Electrochemical device of variable electrical conductance

An electrochemical device includes an electrochemical cell and an electric circuit. The electrochemical cell comprises a first solid component and a second solid component. The two solid components comprise same chemical elements but have different concentrations of at least one type of the chemical elements. A solid electrolyte is arranged between the two solid components. The solid electrolyte is a dielectric material. The electric circuit is connected to the electrochemical cell. The electrochemical cell may be operated according to a redox process, so as to exchange chemical elements of the at least one type between the first solid component and the second solid component and thereby change an electrical conductance of each of the two solid components.

FIELD

The invention relates in general to the field of electrochemical devices with solid electrolytes. In particular, it is directed to electrochemical devices comprising an electrical circuit to change an electrical conductance of a solid component of the devices. An electrochemical device according to various embodiments can advantageously be used as a synaptic element in a neuromorphic hardware apparatus, for example. The invention also relates to methods to operate electrochemical devices.

BACKGROUND

Machine learning often relies on artificial neural networks (ANNs), which are computational models inspired by biological neural networks in human or animal brains. An ANN comprises a set of connected units or nodes, called artificial neurons. Signals are transmitted along connections (also called edges) between artificial neurons, similarly to synapses. That is, an artificial neuron that receives a signal processes it and then signals connected neurons. Connection weights (also called synaptic weights) are associated with the connections and nodes. Each neuron may have several inputs and a connection weight is attributed to each input (the weight of that specific connection). Such weights adjust as learning proceeds.

Neural networks are typically implemented in software. However, a neural network may also be implemented in hardware, e.g., as a resistive processing unit (relying on crossbar array structures) or an optical neuromorphic system. That is, a hardware-implemented ANN is a physical machine that clearly differs from a classic computer (general- or specific-purpose computer) in that it is primarily and specifically designed to implement an ANN (for training and/or inference purposes). Synaptic elements used in neuromorphic hardware apparatuses typically comprise a memristive device, e.g., a phase-change memory device, a resistive random-access memory (RRAM), or a magnetic random-access memory (SRAM).

Aside from neuromorphic hardware apparatuses, various electrochemical devices are known. Electrochemical cells are devices configured to generate electrical energy from chemical reactions or, conversely, to leverage electrical energy to cause some chemical reactions. Solid state electrochemical capacitors have been proposed, as well as computer memory element based on such capacitors, in particular electrochemical random-access memory (ECRAM) devices see, e.g., Sharbati, Mohammad Taghi, et al., “Artificial Synapses: Low-Power, Electrochemically Tunable Graphene Synapses for Neuromorphic Computing (Adv. Mater. 36/2018).”, Advanced Materials 30.36 (2018): 1870273, and J. Tang. et al., “ECRAM as Scalable Synaptic Cell for High-Speed, Low-Power Neuromorphic Computing”, IEDM, p. 13.1.1, 2018.

SUMMARY

In various embodiments, an electrochemical device includes an electrochemical cell. The electrochemical cell may include a first solid component and a second solid component. In addition, the electrochemical cell may include a first solid electrolyte and an electric circuit. The a first solid component may be comprised of one or more particular chemical elements, wherein a first chemical element of the one or more particular chemical elements is present in a first concentration in the first solid component. The second solid component may be comprised of the same one or more particular chemical elements, however, the first chemical element of the one or more particular chemical elements is present in a second concentration in the second solid component, and the first and second concentrations are different. The first solid electrolyte may disposed or arranged between the first and second solid components. The first solid electrolyte is a dielectric material. The electric circuit is coupled with the electrochemical cell and configured to operate the electrochemical cell, according to a redox process, in which the first chemical element is exchanged between the first solid component and the second solid component. The exchange changes an electrical conductance of each of the first and second solid components.

