1 February 2002
Microchip warns of danger
A Swiss Federal Institute of Technology (ETH) team in Zurich has developed a single silicon chip that can detect the presence of and measure dangerous gases, said team member Dr. Andreas Hierlemann (hierlema@iqe.phys.ethz.ch).
The ETH developed the chip during a collaboration project on handheld gas detection units with other European universities. Hierlemann said three types of microsensors pack on to a single silicon chip.
There are many target application areas envisaged for the gas sensor chip. Monitoring air quality in closed rooms is one use. It is also possible to detect the presence of dangerous—even poisonous—substances in the air, such as benzene at fuel stations or perchloroethylene at dry-cleaning installations with the device.
It is just 7 by 7 millimeters in size. This allows for integration in lightweight handheld or even credit-card-size units. The small dimensions and the broad range of candidate applications allow for low-cost mass production of the silicon chip with existing manufacturing facilities of the microelectronics industry.
Along with the sensors, the entire driving and signal-conditioning electronics, as well as a digital interface that serves to control and run the system, integrate on the chip.
Special polymers coat the microsensor area of the chip. They absorb molecules from the air—predominantly volatile organic compounds (VOCs). The volume absorption of the VOCs causes a change in physical properties of the polymer (mass, dielectric coefficient, release of heat), which generates specific electrical signals.
Three types of transducers are present. The principals behind these transducers are proven and not new. This is the first time, though, all three measuring different quantities appear on the same piece of equipment.
The first type, a micromachined resonating cantilever, monitors the mass change upon volatile absorption with a precision of less than a picogram (a billionth of a milligram).
The second transducer monitors changes in the heat budget upon absorption or desorption (condensation or vaporization heat) of the organic volatile in the polymer.
The third type of transducer records the changes in dielectric properties, which makes it very sensitive to polar molecules such as alcohol or water. Because the various volatile organics have different chemical and dielectric characteristics, as well as varying masses, the three transducers produce distinct signals that enable volatile identification. IT
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