EP2591514A1

EP2591514A1 - Ionically controlled three-gate component

Info

Publication number: EP2591514A1
Application number: EP11754280.3A
Authority: EP
Inventors: Ulrich Poppe; Dieter Weber; Yuriy Divin; Mikhail Faley
Original assignee: Forschungszentrum Juelich GmbH
Current assignee: Forschungszentrum Juelich GmbH
Priority date: 2010-07-05
Filing date: 2011-06-03
Publication date: 2013-05-15
Also published as: DE102010026098A9; CN102959750B; WO2012003821A1; CN102959750A; JP5976641B2; JP2013535805A; DE102010026098A1; US20130079230A1

Abstract

The invention relates to a three-gate component which can be switched by the motion of ions. The three-gate component comprises a source electrode (3), a drain electrode (3), and a channel (2) which is connected between the source electrode and the drain electrode and which is made of a material having an electronic conductivity that can be changed by supplying and/or removing ions. According to the invention, the three-gate component has an ion reservoir (5) which is contacted by means of a gate electrode and is connected to the channel in such a way that the ion reservoir (5) can exchange ions with the channel when a potential is applied to the gate electrode. It has been recognized that information can be stored in the three-gate component in the distribution of the total ions present in the ion reservoir and in the channel between the ion reservoir and the channel. The distribution of the ions between the channel and the ion reservoir changes if and only if a corresponding driving potential is applied to the gate electrode. Therefore, in contrast to RRAMs, there is no time-voltage dilemma.

Description

Ionically controlled three-electrode component

The invention relates to a three-element component which can be switched by the movement of ions.

PRIOR ART Electrically erasable programmable read-only memories (EEPROMs) have become established as standard for nonvolatile rewritable electronic data memories. They usually include a plurality of field effect transistors with insulated gates. If a charge is stored on the gate, the field effect transistor is conductive, which represents a logic 1. If the gate contains no charge, the field effect transistor blocks, which represents a logical 0. Information is written to the EEPROM by applying a high voltage pulse to a control electrode which is isolated by a barrier against the gate. This allows electrons to overcome the barrier and charge can be stored on or removed from the gate.

The disadvantage is that the barrier is heavily loaded during each write operation and is therefore subjected to progressive wear, so that the number of write processes per field effect transistor is limited. In addition, the miniaturization of EEPROMs encounters physical limitations, as the likelihood that the stored charge is lost through tunneling increases exponentially as dimensions are reduced. The size of the charges that must be transported to the gate is the limiting factor for the speed with which this can be done.

As an alternative to EEPROMs, resistive memories (RRAMs) have therefore been developed. RRAMs are based on the fact that the electrical resistance of an active material arranged between two electrodes can be changed by applying a high write voltage between at least two stable states and measured by applying a lower read voltage. The review article (R. Waser, R. Dittmann, G. Staikov, K. Szot, "Redox-Based Resistive Switching Memories - Nanoionic Mechanisms, Prospects, and Challenges", Advanced Materials 21 (25-26), 2632-2663 (2009)) gives an overview of the current state of development. Disadvantageous there is, especially with RRAMs, a hitherto unresolved target conflict between the speed with which information can be stored and read out, and the long-term stability of the stored information.

OBJECT AND SOLUTION It is therefore the object of the invention to provide a component which can function both as a long-term stable and as a fast memory.

This object is achieved by a Dreitorbauelement according to the main claim. Further advantageous embodiments will be apparent from the dependent claims. Subject of the invention

In the context of the invention, a three-element component has been developed. This comprises a source electrode, a drain electrode and a channel, which is connected between the source electrode and the drain electrode and made of a material whose electronic conductivity is variable by the addition and / or discharge of ions. In this context, the term "electronic conductivity" also refers to the properties of a superconductivity possibly present in the channel, in which Cooper pairs replace single electrons. The hole line in a p-doped semiconductor is also understood as electronic conductivity in the sense of this invention.

According to the invention, the three-terminal component comprises an ion reservoir contacted with a gate electrode which is connected to the channel in such a way that it can exchange ions with the channel when the gate electrode is acted upon by a potential. The transport of ions between the ion reservoir and the channel changes the concentration of mobile ions in the channel. This doping changes the conductivity of the channel. A small change in the doping is already sufficient to change the conductivity of the channel many times. In this case, the ion reservoir can at the same time function as the gate electrode, provided that it is electronically conductive.

It has been recognized that in the distribution of the total ion reservoir and channel ions present on the ion reservoir and channel information can be stored in the three-element device. The information can be deposited in the component by applying of an appropriate potential to the gate electrode, the distribution of the ions is changed. By measuring the electrical resistance between the source electrode and the drain electrode, this information can not be read destructively. If the ions diffuse sufficiently slowly between the ion reservoir and the channel in the absence of a driving potential at the gate electrode, this memory is not volatile.

The device can store, erase and overwrite digital information. For this purpose, for example, a logical 1 can be coded in the state in which the channel has a low electrical resistance and let a high current flow when a predetermined readout voltage is applied. A logical 0 is then coded in the state in which the channel has a high electrical resistance, so that when applying the read voltage only a small current flows. However, any intermediate values can also be stored. The device is thus also suitable as a storage for analog information, such as measurement data.

It has been recognized that this form of storage solves a fundamental resistive memory (RRAM) conflict. Conventional resistive memories are two-port devices, so that both the storage and the reading out of information occur by the application of voltages to the same electrodes. If a high write voltage is applied to store, the resistance of the memory material changes. This change manifests itself in the application of a significantly lower read voltage in a change of the current driven by this read voltage through the memory.

The write voltage is now limited by the dimensions of the memory and electronic requirements to a few volts. On the other hand, the readout voltage must be sufficiently large to be able to measure the resistance of the memory material with a sufficient signal-to-noise ratio. Thus, write and read voltages can be only about an order of magnitude apart.

