Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0912—Manufacture or treatment of Josephson-effect devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/10—Junction-based devices
  • H10N60/12—Josephson-effect devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/80—Constructional details
  • H10N60/805—Constructional details for Josephson-effect devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/80—Constructional details
  • H10N60/83—Element shape

Definitions

• the invention relates to a method for the production of a device which makes it possible to operate in an inert atmosphere and preferably in ultra-high vacuum, superconducting and majorana.
• the invention relates to a method for the production of "Majorana materials - superconductor" hybrid networks and a hybrid structure produced by the method. Separate materials in various geometries and dimensions with a precision of just a few nanometers and conserve them with a passivating protective layer. Complex networks of said materials can be fabricated with the device. These networks, as the smallest subunit, contain a hybrid structure such as Josephson topological contact, but in yet another embodiment may represent up to a plurality of topological quantum bits. The process guarantees the preservation of the surface properties of the Majorana material as well as a high interfacial quality between the Majorana material and the superconductor.
• distinguishable physical states must be present, which in classical transistor technology are defined by two distinguishable voltage values.
• quantum computer these states are represented by distinguishable quantum mechanical states.
• quantum bits quantum bits
• Such a quantum computer is characterized by a large, in the extreme case arbitrarily large number of distinguishable states, which represent the bits, the so-called quantum bits (qubits).
• quantum bits quantum bits
• certain calculations on a quantum computer can be solved much faster and more efficiently. For example, Google showed in January 2016 that it has a problem of about 100,000 with its D-wave quantum annealer. Solve OOOx faster than with a classic computer.
• a quantum annealer is a special type of quantum computer, but it can only be used for optimization problems.
• quantum objects or particles objects, particles, or quasiparticles that follow the laws of quantum mechanics
• the quantum mechanical quasiparticle on the basis of which the topological quantum computer calculates, is the so-called bound Majorana Nullmode (MZM, English Majorana Zero Mode).
• MZMs are 0-dimensional quasiparticle excitations that promise new concepts for error-tolerant quantum computing due to their non-ablative commutation relationships.
• MZMs can arise when connecting so-called Majorana materials with superconducting materials.
• Majorana materials in this document are all materials in which majorana zero-modes are formed as soon as these materials are brought into contact with a superconductor and the fields required to produce the MZMs (E-field and B-field) are created.
• Majorana materials are, for example, dirac materials, which in turn can be subdivided into exemplary topological insulators and Weyl metals, as well as "half-metals", which should not be confused with semimetals, as well as Ill-V semiconductor nanowires.
• Majorana materials have fermionic states that do not possess spin degree of freedom (in the English language, and later in this document, these states are referred to as "spinless fermions").
• spinless fermions In a subset of the Majorana materials, the so-called topological insulators (Tis), for example, the spin-orbit interaction leads in the solid state in addition, for fermion states on the surface of the Tis, the direction of the spin is coupled directly to the k vector in momentum space. If one induces superconductivity in such a "spinless fermions” system, MZMs are formed under appropriate circumstances (spatial geometry of the majorana material, E and B fields).
• the two states "no electron” and “one electron” form the two eigenstates of the majoran aura, or of the majorana qubit, analogous to the eigenstates “spin-up” and “spin-down” of a conventional spin qubit.
• Majorana qubits A major difference to conventional qubits is in Majorana qubits in that both eigenstates have the same energy, that is degenerate.
• Conventional qubits always have an excited state and a ground state. If the qubit persists in the excited state for a long time, it relaxes into the ground state and the information is lost. That can not happen with the Majorana Qubit.
• These and other properties mean that Majorana Qubits theoretically do not need error correction [2]. This fact significantly reduces the technological complexity of a 50 qubit machine and makes the concept of topological quantum computing so attractive. In order to operate with Majorana's quantum computing, ie to change the state of one or more qubits, one must arrange these 0-dimensional objects in a 2-dimensional plane.
• Majoranas rotates 360 ° around each other, so you change the state to
• US 2016/0035470 A1 discloses a magnetic topological nanowire structure comprising a superconductor and a quasi-1D magnet nanowire.
• the quasi-1 D magnetic nanowire is coupled or embedded to the superconductor to create a self-contained interaction, resulting in a spatially separated pair of majoramic fermions.
• topological insulators were found in topological insulators for the first time in two independent experiments. If the spatial dimensions of the topological insulator are constrained to give an energy gap within the dispersion of surface states, it is also necessary to apply a magnetic field / magnetic flux through the structure. This magnetic field is relative seen to the necessary magnetic fields for Zeeman splitting the Rashba bands in InAs nanowires very small. The characteristic size is half a magnetic flux quantum, which corresponds to a magnetic field of not more than 150 mT for the dimensions used in the following text [5, 6].
• topological insulators such as (Bi (1. X) Sb x ) 2 Te 3 with 0 -S x 1, grow selectively [e.g. On Si (11 1) over Si0 2 or Si 3 N 4 ] [7].