According to a first aspect, the present invention is embodied as an electrochemical device. The device includes an electrochemical cell and an electric circuit. The electrochemical cell comprises two solid components, i.e., a first solid component and a second solid component. The two solid components comprise same chemical elements but have different concentrations of at least one type of said chemical elements. Each of the first solid component and the second solid component may for example be formed as a layer of material. A solid electrolyte is arranged between the two solid components. The solid electrolyte is a dielectric material. The electric circuit is connected to the electrochemical cell. It is generally configured to operate the cell according to a redox process, so as to exchange chemical elements of said at least one type between the first solid component and the second solid component and thereby change an electrical conductance of each of the two solid components, in operation.

Thus, the solid components have a symmetric composition; they play the role of a cathode and an anode. As they differ in terms of concentrations of one or more of the chemical elements they have in common, one of said solid components can be converted to the other one by a redox process, one of the solid components being a reduced form of the other. The operation of the device is very simple and can be exploited so as to read out a conductance (or resistance, or changes to such a conductance or resistance) in the second solid component. The use of solid components makes the above device well amenable to integration in hardware. In particular, such a device can be used as a synaptic element in neuromorphic circuitry, so as to process cognitive workloads. The electrochemical principle exploited makes the device a non-volatile device, which can advantageously be used to store and modify weights of a synaptic element of neuromorphic hardware.

In embodiments, said two solid components comprise, each, a compound of at least two chemical elements, and have different concentrations of one of said at least two chemical elements.

Preferably, each of the two solid components comprises WO3, though one of the component is the reduced form of the other, in operation of the device.

In preferred embodiments, the solid electrolyte comprises a high-κ dielectric material. The solid electrolyte may for example comprise HfO2, through which intercalation ions are exchanged between said two solid components, in operation.

In embodiments, the electric circuit includes two circuits, i.e., a first circuit and a second circuit. The first circuit connects the first solid component to the second solid component, in order to operate the cell according to said redox process, in operation. The second circuit is closed by the second solid component. The second circuit is configured to sense an electrical signal impacted by the change of electrical conductance occurring in the second solid component, in operation of the device.

Preferably, the electrochemical cell further comprises three electrical contacts, the latter consisting of a source contact, a drain contact, and a gate contact. Each of the source contact and the drain contact is in electrical communication with the second solid component, whereas the gate contact is in electrical communication with the first solid component. The first circuit connects to each of the source contact and the gate contact. The second circuit connects to the source contact and the drain contact. For example, the electrochemical cell may be configured as a three-terminal device having three electrical contacts consisting of said source contact, said drain contact, and said gate contact.

Preferably, the device further comprises a substrate, the second solid component extends on top of the substrate, the source contact and the drain contact are, each, in electrical communication with the second solid component, the solid electrolyte extends on top of the second solid component, in contact therewith, the first solid component extends on top of the solid electrolyte, in contact therewith, and the gate contact is arranged on top of the first solid component, in contact therewith.

In embodiments, each of the source contact and the drain contact is arranged on top of the second solid component, in contact therewith, and the solid electrolyte extends between the source contact and the drain contact.

In some embodiments, the substrate comprises a doped substrate. In variants, an insulating (or semiconducting) substrate is used. In preferred embodiments, the electric circuit further includes a third circuit, the latter connecting the doped substrate to a ground.

Preferably, the cell further comprises a third solid component extending between the doped substrate and the second solid component. The third solid component comprises the same chemical elements as the first solid component and the second solid component but has a different concentration of said at least one type of said chemical elements compared to the second solid component. Said solid electrolyte is a first solid electrolyte and a second solid electrolyte extends between the third solid component and the second solid component, so as to be in contact with the third solid component and the second solid component.

In embodiments, the electric circuit further includes a third circuit, the latter connected to the first circuit, so as to connect the doped substrate to the first circuit.

The second solid component may possibly be structured as a fin. In that case, the source contact and the drain contact extend, each, on top of the substrate, so as to laterally contact the fin on each end thereof. In addition, the gate contact, the solid electrolyte, and the first solid component, are at least partly wrapped around the fin, e.g., so as to form a wrapping structure.

