Researchers from the University of Michigan have created what they claim is the world's first millimeter-scale complete computing system, designed as an implantable eye pressure monitor for glaucoma patients. Incorporating a microprocessor, pressure sensor, memory, thin-film battery, solar cell and wireless radio with an antenna that can transmit data to an external reader device, the device is just over one cubic millimeter in size. The scientists see it as the next step in the evolution of ever-smaller and more efficient computers.
"When you get smaller than hand-held devices, you turn to these monitoring devices," said U Michigan's Prof. David Blaauw. "The next big challenge is to achieve millimeter-scale systems, which have a host of new applications for monitoring our bodies, our environment and our buildings. Because they're so small, you could manufacture hundreds of thousands on one wafer. There could be 10s to 100s of them per person and it's this per capita increase that fuels the semiconductor industry's growth."
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The lilliputian computer uses the third generation of the university's Phoenix chip, which utilizes a unique power gating architecture and an extreme sleep mode to achieve ultra-low power consumption. The system wakes itself up every 15 minutes to take readings, consuming an average of 5.3 nanowatts. In order to stay charged, the battery requires exposure to ten hours of indoor light per day, or 1.5 hours of sunlight. Up to a week's worth of data can be stored at one time.
While the device can send data to an external reader, it is so far not able to communicate with other systems like it – something that's imperative if such computers are ever to make up a wireless sensor network. To that end, U Michigan's David Wentzloff and Kuo-Ken Huang have been developing a tiny on-chip antenna that will allow for node-to-node communication.
Part of what allows the sub-cubic-millimeter antenna to keep its size down is the elimination of the crystal. Usually, crystals are required for keeping time, and selecting a radio frequency when two devices are communicating. Instead, the tiny new antenna acts as its own reference, thanks to a size and shape that precisely dictates how it will respond to electrical signals. This reportedly means that a radio equipped with such an antenna would not need to be externally tuned, and that a network of such radios would automatically align themselves at a common frequency. Wentzloff and Huang are now working on reducing the power consumption of their antenna.
The millimeter-scale implantable computer is not expected to be commercially available for several more years.
The research on both technologies was presented this week at the International Solid-State Circuits Conference (ISSCC) in San Francisco.