• Vortechniken can be easily and very complex and complex before the growth by optical or
• the "spinless fermions" in Majorana materials are located on the surface of the solid in the case of topological insulators, and if the surface of the topological insulator is exposed to ambient air outside of an inert environment, the resulting oxidation causes the Dirac states to be called The system of spinless fermions in the surface of a topological insulator, and thus the surface transport are disturbed It has been found that even in the inert atmosphere, especially in ultrahigh vacuum (p .s 1 x 10 "7 mbar, preferably p 1 x 10 "8 mbar), a passivation layer for protecting the topological insulator from oxidation or degradation of the surface states can be arranged on a topological insulator, thereby preserving the surface states
• An inert atmosphere refers to an atmosphere that, adapted to the (majorana) material, prevents any (chemical) reaction of the atoms and molecules in the atmosphere with the surface of the material.
• a superconductor In order to create majorana fashions, a superconductor must be available as a second prerequisite in addition to the topological phase.
• Two superconducting contacts that are closely spaced (5-150 nm) and connected by a material that is not intrinsically superconductive but by the presence of the superconductors at low Temperatures itself in the area between the contacts becomes superconducting, one calls Josephson transition. If the "inherently non-superconducting" material is a majorana material, the Josephson junction is called the topological Josephson junction.
• the Josephson junction is one of the simplest hybrid components, consisting of superconductor and majorana material, and the basic building block for many more complex components.
• the Majorana material or more specifically the topological insulator
• the topological insulator first by a vacuum-based coating process or thin-film technology (physical vapor deposition (PVD), chemical vapor deposition (CVD), advantageously molecular beam epitaxy (MBE)) are deposited.
• PVD physical vapor deposition
• CVD chemical vapor deposition
• MBE molecular beam epitaxy
• the superconducting contacts can then be subsequently defined by electron beam lithography (EBL) in a suitable resist and then vapor-deposited or sputtered in another system.
• EBL electron beam lithography
• the topological insulator has been previously capped (passivated), this must be removed immediately prior to deposition of the superconductor since the superconductor must be in direct contact with the majorana material.
• a nanometer-accurate removal of a arranged on a Majorana material superconducting layer and a subsequent, local, oxidation of this range is not possible because of the surface properties of the superconductor in the rule.
• the surface of the aluminum would also be regularly too rough.
• hard masks allows the structuring of a second, for example, superconducting layer within the inert atmosphere and advantageously in ultra-high vacuum.
• the structuring takes place here in systems with partially directed material flow by mapping the structures defined on the hard mask.
• the object of the invention is to provide a method with which Majorana material - superconductor structures, comprising at least one structured Majorana material and at least one superconducting material arranged thereon, also referred to below as hybrid structures, as the smallest unit of a Majorana material.
• Majorana material - superconductor structures comprising at least one structured Majorana material and at least one superconducting material arranged thereon, also referred to below as hybrid structures, as the smallest unit of a Majorana material.
• Superconductor hybrid network can be generated in a few process steps.
• the process was intended to ensure a high quality of the surfaces and interfaces and, moreover, to guarantee a passivation of the structured Majorana material.
• the method should enable the structured Majorana material and the superconducting material to be aligned with high accuracy relative to each other, and high scalability is ensured.
• hybrid structure comprising at least one structured majorana material, at least one structured superconducting material arranged thereon and a passivation layer arranged on the free surface (s) of the structured majorana material, according to the main claim ,
• a hybrid structure comprising at least one structured majorana material, in particular comprising at least one structured majorana material in the form of a laterally grown (quasi) 1 D nanowire or a laterally grown (quasi) 1 D nanostructure, and at least a structured superconducting material disposed thereon and a passivation layer disposed on the free surface of the structured Majorana material according to the independent claim and by using such a hybrid structure according to further independent claim.
• the invention relates to a method in which with the aid of a near-surface mask a Majorana material - superconductor structure, short hybrid structure, can be produced.
• This hybrid structure comprises at least one structured majorana material which is defined in the context of this invention as a laterally grown (quasi) 1 D nanowire or a laterally grown (quasi) 1 D nanostructure, the latter being able to be in the form of a structured topological thin film, for example.
• the hybrid structure has at least one structured superconductive material disposed on this structured Majorana material and a passivation layer disposed on the free surfaces of the Majorana structured material which is not contacted by the superconducting material.
• a special quality of the interface between, for example, a topological insulator and a superconducting metal is ensured by in-situ and preferably by epitaxial growth of both layers.
• a protective passivation layer can also be produced directly over the exposed areas of the structured Majorana material, which advantageously leads to its surface states neither being destroyed nor altered.
• Surface states in topological insulators are also called dirac states.
• a further mask is advantageously produced directly on the substrate (mask for generating a preliminary structure, "selective area"), which serves to deposit the Majorana material in a defined geometry on a substrate.
• mask for generating a preliminary structure, "selective area" which serves to deposit the Majorana material in a defined geometry on a substrate.
• the formation of two masks on the substrate in the production of the hybrid structure subsequently advantageously leads to the fact that both the deposited, structured Majorana material and the subsequently at least one superconducting structure can be aligned exactly relative to one another during the production. Due to the fact that the process steps take place continuously in an inert atmosphere and preferably in UHV, according to the invention a very good quality and quality of the interfaces of the hybrid structure can be ensured.
• laterally grown heterostructures of superconducting materials and Majorana materials can advantageously be produced of high quality and precise alignment.
• Different geometries and dimensions allow the structured definition of functional devices, ranging from topological Josephson junctions to complex networks for applications in scalable topological qubits as well as topological quantum registers.