In preferred embodiments, the device comprises several wrapping structures arranged along the fin, separated from each other. Each of the wrapping structures is structured similarly as the above wrapping structure, so as to be at least partly wrapped, each, around the fin.

According to another aspect, the invention is embodied as an apparatus comprising a plurality of electrochemical devices such as described above. This apparatus further comprises a controller connected to the electric circuits of the devices, so as to operate the devices according to a redox process. Furthermore, a readout circuit is connected to the electric circuits of the devices. The readout circuit is configured to sense an electrical signal impacted by an electrical conductance of the second solid component of one or more of the electrochemical devices, in operation. The apparatus is preferably configured as an artificial neural network hardware, where each of the devices is configured as a synaptic element of the artificial neural network hardware.

According to a final aspect, the invention is embodied as a method of operating an electrochemical device. The method relies on a device such as described above, i.e., comprising an electrochemical cell, the cell including two solid components, namely a first solid component and a second solid component. The two solid components comprise same chemical elements but have different concentrations of at least one type of said chemical elements. The device further comprises a solid electrolyte arranged between the two solid components, where the solid electrolyte is a dielectric material. Finally, the device also includes an electric circuit connected to the electrochemical cell. According to the method, the electrical circuit is used to operate the electrochemical cell according to a redox process, so as to exchange chemical elements of said at least one type between the first solid component and the second solid component and thereby change electrical conductances of each of the two solid components, and sense an electrical signal impacted by the electrical conductance of the second solid component.

Devices, apparatuses, and methods embodying the present invention will now be described, by way of non-limiting examples, and in reference to the accompanying drawings.

The accompanying drawings show simplified representations of devices or parts thereof, as involved in embodiments. Technical features depicted in the drawings are not necessarily to scale. Similar or functionally similar elements in the figures have been allocated the same numeral references, unless otherwise indicated.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

It has been suggested to use electrochemical devices in place of usual memristive devices for synaptic elements of neuromorphic hardware. Such devices generally have low power budget. However, various difficulties stem from their scalability, the lack of CMOS-compatibility and the allowed control on the reservoir stoichiometry (the reservoir is a component that can provide or store active ions enabling the ECRAM functionality, as a consequence of chemical reactions activated by electrical stimuli). In addition, these devices often rely on liquid electrolytes or organic solid electrolytes, which make them unsuitable for integration in neuromorphic hardware.

Willing to develop suitable electrochemical devices for integration in neuromorphic hardware, the present inventors came to develop various devices, which can satisfactorily be used in neuromorphic hardware. Such solutions are described in detail in the following description.

In reference toFIGS. 1-4, an aspect of the invention is first described, which concerns an electrochemical devices1-4. The electrochemical devices1-4respectively comprise an electrochemical cell30,31,32,33. The electrochemical devices1-3and the apparatus100shown inFIG. 5include an electric circuit110-150, which typically includes several circuit portions, having distinct functions.

The electrochemical cells30,31,32,33include two solid components11,12, i.e., a first solid component11and a second solid component12. The two solid components11,12may comprise the same chemical elements, though one or more of the chemical elements may be present in different concentrations in the solid components11,12. For example, a particular chemical element is present in a first concentration in solid component11and the same particular chemical element is present in a second concentration in solid component12, wherein the first and second concentrations are different. Thus, the components11,12have different concentrations of at least one type of the chemical elements they have in common. In operation, this may result in a low open circuit voltage. For example, the components11,12may include binary compounds differing in terms of concentration of one element.

The electrochemical cells30,31,32,33may also include a solid electrolyte14arranged between the two solid components11,12. The solid electrolyte is a dielectric material. The solid electrolyte14may for example comprise a high-κ dielectric material, e.g., HfO2(Hafnium(IV) oxide), wherein oxygen ions are used as intercalation ions, i.e., ions moving between the components11and12. (Kappa in “high-κ” refers to the dielectric constant.) Such ions pass through the electrolyte14, which plays the role of an ionic conductor, but does not conduct electron current. Using oxygen as intercalation ion makes it possible to circumvent some of the problems posed by the use of Li-based devices, as mostly found in the literature (safety flaws, energy density, etc.).

