Multi-terminal reversibly switchable memory device

• US 20090303773A1
• Filed: 06/18/2009
• Published: 12/10/2009
• Est. Priority Date: 02/06/2004
• Status: Abandoned Application

• Current Assignee: Unity Semiconductor Corporation (Rambus Inc.)
• Original Assignee: Unity Semiconductor Corporation (Rambus Inc.)
• Inventors: Chevallier, Christophe, Ward, Edmond, Rinerson, Darrell, Lambertson, Roy
• Application Number:
  US12/456,677
• Publication Number:
  US 20090303773A1
• Time in Patent Office: Days
• US Class Current: 365/148
• CPC Class Codes: G06F 30/30 Circuit design
• CPC Class Codes: G11C 11/5685 using storage elements comprising metal oxide memory material, e.g. perovskites
• CPC Class Codes: G11C 13/0007 comprising metal oxide memory material, e.g. perovskites
• CPC Class Codes: G11C 13/0009 RRAM elements whose operation depends upon chemical change
• CPC Class Codes: G11C 13/004 Reading or sensing circuits or methods
• CPC Class Codes: G11C 13/0069 Writing or programming circuits or methods
• CPC Class Codes: G11C 2013/0045 Read using current through the cell
• CPC Class Codes: G11C 2013/005 Read using potential difference applied between cell electrodes
• CPC Class Codes: G11C 2013/009 Write using potential difference applied between cell electrodes
• CPC Class Codes: G11C 2213/11 Metal ion trapping, i.e. using memory material including cavities, pores or spaces in form of tunnels or channels wherein metal ions can be trapped but do not react and form an electro-deposit creating filaments or dendrites
• CPC Class Codes: G11C 2213/31 Material having complex metal oxide, e.g. perovskite structure
• CPC Class Codes: G11C 2213/32 Material having simple binary metal oxide structure
• CPC Class Codes: G11C 2213/53 Structure wherein the resistive material being in a transistor, e.g. gate
• CPC Class Codes: G11C 2213/54 Structure including a tunneling barrier layer, the memory effect implying the modification of tunnel barrier conductivity
• CPC Class Codes: G11C 2213/56 Structure including two electrodes, a memory active layer and a so called passive or source or reservoir layer which is NOT an electrode, wherein the passive or source or reservoir layer is a source of ions which migrate afterwards in the memory active layer to be only trapped there, to form conductive filaments there or to react with the material of the memory active layer in redox way
• CPC Class Codes: G11C 2213/71 Three dimensional array
• CPC Class Codes: G11C 2213/79 Array wherein the access device being a transistor
• CPC Class Codes: H10B 63/30 comprising selection components having three or more electrodes, e.g. transistors
• CPC Class Codes: H10B 63/84 arranged in a direction perpendicular to the substrate, e.g. 3D cell arrays
• CPC Class Codes: H10N 70/026 by physical vapor deposition, e.g. sputtering
• CPC Class Codes: H10N 70/24 : based on migration or redistribution of ionic species, e.g. anions, vacancies
• CPC Class Codes: H10N 70/245 : the species being metal cations, e.g. programmable metallization cells
• CPC Class Codes: H10N 70/826 : adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
• CPC Class Codes: H10N 70/828 : Current flow limiting means within the switching material region, e.g. constrictions
• CPC Class Codes: H10N 70/841 : Electrodes
• CPC Class Codes: H10N 70/8833 : Binary metal oxides, e.g. TaOx
• CPC Class Codes: H10N 70/8836 : Complex metal oxides, e.g. perovskites, spinels

Abstract

A memory using mixed valence conductive oxides is disclosed. The memory includes a mixed valence conductive oxide that is less conductive in its oxygen deficient state and a mixed electronic ionic conductor that is an electrolyte to oxygen and promotes an electric field effective to cause oxygen ionic motion.

Claims

1. A three-terminal switch, comprising:

a source electrode;

a drain electrode;

a gate electrode; and

a memory element including

a mixed valence oxide that includes mobile ions, and

an electrolyte that promotes a first electric field operative to transport the mobile ions while under an influence of a voltage, the electrolyte is in contact with the mixed valence oxide and is operative as a repository for the mobile ions,

wherein the gate electrode is physically connected with the mixed valence oxide, and

wherein the source electrode and the drain electrode are physically connected with the electrolyte.