At the same time, it is desirable in the case of the resistive memory element that it can be switched over within a few nanoseconds by applying the write voltage, but that its state remains stable even if the read voltage is constantly applied for at least 10 years. With a voltage difference of only one order of magnitude, therefore, a difference of about 10 orders of magnitude should be justified in the characteristic switching times. This conflict of objectives is known in the professional world as a "voltage-time dilemma". According to the invention, the additional gate electrode is provided for storing information. The distribution of the ions on the channel and on the ion reservoir changes then and only if a corresponding driving potential is applied to the gate electrode. By contrast, the read-out voltage applied between the source electrode and the drain electrode has no influence on the distribution of the ions, since during readout no electric field is built up between the channel and the ion reservoir. Accordingly, it is not necessary to provide for reading and writing very different voltage levels. The circuit complexity is advantageously reduced. However, it is also possible for a current to flow through the channel during readout, which current is considerably larger than the current flowing during writing between the ion reservoir and the channel, without this causing an ion exchange between channel and ion reservoir.

If a lower potential is applied to the gate electrode than would be necessary to initiate an ion transport between the ion reservoir and the channel, then the component acts analogously to a field-effect transistor as an amplifier and can be used as such. In a particularly advantageous embodiment of the invention, the ion reservoir is at

Standard conditions a solid. This may be crystalline, amorphous, but also, for example, a polymer. Then, the ions can move substantially only by diffusion within the ion reservoir and between the ion reservoir and the channel. Other transport mechanisms, such as the convection of a liquid or gaseous Ionenreser- voirs, are the diffusion of priority. The diffusion in turn can be controlled by the potential applied to the gate electrode in connection with the temperature.

In principle, any material which can deliver cations and / or anions into the channel while retaining the charge neutrality is suitable as an ion reservoir. In particular, this ability possesses a material which has at least one cation / anion with variable valence. On such a cation / anion, another type of ion may be loosely bound, or there may be an unoccupied space for an ion of this sort. This ion species is then mobile with comparatively low activation energy and can be exchanged between the ion reservoir and the channel. In particular, the ion that is exchanged between ion reservoir and channel can be oxidized or reduced or ionized or deionized in this exchange. Advantageously, the ion reservoir, the ion conductor and / or the channel have a crystal structure which does not change during the exchange of ions between the ion reservoir and the channel. The ion reservoir, the ion conductor and / or the channel may alternatively be amorphous. It has been recognized that many solid state properties of the ion reservoir, the ionic conductor and the channel, in particular the electronic and ionic conductivity, depend on the respective crystal structure. If the crystal structure of one of these materials is changed by the transport of ions between the ion reservoir and the channel, the solid state properties change. However, a well-ordered crystal structure is usually introduced into the material with elaborate techniques during production, but it can no longer regenerate itself during operation. Any deterioration of the crystal structure during the exchange of ions between ion reservoir and channel thus means irreversible wear of the respective material. Thus, the device can survive a particularly large number of write cycles if the crystal structure of the ion reservoir, the ion guide and / or the channel either does not change in operation or is missing from the outset, because the respective material is amorphous. Amorphous materials, whose properties do not depend on a well-ordered crystal structure, provide the added advantage in manufacturing the device that the latitude for the process parameters is significantly greater.

In a well-ordered crystal structure places can be provided which can absorb and release ions again, without changing the overall crystal structure. For example, the interstitial space ions may be intercalated into the ion reservoir material, may sit on voids in the crystal lattice of the ion reservoir, or may be mobile along crystal defects (such as dislocations, point defects, grain boundaries, and stacking faults). The ion mobility of the ion reservoir at the operating temperature and by the

Voltage drop between the gate electrode and the channel given working field strength significantly determines the speed with which the conductivity of the channel can be changed.

If the ion conductor is not identical to the ion reservoir, then the ion reservoir should have a sufficiently high electronic conductivity so that the potential difference between the gate electrode and the channel drops substantially above the ion conductor, then that it provides the activation energy for the transport of ions through the ion conductor.

However, if the ion reservoir is at the same time an ion conductor, then it should have only a low electronic conductivity so as not to short-circuit the current path from the source electrode through the channel to the drain electrode. In order not to counteract the change in the electronic conductivity in the channel caused by the exchange of ions between the ion reservoir and the channel, the electronic conductivity of the ion reservoir, which also functions as an ion conductor, should change at least an order of magnitude less than that of the channel during this exchange.

In particular, crystalline or amorphous solids with high ionic conductivity are suitable as an ion reservoir. Among the crystalline solids, perovskite structures, of which the crystal is cubic or in the form of layers, are particularly advantageous. Examples of such materials are SrFe0 _3-x and LaNi0 _3-x

In SrFe0 ₃ . _x , the iron can occur as 2+, 3+ and even 4+. The oxygen content varies continuously between SrFe0 ₂ (Fe ²⁺ ) over SrFe0 _2,5 (Fe ³⁺ ) to SrFe0 ₃ (Fe ⁴⁺ ). The crystal lattice is distorted, but the perovskite structure is retained as long as the composition does not deviate too far from the stoichiometric composition. The material can thus absorb or release significant amounts of oxygen without structurally changing too much. There is a parallel to the storage materials for lithium ions in Li-ion batteries, such. B. LiFeP0. Instead of the lithium content in LiFeP0 ₄ the sour material is changed content in SrFe0 _3, and to maintain the charge neutrality, the iron ion changes in both cases, its oxidation number.

Basically, noble metals are particularly well suited as electrodes to contact a p-type oxide as a channel or ion reservoir. By contrast, base metals such as indium or aluminum are particularly suitable as electrodes for contacting an n-type oxide (such as, for example, cerium-doped Nd ₂ CuO). High electrical conductivity oxides such as La ₂ Cu0 ₄ , SrRu0 ₃ or LaNi0 ₃ are all-purpose materials for electrodes. These oxides can, for example with La ₂ Cu0 ₄ , for example, with divalent cations such as Sr or Ba p-doped, or with tetravalent cations such as cerium, n-doped. The doping with the foreign atoms then makes a significantly greater contribution to the electronic conductivity than the doping by oxygen deficit or excess. Thus, the conductivity of normally conducting oxides by doping with impurities in the considerably regardless of the oxygen content. However, the electrodes may also be high-temperature superconductors or comprise combinations of the materials listed here.