• Both the structured Majorana material and the superconducting material are grown laterally according to the invention. Both the structured Majorana material and the superconducting material are patterned in the method according to the invention and applied relative to each other, without the need to perform this treatment after landfilling. Compared to hitherto known methods of in-situ structuring, the method according to the invention offers particular advantages in terms of the abruptness of the interfaces and the possible dimensioning of the individual functional layers.
• Such high-quality hybrid structures produced according to the invention can be used preferably in topological Josephson junctions but also in complex components, such as topological SQUIDs (short for superconducting quantum interference devices), topological qubits (abbreviation for quantum bit) and topological quantum registers, which are known as smallest unit to serve the well-defined transition of a topological material and a superconductor.
• topological SQUIDs short for superconducting quantum interference devices
• topological qubits abbreviation for quantum bit
• topological quantum registers which are known as smallest unit to serve the well-defined transition of a topological material and a superconductor.
• a Josephson junction comprising, for example, such structures according to the invention means two superconducting materials which are separated from one another by a thin, non-superconducting region.
• Weaklink is understood below to mean the region which, in Josephson contact, separates the two superconductors from one another and is by definition non-superconducting.
• the invention is explained in more detail below using the example of a topological Josephson contact as an example of a hybrid structure according to the invention, without being restricted to these.
• the topological Josephson contact comprises two superconducting materials, which are arranged laterally from one another, and a structured Majorana material, which distinguishes the non-superconducting region (Weaklink).
• a weave link as an intermediate region between two superconductors comprising a topological material may also be superconducting if the distance between the superconductors is sufficiently short. Such a distance is sufficiently short if it is smaller than the coherence length of the paired electron states in the topological material.
• the coherence length in the case of aluminum as a superconducting material is known to be 100-400 nm, depending on the quality of the crystalline material as well as the boundary layer between superconductor and topological material. When niobium is used, this characteristic value of the coherence length is somewhat reduced due to the higher transition temperature and is in a range between 50 and 250 nm.
• quality assurance means ensuring, on the one hand, good transport in the area of the wash link, which requires in-situ capping and, on the other, the contact provides a clean and sharp interface between the superconductors and the structured one Majorana material has.
• This can be achieved in particular by in-situ and preferably epitaxial growth of both layers.
• Both the structured and relatively aligned growth of the structured Majorana material, which capping in situ, and the in situ application of the preferably epitaxial, superconducting contacts is made possible by the method according to the invention, without an inert atmosphere and / or one To leave ultrahigh vacuum.
• the invention provides for the generation of such a hybrid structure next to an already known stencil mask (shadow mask) to use a further mask over which the geometry of the structured Majorana material can be defined, and which is also firmly connected to the substrate.
• stencil mask shadow mask
• FIGS. 1 to 6 The individual steps of the method according to the invention can be understood from FIGS. 1 to 6 using the example of the production of a Josephson junction (Josephson junction) as a hybrid structure according to the invention.
• the materials or layer details mentioned by way of example in the following process steps are hereby expressly not restrictive. A person skilled in the art can easily recognize which information relates specifically to the Josephson junction and would have to be correspondingly modified in the production of other hybrid structures.
• the inventive method is divided into a total of three sub-processes.
• the third subprocess comprises two different variations.
• a first additional layer (2) On a cleaned substrate (1) is applied flat and under vacuum, preferably in UHV, a first additional layer (2).
• the substrate can be, for example, a silicon wafer of any size or a silicon wafer section.
• a purified substrate is understood to be one which has been treated with a standard substrate-typical process known to the person skilled in the art for the removal of contaminants on the substrate surface. In this way, a substrate surface is provided which has only intrinsic compounds.
• the material of the substrate must be suitable for allowing a topological insulator to grow on top of it.
• a material can be used which is selectively etchable with respect to the substrate and the second layer (3).
• Silicon dioxide (SiO 2 ) is suitable for this purpose, although this should preferably have a high quality and can be produced by way of example in a process for thermal conversion of the silicon surface.
• this Si0 2 has a very good etch selectivity compared to the silicon of the substrate (1) and the second additional layer (3).
• the SiO 2 layer can be removed isotropically, for example, by hydrofluoric acid, whereby an atomically planar surface suitable for growth is produced on the substrate.
• the Si0 2 layer further has dielectric properties, whereby leakage currents can be suppressed. It is known from the prior art that a 1 to 10 nm thin Si0 2 layer effectively, with the use of stoichiometric silicon nitride (Si 3 N 4 ) as a second additional layer (3), reduces or prevents tensions, which which can exert Si 3 N 4 on the silicon surface. Tensions in the silicon substrate can adversely affect the coverage of the substrate by the first functional layer (6).
• the selected layer thickness of the first layer (2) should compensate for possible stresses on the substrate.
• the layer thickness for the first layer (2) is chosen to be a possible range of 1 to 20 nm, preferably a range of 1 to 5 nm.
• a second additional layer (3) is applied flat and under vacuum. This layer (3) is characterized in that it can be selectively removed from the first additional layer (2).
• the second layer should be HF-resistant and in particular low-stress in the cited embodiment.
• Si 3 N stoichiometric silicon nitride having a low density of parasitic hydrogen compounds is used.
• a suitable method here is the deposition of the nitride from the gas phase under low pressure (narrow low pressure chemical vapor deposit, LP-CVD).
• a transparent Si 3 N 4 layer can be used as a mask in wet-chemical or dry etching processes.
