MEMS integration issues debated

High on the list of obstacles slowing the proliferation of silicon micromachines is the task of integrating the sensors of microelectromechanical systems with signal-conditioning circuitry on the same CMOS chip. When Roger Grace, president of the Micro and Nanotechnology Commercialization Education Foundation and president of Roger Grace Associates (Naples, Fla.), called this phenomenon to our attention, the theme of this InFocus section was established.

As the articles point out, integrating MEMS with signal-conditioning circuitry, embedded microprocessors and controllers is a distinct technological possibility. But for reasons of cost, MEMS solutions typically put the sensor and the signal-conditioning circuitry in the same package-but not on the same die.

MEMS sensors still need special protection that's not available with semiconductors, say Jim Hermanowski and Jeff Dumas, engineers at Suss MicroTec Inc. (Waterbury Center, Vt.). Both Motorola Inc. and Analog Devices Inc. talk up the benefits of incorporating sensor and control circuitry on the same die. "If Itanium uses 100 million transistors, why not MEMS?" asks Analog Devices' Bob Sulouff. Motorola's Dragan Mladenovic and Dave Monk say that high-density mixed-signal processes (like the company's SmartMOS7) would enable competent integration. But a single-chip MEMS controller is still a possibility for the future.

Michael Nagy of Movaz Networks Inc. (Norcross, Ga.) points to a benefit of keeping control and signal-conditioning circuitry separate from the MEMS device. Movaz engineers describe the driver circuitry used to tilt micromirrors in dense-wavelength-division-multiplexing applications. Silicon Microsystems integrates a piezoelectric pressure sensor on the same die as the signal-conditioning circuitry, which compensates for temperature variations and makes the packaged sensors electrically interchangeable.

Janusz Bryzek, a venture capitalist with BN Ventures, examines efforts to integrate MEMS and IC signal-conditioning circuits over the past 40 years. The complete text of Bryzek's historical analysis is available at www.planetanalog.com, as is Grace's MEMS market overview.