Resistance change element, storage device, and neural network apparatus
According to one embodiment, a resistance change element includes a first electrode, a second electrode, a first transition metal compound layer provided between the first electrode and the second electrode and including lithium ions in lattice site locations, a second transition metal compound layer provided between the first transition metal compound layer and the second electrode and including the lithium ions in the lattice site locations, and a lithium ion conductor layer provided between the first transition metal compound layer and the second transition metal compound layer and being a solid material allowing the lithium ions to pass therethrough and resistant to electrons.
1 . A storage device comprising:
a resistance change element including:
a first electrode;
a second electrode;
a first transition metal compound layer provided between the first electrode and the second electrode and including lithium ions in lattice site locations;
a second transition metal compound layer provided between the first transition metal compound layer and the second electrode and including the lithium ions in the lattice site locations; and
a lithium ion conductor layer provided between the first transition metal compound layer and the second transition metal compound layer and being a solid material allowing the lithium ions to pass therethrough and resistant to electrons;
a control circuit connected to the resistance change element and configured to control a write operation and a read operation using the resistance change element;
an output circuit connected to the resistance change element and configured to output an output voltage based on the read operation; and
a first circuit configured to couple the output circuit to one of the first electrode and the second electrode of the resistance change element, wherein
in the read operation, the first circuit switches from a state in which an input pulse is applied to the first electrode and the second electrode is coupled to the output circuit to a state in which the input pulse is applied to the second electrode and the first electrode is coupled to the output circuit.
2 . The storage device according to claim 1 , further comprising:
a second circuit configured to be capable of short-circuiting the first electrode and the second electrode, wherein in the read operation, the second circuit short-circuits the first electrode and the second electrode after application of an input pulse to the resistance change element is finished.
3 . The storage device according to claim 1 , wherein
the output circuit includes a transistor including a gate coupled to the second electrode of the resistance change element,
in the read operation, a normal rotation pulse and a reverse rotation pulse acquired by reversing the normal rotation pulse are alternately applied to the first electrode of the resistance change element, and
in case where the normal rotation pulse is applied to the first electrode, the output circuit outputs a first voltage when the resistance change element is in a low resistive state, and the output circuit outputs a second voltage lower than the first voltage when the resistance change element is in a high resistive state.
4 . The storage device according to claim 1 , wherein the first transition metal compound layer contains at least one of a rock salt type transition metal oxide and a spinel type transition metal oxide.
5 . The storage device according to claim 4 , wherein the rock salt type transition metal oxide contains at least one of LiTiO 2 , Li 7 Ti 5 O 12 , Li 2 [CrTi]O 4 , and (Li 3/2 Fe 1/2 )[Li 1/2 Fe 1/2 Ti]O 4 .
6 . The storage device according to claim 4 , wherein the spinel type transition metal oxide contains at least one of LiTi 2 O 4 , Li 4 T 15 O 12 , Li[CrTi]O 4 , and (Li 1/2 Fe 1/2 )[Li 1/2 Fe 1/2 Ti]O 4 .
7 . The storage device according to claim 1 , wherein the second transition metal compound layer contains at least one of a rock salt type transition metal oxide Li 7 Ti 5 O 12 and a spinel type transition metal oxide Li 4 Ti 5 O 12 .
8 . The storage device according to claim 1 , wherein the second transition metal compound layer is a mixture of a λ type cubic metal oxide λMnO 2 and a spinel type transition metal oxide Li 1/2 MnO 2 .
9 . The storage device according to claim 1 , wherein composition of the lithium ions in the second transition metal compound layer is lower than composition of the lithium ions in the first transition metal compound layer.
10 . The storage device according to claim 1 , wherein a film thickness of the second transition metal compound layer is thinner than a film thickness of the first transition metal compound layer.
11 . The storage device according to claim 1 , wherein a film thickness of the second transition metal compound layer is equal to or thicker than a film thickness of the first transition metal compound layer.
12 . The storage device according to claim 1 changing to a low resistive state or a high resistive state based on composition of the lithium ions included in the second transition metal compound layer.
13 . The storage device according to claim 1 , wherein
the first transition metal compound layer is in contact with a first surface of the lithium ion conductor layer, and
the second transition metal compound layer is in contact with a second surface opposite to the first surface of the lithium ion conductor layer.
14 . The storage device according to claim 13 , wherein the first surface has a shape equal to a shape of the second surface.
15 . The storage device according to claim 1 , wherein, when the resistance change element is set to a low resistive state in the write operation, the control circuit applies a pulse of a positive voltage higher than a voltage of the second electrode to the first electrode.
16 . A storage device comprising:
a resistance change element including:
a first electrode;
a second electrode;
a first transition metal compound layer provided between the first electrode and the second electrode, including lithium ions, and containing at least one of a rock salt type transition metal oxide and a spinel type transition metal oxide;
a second transition metal compound layer provided between the first transition metal compound layer and the second electrode and containing at least one of Li 7 Ti 5 O 12 and Li 4 Ti 5 O 12 ; and
a lithium ion conductor layer provided between the first transition metal compound layer and the second transition metal compound layer and being a solid material allowing the lithium ions to pass therethrough and resistant to electrons;
a control circuit connected to the resistance change element and configured to control a write operation and a read operation using the resistance change element;
an output circuit connected to the resistance change element and configured to output an output voltage based on the read operation; and
a first circuit configured to couple the output circuit to one of the first electrode and the second electrode of the resistance change element, wherein
in the read operation, the first circuit switches from a state in which an input pulse is applied to the first electrode and the second electrode is coupled to the output circuit to a state in which the input pulse is applied to the second electrode and the first electrode is coupled to the output circuit.