Hitachi and Renesas Technology have developed a 512 KB (4-Mb equivalent) phase-change memory module operating from 1.5 V. The device achieves write speeds of 416 KBps and read access times of 20 ns. Using previously developed cells with a 100 mA write current, the two companies developed a peripheral circuit technology to enable the high-speed write and read operations.

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Phase-change memory is a type of nonvolatile memory that exploits phase changes in the electrical resistance of a film caused by ohmic heating. The two phases are the amorphous state (high resistance) and the crystalline state (low resistance). Using these differences in electrical resistance, binary values of "1" and "0" can be represented.

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 mA 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. However, it is critical to have a memory array circuit technology that enables high-speed read operations despite the small read currents.

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 mA. Test results confirmed the possibility of 416 KBps write operations and 20 ns read operations. 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.