Nonvolatile semiconductor memory device comprising memory cell array having multilayer structure
A nonvolatile semiconductor memory device includes a memory cell array where a plurality of memory cell layers having a plurality of first and second wires which cross each other and a memory cell provided at each intersection of these first and second wires are laminated on top of each other, wherein the memory cells have a variable resistance element and a non-ohmic element laminated in the direction in which the memory cell layers are laminated and tapered in such a manner that the area in a cross section gradually becomes smaller from the bottom memory cell layer towards the top memory cell layer, and the variable resistance element and the non-ohmic element in the memory cells in a certain memory cell layer are laminated in the same order as the variable resistance element and the non-ohmic element of the memory cells in another memory cell layer.
1. A nonvolatile semiconductor memory device, comprising a memory cell array in which a plurality of memory cell layers having a plurality of first and second wires which cross each other and a memory cell provided at each intersection of these first and second wires are laminated on top of each other,
the memory cells having a variable resistance element and a non-ohmic element laminated in a direction in which the memory cell layers are laminated,
the variable resistance element and the non-ohmic element of the memory cells being laminated in the same order between a certain memory cell layer and another memory cell layer,
the first or second wires being shared by a first memory cell layer and a second memory cell layer of the plurality of memory cell layers, the first and second memory cell layers being adjacent in the direction in which the layers are laminated, and
the memory cells being tapered in such a manner that an area in a cross section gradually becomes smaller from a bottom of the first memory cell layer towards the top of the second memory cell layer.
2. The nonvolatile semiconductor memory device according to claim 1 , wherein
at least one of a current and a resistance of the memory cells being included in the different memory cell layers are substantially the same.
3. The nonvolatile semiconductor memory device according to claim 1 , wherein
each of the non-ohmic elements comprises a diode made of a P type semiconductor and an N type semiconductor laminated in the direction in which the memory cell layers are laminated, and
the P type semiconductor and the N type semiconductor are laminated in the opposite order between the diodes in the first memory cell layer and the diodes in the second memory cell layer.
4. The nonvolatile semiconductor memory device according to claim 1 , wherein the non-ohmic element and the variable resistance element are laminated in this order in the memory cells in the direction from the bottom layer towards the top layer or from the top layer towards the bottom layer in the memory cell array.
5. The nonvolatile semiconductor memory device according to claim 1 , wherein
the memory cells in an i th (i is a natural number) memory cell layer, counting in the direction in which the plurality of memory cell layers are laminated, and the memory cells in a (i+2) th memory cell layer have substantially the same width in the direction of the first wires at the same height in each layer, and
the memory cells in a (i+1) th memory cell layer and the memory cells in a (i+3) th memory cell layer have substantially the same width in the direction of the second wires at the same height in each layer.
6. The nonvolatile semiconductor memory device according to claim 1 , wherein
sidewalls in the direction of the first wires of the memory cells in the i th (i is a natural number) memory cell layer, counting in the direction in which the plurality of memory cell layers are laminated, and sidewalls of the memory cells in the (i+1) th memory cell layer are formed in substantially the same planes, and sidewalls in the direction of the second wires of the memory cells in the (i+1) th memory cell layer and sidewalls in the direction of the second wires of the memory cells in the (i+2) th memory cell layer are formed in substantially the same planes.
7. The nonvolatile semiconductor memory device according to claim 1 , wherein
at least one of a current and a resistance of the memory cells being included in a i th is a natural number) memory cell layer and a (i+2) th memory cell layer are substantially the same, and
at least one of a current and a resistance of the memory cells being included in a (i+1) th memory cell layer and a (i+3) th memory cell layer are substantially the same.
8. The nonvolatile semiconductor memory device according to claim 1 , wherein a protective film is formed of an oxide film on the sidewalls of the memory cells.
9. A nonvolatile semiconductor memory device, comprising a memory cell array where a plurality of memory cell layers having a plurality of first and second wires which cross each other and a memory cell provided at each intersection of these first and second wires are laminated on top of each other,
the memory cells having a variable resistance element and a non-ohmic element laminated in a direction in which the memory cell layers are laminated,
the variable resistance element and the non-ohmic element of the memory cells in a certain memory cell layer being laminated in the same order and have substantially the same size as the variable resistance element and the non-ohmic element of the memory cells in another memory cell layer,
the first or second wires being shared by a first memory cell layer and a second memory cell layer of the plurality of memory cell layers, the first and second memory cell layers being adjacent in the direction in which the layers are laminated, and
the memory cells being tapered in such a manner that an area in a cross section gradually becomes smaller from a bottom of the first memory cell layer towards the top of the second memory cell layer.
10. The nonvolatile semiconductor memory device according to claim 9 , wherein
each of the non-ohmic elements comprises a diode made of a P type semiconductor and an N type semiconductor laminated in the direction in which the memory cell layers are laminated, and
the P type semiconductor and the N type semiconductor are laminated in the opposite order between the diodes in the first memory cell layer and the diodes in the second memory cell layer.
11. The nonvolatile semiconductor memory device according to claim 9 , wherein the non-ohmic element and the variable resistance element are laminated in this order in the memory cells in the direction from the bottom layer towards the top layer or from the top layer towards the bottom layer in the memory cell array.
12. The nonvolatile semiconductor memory device according to claim 9 , wherein
the memory cells in an i th (i is a natural number) memory cell layer, counting in the direction in which the plurality of memory cell layers are laminated, and the memory cells in a (i+2) th memory cell layer have substantially the same width in the direction of the first wires at the same height in each layer, and
the memory cells in a (i+1) th memory cell layer and the memory cells in a (i+3) th memory cell layer have substantially the same width in the direction of the second wires at the same height in each layer.
13. The nonvolatile semiconductor memory device according to claim 9 , wherein
sidewalls in the direction of the first wires of the memory cells in the i th (i is a natural number) memory cell layer, counting in the direction in which the plurality of memory cell layers are laminated, and sidewalls of the memory cells in the (i+1) memory cell layer are formed in substantially the same planes, and sidewalls in the direction of the second wires of the memory cells in the (i +1) th memory cell layer and sidewalls in the direction of the second wires of the memory cells in the (i+2) th memory cell layer are formed in substantially the same planes.
14. The nonvolatile semiconductor memory device according to claim 9 , wherein a protective film is formed of an oxide film on the sidewalls of the memory cells.