Two-terminal reversibly switchable memory device

• US 9,831,425 B2
• Filed: 09/03/2015
• Issued: 11/28/2017
• Est. Priority Date: 02/06/2004
• Status: Active Grant

• Current Assignee: Hefei Reliance Memory Limited
• Original Assignee: Unity Semiconductor Corporation (Rambus Inc.)
• Inventors: Rinerson, Darrell, Chevallier, Christophe J., Kinney, Wayne, Lambertson, Roy, Sanchez, Jr., John E., Schloss, Lawrence, Swab, Philip, Ward, Edmond
• Primary Examiner(s): Fan, Bo
• Application Number:
  US14/844,805
• Publication Number:
  US 20150380642A1
• Time in Patent Office: 817 Days
• Field of Search: 438459, 438148, 438 43, 438 35
• 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. An apparatus, comprising:

a first electrode;

a second electrode; and

a memory element (ME) comprising tantalum, the memory element positioned between the first and second electrodes, the ME electrically coupled in series with the first and second electrodes, the ME comprising;

a first ion reservoir comprising mobile oxygen ions, the first ion reservoir in contact with the first electrode;

a tunnel barrier in contact with the first ion reservoir, the tunnel barrier made from a material that is an electrolyte to the mobile oxygen ions and is permeable by the mobile oxygen ions responsive to a first voltage applied across the first and second electrodes, and wherein the tunnel barrier is coupled in series with the first ion reservoir; and

a second reservoir in contact with the tunnel barrier and positioned between the second electrode and the tunnel barrier, the second reservoir operative as a repository for the mobile oxygen ions.

2. The apparatus of claim 1, wherein the ME 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 oxygen ion migration.

3. The apparatus of claim 1, wherein the mobile oxygen ions in the first ion reservoir are operative to change a conductivity of the first ion reservoir from a relatively high conductivity to a relatively low conductivity when the mobile oxygen ions are transported into the tunnel barrier or from a relatively low conductivity to a relatively high conductivity when the mobile oxygen ions are transported back into the first ion reservoir.

4. The apparatus of claim 1, wherein the first voltage is operative to generate a first electric field in the tunnel barrier and a second electric field in the first ion reservoir, the first electric field having a greater magnitude than the second electric field and the first electric field extending into the first ion reservoir by a distance of at least one Debye length.

5. The apparatus of claim 1, further comprising:

a line coupled to the first electrode; and

a component coupled to the line, the component configured to energize the line to apply a second voltage across the first and second electrodes, the second voltage operative to generate a read current having a magnitude that is indicative of a present conductivity of the ME, wherein applying the second voltage is non-destructive to the present conductivity of the ME.

6. The apparatus of claim 5, wherein a magnitude of the second voltage is less than a magnitude of the first voltage.

7. The apparatus of claim 5, wherein a polarity of the second voltage is different than a polarity of the first voltage.

8. The apparatus of claim 5, wherein the present conductivity is indicative of stored data.

9. The apparatus of claim 8, wherein the stored data is retained in an absence of electrical power.

10. The apparatus of claim 5, wherein the first voltage is applied as a voltage pulse.

11. The apparatus of claim 5, wherein the second voltage is applied as a voltage pulse.

12. The apparatus of claim 1, the ME comprises a tantalum oxide compound.

13. The apparatus of claim 12, wherein the tantalum oxide comprises tantalum pentoxide.

14. The apparatus of claim 1, wherein at least a portion of the tantalum of the ME is located in the tunnel barrier.

15. The apparatus of claim 1, wherein at least a portion of the tantalum of the ME is located in the second reservoir.

16. An apparatus, comprising:

a first electrode;

a second electrode; and

a memory element (ME) positioned between the first and second electrodes, the ME electrically coupled in series with the first and second electrodes, the ME comprising;

a first ion reservoir comprising mobile ions, the first ion reservoir coupled with the first electrode; and

a tunnel barrier coupled with the first ion reservoir and the second electrode, wherein the tunnel barrier to allow the mobile ions of the first ion reservoir to tunnel through the tunnel barrier responsive to a first voltage applied across the first electrode and the second electrode, and wherein the tunnel barrier is coupled in series with the first ion reservoir.

17. The apparatus of claim 16, wherein the ME comprises a tantalum oxide compound.

18. The apparatus of claim 16, wherein the ME comprises tantalum, wherein at least a portion of the tantalum of the ME is located in the tunnel barrier.

19. The apparatus of claim 16, further comprising a second reservoir in contact with the tunnel barrier and positioned between the second electrode and the tunnel barrier, the second reservoir operative as a repository for the mobile ions, wherein the ME comprises tantalum, wherein at least a portion of the tantalum of the ME is located in the second reservoir.

20. The apparatus of claim 16, further comprising:

a line coupled to the first electrode; and

a component coupled to the line, the component configured to energize the line to apply a second voltage across the first and second electrodes, the second voltage operative to generate a read current having a magnitude that is indicative of a present conductivity of the ME, wherein applying the second voltage is non-destructive to the present conductivity of the ME; and

wherein at least one of the first voltage or the second voltage is applied as a voltage pulse.