• the second additional layer (3) serves to define subregions on which the topological insulator is not selectively deposited over the silicon substrate during growth.
• the surface of the second layer (3) advantageously concludes with the surface of the first functional layer (6) in process step ULI.
• the layer thickness should therefore be selected in the range from 0.2 to 250 nm, preferably in the range from 5 to 100 nm.
• this layer is patterned, advantageously by electron beam lithography (EBL) using a suitable lacquer or resist.
• EBL electron beam lithography
• the structures defined in the resist are transferred to the second additional layer (3) after the development of the resist by means of a subsequent etching process.
• the second additional layer (3) is thus selectively and structured partially removed from the first additional layer (2).
• the reactive ion etching (reactive ion etching, RIE) can be used to precisely produce the desired structures in the second additional layer (3), in particular in an Si 3 N layer.
• reactive ion etching reactive ion etching, RIE
• anisotropic structures are produced by this directed etching process.
• reactive ion etching using exemplary fluoroform and pure oxygen as reactive gas constituents is suitable.
• Alternatives would be, for example, the wet-chemical removal of the silicon nitride by phosphoric acid or the physical removal of the silicon nitride with the aid of accelerated ions, for.
• IBE ion beam etching
• thin trenches having a width of 10 to 10,000 nm, preferably 30 to 200 nm, are defined in the second layer (3).
• the length of the trenches produced preferably varies between 100 nm-100 ⁇ m, preferably between 3 and 10 ⁇ m.
• the trenches can also be defined in ring or rectangle structures.
• a first functional mask is thus formed via the method steps A to C, with the aid of which, according to the invention and advantageously, a defined geometry of the structured Majorana material is made possible.
• the exposed portions of the first additional layer (2) are selectively removed from the second additional layer (3) and the substrate (1).
• a process is used here which does not chemically transform the substrate (1) and / or damage the substrate surface.
• dilute hydrofluoric acid is used using said materials, which selectively etches the silica and exposes the surface of the silicon substrate unaltered.
• a third additional layer (4) is deposited in a first step, flat and under vacuum. This should be selectively removed from the substrate (1) as well as the first (2) and second (3) additional layers.
• silicon dioxide of reduced quality is used here in comparison with the first silicon dioxide layer (2), and it can be deposited from the gas phase at low pressure (low pressure chemical vapor deposition, LP-CVD).
• This second layer of silicon dioxide (4) will etch much more rapidly in dilute hydrofluoric acid, so that by choosing the etching time, this layer can be removed selectively with respect to the first silicon dioxide layer (2).
• the selected layer thickness of the third additional layer (4) defines the distance of the near-surface mask (shadow mask) from the substrate surface (1). Up to four functional layers are deposited on the substrate surface in sub-process III. As a layer thickness for the third additional layer (4) is therefore an area selected from 5 to 500 nm, preferably a range of 10 to 150 nm.
• a fourth additional layer (5) is applied flat and under vacuum. This should be selectively removed from the third additional layer (4). If silicon nitride is used again, the processes mentioned in process step I.C can be used.
• the structures to be produced vary, depending on the desired device. Various embodiments of the structures are exemplified in the section with the embodiments.
• the structures include both large areas and small, narrow transitions, both of which are aligned relative to the structures generated in the first additional layer (2).
• the said transitions which define final Josephson junctions, have at least the width of the structures previously generated in process step IC in the first additional layer (2) and a lateral distance of 10 to 500 nm, preferably 10 to 200 nm. This narrow range is referred to below as a nanoback.
• II.H The third additional layer (4) is selectively removed relative to the substrate (1) as well as the first (2), second (3) and fourth additional layer (5) at least partially.
• step II.G The areas exposed in step II.G are removed. It is necessary for the method according to the invention that the third additional layer (4) is removed isotropically in all directions. As a result, any material of the third additional layer (4) below the nano-bridges defined in step II.G is removed. In addition, the structures defined in subprocess I are partially exposed. From this point on, the nanoblocks are partially floating above the substrate (1). About the method steps D to F, a second functional mask is thus formed, which is often referred to as a shadow mask.
• the two sub-processes I and II serve to prepare for the actual deposition or generation of the functional layers of the hybrid structures on the substrate.
• the following process steps I to K are carried out successively in an inert atmosphere, without the vacuum, and in particular the ultra-high vacuum (p 1 x 10 ⁇ 7 mbar, preferably p -S 1 ⁇ 10 -8 mbar).
• an inert atmosphere for example, pure N 2 gas is considered.
• the sample with the nano-bridges as well as the partially exposed surfaces of the substrate (1) is used for the deposition of the functional layers / structures in a vacuum chamber, eg. B into which a molecular beam epitaxy plant, transferred.
• a vacuum chamber eg. B into which a molecular beam epitaxy plant
• this process step can also take place in other coating plants in which the growth is carried out partially directed.
• Exemplary here is the growth of INA / he nanowires in a chemical vapor deposition (CVD) chemical.
• the first functional layer (6) is deposited. This layer must grow selectively on the exposed substrate surface (1), while unnecessary material deposits on the exposed surfaces of the additional layers (2, 3) and advantageously on the surfaces of the additional layers (4, 5).
• the first functional layer (6) comprises majorana materials.
