DE10323414A1 - Solid state electrolyte memory cell has barrier layer between ion conductive material of variable resistance and the cathode - Google Patents

Abstract

A solid-state electrolyte memory cell comprises a memory region (S) between anode (A) and cathode (K) on an ion-conductive material (I) having regions of different and controllable variable conductance (G). A barrier layer (B) between the ion-conductive and cathode layers suppresses a short, low-resistance error or hard write condition.

Description

The The present invention relates to a solid electrolyte storage cell according to the generic term of claim 1.

at Solid electrolyte memory cells is essentially between a given anode area and one given cathode region, a storage material region essentially formed on the basis of an ion conductor material region. The region of the ion conductor material has a region that can be distinguished Conductivity values controllable variable electrical conductivity. The storage effect of the solid-state electrolyte storage cell is based insist that the value of conductivity clearly an information value and / or an information storage state the solid electrolyte storage cell and in particular can be assigned to the ion conductor material area.

in the Operation can and will when reading across an between the anode area and a potential difference applied to the cathode region Current and / or a conductivity determined from it in the ion conductor material area via the ion conductivity assigned stored information state or information value.

By an embossed Write current becomes ion conductivity during the write process or erase process of the ion conductor material range in defined and non-volatile Modulated and adjusted in such a way that it is independent of time by subsequent ones Read operations via the Reading process already described above by means of a given Potential and a measured current a current flow or conductivity value can be determined which for the material state of the ion conductor material area and thus for the information stored there is representative.

Problematic in known solid electrolyte memory cells is that there are multiple write and / or read operations irreversible changes the storage material area and in particular the ion conductor material area can come. In particular, there are very low-resistance structures in the area of the ion conductor material area, which is the worst Case of a short circuit between the anode area and the cathode area to lead can. The irreversibility of these conditions is also serious which gives rise to the difficulty that these states and clearing it out the high conductivity in the ion conductor material area either not at all or only with very much high effort is feasible.

The The invention is based on the object of a solid electrolyte storage cell to indicate in which an irreversible damage in the sense of a low impedance State between anode and cathode or a short circuit between Anode and cathode on if possible simple way can be prevented.

The The task is in a generic solid electrolyte storage cell according to the invention the characterizing features of claim 1 solved. Advantageous further training the solid electrolyte storage cell according to the invention Subject of the dependent Dependent claims.

The Solid electrolyte memory cell according to the invention is characterized in that between the ion conductor material area and a barrier area is provided for the cathode area and that a comparatively very low impedance due to the barrier area Error state, a short circuit and / or a hard write state between the Anode area and the cathode area reducible, and the cathode area reducible, suppressible, delayed in its occurrence and / or preventable is.

It is thus a core idea of the present invention between which Ion conductor material area of the storage material area and the To form a cathode area a barrier area. This additional The barrier area stands for the formation of material and short-circuiting structures between the anode and the cathode in the way. This can be effective Way too quickly forming short-circuit structures be prevented. If necessary, the formation of short-circuit structures also completely suppressed.

The Anode area can e.g. B. consist of silver Ag or copper Cu. The cathode area can be made of any metal, metal silicide, a combination thereof or a silicon material.

The Ion conductor material can e.g. B. consist of chalcogenide compounds or contain such.

The Barrier area can be any dielectric and / or semiconducting Be or have material.

According to a particularly preferred embodiment of the solid electrolyte memory cell or solid electrolyte memory cell according to the invention, it is provided that a tunnel barrier layer is formed as the barrier region. Through this In particular, an electrical tunnel current can be transported, preferably based on electrons.

alternative or additionally it is envisaged that a non-metallic barrier region Area is formed, for. B. a dielectric and / or semiconducting Area.

According to one another alternative or in addition, it is provided that a non-ion-conducting area is formed as the barrier area, especially with an ionic conductivity that has one or more orders of magnitude is less than that of the ion conductor material area.

alternative for this purpose, it is provided that an ion-conductive area is used as the barrier area is trained. The ion conductivity should be so high that the memory cell has a switching time below or in the range of up to 1 μs reached.

In this case is according to one a further advantageous development of the solid electrolyte storage cell according to the invention at a given temperature and especially at an operating temperature the solid-state electrolyte storage cell according to the invention the ion mobility of ions in the barrier area is reduced than the ion mobility of the same ions in the ion conductor material area.

In other words, these and further aspects of the present invention are also explained further on the basis of the following comments:
Conventional solid-state electrolyte storage cells with ion conductor properties typically consist of an anode or an anode region A, an ion conductor or ion conductor material region I, a storage material region S and a cathode K or a cathode region K.

A solid-state electrolyte storage cell is a resistively switching element, the overall conductivity of which can be assigned to a storage state. To detect the status, information status or stored information content of the cell, for example in the sense of a logic 1 or a logic 0, the current is evaluated when the _read voltage U _{read is applied} .

