Small, Cheaper Flash Memory

Freescale Semiconductor is using nanoscale materials to halve the size of flash memory and make it much less expensive.

Motorola spinoff Freescale Semiconductor of Austin, TX, is using nanoscale materials to develop a new generation of flash memory that will be half the size of conventional flash devices and could cost much less. In addition, the technology would make it possible to affordably embed flash and logic devices on the same chip, a move that would save space and energy and improve chip speed. Freescale has already demonstrated a 24-megabit flash device using the materials, and it plans to produce commercial products by the end of 2008.

The world's first four-megabit, magnetoresistive random access memory (MRAM) chip, according to Freescale Semiconductor, Austin, TX. (Image courtesy of Freescale Semiconductor, Austin, TX.)

[For an illustration of the new flash memory structure click here.]

Flash memory, which is a nonvolatile form of memory (it requires no power to store information), is increasingly common in consumer devices. Today's flash devices store information by applying an electric field to a "floating gate" -- basically a chunk of polycrystalline silicon -- at the center of a transistor. This gate is surrounded by an insulating material, which needs to be relatively thick so that small defects in it don't allow the charge to leak out. As a result, a device like the flash-based iPod Nano, which packs four gigabytes of memory into its small frame, is still carrying around a lot of inactive material.

Freescale's technology, described by Bruce White, manager of advanced CMOS at Freescale, this week at a nanotech conference in Boston, replaces the solid silicon gate with a large number of tiny silicon crystals separated by minute amounts of insulation. In this configuration, a defect in the insulation would let charge escape from only a couple of neighboring nanocrystals, leaving most of the stored charge intact.

The result: much less insulation is needed, so that the memory occupies half as much space. Or, in other words, a flash-based gadget can carry twice as many songs. Cutting down on insulation also decreases the voltage needed to store information. This makes it much easier to integrate flash memory with information processing on the same chip, which reduces costs since the number of steps needed to make the device drops by more than half. "It helps from a cost point of view. It helps from the density point of view," White says. "So overall it's a much better way of making the embedded nonvolatile memory technology."