The memory device has constituent cells which include a structural phase-change material to store the cells data. This material may be, for instance, a chalcogenide alloy. A first pulse is applied to the cell to leave the material in a first state, such as a reset state in which the material is relatively amorphous and has relatively high resistivity. Thereafter, a second pulse is applied to the cell to change the material from the first state to a second, different state, such as a set state in which the material is relatively crystalline and has relatively low resistivity. This second pulse has a generally triangular shape, rather than a rectangular one.
A semiconductor memory device includes: phase-change memory cells whose states change to a set resistance state or a reset resistance state in response to an applied current pulse; a set pulse driving circuit outputting a set current pulse having first through n-th stages in response to a first control signal and a set control signal wherein current amounts of the first through n-th stages are sequentially reduced and are all greater than a reference current amount; a reset pulse driving circuit outputting a reset current pulse in response to a second control signal; a pull-down device activating the set pulse driving circuit and the reset pulse driving circuit in response to a third control signal; and a write driver control circuit outputting the first through third control signals in response to write data, a set pulse width control signal, and a reset pulse width control signal.
A semiconductor memory device includes: phase-change memory cells whose states change to a set resistance state or a reset resistance state in response to an applied current pulse; a set pulse driving circuit outputting a set current pulse having first through n-th stages in response to a first control signal and a set control signal, wherein current amounts of the first through n-th stages are sequentially reduced and are all greater than a reference current amount; a reset pulse driving circuit outputting a reset current pulse in response to a second control signal; a pull-down device activating the set pulse driving circuit and the reset pulse driving circuit in response to a third control signal; and a write driver control circuit outputting the first through third control signals in response to write data, a set pulse width control signal, and a reset pulse width control signal.
A circuit for accessing a chalcogenide memory array is disclosed. The chalcogenide memory array includes multiple subarrays with rows and columns formed by chalcogenide storage elements. The chalcogenide memory array is accessed by discrete read and write circuits. Associated with a respective one of the subarrays, each of the write circuits includes an independent write 0 circuit and an independent write 1 circuit. Also associated with a respective one of the subarrays, each of the read circuits includes a sense amplifier circuit. In addition, a voltage level control module is coupled to the read and write circuits to ensure that voltages across the chalcogenide storage elements within the chalcogenide memory array do not exceed a predetermined value during read and write operations.
A read/write circuit for accessing chalcogenide non-volatile memory cells is disclosed. The read/write circuit includes a chalcogenide storage element, a voltage limiting circuit, a current-to-voltage converter, and a buffer circuit. The voltage limiting circuit, which is coupled to the chalcogenide storage element, ensures that voltages across the chalcogenide storage element will not exceed a predetermined value during a read operation. During a read operation, the current-to-voltage converter, which is coupled to the voltage limiting circuit, converts a current pulse read from the chalcogenide storage element to a voltage pulse. By sensing the voltage pulse from the current-to-voltage converter, the buffer circuit can determine a storage state of the chalcogenide storage element.
A phase-change memory device includes a phase-change memory cell having a volume of material which is programmable between amorphous and crystalline states. A write current source selectively applies a first write current pulse to program the phase-change memory cell into the amorphous state and a second write current pulse to program the phase-change memory cell into the crystalline state. The phase-change memory device further includes a restore circuit which selectively applies the first current pulse to the phase-change memory cell to restore at least an amorphous state of the phase-change memory cell.
