A revolution in information gathering

By Kensall D. Wise, PhD, University of Michigan

One of the hottest topics in microelectronics today is microsystems in which low-power electronics and wireless interfaces are being merged with sensors to form networks of miniature information-gathering devices. An important leader in this revolution has been the Engineering Research Center (ERC) for Wireless Integrated MicroSystems (WIMS-www.wim serc.org), led by the University of Michigan and involving Michigan State, Michigan Tech, and five other universities. Formed in 2000 and funded by the National Science Foundation, the WIMS ERC is creating devices capable of measuring a variety of physical parameters, interpreting the data, and communicating over a bi-directional wireless link.

WIMS are expected to become pervasive during the next two decades in applications ranging from healthcare to environmental monitoring and homeland security. They will make the automated gathering of information a reality, extending the electronic connectivity represented by personal communications and the Web to information provided directly by the environment. They will gather highly accurate data, operate at less than 1mW, occupy less than 1cc, and communicate over distances from a few centimeters to a few kilometers. To achieve these goals, the center is exploring ways of reducing the power dissipation of embedded computers (e.g., to less than 1µW), using innovative combinations of low-power circuits and micromechanical devices to collapse the size and power of wireless transceivers, and developing hermetic wafer-level packages to ensure long-term reliability. Finally, it is exploring the materials, processes, and structures that will be needed to realize a new generation of sensors for interfacing with the non-electronic world. Overall, the ERC comprises 118 projects involving 32 faculty, 174 graduate students, and 190 undergraduates.

This prototype cochlear microsystem includes a 32-site electrode array capable of insertion into the scala tympani of the inner ear, where electrical stimulation is used to bypass defective hair cells and restore hearing to the profoundly deaf.
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Because many applications begin at relatively low volumes, the WIMS ERC is developing a generic architecture for microsystems that can work across many applications, lowering cost, speeding development, and facilitating the use of high-volume semiconductor processing. A microcontroller, optimized for data acquisition and containing a wireless interface and circuitry for energy scavenging, interfaces with front-end sensors over a standardized sensor bus. The same platform can thus be tailored for different applications just by choosing an appropriate suite of sensors and accompanying software. An increasing share of these microsystems is based on nanotechnology.

Research thrust activities in micro-power circuits, wireless interfaces, packaging, and sensors are joined to realize a number of testbed microsystems: an implantable intraocular pressure sensor for treating glaucoma; a family of implantable neural prostheses for disorders such as deafness, paralysis, epilepsy, and Parkinson’s disease; and an environmental monitor for pressure, temperature, humidity, radiation level, and air quality. Important in their own right, these testbeds also represent the broad range of expected microsystem applications.

An integrated gas chromatograph module (top) containing two 50cm CVD-sealed separation columns and a multi-element detector. The columns (middle) operate at 100°C with an input power of only 11mW. A chromatograph of 30 air pollutants from a 3m silicon-glass column is shown below.
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Thirty-two-site, high-density thin-film electrode arrays have been realized in a cochlear microsystem for the deaf, and a cortical microsystem, operating at less than 15mW, captures command signals in motor cortex from as many as 64 sites simultaneously as a first step toward returning to quadriplegics limited control over their surroundings.

An integrated gas chromatography (µGC) system, being developed as part of the environmental monitor, has the potential to be at least 100 times faster, smaller, and less expensive than its tabletop predecessors. Using MEMS technology to integrate an inlet filter, calibration source, preconcentrator, microvalves, separation columns, detectors, and a micropump into a wristwatch-size package, the goal is a device implemented on no more than a few chips and capable of complex gas analysis in seconds with parts-per-billion detection limits.

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A family of custom WIMS microprocessors has already achieved operating power levels from 1nW to 100µW, consistent with energy scavenging. New transceiver designs together with miniature RF-MEMS antennas are setting new records in low-power, low-data-rate wireless communications, and packages sealed at wafer-level using anodically bonded gold-silicon eutectics have achieved pressures stable to ±1mTorr.

Microsystems are ideal tools with which to encourage more young people to pursue careers in engineering, and the WIMS ERC offers educational programs at the K-12, university, and professional levels.

Ken Wise is director, Center for Wireless Integrated MicroSystems, an NSF Engineering Research Center at the University of Michigan. He can be contacted at (734) 764-3346 or at wise@umich.edu.


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