Advantageously, the bridged by the channel distance between the source electrode and the drain electrode between 20 nm and 10 μηι, preferably between 20 nm and 1 μιη. Advantageously, the channel is formed as a thin layer with a thickness between 3 and 50 nm, preferably between 5 and 20 nm. These measures, individually or in combination, reduce the capacity of the channel and hence the amount of charge, both for change

(Write) and to measure (read) its electrical resistance must be transported. The speed of writing and reading is thereby advantageously increased.

In a particularly advantageous embodiment of the invention, the ion reservoir is connected to the channel via an ion conductor which has an electronic conductivity which is at least 2 orders of magnitude lower than the channel. Then, the distribution of the ions on the channel and ion reservoir in the absence of a potential at the gate electrode as a driving force for the diffusion is particularly stable. As a rule of thumb, the specific resistances r _{L of} the ion guide and rj of the channel should be: r _L > r _K * l ² / (d _L * d _K ), where dL and d _{& are} the thicknesses of the ion conductor and the channel and where 1 is the Length of the channel between source and drain is. If the channel is shortened, the required ionic resistivity r _{L of} the ion conductor decreases disproportionately. In this respect, it is advantageous to downscale the component laterally, because more materials than ion conductors thereby become usable.

In a further particularly advantageous embodiment of the invention, in which the ion reservoir is able to exchange oxygen ions with the channel, the potential difference between the gate electrode and the channel is of particular importance as a driving force for the ion exchange. In all known ionic conductors, oxygen ions do not diffuse immeasurably slowly at room temperature without a sufficiently strong electric field as a driving force. Therefore, for example, fuel cells with solid electrolytes in which as the driving force for the oxygen ions to be passed through the electrolyte only the voltage generated by the fuel cell in the order of 1 volt available at Temperatures in the order of 800-1000 ° C are operated.

However, in a fuel cell, the ion conductor has a thickness of several hundreds of micrometers. On the other hand, in the three-terminal device according to the invention, the ion conductor advantageously has a thickness of 100 nanometers or less, preferably 50 nanometers or less and most preferably 30 nanometers or less. A thickness of 100 nanometers amplifies the electric field by a thousandfold for the same voltage across the ion conductor. Because this electric field provides the activation energy for the ion transport, the transport increases disproportionately. Thus, the writing of information in the Dreitorbauelement is also possible at room temperature. A significantly lower electronic conductivity of the ion conductor compared to the ionic conductivity has the further effect that a potential applied to the gate electrode can be fully utilized for the formation of an electric field between ion reservoir and channel. If the ionic conductor conducts electrons too well, the potential is partially short-circuited and is only available to a limited extent as a driving force for the exchange of ions. In addition, it is prevented that the channel is short-circuited by the parallel-connected reservoir.

In particular, in each case a solid electrolyte is suitable as an ion conductor, as an ion reservoir and / or as a channel. It has been recognized that it is precisely a solid electrolyte which can combine good ionic conductivity with good electronic isolation between ion reservoir and channel. In particular, in any stable oxide with low electronic conductivity, the transport of ions can be forced in principle, if the potential difference between the gate electrode and the channel provides a sufficiently strong electric field for this purpose. Examples of such materials are SrTiCh, Sr _1-x Ba _x Tb0 ₃ or Al ₂ O ₃

Advantageously, the solid electrolyte is a material in which the activation energy for the diffusion of oxygen ions at temperatures above 400 ° C less than 1 eV, preferably less than 0.1 eV, is. Examples of such materials are yttrium-stabilized zirconium oxide (YSZ) and Mn- and / or Mg-doped LaGa0 ₃ . In such a material, oxygen ions are transported by changing places with vacancies. They have to overcome a potential barrier. Room temperature at which he inventions device according to the rule is used, does not provide sufficient activation energy for overcoming this potential barrier. Therefore, no oxygen transport takes place and one into the building Element written information is stable for a long time at room temperature. Only an electric field generated in the ion conductor by applying a potential to the gate electrode provides the activation energy for the exchange of ions between the ion reservoir and the channel. The ion current follows the equation I = I ₀ * exp (- [AH-0.5 * q * d * E] / [k * T]), where I is the current, I ₀ a proportionality factor, ΔΗ the activation energy for the jump of an occupied to an unoccupied lattice site (order of magnitude 1 eV), q the amount of charge of the transported ion (multiple of the elementary charge), d the jump distance of the ion from an occupied to an empty lattice site (order of magnitude 200 pm), E the field strength, k the Boltzmann constant and T is the temperature in Kelvin. In the field of low field strength, ie in high temperature fuel cells (SOFC) as an important application of ionic conductors, the current is approximately proportional to the field strength and the ionic conductor follows Ohm's law. However, in the high field strength region of interest for the present invention, the electric field provides a significant contribution to the activation energy. The field strength is in the range of 0.1-1 GV / m, ie when an ion jumps into an adjacent space in the direction of the Coulomb force, the energy barrier for the jump is reduced by 1/10 or more, which reduces the transport Speeds orders of magnitude.

Also suitable for the component are materials that have too high an electronic conductivity for applications in SOFC. The shorter the channel becomes, the higher the conductivity of the ion conductor can be. The activation energy is particularly low at dislocations, grain boundaries, twin boundaries, stacking faults, and other extended lattice defects, thereby facilitating transport along these defects.

