006±0.001Å and 5442.195±0.001Å followed by deposition of ⁶³Ni photons by electric field on semiconductor chip surface, wherein semiconductor chip is fixed in vacuum chamber on surface of heated collector and heated to temperature of 800÷1,500 K, while increasing density of metallic nickel film due to crystallisation of ⁶³Ni, followed by cooling collector with chip to room temperature in vacuum.

EFFECT: invention enables to obtain ready beta-voltaic chips with isotopic enrichment fixed at the moment of manufacture in one device and in a single closed process.

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Description

Technical field

The invention relates to a method for manufacturing semiconductor beta-voltaic converters based on radionuclide nickel-63 for use in stand-alone electrical power sources.

State of the art

Autonomous power supplies with a long service life are needed in many areas: medicine - for implanted sensors, stimulants; technology - for sensors built into building structures; space technology, defense industry, etc.

Due to the high energy density, long life time and resistance to extreme external conditions, radioisotope energy sources are considered as promising autonomous micro-energy devices.

In the general case, radioisotope batteries convert the ionizing radiation of a radioisotope source into electrical energy.

In beta-voltaic cells, radioactivity is directly converted into electrical energy using a semiconductor converter, and the use of beta particles allows you to create the most compact sources that work for decades without significant changes in their properties.

Nickel radionuclide ⁶³ Ni is one of the most promising emitters of beta particles for creating beta-voltaic cells (Nagornov Yu.S. "Modern aspects of the application of the beta-voltaic effect" - Ulyanovsk: UlGPU, 2012; Pustovalov AA, Gusev V.V. ., Zadde VV, Petrenko NS, Tikhomirov AV, Tsvetkov LA “Beta-voltaic current source based on nickel-63” - “Atomic energy”, t. 103, issue 6 December 2007).

Cells based on the effect of direct conversion of ⁶³ Ni beta radiation into electrical energy contain two main parts:

1) beta emitting radioactive source;

2) a beta particle collecting semiconductor device (RF Patent No. 90612, US Application No. US 2012186637, US Patent No. US 7939986, US Patent No. US 8487507, US Patent No. US 8134216, RF Patent No. 2452060, US Patent No. 6774531, US Patent US No. US 8487392, patent No. EP 1810342. Moreover, to increase the efficiency of collecting beta particles, a layer of isotopically enriched nickel is applied directly to the surface of the semiconductor chip.

In the manufacture of such cells, a problem arises related to the incompatibility of radiochemical methods for handling radioactive isotope material and technological requirements for the purity of microelectronic production. In particular, for the treatment of radioactive isotopes, only liquid radiochemistry technologies are regulated and applied, which helps to minimize accidental losses of radioactive substances and possible radiation pollution. There are no devices and regulations that allow, for example, vacuum deposition of radioactive metals, by analogy with the deposition of conventional metals in microelectronic technology, which is associated primarily with the inevitable and uncontrolled contamination of spraying equipment with atomized radioactive metal. At the same time, chemical compounds used in liquid radiochemistry do not allow applying a film of radioactive nickel to the surface of a previously prepared alloyed semiconductor wafer, for example, by the electrochemical method, without spoiling the properties of the wafer itself as a result of the formation of defects at the metal-semiconductor interface. These defects in finished beta-voltaic structures act as traps for the generated electron-hole pairs, leading to the appearance of significant leakage currents, and often to a direct violation of the adhesion between the metal layer and the semiconductor, followed by delamination.

To solve this problem, the present application proposes a new combined “nuclear microelectronic” technology that allows for the selective photoionization of atoms of the target radioactive 63Ni nickel isotope in a single closed process and in one device using laser separation of isotopes in an AVLIS atomic pair, as well as simultaneous narrow-focus deposition obtained photoions on a semiconductor substrate using an external electric field. As a result, at the exit from the chamber of the laser "isotope separation" installation, it is possible to obtain not just isotope-enriched material, but finished beta-voltaic chips.

A known method for the production of nuclear batteries (US 20110241144 A1), including the manufacture of beta-voltaic batteries based on the ⁶³ Ni isotope by fixing metal foils made of ⁶³ Ni, on the surface of semiconductor devices of different geometries, or electrolytic deposition of ⁶³ Ni on a sublayer of metallic nickel of natural isotopic composition previously applied to the surface of semiconductor devices by vacuum deposition.