The electric circuits110-140are connected to the electrochemical cells30,31,32. The electric circuit150is connected to the electrochemical cells of apparatus100. The circuits are generally configured to operate the cells according to a redox process. The redox process can be chemical (e.g., in hydrogen atmosphere), or electrochemical (e.g., by applying a negative/positive bias voltage). This causes an exchange chemical elements of said at least one type between the first solid component11and the second solid component12, in operation of the device. This exchange, in turn, causes a change in the electrical conductance of each of the two solid components11,12.

Thus, the solid components11,12play the role of a cathode and an anode. As they differ in terms of concentrations of one or more of the chemical elements they have in common, one of the solid components can be converted to the other one by a redox process, in operation of the devices1-4. That is, one of the solid components is a reduced form of the other, in operation. This can be exploited so as to read out a conductance (or resistance, or changes to such a conductance or resistance) in the second solid component, as in embodiments discussed later.

The devices1-4may be fabricated as a multilayer device, see, e.g.,FIGS. 1-4. The solid electrolyte14and the solid components11,12of the electrochemical cells30,31,32,33may, for instance, be formed as material layers, possibly structured. The use of solid components makes the device amenable to integration in hardware. In particular, such a device can be used as a synaptic element in neuromorphic circuitry, so as to process cognitive workloads. The electrochemical principle exploited makes the device a non-volatile device, which can advantageously be used to store and modify weights of a synaptic element of neuromorphic hardware.

All this is now described in detail, in reference to particular embodiments of the invention. To start with, the two solid components11,12shall preferably comprise, each, a compound of at least two chemical elements, and have different concentrations of one of the at least two chemical elements. For example, the solid components11,12may comprise exactly two elements. E.g., they may comprise WO3(tungsten trioxide). The use of symmetric, WO3-based solid components makes the device CMOS-compatible and a device can be integrated in the back end of the line (BEOL) of a CMOS process. Incidentally, using WO3-based solid components is particularly advantageous when using a high-κ dielectric material such as HfO2, as HfO2is a good ion conductor (but not electron conductor), allowing oxygen ions to be suitably (de-)intercalated between the two solid components of WO3.

In various embodiments, other materials can be contemplated for the solid components11,12and the solid electrolyte14. For example, the solid components11,12may comprise, each, strontium titanate oxide (SrTiO3, or STO for short). In variants, they may for example include Perovskites (SrFeOx, SrCoOx, CaCrOx), solid solutions: BaInOx—BaZrOx, SrTiOx—SrCoOx, other oxides (La2NiO4, La2CuO4), or non-oxygen-based compounds (such as LixCoO2and NaxCoO4). Moreover, the solid electrolyte14may, for instance, comprise Ta2O5, or yttrium-doped zirconium oxide (Y:ZrO2, or YZO), or CeO2, or a non-oxide oxygen electrolyte (LaF3), or any other electrolyte suited for the (de-)intercalated species.

In embodiments such as depicted inFIGS. 1-3, the electric circuit of the devices1-3decomposes into two distinct (though connected) electrical circuits (or circuit portions), i.e., a first circuit110and a second circuit120. The first circuit110connects the first solid component11to the second solid component12via a contact21. The circuit110is generally designed to allow the cell30,31,32to be operated according to a redox process, as recited above. The first circuit110typically comprises a voltage or current source, to drive the redox process, as assumed in the accompanying drawings. A current source is preferred as it makes it easier to gauge ionic charges moving during the redox process.

The second circuit120is provided to sense some electrical signal impacted by the change of electrical conductance that notably occurs in the second solid component12, in operation of the devices1-4. Note, the second circuit120is closed by the second solid component12(also referred to as a “channel” in this document) and is thus impacted by electrical properties of the the second solid component12. The second circuit120may for example be designed to sense a current and thereby read, e.g., a resistance or a conductance, of the second solid component12. The change of conductance of the channel12is due to ions that reached or left the channel12due to the redox process; it can be regarded as a non-volatile change of the channel's conductivity.