Advantageously, the solid electrolyte is an amorphous material. Advantageously, this does not tend to crystallize and is chemically stable over a wide temperature range. In principle, there are no grain boundaries, dislocations and other imperfections in the solid-state electrolyte which would occasionally lead to strongly changed properties. Its properties are therefore spatially homogeneous. If the material does not tend to form a crystalline order, voids of the type mentioned do not form even after a high number of write cycles. Its properties are thus long-term stable and do not degrade during operation. Examples of such solid-state electrolytes are GdSc0 _3; LaLu0 ₃ and Hf0 ₂ . GdSc0 ₃ - Thin films are stable even at temperatures up to 1000 ° C for a short time (10 s-20 s) and remain amorphous. Advantageously, the solid state electrolyte is an open structure oxide, i. h, large interstitial spaces or channels where ions can drift. Examples of such materials

Advantageously, the ion conductor and / or the solid electrolyte has an anisotropic mobility for ions. For this purpose, it may, for example, contain one-dimensional channels in which dopants are intercalated. But it may also contain interfaces between different materials along which ions can move in two dimensions between the ion reservoir and the channel. Advantageously, the channels and / or interfaces substantially perpendicular to the direction of flow through the channel to the channel. Then, ions are essentially only injected into or withdrawn from the channel where the channels and / or interfaces strike. Thus, for example, the ion content of the weak-left can be selectively influenced in a Josephson junction, without thereby changing the superconducting electrodes, which are separated by the weak-link.

Anisotropic mobility for ions can be realized, for example, by the ion conductor or solid electrolyte having a layer structure, wherein the ionic transport along these layers is favored over the transport perpendicular to these layers by at least an order of magnitude. Examples of such materials are yttrium-barium-copper oxide (YBa ₂ Cu 3 C) 7 _× ) and lanthanum-barium-copper oxides (La ₂ CuO _{4 + x} ).

If such an ionic conductor or solid-state electrolyte is to exchange ions with an adjacent material, it is advantageous if the interface with the adjacent material intersects the layers. This can be controlled by the crystal orientation of the substrate surface in interaction with the growth parameters, in particular with the substrate temperature. Such a growth process is described in Divin et al. (YY Divin, U. Poppe, CL Jia, JW Seo, V. Glyantsev, "Epitaxial (101) YBa ₂ Cu ₃ O ₇ thin films on (103) NdGa03 Substrates", Conference Paper "Applied Superconductivity", Spain, 14.- 17.09.1999).

The electronic conductivity usually has the same preferred directions as the ionic conductivity.

Instead of oxygen ions, other ions can also be used for switching. Suitable solid electrolytes for silver cations include, for example, silver iodide, silver rubidium iodide and silver sulfide. For alkali cations, for example, WO ₃ or Na ₃ Zr ₂ Si ₂ PO | come ₂ (NASICON) in question. Certain polymers like Nafion have a high conductivity for protons.

For the letter it depends on the total number of transported ions. In order to reach this total number, a small voltage may be applied to the gate electrode for a long time, or a higher voltage may be applied for a short time. The transport of ions through a solid electrolyte is a nonlinear effect in the high field region. If a higher voltage drops across the solid-state electrolyte, a disproportionately higher number of ions are transported per unit time. Thus, the writing speed can be significantly increased when a short pulse having a higher writing voltage is applied to the gate electrode.

Gate electrode and channel form a capacitor that is charged by the charge transport between gate and channel. If the electronic resistance of the ion conductor is very high, this capacitor discharges only very slowly. Then it may be advantageous, after applying the short pulse with the high write voltage to apply a longer pulse with significantly lower voltage and opposite polarity. This discharges the capacitor formed from gate electrode and channel, but only reverses the previous ion transport between gate electrode and channel to a small extent, because this transport proceeds disproportionately slower at low voltages. Advantageously, the potential in the ion conductor along the path from the ion reservoir to the channel has an asymmetrical course. How such a potential landscape can be realized is given for example in EP 1 012 885 B1. Then the activation energy for the ion transport through the ion conductor depends on the direction of transport. For the ion transport from the ion reservoir to the channel on the one hand and for the reverse ion transport from the channel to the ion reservoir on the other hand, significantly different activation energies have to be applied. As a result, for example, the ion transport from the ion reservoir to the channel can be energetically preferred over the reverse path. There are then activation energies in which the ion conductor is permeable to ions substantially only in one direction and thus acts as an ion rectifier. This can be realized, for example, by producing the ion conductor and / or the channel from at least 3 multilayers whose potential profiles form a superlattice. The ion reservoir can also be ion conductors, which simplifies the manufacture of the three-element component. However, there is then a trade-off between the property as an ion reservoir, whose loading state with ions must be variable, and the property as an ion conductor, which should not change its stoichiometry and should retain a low electronic conductivity. Examples of materials that give charge neutrality cations and / or release anions into the channel while simultaneously keeping a comparatively low electronic conductivity, are LaMn0 _3, EuSc0 _3-x, _-x EuTi0 and LaNi0 ₃ - _x. The oxygen content of these materials can be changed by the variable valency of a cation. Many oxides, such as TiO _{2 + x} , can be generated by increasing or decreasing the oxygen content of electronic n-conductor (oxygen deficit, x <0) via insulator (stoichiometric composition, x = 0) to electronic p-conductor (oxygen excess , x> 0). In a particularly advantageous embodiment of the invention, therefore, the channel comprises a metal oxide whose electronic resistance is variable by the inclusion or removal of ions from the ion reservoir by at least one order of magnitude. This can be realized, for example, in that the metal oxide in its stoichiometric composition is an electronic insulator and becomes conductive in the event of deviation from this composition (or vice versa). Advantageously, this metal oxide has a perovskite structure. It can then be realized particularly well as an epitaxial layer system on an oxide single crystal as a substrate. As a substrate, for example, SrTi0 ₃ , LaAl0 ₃ , MgO or NdGa0 are suitable.