2. The three-terminal switch of claim 1, wherein the memory element has an electrical conductivity that can be reversibly switched between a first conductivity and a second conductivity that is greater than the first conductivity as a function of mobile ions that are transported from the mixed valence oxide and into the electrolyte or transported out of the electrolyte and into the mixed valence oxide.

3. The three-terminal switch of claim 1, wherein the electrolyte includes a thickness that is approximately 50 Å

or less.

4. The three-terminal switch of claim 1, wherein the mixed valence oxide includes a thickness that is approximately 500 Å

or less.

5. The three-terminal switch of claim 1, wherein the mobile ions in the mixed valence oxide comprise a species of ion selected to change a conductivity of the mixed valence oxide from a relatively high conductivity to a relatively low conductivity when a portion of the mobile ions are transported into the electrolyte or from a relatively low conductivity to a relatively high conductivity when the portion mobile ions are transported back into the mixed valence oxide.

6. The three-terminal switch of claim 5, wherein the mobile ions comprise cations or anions.

7. The three-terminal switch of claim 6, wherein the anions comprise oxygen ions.

8. The three-terminal switch of claim 1, wherein the voltage is operative to generate the first electric field in the electrolyte and a second electric field in the mixed valence oxide, the first electric field having a greater magnitude than the second electric field and the first electric field extending into the mixed valance oxide by a distance of at least one Debye length.

9. The three-terminal switch of claim 1, wherein the electrolyte comprises a metal oxide.

10. The three-terminal switch of claim 9, wherein the metal oxide comprises a material selected from the group consisting of Al₂O_x, Ta₂O_x, HfO_x, RuO_x, CuO_x, and ZrO_x.

11. The three-terminal switch of claim 9, wherein the metal oxide is stabilized with CaO, MgO, or Y₂O_x or the metal oxide is doped with Sc.

12. The three-terminal switch of claim 1, wherein the electrolyte is operative as a gate oxide.

13. The three-terminal switch of claim 1, wherein the mixed valence oxide comprises a conductive oxide.

14. The three-terminal switch of claim 13, wherein the conductive oxide comprise a material having a form of an ABX₃ structure.

15. The three-terminal switch of claim 13, wherein the ABX₃ structure comprises a perovskite.

16. The three-terminal switch of claim 1, wherein a selected one or more of the gate, source, or drain electrodes comprises platinum.

17. A method of operating a three-terminal switch, comprising:

providing a memory element including, a mixed valence oxide having mobile ions and physically connected with a gate electrode, and an electrolyte in contact with the mixed valence oxide and operative as a repository for the mobile ions, the electrolyte physically connected with a source electrode and a drain electrode;

applying a first write voltage across the gate electrode and a selected one or both of the source and drain electrodes, the electrolyte promotes a first electric field operative to transport a portion of the mobile ions from the mixed valence oxide and into the electrolyte while the first write voltage is applied, the transport operative to change a conductivity of the memory element to a first conductivity; and

applying a second write voltage across the gate electrode and a selected one or both of the source and drain electrodes, the electrolyte promotes a second electric field operative to transport the portion of the mobile ions from the electrolyte and back into the mixed valence oxide while the second write voltage is applied, the transport operative to change the conductivity of the memory element to a second conductivity that is different than the first conductivity.

18. The method of operating a three-terminal switch of claim 17, wherein the first conductivity and the second conductivity are indicative of stored data.

19. The method of operating a three-terminal switch of claim 18, wherein the stored data is retained in the absence of power.

20. The method of operating a three-terminal switch of claim 17 and further comprising:

applying a read voltage across the across the gate electrode and a selected one or both of the source and drain electrodes, the read voltage operative to generate a read current having a magnitude that is indicative of the first conductivity or the second conductivity, wherein the first write voltage and the second write voltage have magnitudes that are greater than a magnitude of the read voltage, and wherein applying the read voltage is non-destructive to the first conductivity or the second conductivity.

21. The method of operating a three-terminal switch of claim 20, wherein the read voltage is applied as a voltage pulse.

22. The method of operating a three-terminal switch of claim 17, wherein the first conductivity is lower than the second conductivity.

23. The method of operating a three-terminal switch of claim 17, wherein the first write voltage has a magnitude and/or a polarity that is different than the second write voltage.

24. The method of operating a three-terminal switch of claim 17, wherein the first write voltage and the second write voltage are applied as voltage pulses.