With such a solid-state electrolyte storage cell, it is possible to have metallic ions diffuse in a controlled manner through the generally poorly conductive ion conductor I by applying bipolar voltage pulses. In the simplest case, these metallic ions are identical to the anode material, ie metallic anode material is oxidized and dissolves in the ion conductor I when a positive write voltage U _write > U _{read is applied} . The ion diffusion can be controlled by the duration, the amplitude and the polarity of the externally impressed electrical voltage in the cell. When a positive electrical voltage U _{write is applied} to the solid electrolyte cell described here, the metallic cations diffuse under the influence of the external electrical field through the ion conductor I in the direction of the cathode K. As soon as a sufficient number of metal ions have diffused, a low-resistance metallic bridge can form between the anode Form A and the cathode (K) so that the electrical resistance of the memory cell drops sharply.

• (a) Sobald sich zu viele Ionen infolge der Felddriftbewegung an der Kathode K gesammelt haben, ist dieser Status durch Umpolen der externen Spannung nicht mehr reversibel umschaltbar. Die Speicherzelle befindet sich in einem sehr niederohmigen Zustand, dem so genannten „hard-write"-Zustand. Dies stellt ein OTP dar, also ein One-Time-Programmable Memory.
• (b) Andererseits, wenn zu wenige Metallionen an dem Brückenbildungsprozess beteiligt sind – also keine stabilen metallische Filamente gebildet worden sind – ist der Spei chereffekt flüchtig, d.h. der niedrigohmige Zustand verschwindet nach einer gewissen Zeit. Unter anderem ist aus diesem Grund bislang auch noch keine Festkörperelektrolytspeicherzelle als wirkliche nichtflüchtige Speicherzelle realisiert worden.
• (c) Das Widerstandsverhältnis der Zelle im OFF- und ON-Zustand wird nur durch die Eigenschaften des Elektrolyten und der metallischen Brücke bestimmt und liegt oft nicht in einem für die weitere Signalverarbeitung günstigen Bereich.

However, the function of the memory cell described above is associated with several technical problems:

• (a) As soon as too many ions have collected on the cathode K as a result of the field drift movement, this status can no longer be reversibly switched by reversing the polarity of the external voltage. The memory cell is in a very low-resistance state, the so-called "hard-write" state. This represents an OTP, that is to say a one-time programmable memory.
• (b) On the other hand, if too few metal ions are involved in the bridging process - that is, no stable metallic filaments have been formed - the storage effect is volatile, ie the low-resistance state disappears after a certain time. For this reason, among other things, no solid-state electrolyte memory cell has yet been implemented as a real non-volatile memory cell.
• (c) The resistance ratio of the cell in the OFF and ON state is only determined by the properties of the electrolyte and the metallic bridge and is often not in a range that is favorable for further signal processing.

It is not yet a description described in the literature, with of the technical problems described can be solved. The only way a hard write state to avoid, is to keep the programming pulses short and their Limit amplitude. Nevertheless, even with this operating mode, there remains the risk that such a hard write state occurs repeatedly, if not a complete delete after every letter is done.

An embodiment can be implemented in such a way that a non-metallic and at the same time non-ion-conducting barrier layer B is introduced between the cathode K and the ion conductor I. This prevents the low-resistance hard-write state described above from occurring in the solid-state electrolyte cell, which irreversibly short-circuits the anode A with the cathode K. Additional advantage of this realization of a solid electrolyte Memory cell is that the resistance of the high-resistance OFF state and the low-resistance ON state can be adjusted by choosing the thickness of the barrier, since the arrangement is in principle a series connection of two resistors, the first resistor R1 being determined by the Ion conductor I with the ions and the second resistance R2 being determined by the barrier B. In addition, the low-resistance ON state can be programmed reliably low, since the interface K or contact surface K between the barrier B and the ion conductor I has a high metal ion density can be without a metallic short circuit.

In a modification of the invention, the barrier B is also a ion conductive Material, however the ionic conductivity, i.e. the mobility of ions at a given temperature in this barrier layer (B) worse than that of the actual ion conductor layer I. Thus can also prevent irreversible hard-write states from occurring, since repeated and or long voltage pulses are not necessarily to a supercritical Accumulate metal ions in the ion-conductive barrier layer B. This can be varied by varying the layer thickness of the barrier material B in dependence the ionic conductivity will be realized.

A The idea of the invention is instead of the standard solid electrolyte cell configuration a new cell structure with a sequence of the type anode A / ion conductor I / tunnel barrier layer B / cathode K to realize. Through the described Insert the Tunnel barrier layer B can make the novel cell in the ON state build a long-term stable metallic bridge and thus provides a non-volatile memory element The function differs from a conventional one Solid electrolyte cell that in operation, a tunnel current flows through the tunnel barrier layer instead of an electron current flowing through the metallic bridge. This step means a very significant improvement in the electrical properties compared to a conventional solid electrolyte storage cell and the applicability for future non-volatile memory applications.