In order for ions to be exchanged between the channel and the ion reservoir at a rate sufficient for storage applications, both the channel and the ion reservoir should have sufficient conductivity for the ions of at least 2 * 10 ^-8 Sm ^-1 at a field strength of 1 GV. m have. The necessary conductivity for a specific application can be calculated with the known transport laws from the number of ions to be transported, the available field strength, the desired switching time and geometric factors. For example, for most applications with a Josephson junction, such as in a superconducting quantum interference interferometer (SQUID), significantly longer switching times than in a memory are sufficient, up to the order of 1 min. In a particularly advantageous embodiment of the invention, the ion reservoir and the channel comprise semiconductors with rectified dopants (p or n), and the ion conductor comprises a semiconductor with the opposite doping. Then, similar materials which are compatible with each other for the production of the channel, ion reservoir and ion conductor can be used. It can even be used the same material, so that the difference between the channel, ion reservoir and ion conductor is only in the different dopants. Stoichiometrically, this difference then exists only in quantities of the dopants used, the concentration of dopants in the case of oxides generally being only in the percent range. The pn junctions between channel and ion conductor as well as between ion conductor and ion reservoir can additionally provide electrical isolation of the channel.

In a further advantageous embodiment of the invention can be completely dispensed with an ion conductor. The ion reservoir and the channel in this embodiment comprise semiconductors with opposite dopings (p and n, respectively). Then the ion reservoir can act as part of the channel, with appropriate distribution of the ions. For example, if the ion reservoir is n-type and the channel is p-type, the conductivity of the ion reservoir and channel increases simultaneously as oxygen ions are transported from the n-type to the p-type region. If oxygen ions are transported in the opposite direction, the conductivity of the ion reservoir and the channel decreases accordingly. In a particularly advantageous embodiment of the invention, at least a portion of the channel to a transition temperature, below which it is superconducting. Then, the properties of this superconductor defined by material constants in the prior art can be changed by applying a potential to the gate electrode. In particular, the critical current and the normal conducting resistance, which occurs when the critical current is exceeded, can be changed. For example, resonant circuits in sources or detectors or oscillators for terahertz frequencies can be tuned. A thin film can even be switched back and forth between the superconducting and the normal conducting state. In the prior art, superconductors and Josephson junctions could be switched only locally by an electric field, a magnetic field, or by laser irradiation between the normal conducting state and the superconducting state. In contrast to the invention enabled switching enabled these effects were purely electronic nature and therefore volatile. According to the invention In contrast, nonvolatile reversible switches or components with adjustable properties of superconductors can be realized.

The superconducting portion may be realized as a single crystal. In particular, the entire channel between the source electrode and the drain electrode can be realized as a superconducting single crystal. However, the superconducting portion may also include a plurality of defects electrically connected in series, for example, not being parallel to the current path between the source electrode and the drain electrode. In particular, they can be transverse to this current path. Such defects may be, in particular, grain boundaries, stack errors and twin boundaries. The transport of ions from the ion conductor and the channel then preferably takes place at the defects, and the switching effect is multiplied by the series connection of the grain boundaries as weak-left. The non-parallel orientation of the defects to the current path prevents a short circuit between the source electrode and the drain electrode.

Even if the section is not superconducting, for example, if it is above its critical temperature T _c or generally not at all made of a superconducting material, the electrical resistance of the channel is largely determined by the loading of the grain boundaries with ions and can thus on the Loading be varied specifically.

Alternatively, the defects can also run parallel to the current direction in the channel. Although they can not serve as weak links, they can facilitate the ion exchange of the channel with the ion conductor or ion reservoir.

The switching of superconducting properties by ion transport is particularly useful in a further particularly advantageous embodiment of the invention. In this embodiment, two portions of the channel that are superconducting below a transition temperature are spaced by a barrier that is capable of exchanging ions with the ion reservoir. In particular, the barrier may be a weak-link such that the two portions of the channel together with the weak link form a Josephson junction. In particular, the weak link can exist in a grain boundary between the superconducting sections. Both the macroscopic conductivity of the barrier and the quantum mechanical barrier height for the Cooper pairs tunneling between the superconducting sections are then formed by introducing and removing ions into the weak link by applying the appropriate Potentials at the gate electrode adjustable. In particular, the critical current and the resistance in the normal conducting state as the basic parameters of each Josephson junction can be adjusted in this way. Such variable Josephson junctions can be used in quantum electronic devices, in particular in superconducting quantum interference (SQUIDs) or in high-frequency components for terahertz electronics, for example in sources (oscillators) or detectors for radiation in the frequency range between 0.1 and 10 THz , Radiation in this frequency range is needed, for example, for the chemical analysis of samples by Hilbert spectroscopy. Josephson contacts which can be tuned according to the invention can also be used in digital circuits based on Rapid Single Flux Quantum Technology (RSFQ) or in quantum computers.

The transition temperature is advantageously above 77 K. Then, cooling with liquid nitrogen is possible. Examples of high-temperature superconductors which can be used in the three-element component according to the invention are cuprates, in particular cuprates of the formula RBa ₂ Cu ₃ O ₇ . _x or alkaline earth doped cuprates of the formula R ₂ CuO _{4 + x} , where R is a rare earth metal or a combination of rare earth metals. In particular, R can be a rare earth metal from the group (Y, Nd, Ho, Dy, Tb, Gd, Eu, Sm). Bi-, Tl- and Hg-Cu oxides can also be used as high-temperature superconductors. Pnictides and iron-based oxypic tides may also be used if they reach a sufficiently high transition temperature. For iron pnictides, so far transition temperatures up to about 55 K have been achieved.

In a further advantageous embodiment of the invention, the channel comprises a material which can be transformed by a change in its oxygen content or fluorine content of a normal conductor in a superconductor and more preferably in a semiconductor. Such materials are, for example, iron or copper oxides which additionally contain one or more alkaline earth metals, such as La ₂ CuO _{4 + x} , (Sr, Ba, Ca) CuO ₂ - _x , La ₂ CuO ₄ F _x or (Sr, Ba, Ca) Cu0 ₂ F _x .

