Memory device and method of manufacturing the same

1. A memory device comprising:

a plurality of memory cells; and

a lead-out line provided in common to said plurality of memory cells,

wherein each of said memory cells includes:

a transistor formed above a substrate; and

a variable resistance element which includes a lower electrode, an upper electrode comprising a noble metal, and a variable resistance layer disposed between said lower electrode and said upper electrode,

said variable resistance layer has a resistance value that changes reversibly in response to an electric pulse that goes through said transistor and is applied between said lower electrode and said upper electrode,

said lead-out line is in direct contact with said upper electrode included in each of said memory cells, and the bottommost surface of the bottom surface of said lead-out line is formed to be lower than the top surface of said upper electrode and higher than the top surface of said lower electrode, and

said upper electrode is completely covered by said lead-out line.

2. The memory device according to claim 1 ,

wherein said variable resistance layer includes a first layer comprising an oxygen-deficient first transition metal oxide having a composition represented as MO x (where M denotes a transition metal and O denotes oxygen) and a second layer comprising a second transition metal oxide having a composition represented as MO y (where x<y) formed on the first layer, and

the second layer is in contact with said upper electrode.

3. The memory device according to claim 1 ,

wherein at least a portion of a side wall of said variable resistance layer is covered by an insulating layer.

4. The memory device according to claim 1 ,

wherein said variable resistance layer comprises a transition metal oxide selected from the group consisting of tantalum, hafnium, and zirconium.

5. The memory device according to claim 1 ,

wherein said lead-out line has a stacked structure comprising an electrically conductive material, and a portion of said lead-out line that is in direct contact with said upper electrode comprises an electrically conductive material including at least one of chromium, molybdenum, niobium, tantalum, tungsten, titanium, vanadium, zirconium, hafnium, silicon, nitrogen, carbon, and boron.

6. A method of manufacturing a memory device including a plurality of memory cells each of which includes a transistor and a variable resistance element, the method comprising:

forming the transistor above a substrate;

forming a lower electrode of the variable resistance element to correspond to the transistor;

forming a variable resistance layer on the lower electrode;

forming an upper electrode comprising a noble metal on the variable resistance layer;

forming an interlayer insulating layer so as to cover the variable resistance element;

exposing at least a portion of a top surface of the upper electrode; and

forming a lead-out line that is provided in common to the plurality of memory cells so as to be in direct contact with the upper electrode and such that the bottommost surface of the bottom surface of the lead-out line is lower than the top surface of the upper electrode and higher than the top surface of the lower electrode,

the lead-out line being formed such that the upper electrode is completely covered by the lead-out line.

7. The method according to claim 6 , comprising:

forming, in the variable resistance layer, a first layer comprising an oxygen-deficient first transition metal oxide having a composition represented as MO x (where M denotes a transition metal and O denotes oxygen); and

forming, on the first layer, a second layer comprising a second transition metal oxide having a composition represented as MO y (where x<y).

8. The method according to claim 6 ,

wherein said exposing

includes planarizing the interlayer insulating layer, and

exposes at least a portion of the upper electrode on a surface of the interlayer insulating layer after planarizing the interlayer insulating layer.

9. The method according to claim 6 ,

wherein in said forming of a lead-out line, the lead-out line and an other line are formed at the same time.