As shown inFIGS. 1-4, the electrochemical cells30,31,32,33preferably comprise three electrical contacts, i.e., a source contact21, a drain contact23, and a gate contact22. The source contact21and the drain contact23are, each, in electrical communication with the second solid component12, whereas the gate contact22is in electrical communication with the first solid component11. As seen, the first circuit110connects to each of the source contact21and the gate contact22, while the second circuit120connects to the source contact21and the drain contact23.

As such, the devices1-4can be regarded as a FET-like device (i.e., a device resembling a field-effect transistor), inasmuch as the flow of current can be controlled by the application of a voltage to the gate which may be supplied by the first circuit110, which in turn alters the conductivity between the drain and the source, as measured by the second circuit120. In particular, the electrochemical cells30,31,32,33can be configured as a three-terminal device1-4, i.e., a device having three electrical contacts consisting of the source contact21, the drain contact23, and the gate contact22.

In the example ofFIG. 1, the device includes only three electrical contacts21-23and the substrate10is electrically insulating. The substrate must indeed be insulating in this case, in order to prevent reading current passing through the substrate when reading the channel12. Note, however, that the substrate10may include or be an undoped semiconductor material like silicon.

As seen inFIGS. 1-4, the device1-4may essentially have a layer structure. For example, each of the first solid component11and the second solid component12may be formed as a layer of material. Similarly, the solid electrolyte14may be formed as a layer of material too, though the solid electrolyte14is preferably structured (e.g., to exhibit a raised rim, as shown in the figures), so as to avoid shorts between the source contact21or drain contact23and the first solid component11.

The devices1-3are preferably structured as follows. The second solid component12extends on top of a substrate10. The source contact21and the drain contact23are, each, in electrical communication with the second solid component12. In addition, the solid electrolyte14extend on top of the second solid component12, so as to contact the latter. Next, the first solid component11extends on top of the solid electrolyte14, in contact therewith. And finally, the gate contact22is arranged on top of the first solid component11, in contact with this component11. Note, “on top” means “above, and either in contact with or at a distance of.” That is, intermediate layers of additional materials may possibly be needed, provided they do not significantly alter the desired electrical paths. “Above” is in the z direction.

In the example structures shown inFIGS. 1-3, each of the source contact21and the drain contact23is arranged on top of the second solid component12, in contact therewith. In addition, the solid electrolyte14extends between the source contact21and the drain contact23. Note, the source21and drain contact23may possibly be in direct contact with the solid electrolyte14, laterally, for the sake of compactness or footprint, as assumed inFIGS. 1-3. This, however, has no consequence since the solid electrolyte is a dielectric material.

In the examples ofFIGS. 2 and 3, the substrate10acomprises a doped material, contrary toFIG. 1, because of the additional contact to the substrate. Practically, the substrate10can for instance include a doped region, implanted so as to be isolated from the ground, similar to implanted n-wells in p-type silicon of usual MOSFET circuits.

In the example ofFIG. 2, the overall electric circuit further includes a third circuit portion130that connects the doped substrate10ato the ground. Note, the device2can still be regarded as a FET-like device, despite the additional contact. The third circuit130and the additional contact on the doped substrate are meant to dynamically control the FET. This circuit130allows, together with the top contact22, ions to intercalate to layer12or, conversely, to de-intercalated from this layer12. The circuit130acts as a volatile field effect. Thus, two effects are obtained in the same device2in that case. The first effect is a non-volatile effect, obtained from the electrochemical operation via the circuit110, while the second effect obtained via the circuit130is volatile. In other words, the circuit130allows an electrical potential to be applied to the substrate10awith respect to the ground, making the substrate act as a gate.

In addition, inFIGS. 2 and 3, another dielectric layer16extends on top of the doped substrate10a, i.e., between the second solid component12and the substrate10a. This layer16can for instance comprise HfO2, just like the solid electrolyte14, or any other dielectric material, such as Ta2O5, or YZO.