The properties of the channel, ion reservoir and / or ion conductors can be tailored by means of deliberately generated defects (grain boundaries, dislocations, stacking faults) and by targeted orientation of the crystal lattice. For example, a Josephson junction can be realized as a channel by arranging two sections of one and the same superconducting material with different crystal orientations adjacent to one another. The grain boundary between the two sections then forms the barrier. In addition, that can Crystal lattice be oriented so that the direction coincides with high ion mobility with the switching field direction.

Especially the high-temperature superconducting cuprates are particularly advantageous for the realization of a grain boundary Josephson junction. In these cuprates, the oxygen transport takes place preferably along grain boundaries as well as in the CuO chain planes between the layers. If the layers are now aligned parallel to the interface between channel and ion conductor, in particular parallel to the crystal orientation of the substrate, only a few ions can pass the interface between the superconducting sections of the channel and the ion conductor. The ion exchange between the channel and the ion reservoir via the ion conductor then essentially concentrates on the grain boundary between the superconducting sections of the channel, which also forms the weak link of the Josephson junction. But the properties of this weak-left but are to be changed by the ion exchange. The effect can be further enhanced if the grain boundary in the channel adjoins a grain boundary in the ion conductor. Advantageously, the ionic conductor facing away from the interface of the weak-left contacted with a second gate electrode. If this gate electrode is also subjected to a potential which preferably has a different polarity than the potential applied to the first gate electrode, the total voltage drop across the ion conductor and thus the transport of ions can be increased. The channel, ion reservoir and / or ion conductor materials may be in pure form or doped with suitable elements to optimally adjust properties such as electrical conductivity or ionic conductivity. They may be present in stoichiometric composition or may be increased or decreased relative to this composition in the content of one or more elements, such as oxygen. In particular, advantageously, the channel can be increased or decreased in the content of that element whose ions can be exchanged between the channel and the ion reservoir. In this way, an operating point of the three-element element can be preset. By applying a voltage to the gate electrode, the characteristics of the channel can then be varied around this operating point. 0 channel, ion reservoir and / or ion conductors can be realized as thin layers on a substrate. You can, for example, by sputtering (especially high-pressure oxygen Sputtering), vapor deposition, PLD or CVD.

In a particularly advantageous embodiment of the invention, the channel comprises a conductive boundary layer between two by at least an order of magnitude poorer conductive materials. This boundary layer can be, for example, a two-dimensional electron gas. However, it can also be formed, for example, by interdiffusion between adjacent materials that dope each other. These materials may in particular be semiconductors.

For example, a conductive boundary layer is formed between lanthanum-aluminum-oxide (LaA10 ₃ ) and strontium-titanium-oxide (SrTi0 ₃ ). Not only does it have a high degree of electronic mobility, it is also extremely thin at the same time. Thus, only a few ions must be added or removed to change the conductivity of such a channel very strong. This is possible in a very short time, so that the component with such a channel is a particularly fast switch.

On a maximum switching and thus write speed, it is particularly important if a memory is realized with the device, which is analogous to the conventional

DRAM is read destructively. Then it is necessary to re-write the information after each read. Here, the reversibility of storage in the device according to the invention over a very large number of write cycles is advantageous.

In order to facilitate the writing of information in the three-element element, this can be briefly heated by applying the channel with an increased current pulse or by a separate heating cable provided for this purpose. The ion conductor, whose temperature arrives during writing, can be heated in particular at the same time by resistively heating the channel and by the current pulse applied for writing to the gate electrode. The device can be produced for example by high-resolution lithography and chemical and / or physical etching. A suitable etchant for La ₂ Cu0 ₄ and YBa ₂ Cu 07. _x is, for example, ethanolic bromine solution. Generally, anhydrous etchants are beneficial because some of the mixed oxides hydrolyze and form hydroxides, affecting the surface. Advantageously, the device is produced under protective gas atmosphere. This avoids that the channel, the ion reservoir and / or the ion conductor can absorb moisture and / or C0 ₂ or other gases from the environment. After fabrication and before discharge, the device may be provided with a thin cover layer, such as strontium titanium oxide, to absorb moisture and other hazards

To prevent degradation of the surface. Already 1 nm strontium titanium oxide has been found to be effective in the experiments of the inventors.

The device can be heat treated after production in a defined atmosphere. As a result, for example, an interdiffusion of dopants into the respective material to be doped can be brought about in order to distribute the doping homogeneously in the material. However, it is also possible for the ion reservoir to be filled up, for example with oxygen ions. If this is not possible with molecular oxygen alone, the loading can be assisted by a microwave plasma, by atomic oxygen or by ozone.

In general, it is not absolutely necessary for the functioning of the component that the interfaces between ion reservoir, ion conductor and channel are absolutely sharp. Rather, all components can also be realized as multilayers or gradient layers.

The materials for ion reservoir, ionic conductor and channel are usually not elements, but compounds. If these compounds are grown epitaxially on a substrate, the respective surface has an excess of the element with which the epitaxy was terminated. This element can serve as a dopant for the next component to be applied.

The affinity of layered ion transport materials can be selectively manipulated during device fabrication by mechanically straining the substrate during deposition of the layers. This allows, for example, channels along which ions are transported to be widened, which promotes ion transport.

Special description part

The subject matter of the invention will be explained in more detail below with reference to figures, without the subject matter of the invention being restricted thereby. It is shown: Figure 1: cross-section of an exemplary embodiment of the inventive Dreitorbauelements.

FIG. 2 shows a change in the resistance between the source electrode and the drain electrode of a component according to the invention after successive application of increasing and alternating polarity in the gate voltages, the respective same charge of 10 mC being transported.

FIG. 3: Change in the resistance between source electrode and drain electrode of a component according to the invention after successive application of currents of the same magnitude alternating in polarity for an increasing duration.

FIG. 4: Calculation of the field-dependent ion current I for two hypothetical materials o with an activation energy ΔΗ of 0.4 eV or 1.3 eV for the jump from one occupied lattice site to the next unoccupied lattice site, shown for three different temperatures.

FIG. 5 shows a further exemplary embodiment of the three-element component according to the invention with a channel which has an anisotropic ion conductivity.

