April 05, 2012

MIT Developing MEMS fabrication methods with costs that match the smaller size of MEMS markets

MEMS (microelectromechanical devices) have wrought revolutions in several industries: Arrays of micromirrors, for instance, enabled digital film projectors, and accelerometers like those in Microsoft’s Wii controller have changed gaming. But commercially successful MEMS represent a tiny sampling of the prototypes developed in academic and industry labs — from supersensitive biological sensors to films that can turn any surface into a loudspeaker to devices that harvest energy from motion.

The problem is that most current MEMS are built using the same techniques used to produce computer chips, and those techniques are expensive.

MEMS fabrication needs to have capital cost that is well-matched to the size of the MEMS markets.

New MEMS fab approaches

* ink-jet printing technology to deposit metallic nanoparticles on some type of substrate
* stamping patterns into plastics

Henry Smith is developing a maskless MEMS fab method. Masks themselves are one of the major expenses in chip manufacturing; Smith’s technique does away with them. Instead, it produces patterns using an array of 1,000 tiny lenses. A wafer of material moves back and forth beneath the lenses, and the light passing through them turns on and off. Where photolithography can, at best, transfer a pattern to a rectangle that’s 20 millimeters by 30 millimeters, Smith’s technique can impart a single pattern to the entire surface of a six-inch wafer.

LumArray is commercializing a maskless lithography system

Schematic depiction of zone-plate-array lithography (ZPAL), invented at MIT and being commercialized by LumArray, Inc. A CW laser source illuminates a spatial-light modulator (Silicon Light Machines) containing 1000 pixels. Each pixel controls the level of light to one zone plate of the array, adjusting the intensity from zero to the maximum in a quasi-continuous manner, enabling grey-tone control of linewidth. By moving the stage under computer control, patterns of arbitrary geometry can be written in a dot-matrix fashion

Smith says, “as impressive as integrated circuits are, the only thing on them is transistors, transistors and wires. Now, a MEMS device might have a diving board, a heavy weight here, a rotating part there — every single MEMS device is different than the previous one.” With its 1,000 beams of light flashing on and off as they scan across the wafer, Smith’s system can impart one set of arbitrary patterns to one wafer and a completely different pattern to the next.

Smith founded a company, called LumArray, to commercialize his system. The firm has already sold one machine to the National Institute of Standards and Technology and is delivering another to the Defense Microelectronic Activity.

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