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Tech lets ICs sense surroundings

Posted: 05 Oct 2007 ?? ?Print Version ?Bookmark and Share

Keywords:dielectric sensor? IC surfaces? mixed-signal CMOS? capacitive sensor?

ChipSensors Ltd unveiled a technology that it claims will let the surface of an IC sense temperature, humidity, pathogens and certain gases.

Sitting above a conventionally manufactured complex CMOS IC, the embedded-sensor technology may be used to create miniature yet conventional industrial, scientific and medical sensors, with the IC implementing the MCU and a wireless transmitter to send collected data off-chip.

Central to the technology is the low-k dielectric found in standard submicron CMOS processes. The material's porous nature makes it possible to change its dielectric constant by selectively admitting or blocking ingress of the agent to be sensed, thus forming the basis of a capacitive sensor.

Normally, the surface of an IC is passivated, so ambient conditions don't affect it. Similarly, the pores of low-k materials are often closed using surface treatment. But ChipSensors claims that exposing a prepared area to ambient conditions allows the resulting electrical characteristics to be detected and measured by means of on-chip circuitry.

Challenging the prevailing view that moisture compromises an IC's long-term reliability, ChipSensors CEO Tim Cummins insists that modern low-k dielectrics aren't prone to swelling. "We can selectively open up part of the surface of the chip," he said. "We usually use only the top level of a multilevel interconnect. The etch-stop layer can prevent buried layers from being affected." The variation in dielectric constant due to moisture or gas ingress can be measured using an 18bit Sigma delta ADC the company has developed.

In-circuit heater element
The sensor technology may be applied as a separate process after conventional chip production or as a method for measuring the fringe capacitance of a prepared dielectric on the surface of a chip, Cummins said. Chip-Sensors has proposed the use of an in-circuit heater element to purge moisture and return the porous dielectric to its original condition, ready for reuse.

Cummins expressed confidence that the technology will work with chemical vapor deposition and spin-on dielectrics from multiple suppliers. "We've made 0.18?m CMOS prototypes with United Microelectronics Corp. through the Europractice multiproject wafer service without any special steps," he said.

ChipSensors has also attracted the attention of a U.S. company, which is providing 0.13?m devices. Cummins would identify the partner only as "an MCU company."

Though it appears the technology would readily allow the development of a single-chip wireless sensor, ChipSensors' current demos comprise a chip-based sensor and an off-chip wireless link communicating to a laptop that displays real-time measurements.

The technology could serve as an all-electronic replacement for electromechanical thermostats and humidistats. It may also prove effective for monitoring the behavior of processors and other complex chips, with the results fed back to help them control their own performance and power consumption.

ChipSensors is also developing an ultralow-power wireless version of the technology for passive and active ID tags. So far, the startup has no products on the market. It expects to provide chip sensors without the radio or MCU integrated.

- Peter Clarke
EE Times Europe

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