Phase Change Memory Technology May Succeed Flash
Marcus Yam (Blog)- December 11, 2006 11:49 AM
Semiconductor & Patent Expert Consulting
Litigation expert consultant and patent expert witness for process, device, and circuit of Dynamic
Ram (DRAM), Flash (NAND, NOR, EEPROM), and Static Ram (SRAM) Memories,
and Microprocessor, Logic, and Analog Devices
A new memory
technology using semiconductor alloy is faster, smaller and more
resilient than flash
Working together at IBM Research labs on both U.S. coasts, the scientists designed, built and demonstrated a prototype phase-change memory device that switched more than 500 times faster than flash while using less than one-half the power to write data into a cell. The device’s cross-section is a minuscule 3 by 20 nanometers in size, far smaller than flash can be built today and equivalent to the industry’s chip-making capabilities targeted for 2015. This new result shows that unlike flash, phase-change memory technology can improve as it gets smaller with Moore’s Law advancements.
Flash memory cells, while also non-volatile, degrade and become unreliable after being rewritten about 100,000 times. This is not a problem for many consumer uses, but is a showstopper in applications that must be frequently rewritten, such as computer main memories or the buffer memories in network storage systems. A third concern for flash’s future is that it may become extremely difficult to keep its current cell design non-volatile as designs shrink below 45 nanometers.
The IBM/Macronix/Qimonda joint project’s phase-change memory achievement is important because it demonstrates a new non-volatile phase-change material that can switch more than 500 times faster than flash memory, with less than one-half the power consumption, and most significantly, achieves these desirable properties when scaled down to at least the 22-nanometer node, two chip-processing generations beyond floating-gate flash’s predicted brick wall.
At the heart of phase-change memory is a tiny chunk of a semiconductor alloy that can be changed rapidly between an ordered, crystalline phase having lower electrical resistance to a disordered, amorphous phase with much higher electrical resistance. Because no electrical power is required to maintain either phase of the material, phase-change memory is non-volatile.
The material’s phase is set by the amplitude and duration of an electrical pulse that heats the material. When heated to a temperature just above melting, the alloy’s energized atoms move around into random arrangements. Suddenly stopping the electrical pulse freezes the atoms into a random, amorphous phase. Turning the pulse off more gradually – over about 10 nanoseconds – allows enough time for the atoms to rearrange themselves back into the well-ordered crystalline phase they prefer.
The new memory material is a germanium-antimony alloy (GeSb) to which small amounts of other elements have been added (doped) to enhance its properties. Simulation studies enabled the researchers to fine-tune and optimize the material’s properties and to study the details of its crystallization behavior. A patent has been filed covering the composition of the new material.
The view a couple animations of how phase-change memory works, click here. The technical details of this research will be presented this week at the IEEE’s 2006 International Electron Devices Meeting in San Francisco.
Diagram of test setup
Micrograph of test setup
Closeup of test setup
Cross-section of test setup
Closeup cross-section of phase change bridge
A new memory technology using semiconductor alloy is faster, smaller and more resilient than flash