• topological insulators of the form grow with 0x ⁇ 1 and 0 -S y ⁇ , 1, on a silicon (111) surface selective to silicon dioxide (2, 4) and silicon nitride (3, 5) surfaces.
• the first functional mask produced by method steps A to C thereby defines the structure of the majorana material.
• the layer thickness is adjusted in particular in such a way that the surface of the topological thin film (6) terminates preferably with the exposed surface of the second layer (3).
• a second functional layer (7) which is capable of forming a native oxidation layer, is applied over the entire surface by way of example of aluminum or niobium or tungsten, titanium, hafnium or platinum.
• a superconducting metal is used, exemplified by aluminum or niobium.
• This layer is also deposited below the nano bridges due to substrate rotation.
• the layer thickness of the second functional layer (7) must not exceed the thickness of the native oxide of the particular material selected in order to be able to form a passivation layer for the topological insulator in subsequent steps.
• a thin film, comprising aluminum is applied, since a passivation layer can advantageously be specifically formed in aluminum.
• the thin film, comprising aluminum can be applied with a layer thickness of at most 3 nm, because at this layer thickness it is ensured that in a subsequent oxidation the aluminum layer as the second functional layer (7) is completely oxidized as soon as it is in contact with air comes.
• the nano-bridges defined in the fourth additional layer (5) partially mask the atomic / molecular flow. Due to this partial shading of the atomic / molecular flow, the second functional layer (7) is not completely flat, but only partially coated.
• the layer thickness of the now deposited material (8) should be on the one hand at least the critical thickness for obtaining the superconducting properties of the material, but on the other hand not to fall below the thickness of a formed in a subsequent step native oxide of the material used.
• the layer thickness of the third functional layer (8) should not exceed the distance between the surface of the second functional layer (7) and the lower edge of the fourth additional layer (5), since otherwise unwanted contacting of the generated hybrid structure and the shadow mask can not be excluded ,
• the layer thickness of the deposited subareas (8) is thus regularly 5 - 500 nm, depending on the selected layer thickness of the first additional layer (2).
• the layer thickness should be between 30 and 100 nm to ensure the superconducting properties of most superconducting metals, whereby the subsequent formation of the oxide layer should also be taken into account.
• the material of the second functional layer (7) can be selected identical to the material of the third functional layer (8), ie a superconducting material.
• the two materials can also be chosen differently, since superconductivity is not absolutely necessary for the function of the second functional layer, but the formation of a native oxide layer as the passivation layer is a priority.
• a non-superconducting material as an interdiffusion barrier, it should be noted that it is selected to be thin enough so that the proximity-induced superconductivity is ensured via the defined weave link.
• titanium as the second functional layer (7), since it can serve as an interdiffusion barrier between the first functional layer (6) and the third functional layer (8), but another superconducting metal , For example, aluminum or niobium, to choose as a third functional layer (8), since these metals have particularly advantageous superconducting properties over the titanium.
• another superconducting metal For example, aluminum or niobium, to choose as a third functional layer (8), since these metals have particularly advantageous superconducting properties over the titanium.
• the nano-bridges defined in the fourth additional layer (5) partially mask the AtonW molecular flow. Similar to 11 I.K.
• the structured Majorana material (6) is not completely flat, but is structured and only partially coated with the superconducting material of the second functional layer (9).
• the second functional layer (9) may also be applied as a layer system consisting of a thin interdiffusion barrier and a thick superconducting layer.
• a metal or a superconductor may preferably be selected.
• the critical thickness for obtaining the superconductivity must once again be taken into account.
• interdiffusion barrier thin layers of platinum, tungsten or titanium are known from the literature.
• the thickness of the deposited material for the second functional layer (9) should be at least the critical thickness for obtaining the superconducting properties of the material, in addition, the layer thickness of the native oxide must be taken into account. This forms when the material used comes into contact with atmospheric oxygen or oxygen in any other form after the deposition.
• the thickness of the subregions of the second functional layer (9) is therefore between 50-100 nm, wherein the thickness of the material should not exceed the distance between the surface of the first functional layer (6) and the fourth additional layer (5).
• a third functional layer (10) comprising an electrically insulating material is applied to the second functional layer (9) / the layer system, as well as the exposed areas of the first functional layer (6), area-covering.
• This definition includes oxidizing metals as referred to in process step INJ.
• the materials used should have a sufficiently large band gap, so that no coherent tunneling of charge carriers in the selected material can occur in the technically relevant temperature range, taking into account the actual electron temperature.
• the technically relevant range is defined by the characteristic, critical temperature of the superconductor used.
• this third functional layer (10) does not react / interdiffuse with either the first (6) or the second functional layer (9).
• silicon nitride may be used as the third functional layer (10).
• inert metal-oxide compounds such as for example Al x O y, Nb x O y, Ti x O y, where 0 £ x, y: s 1, suitable or inert metal compounds with other Group VI elements such as sulfur, Tellurium or selenium.
• layers of pure tellurium or selenium can be used as temporary protection of topological surface states. to be divorced.
• laterally grown heterostructures of structured superconducting materials and structured Majorana material can advantageously be produced of high quality and precise alignment. This is important, for example, for the characterization of the superconducting properties of topological materials, but also for applications in scalable topological qubits as well as quantum registers.
• Devices that are known to those skilled in the art to grow prior to growth can grow devices having contact pads, saw markers, lateral superconducting structures, and patterned topological thin films.
