Hitachi Ltd and Renesas Technology Corp. announced the development of a 512-kbyte (4-Mbit equivalent) phase change memory module operating at a 1.5-V power supply voltage, which achieves 416-kbyte/sec high-speed write and read speeds with a 20-nanosecond access time. Using the previously developed low-power phase change memory cells with a 100-μA (micro-ampere) write current, the two companies developed a peripheral circuit technology to enable the high-speed write and read operations.
Phase change memory is a type of nonvolatile memory that exploits two-phase changes in electrical resistance of a film caused by Joule heat, which is generated by a current—an amorphous state (high resistance) and a crystalline state (low resistance). Using these differences in electrical resistance as 1 and 0 information, it performs storage and readout operations. Hitachi and Renesas have previously developed a low-power-operation phase change memory that can be written with a 1.5-V power supply voltage and 100-μA current using tantalum pentoxide for the interfacial layer. As the write voltage can be lowered compared with conventional on-chip nonvolatile memory, this memory offers advantages such as eliminating a need for a power supply circuit that generates a high voltage within a chip, helping to reduce the module size, and achieving a high level of density. However, because the readout current is small, it is critical to have a memory array circuit technology that enables high-speed operation despite its small current.
An experimental 512-kbyte memory module was fabricated using a 130-nm CMOS process, employing the newly developed circuit technology for cells writable at 100 μA. Test results confirmed the possibility of 416-kbyte/sec write operations and 20-anosecond read operations, and high-speed operation was achieved while maintaining the performance of low-power-operation phase change memory cells.
This technology is expected to promote the implementation of next-generation highly-integrated on-chip nonvolatile memory, and to support significant advances in the development of future microcontrollers for embedded systems.