The The invention is further illustrated by a schematic drawing on the basis of preferred embodiments of the solid electrolyte memory cell according to the invention explained in more detail.

1 is a schematic and side cross-sectional view of a first embodiment of the solid electrolyte memory cell according to the invention.

2A , B show a schematic and lateral cross-sectional view with the aid of a further embodiment of the solid-state electrolyte memory cell according to the invention with regard to an ON state or an OFF state of the memory cell.

3 11 is a schematic and side cross-sectional view of a conventional solid electrolyte memory cell.

in the The following are similar in terms of elements and structures or comparable structures or elements with the same reference symbols referred to without the each time these reference numerals occur Detailed descriptions of the respective structures and elements repeated become.

1 shows a schematic and sectional side view of an embodiment of the solid electrolyte memory cell according to the invention 10 , In a material area 20 , for example an insulator or a semiconducting material with a bottom or bottom 20a and a surface or top 20b , A cathode area K or a cathode K, a storage area S or storage material area S and then an anode A or an anode area A are provided. According to the invention, the storage area S or storage material area S consists of a barrier area or a barrier layer B, which is formed in the storage material area S facing the cathode area K. This is followed by an ion conductor I or ion conductor material region I facing the anode region A, in such a way that a common interface G is formed between the barrier region B or the barrier layer B and the ion conductor material region I.

in the Operation is through a write operation in the ion conductor material area I formed a structure, for example in the form of filaments from metal ions, which is the inherently poor conductivity or electrical conductivity of the ion conductor material region I increases by, for example, one logical one with a correspondingly high conductivity value for the To represent ion conductor material area I. To write one logical zero or to delete a written logical one becomes corresponding, for example a, possibly original, conductivity state with a comparatively low conductivity in the area of the ion conductor material I made or restored.

2A shows the in 1 already discussed Solid electrolyte memory cell according to the invention 10 in the so-called ON state, which for example represents a logical one. In this ON state, as has already been explained in advance, the ion conductor resistance of the ion conductor material region I is comparatively low, so that a significant tunnel current can be measured via the barrier region B in the form of a tunnel layer T, which is indicated by arrows.

In contrast, shows 2 B same cell in the so-called OFF state, in which the electrical resistance and therefore the ion conductor resistance of the ion conductor material region I is comparatively high, so that no significant tunnel current can be measured over the barrier region B or over the tunnel barrier T.

3 also shows a schematic and sectional side view of a conventional solid electrolyte storage cell 100 , in which the conventional storage material region S 'consists essentially exclusively of the ion conductor material region I with the disadvantages already mentioned above. A barrier layer B or tunnel barrier T, as is and is provided according to the invention, is found in the conventional solid electrolyte storage cell 100 Not.

10

Solid-state electrolyte storage according to the invention

cell

20

Material area, Semiconductor material region

20a

Bottom, undersurface

20b

top, surface

100

conventional Solid electrolyte memory cell

A

Anode, anode region

B

Barrier region, barrier layer

G

Interface area, transition area

I

Ion conductor material area, inner conductor

K

Cathode, cathode region

S

Storage material area the invention

Solid electrolyte memory cell

S '

Storage material area the traditional festival

body electrolyte memory cell

T

Tunnel barrier, Tunneling barrier layer

Claims (6)

Solid state electrolyte storage cell, with. - an anode area (A), - a cathode area (K) and - a storage material area (S) provided essentially between the anode area (A) and the cathode area (K), - the storage material area (S) being based essentially on an ion conductor material area (I) and - where the ion conductor material region (I) has an electrical conductivity (G _I ) which can be varied in a range which is distinguishable in a range of conductivity values (G), - whose value (G _I ) clearly represents an information value and / or information storage state of the solid electrolyte storage cell ( 10 ) and the ion conductor material region (I), characterized in that - a barrier region (B) is provided between the ion conductor material region (I) and the cathode region (K) and - that a comparatively very low-resistance fault state occurs due to the barrier region (B) Short circuit and / or a hard-write state between the anode area and the cathode area can be reduced, suppressed, delayed in its occurrence in time and / or prevented. Solid electrolyte memory cell according to claim 1, characterized in that as a barrier area (B) a tunnel barrier layer (T) is provided through which in particular an electrical tunnel current can be transported. Solid electrolyte memory cell according to one of the preceding claims, characterized in that that a non-metallic area is provided as the barrier area (B) is. Solid electrolyte memory cell according to one of the preceding claims, characterized in that that a non-ion-conducting area is provided as the barrier area (B) is. Solid electrolyte memory cell according to one of the claims 1 to 3, characterized in that as a barrier area (B) ion-conductive Area is provided. Solid electrolyte storage cell according to claim 5, characterized in that at a given temperature, in particular the operating temperature of the solid electrolyte storage cell ( 10 ) the ion mobility of ions in the barrier area (B) is less than the ion mobility of the same ion in the ion conductor material area (I).