• the method according to the invention advantageously combines high scalability with low cost and time expenditure.
• the method according to the invention in contrast to conventional methods for producing nanowire qubits from the prior art, in the method according to the invention not every nanowire or nanostructure has to be manually positioned and contacted, but it can selectively and selectively deposit structured majorana material on a suitably prepared substrate To be defined.
• the method according to the invention offers advantages as soon as the size and complexity of the desired devices, such as qubits or quantum registers, increases.
• suitable methods for applying layers for the process according to the invention are in particular chemical vapor deposition at low pressure (liquid phase-chemical vapor deposition, LP-CVD) and molecular beam epitaxy (MBE) call.
• PVD physical vapor deposition
• suitable methods for applying layers for the process according to the invention are in particular chemical vapor deposition at low pressure (liquid phase-chemical vapor deposition, LP-CVD) and molecular beam epitaxy (MBE) call.
• the chemical vapor deposition is especially for the generation of planar, Silicon-containing layers for the deposition of the first and second, and the third and fourth additional layer according to the process steps IA, IB, II.E and II.F suitable.
• Molecular beam epitaxy is particularly suitable for applying the functional layers according to process steps I to K.
• Epitaxial growth is understood in particular to mean that a further crystalline layer is deposited on a crystalline layer or a crystalline substrate, wherein at least one crystallographic orientation of the growing crystal layer corresponds to an orientation of the crystalline layer or of the crystalline substrate.
• a protective passivation layer which protects the topological insulator (structured Majorana material) against contamination or chemical restructuring of the surface is realized in situ.
• the topological material is effectively protected from any exchange with atmospheric oxygen or other components of the natural environment.
• a passivation layer for example, a 2 nm, at most 3 nm thick aluminum layer can be grown on the topological insulator, which after the removal of the sample from the inert atmosphere and possibly the ultrahigh vacuum completely oxidized and so the surface states of the structured Majorana material underneath protects.
• inert metal-oxide compounds are already suitable, such as, for example, Al x O y , Nb x O y , Ti x O y , where 0 ⁇ x, y .5 1, and also inert metal compounds with other group VI elements, such as sulfur, Tellurium or selenium, to use.
• pure layers such as, for example, Al x O y , Nb x O y , Ti x O y , where 0 ⁇ x, y .5 1, and also inert metal compounds with other group VI elements, such as sulfur, Tellurium or selenium, to use.
• pure layers such as, for example, Al x O y
• Tellurs or selenium have proven to be a temporary protection of topological surface states.
• the method according to the invention makes it possible here, by way of example by way of example with the production of a Josephson contact using topologically induced superconductivity, to advantageously produce a particularly epitaxial production of the in-situ contacts, which leads to a particularly high quality of the interface.
• the quality of the interface is indicated by the transparency.
• Transparency is generally understood to be the probability of successful exchange of paired electron states across the interface, also known as Andreev reflection.
• the Andreev reflection process at the interface faces the direct backscattering of the individual electrons at the interface.
• the probabilities Andreev and normal reflection add up to 100%.
• a method for producing a topological Josephson junction as an example of a hybrid structure according to the invention, while maintaining the surface properties of the topological material for current transport between the structured superconducting contacts is presented, in which also the interfaces between the superconductors and the structured Majorana material as a topological insulator have a special quality and are designed so sharp and clean that advantageously also Majorana physics can be operated with it.
• a topological qubit can be produced with such a hybrid structure, in which-unlike conventional qubits-theoretically no error correction is required.
• the preparation of the hybrid structures according to the invention including the structured definition of the deposited Majorana material, the in-situ and preferably epitaxially grown, structured superconducting contacts, as well as the passivation without interrupting the inert atmosphere, in particular in ultra-high vacuum, within a Clean room system, for example, with the help of a molecular beam epitaxial system, done.
• the topological material, the in-situ and preferably epitaxially grown, superconducting contacts, as well as the passivation layer can be deposited well defined in the inventive method in a wide range of lateral dimensions of 5 nm to 10,000 ⁇ .
• an alignment of the structures relative to each other with deviations in the range of 2.5 nm to a maximum of 20 nm is given by the structure definition with electron beam lithography.
• any 2D layouts of insulating, passivating and (supra-) conducting regions can be defined in-situ.
• the invention provides for the generation of the structured Majorana material in addition to a shadow mask to use a further mask (2, 3), via which the geometry of, for example, a topological thin film can be defined.
• a further mask 2, 3
• the property of the topological materials used is advantageously used to grow selectively.
• an additional layer can be applied to the substrate, on which the topological layer can be applied Material does not grow at all or only in the choice of different growth parameters. If the substrate is exposed in places, the topological material separates only in these defined areas. The majorana material will then selectively grow in the exposed portions of the silicon substrate over the additional layer, depending on the choice of growth parameters.
• Molecular beam epitaxy is advantageous for applying the structured superconducting layers as well as the structured Majorana material, since the directed
• Atomic / molecular flow of the materials during the evaporation from the solid phase advantageous in the inventive method using the defined mask, or using the defined nanobars, partially shaded.
• the method according to the invention makes it possible to overgrow or steam or cover or vaporize an air- and / or ambient-sensitive functional layer, for example the surface of a topological insulator, in situ and selectively.
