Memory cells with vertically integrated tunnel access device and programmable impedance element
View Patent ↗A memory device can include a plurality of memory cells formed over a substrate, each memory cell including a tunnel access device that enables current flow in at least one direction predominantly due to tunneling, and a storage element programmable between different impedance states by a reduction-oxidation reaction within at least one memory layer formed between two electrodes; wherein the tunneling access device and programmable impedance element are vertically stacked over one another.
1. A memory device, comprising:
a plurality of memory cells formed over a substrate, each memory cell including
a tunnel access device that enables current flow in at least one direction predominantly due to tunneling, the tunnel access device comprising
a conductive contact structure formed through an insulating layer,
a first insulating layer formed on the contact structure, and
a second insulating layer, different from the first insulating layer, formed on the first insulating layer, and
a storage element programmable between different impedance states by a reduction-oxidation reaction within at least one memory layer formed between two electrodes; wherein
the tunneling access device and programmable impedance element are vertically stacked over one another.
2. The memory device of claim 1 , wherein:
the first insulating layer is an oxidized portion of the conductive contact structure.
3. The memory device of claim 1 , wherein:
the tunnel access device comprises a tunnel diode that enables a predominantly tunneling current in one direction under first bias conditions.
4. The memory device of claim 3 , wherein:
the tunnel diode is vertically integrated with the storage element, a first electrode of the tunnel transistor forming one electrode of the programmable impedance element.
5. A memory device, comprising:
a plurality of memory cells formed over a substrate, each memory cell including
a tunnel access device that enables current flow in at least one direction predominantly due to tunneling, and
a storage element programmable between different impedance states by a reduction-oxidation reaction within at least one memory layer formed between two electrodes; wherein
the tunneling access device and programmable impedance element are vertically stacked over one another, and
the tunnel access device comprises a tunnel transistor that controls a tunneling current flow between a first electrode and second electrode according to a state of a control electrode.
6. The memory device of claim 5 , wherein:
the tunnel transistor is vertically integrated with the storage element, a first electrode of the tunnel transistor forming one electrode of the programmable impedance element.
7. The memory device of claim 6 , wherein:
each memory cell includes
a bottom contact that operates as the first electrode of the tunnel transistor,
at least one insulating layer formed on a top surface of the bottom contact,
a first conductive layer formed over the insulating layer that operates as the control electrode of the tunnel transistor,
the at least one memory layer formed over the first conductive layer, and
a second conductive layer formed over the memory layer that operates as the second electrode of the tunnel transistor.
8. The memory device of claim 1 , wherein:
the at least one memory layer includes
a switch layer programmable between different impedance states, and
an anode layer in contact with the switch layer comprising at least element that is ion conductible in the switch layer.
9. The memory device of claim 8 , wherein:
the anode layer comprises a metal and a chalcogen, and
the switch layer comprises a metal oxide.
10. A memory device, comprising:
a plurality of bottom electrodes;
a plurality of first conductive plates, each first conductive plate formed over a corresponding group of bottom electrodes;
memory cells formed between each bottom electrode and the corresponding conductive plate, each memory cell including
a tunnel access device configured to pass a tunneling current in response to a first bias voltage, and
a storage element programmable between different impedance states by a reduction-oxidation reaction within at least one memory layer; and
a contiguous memory layer section between each first conductive plate and the corresponding group of bottom electrodes, each memory layer section providing the memory layer for the memory cells of its corresponding group of bottom electrodes.
11. The memory device of claim 10 , wherein:
each bottom electrode is plug comprising a conductive material selected from the group of tantalum, aluminum, titanium, tungsten, tantalum nitride, and zirconium.
12. The memory device of claim 10 , wherein:
the memory layer includes
a switch layer programmable between different impedance states, and
an anode layer in contact with the switch layer comprising at least element that is ion conductible in the switch layer.
13. The memory device of claim 10 , further including:
a plurality of lower conductive structures, formed below and electrically connected to, the bottom electrodes, the lower conductive structures being oriented such that each bottom electrode is disposed between a different conductive plate and lower conductive structure.
14. The memory device of claim 10 , further including:
the tunnel access device of each memory cell comprises a tunnel diode, having
a first terminal formed by the corresponding bottom electrode,
a second terminal formed by the corresponding first conductive plate,
a first metal oxide formed over the bottom electrode and below the corresponding first conductive plate, and
a second metal oxide, different from the first metal oxide, formed over the first metal oxide and below the corresponding first conductive plate.
15. The memory device of claim 14 , wherein:
each storage element is integrated with the corresponding tunnel diode, the memory layer being formed between the second metal oxide and first conductive plate.
16. The memory device of claim 10 , wherein:
the tunnel access device of each memory cell comprises a tunnel transistor, having
a first terminal formed by the corresponding bottom electrode,
a second terminal formed by the corresponding first conductive plate, and
a control terminal formed by a control conductive layer formed between each first conductive plate and the corresponding group of bottom electrodes.
17. The memory device of claim 16 , wherein:
each storage element is integrated with the corresponding tunnel transistor, the memory layer being formed between the control conductive layer and first conductive plate.
18. The memory device of claim 5 , wherein:
the at least one memory layer includes
a switch layer programmable between different impedance states, and
an anode layer in contact with the switch layer comprising at least element that is ion conductible in the switch layer.
19. The memory device of claim 18 , wherein:
the anode layer comprises a metal and a chalcogen, and
the switch layer comprises a metal oxide.