A known method of manufacturing betavoltaic batteries (KR 1020150020769 A), consisting of five stages. At the first stage, the radioactive isotope nickel 63 is produced. At the second stage, radioactive nickel sulfate ⁶³ NiSO ₄ × 6Н ₂ О is produced by dissolving radioactive nickel in an aqueous solution of sulfuric acid. In a third step, a solution for electrolytic deposition is prepared by mixing an aqueous solution of radioactive nickel sulfate 63 and an aqueous solution of gold sulfate. At the fourth stage, electrolytic deposition of the radioisotope layer on the surface of the semiconductor pn junction is carried out. At the fifth stage, drying and heat treatment of the radioactive layer deposited on the semiconductor pn junction is carried out. At the same time, the first stage of the preparation of radioactive nickel includes the gasification of metallic nickel, centrifugation of gaseous nickel to isolate the Ni-62 isotope, cooling gasified Ni-62 to obtain Ni-62 in a solid powder state, and neutron irradiation of the Ni-62 isotope in solid powder state in order to obtain radioactive Ni-63.

с последующим выделение фотоионов ⁶³Ni электрическим полем на коллекторе, расположенном в вакуумной камере.The closest in technical essence to the claimed invention is a method for producing a nickel-63 radionuclide (RF patent No. 2614021), comprising heating metallic nickel containing a ⁶³ Ni radionuclide to its evaporation temperature in a vacuum chamber, a three-stage selective photoionization of atoms of the target ⁶³ Ni isotope by simultaneous pulsed irradiation atoms of spatially aligned laser beams with a wavelength

followed by the separation of ⁶³ Ni photoions by an electric field on a collector located in a vacuum chamber.

The disadvantages of all of the above methods is the separation in time and space of the process of preparation of radioactive nickel 63 Ni and the process of applying it to a semiconductor chip. The work of applying a prefabricated highly active substance to a semiconductor chip is technically complicated and is accompanied by a constant danger of leaks during additional transportation, physical and chemical conversions, and also leads to contamination of equipment and radiation to microelectronic production personnel. Storage of pre-prepared 63 Ni radioactive nickel in a warehouse in anticipation of its application to a semiconductor chip is accompanied by its constant radioactive decay, leading to a change in its activity and composition. As a result, ⁶³ Ni beta - voltaic chips manufactured at different times using the same technology and from the same batch of radioactive nickel demonstrate different values of the generated current and power depending on the time of their manufacture.

The technical problem to which this invention is directed is to increase the efficiency of the manufacturing technology of beta-voltaic elements.

Disclosure of the invention

The technical result is to obtain ready-made beta-voltaic chips with fixed at the time of manufacture isotope enrichment in one device and in a single closed process.

с последующим осаждением фотоионов 63Ni электрическим полем на поверхность полупроводникового чипа, при этом полупроводниковый чип закрепляют в вакуумной камере на поверхности прогреваемого коллектора и нагревают до температуры 80÷1500 К, при этом увеличивая плотность пленки металлического никеля за счет кристаллизации ⁶³Ni с последующим охлаждением коллектора с чипом до комнатной температуры в вакууме.To achieve this result, a method is proposed for manufacturing semiconductor beta-voltaic cells based on nickel-63 radionuclide, which consists in heating metallic nickel containing ⁶³ Ni radionuclide to its evaporation temperature in a vacuum chamber, three-stage selective photoionization of atoms of the target ⁶³ Ni isotope by simultaneous pulsed irradiation of atoms by spatially combined laser wavelength beams

followed by the deposition of 63Ni photoions by an electric field on the surface of the semiconductor chip, while the semiconductor chip is fixed in a vacuum chamber on the surface of the heated collector and heated to a temperature of 80 ÷ 1500 K, while increasing the density of the metal nickel film due to crystallization of ⁶³ Ni with subsequent cooling of the collector with chip to room temperature in vacuo.

In addition, a negative voltage of 500-1000 V is applied to the surface of the chip.

In addition, before starting photoionization deposition of ⁶³ Ni, the surface of the chip is slowly heated in a vacuum to a temperature of 400 ÷ 1000 K.

In addition, before starting photoionization deposition of ⁶³ Ni, the surface of the chip is cleaned with a stream of argon ions using special ion sources or a glow discharge ignited in a vacuum chamber when the argon is admitted to a pressure of 1 ÷ 10 ^-1 Pa.

The implementation of the invention

The method is as follows.

The starting material is a target of metallic nickel with an arbitrary content of ⁶³ Ni radionuclide. The method of obtaining ⁶³ Ni does not matter. In particular, it is possible to produce a ⁶³ Ni radionuclide by irradiating natural nickel with a neutron flux in a reactor. In this case, the ⁶² Ni core absorbs the neutron and turns into ⁶³ Ni.

