PROGRAMMABLE IMPEDANCE MEMORY ELEMENTS AND CORRESPONDING METHODS

1 . A memory element programmable between different impedance states, comprising:

a first electrode;

a switching layer formed in contact with the first electrode and including at least one metal oxide;

a buffer layer in contact with the switching layer and comprising

a first metal,

tellurium,

a third element, and

a second metal distributed within the buffer layer; and

a second electrode in contact with the buffer layer.

2 . The memory element of claim 1 , wherein the switching layer metal oxide is selected from hafnium oxide, gadolinium oxide, tantalum oxide, copper oxide, aluminum oxide, ruthenium oxide, zirconium oxide, and silicon oxide.

3 . The memory element of claim 1 , wherein the switching layer comprises the metal oxide and at least one other metal.

4 . The memory element of claim 3 , wherein the other metal is selected from the group of: a metal that is not ion conductible in the switching layer and a multivalent metal.

5 . The memory element of claim 1 , wherein the buffer layer further includes the first metal being selected from copper, silver and zinc.

6 . The memory element of claim 1 , wherein the buffer layer further includes the third element being selected from germanium, gadolinium, silicon, tin and carbon.

7 . The memory element of claim 1 , wherein the third element amorphizes a structure of the buffer layer.

8 . The memory element of claim 1 , wherein the second metal can form an alloy with tellurium.

9 . The memory element of claim 1 , wherein the second metal reduces the at least one metal oxide layer.

10 . The memory element of claim 1 , wherein the buffer layer further includes the second metal being selected from titanium, hafnium, tantalum, aluminum, and zirconium.

11 . The memory element of claim 1 , wherein the second metal amorphizes a structure of the buffer layer.

12 . The memory element of claim 1 , wherein a vertical order of the layers and electrodes is, from top to bottom: the first electrode, the switching layer, the buffer layer, and the second electrode.

13 . The memory element of claim 1 , wherein at least a portion of the buffer layer is formed in an opening of a dielectric layer.

14 . The memory element of claim 1 , wherein:

within the buffer layer

the first metal is present in a range of about 1-75 atomic percent,

tellurium is present in a range of about 10-75 atomic percent,

the third element is present in a range of about 1-25 atomic percent, and

the second metal is present in a range of about 0.1 to 25 atomic percent.

15 . A memory element programmable between different impedance states, comprising:

a first electrode;

a switching layer formed in contact with the first electrode and including at least one metal oxide;

a buffer layer in contact with the switching layer and comprising

a first metal that is ion conductible in the buffer layer,

tellurium,

a third element selected from the group of germanium, gadolinium, silicon, tin and carbon, and

titanium distributed within the buffer layer; and

a second electrode in contact with the buffer layer.

16 . The memory element of claim 15 wherein the switching layer metal oxide is selected from hafnium oxide, gadolinium oxide, tantalum oxide, copper oxide, aluminum oxide, ruthenium oxide, zirconium oxide, and silicon oxide.

17 . The memory element of claim 15 , wherein the switching layer comprises the metal oxide and at least one other metal selected from the group of: a metal that is not ion conductible in the switching layer and a multivalent metal.

18 . The memory element of claim 15 , wherein the first metal is selected from copper, silver and zinc.

19 . The memory element of claim 15 , wherein

the first metal and third element are copper and germanium, respectively.

20 . The memory element of claim 15 , wherein

the second electrode comprises titanium.

21 . A method of forming a memory element programmable between different impedance states, comprising:

forming a switching layer in contact with a first electrode that includes at least one metal oxide;

forming a buffer layer in contact with the switching layer that includes

a first metal that is ion conductible in the buffer layer,

tellurium,

a third element, and

forming a second electrode in contact with the buffer layer that includes a second metal; and

diffusing the second metal through the buffer layer to an interface of the buffer layer and switching layer.

22 . The method of claim 21 , wherein the switching layer metal oxide is selected from hafnium oxide, gadolinium oxide, tantalum oxide, copper oxide, aluminum oxide, ruthenium oxide, zirconium oxide, and silicon oxide.

23 . The method of claim 21 , wherein diffusing the second metal includes at least one heat treatment step.

24 . The method of claim 23 , wherein the at least one heat treatment step includes a heat cycle from a process step that follows the formation of the memory element layers.

25 . The method of claim 21 , wherein:

the second metal can form an alloy with tellurium.

26 . The method of claim 21 , wherein:

the second metal can reduce the at least one metal oxide.

27 . The method of claim 21 , wherein the buffer layer further includes the third element being selected from germanium, gadolinium, silicon, tin and carbon.

28 . The method of claim 21 , wherein:

the switching layer metal oxide is selected from aluminum oxide and gadolinium oxide;

the first metal of the buffer layer is selected from copper and silver; and

the third element of the buffer layer is selected from germanium and gadolinium; and

the second metal is titanium.

29 . A method of sensing states of programmable impedance elements, comprising:

in a first mode

coupling a first element from a first group of the elements to a first input of a sense amplifier circuit, and

coupling a second element from a second group of the elements to a second input of the sense amplifier circuit; wherein

the first and second elements are programmed to different impedance states to represent one data value.

30 . The method of claim 29 , wherein:

in a second mode

coupling a selected element from the first group of the elements to the first input of the sense amplifier circuit, and

coupling a reference element to the second input of the sense amplifier circuit; wherein

the sense amplifier circuit is configured to compare an impedance between the selected element and the reference element to determine a data value stored by the selected element.

31 . The method of claim 29 , wherein:

in a second mode

coupling a selected element from the first group of the elements to the first input of the sense amplifier circuit, and

coupling a reference current to the second input of the sense amplifier circuit; wherein

the sense amplifier circuit is configured to compare a current through the selected element to the reference current to determine a data value stored by the selected element.

32 . A method of setting a state of a programmable impedance element in a memory device, comprising:

applying a programming voltage between a first terminal of an element and a bit line; and

while the programming voltage is being applied, controlling a current flowing through an access device connected between a second terminal of the element and the bit line to by controlling the impedance of the access device via its gate voltage.

33 . The method of claim 32 , further including:

applying the programming voltage programs the element to a first resistance;

applying an erase voltage between the first terminal of the element and the bit line; and

while the erase voltage is being applied, controlling a current flowing through the access device to by controlling the impedance of the access device via its gate voltage; wherein

the eraes voltage has a polarity opposite to that of the programming voltage with respect to terminals of the element.