In the example ofFIG. 3, the cell32further comprises a third solid component13, which extends between the doped substrate10aand the second solid component12. The third solid component13comprises the same chemical elements as the first solid component11and the second solid component12. However, the third solid component13will have a different concentration of one or more of the chemical elements that layers11-13have in common, at least when compared to the second solid component12. As before, the difference of concentration may concern only one element. Still, the initial concentrations of this element could for instance be the same in the first and third solid component13, to achieve a symmetric ion exchange layer structure.

The cell32also includes a second solid electrolyte16in this example. That is, two solid electrolytes are provided in that case. The solid electrolyte16extends between the third solid component13and the second solid component12. The second electrolyte16is in contact with each of the lower layer (the third solid component13) and the upper layer (the second solid component12).

Preferably, the electric circuit of the device3also includes a third circuit140. However, contrary to the circuit130ofFIG. 2, here the circuit140connects to the first circuit110, so as to connect the doped substrate10ato the first circuit110. Again, the third circuit140may include a voltage source or a current source, as assumed inFIG. 3. The device3can be regarded as a four-terminal, dual gate-like device (with a symmetric ion exchanging layer structure).

The circuit140is meant to operate the device using two gates, i.e., the top gate (based on circuit110, as inFIG. 1) and the substrate (based on circuit140). This feature offers more flexibility in, e.g., operating artificial synapses comprising the device3. Namely, the third circuit140may provide another source of pulses (e.g., current or voltage pulses) like the circuit110. The total synapse response can, for example, stem from a double redox process occurring in the channel12, due to the first gate, the second gate, or a combination of effects arising from both gates. In other words, a structure such as shown inFIG. 3provides another way to increase the active section of the channel material, which changes the conductance of the channel12, similarly as in FinFETs where multiple interfaces between the gate and the channel can be exploited for deintercalation purposes. The circuit140, however, is optional.

The embodiment shown inFIG. 4involves an alternative structure, in which the second solid component12is structured as a fin. In addition, the source contact21and the drain contact23extend, each, on top of the substrate10, so as to laterally contact the fin12on each end thereof. Moreover, the solid electrolyte14, the first solid component11, and the gate contact22, are at least partly wrapped around the fin12, as successive layers14,11,22(in this order). The wrapping structure formed by the gate contact22, the solid electrolyte14, and the first solid component11may thus possibly contact the fin12on two or more sides thereof (e.g., on three sides, assuming a rectangular cross-section for the fin, as in the example ofFIG. 4). Such a structure can be regarded as a FinFET-like device4with multiple ion exchanging layers, which again allows more flexibility in the operation of the device (compared to the example ofFIG. 1), in a compact and easy-to-fabricate way.

The substrate is also insulating in this example, at least if only two components11,12are used, which are separated by the electrolyte14. The need of doped substrate comes into play when additional circuits are present, in order to obtain multi-gates (from the top and bottom or when use is made of the FET function).

Note, however, that the device4may optionally comprise several wrapping structures (not shown for the clarity of depiction), each being similar to the wrapping structure shown inFIG. 4described above, that is, the succession of layers14,11, and22, wrapping around the fin and shaped complementarily therewith. That is, each of the resulting wrapping structures is structured similarly as the single wrapping structure shown inFIG. 4, so as to be at least partly wrapped around the fin12. The multiple wrapping structures are arranged along the fin12, though separated from each other, laterally.

A structure comprising multiple wrapping structures as described above makes it possible to obtain several gates, which are separated from each other. Using several gates allows a higher density to be achieved as it enables a parallel operation of a single fin12. In particular, this may be used to increase the tunability of synaptic weights, when the device4is used in a neuromorphic apparatus. The weight is, in that case, captured by a value of resistance or conductance of the channel12. The artificial synapse carries a weight for incoming stimuli arriving from the connected nodes and therefore changes the way the signal is further processed/propagated along the nodes. The weight value impacts currents read in output, as explained later in reference to a second aspect of the invention.