The first stage of the process is that metallic nickel is evaporated in a vacuum. A vacuum is necessary in order to prevent oxidation of metallic nickel, and also in order to minimize collisions of nickel atoms with residual gas atoms. Typical residual gas pressures are 10 ^-5 ÷ 10 ^-9 mm. Hg Marked evaporation of nickel occurs when it is heated to a temperature of 1600 ÷ 1700 ° C. The method of heating does not matter. A beam of atoms with a divergence of 5–20 ° is cut out from the evaporation stream using diaphragms. Thus, a collisionless flow of nickel atoms with low divergence is formed. Typical values of the density of atoms in a stream are 10 ¹¹ ÷ 10 ¹⁴ atoms / cm ³ .

The second stage of the process is the isotopically selective photoionization of ⁶³ Ni atoms in the working volume of the vacuum chamber. To carry out photoionization of nickel atoms, a three-step photoionization scheme has been developed, described in patent RU No. 2614021.

For the implementation of selective photoionization, pulsed pulsed dye lasers tuned along the wavelength are used. In particular, copper vapor lasers are possible. Typical values of the pulse repetition rate are 10 kHz, and the pulse duration is 20 ns. In this case, for effective and selective photoionization, the average power density of the laser radiation of the first stage should be in the range of 40 ÷ 100 mW / cm ² , the second stage - 5 ÷ 40 mW / cm ² , the third stage - 3 ÷ 5 W / cm ² . With these parameters, photoionization is saturated, and the selectivity of photoionization exceeds 1000.

Lasers with a pulse frequency of 5 kHz or 20 kHz can be used. When using lasers with a reduced frequency, it is necessary to proportionally increase the length of the working volume in order to ensure the probability of atomic radiation. When pumped by solid-state lasers, the pulse duration can reach 100 ns.

The resulting stream of nickel atoms is irradiated with pulsed laser radiation, which is three laser beams with different wavelengths, combined spatially (in one beam) and in time (simultaneous arrival of pulses). A typical beam diameter is 5–30 mm. The average path length of atoms during the time between two pulses at a pulse repetition rate of 10 kHz is 5 cm; therefore, to increase the probability of irradiation of atoms by pulsed laser radiation, it is advisable to increase the size of the irradiation region along the atomic flux to 7–9 cm. This can be done through multiple passage laser radiation through a beam of atoms due to reflection with the help of mirrors of a laser egret at the end of the working volume. The reflected beam is directed back into the working volume with a slight offset so as to irradiate areas of the working volume that were not irradiated during the first passage of the beam. Similarly, the third, fourth and all subsequent passages of the laser beam are formed.

The third stage consists in the deposition of ⁶³ Ni photoions by an electric field on the surface of a semiconductor chip. For this, the semiconductor chip is fixed in a vacuum chamber on the surface of a heated collector. A negative voltage of 500-1000 V is applied to the surface of the chip.

The surface of the chip is pre-cleaned with a stream of argon ions using special ion cannons or a glow discharge ignited in a vacuum chamber when the argon is admitted to a pressure of 1 ÷ 10 ^-1 Pa.

Before the start of the process, as well as during the process, the collector with a fixed chip is heated to a temperature of 600 ÷ 1000 K. As a result of the process, only ⁶³ Ni photoions get on the chip surface, forming a film of metallic nickel. After the process of deposition of photoions, the collector is heated to a temperature of 800 ÷ 1500 K to increase the density of the film due to crystallization. After the collector with the chip is cooled to room temperature in vacuo, the film-coated chip is removed through a vacuum gateway and can be used as a power source.

All the specific parameters of the method are selected from the capabilities of the equipment and are determined in each case.

An example implementation of the method.

