In recent years, an increase in capacity has been demanded in non-volatile memories for data storage. The non-volatile memories for data storage are typified by resistance-change memories such as ReRAMs (Resistance Random Access Memories) and PRAMs (Phase-Change Random Access Memories). However, in a resistance-change memory using an existing access transistor, a floor area per unit cell is increased. Accordingly, for example, as compared with flash memories such as NAND flash memories, it is difficult to achieve an increase in capacity of the resistance-change memory even in a case in which the resistance-change memory is miniaturized with use of same design rules. In contrast, in a case in which the resistance-change memory uses a so-called cross-point array configuration in which memory devices are each provided at corresponding one of intersections (cross points) of intersecting wiring lines, a floor area per unit cell in the resistance-change memory is reduced, which makes it possible to achieve the increase in capacity of the resistance-change memory.
In a cross-point type memory cell, a selection device (switch device) for cell selection is provided in addition to a memory device. Examples of the switch device may include a PN diode, an avalanche diode, a switch device configured with use of a metal oxide (for example, refer to NPTLs 1 and 2), and a switch device that is switched at a certain threshold voltage by Mott transition to abruptly increase a current (for example, refer to NPTLs 3 and 4). However, since a threshold voltage at which the switch devices are switched is not sufficient and a leakage current during non-selection is large, the switch devices do not have sufficient characteristics as switch devices used in combination with the memory device (in particular, a resistance-change memory device having a large writing threshold voltage) in the cross-point type memory cell.
Examples of the switch device other than the above-described switch device configured with use of the metal oxide may include a switch device using a chalcogenide material (ovonic threshold switch (OTS) device; for example, refer to PTLs 1 and 2). The OTS device has a characteristic in which a current abruptly increases at a switching threshold voltage or higher, which makes it possible to obtain relatively large current density in a selection (ON) state. Moreover, a microstructure of a layer (an OTS layer) made of a chalcogenide material is amorphous, and it is therefore possible to form the OTS layer under room-temperature conditions such as a physical vapor deposition (PVD) method and a chemical vapor deposition (CVD) method. Accordingly, the OTS layer has an advantage of high process affinity.