Many of the features described in reference toFIGS. 1-4may be combined. For example, embodiments can be directed to an electrochemical device, wherein the top layer and bottom layer (i.e., the solid components11,12forming the anode and cathode) are composed of the same chemical elements (e.g., “A” and “X” for a binary compound), but one of the elements (say “X”) differs in terms of concentration, resulting in low open circuit voltage. This distinguishes the electrochemical device from solid-state batteries and solid oxide fuel cells, inasmuch as this feature results in low cell voltages, which is undesirable for batteries but desirable for devices such as synaptic devices. As explained earlier, one compound (solid component11) can be converted into the other compound (solid component12) by virtue of the redox process. A first electrical circuit110is formed between a contact on the top layer and a contact on the bottom layer, while a second electrical circuit120is formed between contacts on the same bottom layer. The element of variable concentration (“X”) is exchanged between the layers corresponding with solid components11and12through a solid electrolyte14by means of an electrical signal applied through the first electrical circuit110, as opposed to conventional field-effect devices. The conductivity of the bottom layer changes as a function of the concentration of the variable concentration element (“X”) therein. The device can for instance be structed as a 3-terminal device, using decoupled programming and reading operations. The solid component11(which may be considered a reservoir) and the channel12can advantageously comprise WO3, where the composition in one of the components11,12is the reduced form of the other. Finally, the solid electrolyte preferably includes HfO2. The starting WOxresistivity can be controlled and tuned during the deposition, using, e.g., a H+/Ar reducing treatment. For the rest, the device can be fabricated using conventional lithographic processes.

Referring toFIG. 5, another aspect of the invention is now described, which concerns an apparatus100.

As seen inFIG. 5, the apparatus100includes a plurality of electrochemical devices4such as described above. In addition, the apparatus includes a controller170(i.e., a programming circuit), which is connected to the electric circuits (e.g., circuit portions110as shown inFIGS. 1-3) of the electrochemical devices4, so as to operate the devices4according to a redox process, as described earlier. Note the electrical connections between the controller170and the individual devices4are now shown, for the clarity of depiction.

Moreover, a readout circuit160is provided, which is again connected to the electric circuits (e.g., circuit portions120as shown inFIGS. 1-3) of the devices4. The readout circuit160is configured to sense one or more electrical signals impacted by the electrical conductance of the channel(s). The channel(s) is(are) formed by the second solid component12of one or more of the electrochemical devices4, in operation. Further components like an input circuit150and a processing unit may be needed, for reasons that will become apparent later.

Note, inFIG. 5, the input circuit150, the readout circuit160, and the controller170are typically meant to form part of a same processing core, together with the connecting structure formed by the electrical conductors155and165. In variants, however, the components150,160, and170may be provided on separate chips, for example.

The apparatus100may notably be configured as a neuromorphic apparatus, as assumed inFIG. 5. There, each device4may form part of a respective synaptic element. Note, each device4may possibly include several wrapping structures, as noted earlier in respect toFIG. 5, while still playing the role of a single synaptic element4. Each of the structures may include the solid electrolyte14, the first solid component11, and the gate contact22, which are at least partly wrapped around the fin12. Each of these wrapping structures may be spaced away or separated from each other along the fin12, as shown inFIG. 5. Such an embodiment may for instance be compared to PCM synaptic elements, where multiple PCM devices are used to provide the total response of each synaptic element. An advantage of using several wrapping structures for each single synaptic element is to increase the tunability of the total resistance/conductance of the channel of said each synaptic device.

In the example ofFIG. 5, the apparatus100comprises a crossbar array structure formed by N input lines155and M output lines165. Only five input lines and five output lines are depicted in this example, for the sake of depiction. In practice, however, hundreds of input lines would likely be involved. Similarly, hundreds of output lines may be needed. The input lines and the output lines are interconnected at junctions, via N×M electronic devices, which include, each, an electrochemical device4such as described earlier.

