Semiconductor devices are commonly utilized for data storage and processing. The data storage may utilize an array of memory devices. Some memory devices are particularly well-suited for long-term storage of data, while others are better suited for rapid reading and writing (in other words, rapid access).
Among the memory devices that are particularly well-suited for rapid access are dynamic random access memory (DRAM) devices. A traditional DRAM unit cell may include a transistor in combination with a capacitor. Voltage stored in the capacitor represents digital bits of information.
The capacitors of the DRAM devices leak stored charge. Accordingly, electric power is supplied to the capacitors in frequent refresh cycles to avoid dissipation of stored charge, and consequent loss of information. Memory devices that utilize frequent refresh are often referred to as volatile memory devices.
Another type of memory device is a so-called nonvolatile memory device. Nonvolatile memory devices do not need frequent refresh cycles to preserve stored information. Accordingly, nonvolatile memory devices may consume less power than volatile memory devices; and, unlike volatile memory devices, may operate in environments where power is not always on. Among the applications in which nonvolatile memory devices may provide particular advantages are mobile device applications where power is supplied by batteries (for instance, cell phones, laptops, etc.), and/or and applications where power may be turned off during retention of data (for instance, control systems of automobiles, military devices, etc.).
An advantage of conventional DRAM devices is the speed with which data may be written to and read from the memory devices. It would be desirable to develop a nonvolatile memory device which may be accessed with speeds approaching, or even exceeding, the speeds of conventional DRAM devices.
A continuing goal of semiconductor fabrication is to reduce the amount of semiconductor real estate consumed by various components, to thereby increase integration. It would be desirable to develop memory devices which may be highly integrated, and which may be readily vertically stacked in order to conserve semiconductor real estate.
Phase change materials are a class of materials that change phase upon being exposed to thermal and/or other conditions. Phase change materials may be utilized in memory devices as data storage elements. Specifically, when the phase change materials are in one phase they may be considered to correspond to one binary digit (i.e., either a “0” or a “1”), and when in another phase they may be considered to correspond to the other binary digit. Thus, phase change materials may be utilized to store a data bit. It would be desired to develop improved methods for incorporating phase change materials into memory devices, and to develop improved devices that utilize phase change materials.