формируется лазерной системой на красителях с накачкой лазерами на парах меди. Частота следования лазерных импульсов 10 кГц, длительность импульсов 20 не. Средняя плотность мощности лазерного излучения первой ступени 50 мВт/см², второй ступени 10 мВт/см² и третьей ступени - 4 Вт/см². При настройке длин волн лазеров на фотоионизацию изотопа ⁶³Ni, средний фотоионный ток на кремниевую пластину составляет 0.1 мА. После сеанса фотоионизационного осаждения длительностью 1 час, нагрев тигля и лазерная система выключается. Затем, при сохранении вакуума, включается нагрев коллектора, и температура кремниевой пластины с осажденными никелем в течение 1 часа доводится до температуры 900 К. После этого, нагрев выключается, и пластина остывает в вакууме в течении 2 часов. Таким образом, на поверхности полупроводниковой подложки формируется слой радионуклида ⁶³Ni, который является основой бета вольтаических преобразователей любого типа.Metallic nickel with an isotope content of ⁶³ Ni 5 ÷ 15% is placed in a crucible made of KVPT ceramic and heated in vacuum (residual gas pressure 10 ^-5 mm Hg) to a temperature of 2000K. As a result, a diverging stream of atoms with a diameter of 5-10 mm is formed. Away from the flow is a collector mounted on an insulated holder. A voltage of minus 1000 V relative to the housing of the vacuum chamber is applied to the collector. A laser beam with a diameter of 10 mm passes through a stream of steam opposite the collector. To increase the interaction region, mirrors are installed in the vacuum chamber, which provide an 8-fold passage of the laser beam through the stream of atoms, each time the spot of the beam in the pair is shifted along the stream of atoms by the value of the diameter of the beam. As a result, a working zone is formed with dimensions of 1 cm by 8 cm, elongated along the direction of the atomic flow to increase the probability of irradiation of atoms with pulsed laser radiation. As a starting material for the creation of a beta-voltaic element of the Schottky diode type with an electrode from a nickel-63 film, n-type conductivity substrates KEF-4,5 with a crystallographic orientation of the planar surface (100) and a thickness of 450-460 μm were used. A substrate with dimensions of 20 mm by 40 mm is placed on the collector from the side facing the atomic stream. Three-wavelength laser beam

formed by a dye laser system pumped by copper vapor lasers. The laser pulse repetition rate is 10 kHz, and the pulse duration is 20 ns. The average power density of the laser radiation of the first stage is 50 mW / cm ² , the second stage is 10 mW / cm ² and the third stage is 4 W / cm ² . When tuning the laser wavelengths for photoionization of the ⁶³ Ni isotope, the average photoionic current to the silicon wafer is 0.1 mA. After a photoionization deposition session lasting 1 hour, the crucible heating and the laser system are turned off. Then, while maintaining the vacuum, the collector heating is turned on, and the temperature of the silicon wafer with precipitated nickel is brought to 900 K for 1 hour. After that, the heating is turned off and the wafer cools in vacuum for 2 hours. Thus, a ⁶³ Ni radionuclide layer is formed on the surface of the semiconductor substrate, which is the basis of beta-voltaic converters of any type.

Thus, the proposed method for the manufacture of semiconductor beta-voltaic cells based on the nickel-63 radionuclide allows in a single closed process and in one device to simultaneously perform both selective photoionization of the target radioactive nickel ⁶³ nickel isotope by laser separation of isotopes in the AVLIS atomic pair and narrowly directed deposition obtained photoions on a semiconductor substrate using an external electric field. As a result, at the exit from the chamber of the laser "isotope separation" installation, it is possible to obtain not just isotope-rich material, but finished beta-voltaic chips with isotope enrichment fixed at the time of manufacture.

The method is applicable on an industrial scale, in particular, for the production of autonomous power sources.

Claims (4)

1. A method of manufacturing semiconductor beta-voltaic cells based on nickel-63 radionuclide, which consists in heating metallic nickel containing ⁶³ Ni radionuclide to its evaporation temperature in a vacuum chamber, three-stage selective photoionization of atoms of the target ⁶³ Ni isotope by simultaneous pulsed irradiation of spatially aligned atoms wavelength laser beams

followed by the deposition of ⁶³ Ni photoions by an electric field on the surface of the semiconductor chip, characterized in that the semiconductor chip is fixed in a vacuum chamber on the surface of a heated collector and heated to a temperature of 800 ÷ 1500 K, while increasing the density of the metal nickel film due to crystallization of ⁶³ Ni, s subsequent cooling of the collector with the chip to room temperature in vacuum. 2. The method according to p. 1, characterized in that a negative voltage of 500-1000 V is supplied to the surface of the chip. 3. The method according to p. 1, characterized in that before starting the photoionization deposition of ⁶³ Ni, the surface of the chip is slowly heated in vacuum to a temperature of 400 ÷ 1000 K. 4. The method according to p. 1, characterized in that before starting the photoionization deposition of ⁶³ Ni, the chip surface is cleaned with a stream of argon ions using special ion sources or a glow discharge ignited in a vacuum chamber when the argon is admitted to a pressure of 1 ÷ 10 ^-1 Pa.