The controller170may advantageously be an analog circuit, connected to a first circuit110as shown inFIGS. 1-3. The controller is used to program the devices4, for them to store values or, more exactly, to have properties (e.g., electrical conductance) interpretable as such values. The devices4may accordingly be programmed to store synaptic weights.

A distinct analog circuit150can, for instance, be used to couple input signals (e.g., apply voltage biases) into the input lines155, as indicated inFIG. 5.

The readout circuit160is configured to read out M output signals (e.g., electrical currents) obtained from the M output lines165. The readout is typically carried out according to a multiply-accumulate operation, which takes into account signals (e.g., currents or voltages biases) coupled into each of the input lines155. As per the multiply-accumulate operations performed, values stored on each of the electrochemical devices4impact the readout. The multiply-accumulate operation typically results in that signals coupled into the input lines are respectively multiplied by values stored on the devices4at the junctions.

Note, the architecture shown inFIG. 5corresponds to a single layer of nodes of an ANN, rather than a multilayer network. This architecture may, in principle, possibly be expanded (or stacked) to embody several connected layers (hence capable of representing a multilayer network), or be connected to a core-to-core communication bus, possibly including digital processing units. Several crossbar array structures such as shown inFIG. 5may possibly be interconnected via this communication bus. Note, each or any of the circuit150-170may possibly be embodied as a digital processing units too, provided that suitable convertors are provided to translate the signals (preferred is to rely on analog circuits, though, for efficiency reasons).

The weights as stored on the devices4are constant for inference purposes (they benefit from the stability of the electrochemical devices4), whereas they need be iteratively reprogrammed for learning purposes. The computation of the weight updates is normally performed by a processing unit, whereas the crossbar array structure(s) is used to perform all the basic operations needed for the ANN (i.e., matrix vector products for the forward evaluation, products of transposed matrices and error gradient vectors for the backward evaluation, and vector outer products for updating weights), which involve large vector-matrix multiplications. For the learning phase, the analog circuit170can be used to re-program the devices4, so as to alter synaptic weights stored thereon and, this, according to any suitable automatic learning process. However, a structure or neuromorphic device100such as shown inFIG. 5can serve for both learning and inference purposes.

Referring toFIG. 6, a final aspect of the invention is now described, which concerns a method of operating an electrochemical device1-4or, by extension, an apparatus100such as described earlier in reference toFIGS. 1-5. Essential aspects of this method have already been described in reference to the present devices and apparatuses. This method is thus only succinctly described in the following.

In S10an electrochemical device1-4, such as described earlier is provided. That is, a device1-4is provided, where in the device comprises an electrochemical cell30,31,32,33with two solid components11,12that comprise same chemical elements but have different concentrations of one or more of the chemical elements they have in common. The electrochemical cell30,31,32,33further comprises a solid electrolyte14(a dielectric material) arranged between the two solid components11,12. The device additionally includes an electric circuit110-150connected to the electrochemical cell.

As illustrated in the flowchart ofFIG. 6, in S20, an electrical circuit is used to operate the cell30,31,32,33according to a redox process, so as to exchange chemical elements between the solid components11,12and thereby change conductances of each of the two components11,12.

In addition, in S30, an electrical circuit is used to sense an electrical signal impacted by the electrical conductance of the channel, i.e., the second solid component12. The same principle can be exploited for a plurality of devices1-4, as explained earlier in reference toFIG. 5. Also, steps S20and S30will typically be intermingled, e.g., for the purpose of training synaptic weights of a neuromorphic device100.

While the present invention has been described with reference to a limited number of embodiments, variants and the accompanying drawings, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In particular, a feature (device-like or method-like) recited in a given embodiment, variant or shown in a drawing may be combined with or replace another feature in another embodiment, variant or drawing, without departing from the scope of the present invention. Various combinations of the features described in respect of any of the above embodiments or variants may accordingly be contemplated, that remain within the scope of the appended claims. In addition, many minor modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims. In addition, many other variants than explicitly touched above can be contemplated. For example, other materials than those explicitly cited herein may be used.