• a thick superconducting layer is applied to the topological insulator, while at other selected locations only a thin layer is placed, exemplifying the use of oxidizing materials after aging in air to provide an insulating protective layer for the topological insulator with the topological insulator Environment can react.
• This advantageously ensures a local contacting of the functional layer and at the same time guarantees a passivation layer protecting the entire component.
• the functional layers can be applied without interruption of the inert atmosphere and preferably in ultra-high vacuum in, for example, the molecular beam epitaxy system. After discharging the substrate with the defined structures from the inert atmosphere, in the presence of atmospheric oxygen, oxidation of the surfaces of the superconducting material near the surfaces takes place.
• a passivating oxide layer takes place for partial regions with a layer thickness below the layer thickness of the native oxide of the respective material. The formation of this passivation layer on the surface of the topological insulator between the two superconductive contacts causes the surface as well as the current-carrying surface states of the topological material to be protected.
• Oxidation layer corresponding to the native oxide thickness, in a near-surface area.
• the material still has superconducting properties despite the oxidation of the topmost layer at the interface to the topological material.
• the superconducting contacts are still defined by targeted shadowing of the atomic / molecular flow.
• a passivating layer can be deposited over remaining, exposed portions of the structured Majorana material.
• the aforementioned materials can be used.
• laterally grown heterostructures of superconducting materials and majorana materials of high quality and precise alignment can be produced.
• Different geometries and dimensions allow the structured definition of functional devices, such as topological Josephson junctions, to complex networks for applications in scalable topological qubits as well as topological quantum registers.
• first preferred embodiments of the method according to the invention for producing a Josephson junction using a structured Majorana material and a superconducting metal are given.
• the definition of the Josephson junction is not intended to be limiting but at the same time serves as the smallest unit of a topological qubit as an intuition of the subsequent embodiments.
• the letters of the process steps for producing a single topological Josephson contact correspond to those in FIGS. 1 to 6.
• the inventive method comprises a plurality of functional layers, wherein in the following embodiments, concrete materials for use are mentioned, which are not intended to be limiting.
• the method is subdivided into a total of three sub-processes: the preparation of the substrate for a structured deposition of the topological materialies (process step (I) "selective area"), the application of a surface-near stencil mask or shadow mask for the defined application of the superconducting metal (process step (II) "Stencil Mask”) as well as the method during the deposition within a molecular beam epitaxy installation for the directed application of the functional layers (process step (III) "coating process”).
• IA Of a 525 ⁇ thick, boron-doped (> 2000 ⁇ -cm), 4 "silicon wafer (1), with an orientation of the surface normals in the ⁇ 111> direction are nominal, starting from the surface of the substrate, under Vacuum the first 5 nm into silica (Si0 2 ) (2) using a Tempress TS 8 horizontal oven for dry oxide formation After oxidation at 820 ° C with the aid of molecular oxygen, an actual layer thickness of 5.8 nm achieved in this way.
• the silicon dioxide has an etching rate in dilute hydrofluoric acid (1% HF) of 6 nm / min.
• a nominally 20 nm thick layer of stoichiometric silicon nitride (Si 3 N 4 ) (3) is applied flatly and under vacuum.
• the silicon nitride is deposited in a Centrotherm LPCVD system E1200 R & D furnace at 770 ° C. with the aid of 120 sccm of ammonia (NH 3 ) and 20 sccm of dichlorosilane (DCS). An actual layer thickness of 25.6 nm is achieved.
• the resulting silicon nitride etches at a rate of 0.4 nm / min in dilute hydrofluoric acid (1% HF).
• IC After the application of the stoichiometric silicon nitride (3), a structuring of this layer takes place.
• first 120 nm AR-P 6200 resist are applied, which is structured in a Vistec EBPG 5000+ electron beam lithography system.
• the electrons experience a 50 kV acceleration voltage with a 100 pA beam current.
• a step size of 5 nm and a proximity-corrected dose of 250 ⁇ / cm 2 were chosen.
• the resist is then developed at 0 ° C for 60 s in AR 600-546. The development is stopped in a 60 s 2-propanol bath.
• the structures defined in the resist are transferred into the stoichiometric silicon nitride (3) after development of the resist by means of an Oxford Plasmalab 100 system.
• the plasma used is ignited from fluoroform (CHF 3 ) and molecular oxygen (0 2 ) in a ratio of 22 sccm CHF 3 to 2 sccm 0 2 at a selected power of 50 W RF power.
• the etching time is 90 s.
• the exemplary method for structuring the stoichiometric silicon nitride (3) defines thin trenches with a width of 40-10,000 nm.
• the length of the trenches produced varies from 3 ⁇ to 100 ⁇ .
• a nominally 400 nm thick layer of silicon dioxide (4) is deposited in a first step, flat and under vacuum. This is deposited in a Centrotherm LPCVD system E1200 R & D furnace at 650 ° C and with the aid of tetraethoxysilane. This silicon dioxide layer (4) replicates and fills the lower silicon dioxide (2) and silicon nitride layers (3). The upper silicon dioxide layer (4) is chemically mechanically polished (chemical-mechanical planarization, CMP) and thus leveled. II.F On the second silicon dioxide layer (4), a further layer of stoichiometric silicon nitride (5) is applied flatly and under vacuum.
• CMP chemical-mechanical planarization
• the transitions therefore have at least the width of the structures previously produced in process step IC in the first layer of stoichiometric silicon nitride (3) and a lateral distance of 20-200 nm.
