Microdischarge-based pressure controlling devices and their applications to chemical sensing in harsh environments.

摘要

Microdischarges offer an alternative and often advantageous sensing and actuation method that has not been significantly exploited in microtransducers. This thesis explores the capabilities of microdischarges to address problems such as cavity pressure control, cavity pressure detection, and purity control of fill gases, which are relevant to microsystems. Microdischarge-based transducers have been developed for these purposes. One interesting aspect of microdischarge-based transducers is the wide latitude of operating temperatures, as they are advantageous for room and high temperature operation.;On-chip sputter-ion pumps control the pressure and gas purity in cavities. They consist of thin-film titanium electrodes patterned on glass substrates. Microdischarges sputter the cathodes, resulting in the selective chemisorption of titanium-reactive gases. Using DC discharges, these devices have reduced the pressure by 168 Torr in an air-filled, hermetically sealed, 6.33 cm 3 package. Starting at 200 Torr, the pressure reduction rate of air is 7.2 Torr/h; oxygen 11.5 Torr/h, and nitrogen 3.4 Torr/h. Relative humidity is reduced at 6%/h. The pumps do not remove helium, purifying gas environments by selectively removing contaminating nitrogen and oxygen. A theoretical model outlining the dependency of gas removal rates on microdischarge parameters is presented.;Microdischarge-based pressure sensors operate by correlating the measured change in spatial current distribution of pulsed DC microdischarges with pressure. One sensor version uses three-dimensional arrays of horizontal bulk metal electrodes embedded in quartz substrates with electrode diameters of 1--2 mm and 50--100 microm interelectrode spacing. These devices have been operated over 10--2,000 Torr, at temperatures as high as 1,000°C. The maximum measured sensitivity is 5,420 ppm/Torr, while the minimum temperature coefficient of sensitivity is -550 ppm/K. Sensors of a second version use planar electrodes, with 0.13 mm2 active areas.;To explore the utility of pressure controlling devices, these transducers are combined with an optical emission sensor to create a high temperature gas phase chemical detection microsystem. The microdischarge-based pressure sensor determines the sample and backfilling gas pressure while the microscale-sputter-ion pump purifies the gas environment. The contaminating nitrogen concentration has been reduced by 56.5x relative to helium and the spectral detection limit has been improved by 8x for carbon at 200°C.