FIG. 6 shows another exemplary embodiment of the three-element component according to the invention with one

Channel formed as a Josephson junction.

Figure 1 shows a sketch of an embodiment of the invention Dreitorbauelements in cross section. On an insulating substrate 1, the channel 2 connecting two electrodes 3 (source electrode and drain electrode) is realized as a thin layer. On the channel 2, an ion conductor 4 and an ion reservoir 5 are also structured as thin layers. The ion reservoir is contacted with a gate electrode 6. If a potential is applied to this gate electrode via the feed line 7.3, the ion reservoir 5 can exchange ions with the channel 2 through the ion conductor 4, while it remains isolated electronically from the channel. As a result, the electronic conductivity of the channel 2 changes. In this way, information can be stored in the three-element component. The information can be read out again by the electrodes 2 connected to the channel 2 being supplied with a read-out voltage via the leads 7.1 and 7.2 and the current driven by the channel 2 being measured. The layer sequence may also be inverted with respect to the substrate, so that the gate electrode is first deposited on the substrate and thus the channel is on top.

The devices used in the following tests were fabricated with shadow masks, which localized the layers on the substrate. The channel of La ₂ Cu0 ₄ was 2 mm wide, 5 nm thick and bridged a distance of 1 mm between the source electrode and the drain electrode. The ionic conductor of SrTi0 ₃ was about 10 nm thick. The source electrode, drain electrode and gate electrode were made of highly conductive Lai 85Sro _> i5Cu04. The gate electrode also provided the oxygen ion reservoir at the same time. The device was realized on a rhombohedral LaAlO ₃ (100) substrate.

In FIG. 2, the resistance between the source electrode and the drain electrode after successive application of the gate electrode with magnitude-higher voltages over the test time is plotted for this component. In each case, the sign of the voltage applied to the gate electrode changed between two applications, so that the resistance between the source electrode and the drain electrode alternately increases and decreases. The voltages were chosen so that the product of the current driven by the ion conductor and the pulse duration always gives the same transported charge of 10 mC. Current and pulse duration are noted at each measuring point. The resistance change becomes noticeably larger with higher applied voltage, although the same charge is transported. This is evidence that the transport of the ions is a nonlinear effect and that the ions distribute better in the ion conductor and in the channel at higher voltages.

Despite the large transported charge density of 5000 C / m ² , the resistance between source and drain changes by only about 2%. Thus, the total achievable partial ionic conductivity is very low. The inventors attribute this to the fact that the component is a macroscopic "proof of concept" whose production still offers considerable potential for improvement, for example by scaling down the component laterally to the micrometer or even nanometer dimension Saturation of the effect at this small switching amplitude may result in point switching, for example, defects, and the channel also seems to have been doped by interdiffusion during fabrication, causing its resistance to be unexpectedly low and less variable by oxygen deposition.

In FIG. 3, the component investigated in FIG. 2 was switched again with alternating polarities. The arrows drawn in FIG. 2, which illustrate the sequence of the measuring points. Chen, are omitted in Figure 3 for reasons of clarity. The same current always flowed through the ion conductor, but for different times between 1 ms and 66 s, so that in longer switching times a larger charge was transported. The device switches 1% of the total resistance in 1 ms and in 66 s it switches by slightly more than 4%.

In FIG. 4, the field-dependent ion current I calculated in accordance with the equation I = Io * exp (- [AH-0.5 * q * d * E] / [k * T]) for two hypothetical materials with an activation energy ΔΗ of 0.4 eV (very low value for oxygen ion conductor) and 1.3 eV (comparatively high value for oxygen ion conductor) for the jump from one occupied lattice site to the next lattent lattice site. The calculation was carried out for three different temperatures (liquid nitrogen, room temperature, SOFC operating temperature). From about 100 MV / m, the transport is disproportionately accelerated. This roughly corresponds to the field strengths at which the material shorts electronically.

It can be seen that a material with low activation energy is more favorable because of the

15 Transport is already accelerated at lower field strength. The maximum achievable in the material field strength is limited by its electronic conductivity. The higher this conductivity is, the greater the current needed to maintain a given potential difference and thus field strength across the material. This current increases disproportionately with the field strength. The limit for the achievable field strength is reached when 20 electronically short-circuits the material.

FIG. 5 shows a sketch of a further exemplary embodiment of the three-element component according to the invention in a perspective drawing. In this exemplary embodiment, the channel 2 and the ion conductor 4, which also functions as ion reservoir 5, are realized in the form of epitaxial layers on a monocrystalline substrate 1. The limits of the unit cells of

25 substrate 1 and channel 2 are indicated by the hatching for clarity of the respective crystal orientations. The crystal structure of the channel material, such as

YBa ₂ Cu ₃ 07 _-x or La ₂ Cu0 _{4 + x} , is layered with high oxygen mobility in preferred, here tinted drawn crystal planes E. This leads to a strongly anisotropic ion conductivity. The channel conducts along the preferred crystal planes E by a factor of 1000

3 o better than perpendicular to these planes. Accordingly, ions between the ion conductor / reservoir and the channel 2 can preferably be exchanged along these planes E. The orientation of the planes E relative to the substrate surface is determined by the on the crystal orientation of the substrate surface in conjunction with the growth parameters. Advantageously, the preferred planes E are oriented such that the electric field resulting from the application of a potential to the gate electrode 6 in the ion conductor / reservoir can be decomposed into a linear combination in which a component is parallel to the preferred planes E. This should also apply to the preferred planes E of the ion reservoir 4 or ion conductor 5, provided that the ion reservoir 4 and / or the ion conductor 5 also have anisotropic ion conductivities.

If the channel material is YBa ₂ Cu ₃ 0 _7-x , the preferred levels E are the CuO chain planes. If the channel material is La ₂ Cu0 _{4+) t} , the preferred planes E are planes of interstices between the LaO planes.