• the orientation of the nanobars relative to the trenches is effected by means of corresponding markers.
• II.H The second layer of silicon dioxide (4) becomes selective both towards the silicon
• the second layer of silicon dioxide (4) is removed isotropically in all directions.
• any material of the second layer comprising stoichiometric silica (4) is removed below the nanobars defined in step II.G.
• the structures defined in subprocess I are partially exposed. From this point on, the nanoblocks are partially suspended above the silicon substrate (1).
• the sample with the nano bridges as well as the partially exposed surfaces of the silicon substrate (1) is transferred into a molecular beam epitaxy system for the deposition of the functional layers / structures. It is an ultra-high vacuum of p ⁇ 1 x 10 -9 kPa (z. B. 5 x 10 "10 hPa) is set. It is a topological insulator (6) of the composition (Bio.o6Sbo.94) 2 Te 3 is deposited which selectively on the exposed substrate surface grows. The substrate rotation of 10 revolutions per minute guarantees that the above-mentioned topological insulator also grows on the exposed subareas below the nanobars. III.
• a nominally 2 nm thin layer of titanium (7) which is able to form a dense, native oxidation layer, is applied over the entire area in the same molecular beam epitaxy system. This layer is also deposited below the nano bridges due to substrate rotation.
• the layer thickness of the titanium layer does not exceed the thickness of the native oxide of titanium and forms a passivation layer for the topological insulator in subsequent steps, when discharging from the plant.
• titanium as the second functional layer (7), since it can serve as an interdiffusion barrier between the first functional layer (6) and the third functional layer (8), but another superconducting metal such as aluminum or niobium, to be selected as the third functional layer (8), since these metals have particularly advantageous superconducting properties relative to the titanium.
• the sample with the nano-bridges as well as the partially exposed surfaces of the silicon substrate (1) is transferred into the ultra-high vacuum (plant specific p ⁇ , 1 x 10 "9 hPa) of a molecular beam epitaxy plant for the deposition of the functional layers / structures
• a majorana material comprising (Bi 0 .o 6Sbo , 94) 2Te 3 is selectively deposited on the exposed substrate surface and the substrate rotation of 10 min "1 ensures that the majorana material is also deposited on the exposed areas the nano bridge grows.
• the sample is transferred to a molecular beam epitaxial system for the deposition of a nominally 70 nm thick layer of niobium (9)
• Substrate rotation is applied to subregions of the second functional layer
• the nanobars defined in the second layer by stoichiometric silicon nitride (5) partially mask the atomic / molecular flux.
• III. K * The sample is transferred without interruption of the vacuum into an adjacent molecular beam epitaxy plant.
• the layers (6) and (9) are kept in an inert atmosphere throughout the application of the dielectric layer (10).
• a 10 nm thick layer of stoichiometric Al 2 O 3 (10) is spread over the entire surface of the
• the structured majorana material (6) with a second functional layer (7) arranged thereon and the two regions of the third functional layer (8) present separately, each comprising a superconducting material, are present.
• the layer thickness of the second functional layer (7) has been selected to be correspondingly thin, here (11) there is complete oxidation of the layer and thus the desired capping for the topological insulator (6) between the regions (8 ) of the third functional layer while the non-exposed portions of the first functional layer (7) in contact with the second functional layer (8) do not oxidize.
• the structured majorana material (6) is provided with the two separately arranged regions of the second functional layer (9) and a third functional layer (10) formed thereon, each comprising a superconducting material.
• a third functional layer (10) formed thereon, each comprising a superconducting material.
• the layer thickness of the third functional layer (10) has been selected to be correspondingly thin overall, (13) complete oxidation of the layer occurs here.
• the desired capping for the topological isolator (6) is achieved between the separately present regions (9) of the second functional layer.
• this layer (10) can be chosen arbitrarily thick.
• the hybrid structures produced according to the invention can advantageously be constructed into complex networks. These networks include, for example, the topological Josephson junction as the smallest subunit, but in yet another embodiment may represent up to a plurality of topological quantum bits.
• the inventive method guarantees the preservation of the surface properties of the structured Majorana material as a topological insulator, as well as a high interfacial quality between the structured Majorana material and the superconductor.
• FIG. 7 shows further applications for the invention.
• other geometries of Josephson junctions such as a topological insulator in wire form (6) with a superconducting island (9 ), whereby the superconducting island (9) can completely cover the topological insulator (Var. A) as well as cover it only partially (Var. B).
• the left-hand column shows the plan views of process step I, the front views of process step J 'in the middle column, and the front views of process step K' in the right-hand column.
• the Josephson junctions to Var. B can be designed advantageously as a bi-junction and also as a tri-junction, as shown in FIG. 8, in the left column, the plan views according to process step I, in the middle column the front views according to process step J 'and in the right column the front views according to process step K' are shown, in each case for the geometry G2 (Var B), see Figure 7 as Bi and tri-junction.
• isessionid 7B6A386E471815BB16B2CCDF05CF2B34.c3.iops cience.cld.iop.org
• Nonorganic evaporation mask for superconducting nanodevices T. Hoss, C. Strunk, C. Schoenenberger, Microelectronic Engineering, Volume 46, Issues 1 - 4, May 1999, Pages 149-152.

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