In order to achieve low channel 2 electronic resistance between the source and drain electrodes (not shown), it is advantageous to attach the electrodes in the illustrated figure to the leading and trailing edges of the channel. The source-drain current then flows vertically through the plane of the drawing. Thus, the high electronic conductivity planes of the example materials, which are parallel to the E high-mobility planes, are uninterrupted in the current path.

Figure 6 is a sketch of another exemplary embodiment of the invention Dreitorbauelements in perspective drawing. In this embodiment, the channel 2 is formed as a Josephson junction and realized in the form of epitaxial layers on a bicrystal substrate 1. A targeted grain boundary K forms the weak link in the superconducting channel 2. The channel is contacted by two electrodes 3 (source electrode and drain electrode). The weak-link can exchange oxygen ions with the ion reservoir 4 or ion conductor 5 if a potential is applied to the gate electrode 6. As a result, its electronic properties can be changed when installed. The boundaries of the unit cells of substrate 1 and channel 2 are indicated by the hatching as in FIG.

Claims

Patent claims

A three-terminal device having a source electrode, a drain electrode and a channel connected between the source electrode and the drain electrode made of a material whose electronic conductivity is variable by the supply and / or removal of ions,

characterized in that

it comprises an ion reservoir contacted with a gate electrode which is in communication with the channel in such a way that it can exchange ions with the channel when the gate electrode has a potential.

2. Three door construction element according to the preceding claim, characterized in that the ion reservoir is a solid under standard conditions.

3. Dreitorbauelement according to the preceding claim, characterized in that the ion reservoir has at least one cation or anion with variable valence.

4. Dreitorbauelement according to any one of the preceding claims, characterized in that the ion reservoir via an ion conductor, the electronically by at least an order of magnitude worse than the channel, is connected to the channel.

5. Dreitorbauelement according to the preceding claim, characterized in that the activation energy for the ion transport through the ion conductor depends on the direction of transport.

6. three-terminal device according to one of the preceding 2 claims, characterized in that the ion conductor has a thickness of 100 nanometers or less.

7. three-terminal device according to one of the preceding 3 claims, characterized in that the ion reservoir is also ion conductor.

8. Dreitorbaulement according to one of the preceding claims, characterized in that the ion conductor, the ion reservoir and / or the channel in each case comprises a solid electrolyte.

9. Dreitorbauelement according to the preceding claim, characterized in that the solid electrolyte is a material in which the activation energy for the diffusion of oxygen ions at temperatures above 400 ° C less than 1 eV, preferably less than 0.1 eV, is.

10. three-terminal device according to one of the preceding claims, characterized in that the ion conductor and / or the solid electrolyte has an anisotropic mobility for ions.

1 1. three-terminal device according to one of the preceding claims, characterized in that the channel comprises a metal oxide whose electronic resistance is variable by incorporation or removal of ions from the ion reservoir by at least one order of magnitude.

12. The three-terminal device according to one of the preceding claims, characterized in that the ion reservoir and the channel comprise semiconductors with rectified dopants (p or n) and the ion conductor comprises a semiconductor with the opposite doping.

13. Three-element component according to one of the preceding claims, characterized in that the ion reservoir and the channel comprise semiconductors with opposite dopants (p or n).

14. three-element according to any one of the preceding claims, characterized in that bridged by the channel distance between the source electrode and the drain electrode between 20 nra and 10 μηι amounts.

15. Three door construction element according to one of the preceding claims, characterized in that the channel is formed as a thin layer with a thickness between 3 and 50 nm.

16. Three-element component according to one of the preceding claims, characterized in that the ion reservoir is capable of exchanging oxygen ions with the channel.

17, three-element device according to one of the preceding claims, characterized in that the channel, the ion reservoir and / or the ion conductor each having either a crystal structure that does not change when exchanging ions between the ion reservoir and the channel, or is amorphous.

18. A three-element component according to one of the preceding claims, characterized in that the material of the channel is increased or decreased in relation to its stoichiometric composition in the content of an element whose ions can be exchanged between the channel and the ion reservoir.

19, three-element device according to one of the preceding claims, characterized in that the channel comprises a conductive boundary layer between two by at least an order of magnitude poorer conductive materials.

20. The three-element component according to one of the preceding claims, characterized in that at least a portion of the channel has a transition temperature, below which it is superconducting.

21, three-element component according to the preceding claim, characterized in that in the section a plurality of defects is electrically connected in series.

22. The three-element component according to one of the preceding 2 claims, characterized in that two portions of the channel, which are superconducting below a transition temperature, are spaced by a barrier, which is capable of exchanging ions with the ion reservoir.

23. Three-element component according to the preceding claim, characterized in that the channel is designed as a Josephson contact whose weak-link is the barrier.

24. The three-terminal device according to one of the preceding 2 claims, characterized in that the sections consist of the same superconducting material, but have different crystal orientations, so that the grain boundary between the sections forms the barrier.

25. The three-element component according to one of the preceding 3 claims, characterized in that the sections have the same crystal orientation as the substrate on which they are arranged.

26. Dreitorbauelement according to any one of the preceding 6 claims, characterized in that the transition temperature is above 77 K.

27, three-element device according to one of the preceding claims 7, characterized in that the channel comprises a cuprate, in particular a cuprate of the formula RBa ₂ Cu ₃ 0 _7-x or an alkaline earth-doped cuprate of the formula R ₂ Cu0 _{4 + x} , wherein R is a rare earth metal or a combination of rare earth metals.

28. The three-element component according to one of the preceding 8 claims, characterized in that the channel comprises a material from the class of iron pnictides or iron Oxopniktide.

29. The three-element component according to one of the preceding 9 claims, characterized in that the channel comprises a material which can be transformed by a change in its oxygen content or fluorine content of a normal conductor in a superconductor.

30. Quantum electronic component, in particular superconducting quantum interferometer or source or detector for electromagnetic radiation in the frequency range between 0.1 and 10 THz, comprising at least one Dreitorbauelement according to one of the preceding 10 claims.