Biomedical Engineering Reference
In-Depth Information
8
Conclusions and Outlook
The PIMMS is presently able to detect molecules in a mass range from 1 to about
several 100 amu with a resolution of 43.
Due to the batch oriented fabrication by standard MEMS processes the PIMMS
has a high potential for a cost-effective fabrication in large volumes. Because of its
small size it allows to access application areas, where conventional mass spec-
trometers can or will not be applied, e.g., mobile applications or in line real-time
monitoring in the chemical industry, environmental surveillance, patient or air
condition monitoring in buildings or vehicles.
However, to address these applications a size reduction of the periphery will be
essential. This holds for the electronics as well as for the vacuum system and sample
supply. Since there is presently not much research in this field, these problems have
been also addressed in course of the PIMMS development.
Microsubsystems presently under investigation are:
an integrated ion/electron ampli fi er
a sample and plasma pressure stage with low dead volume
a liquid sample vaporizer and
vacuum pumps
8.1
Integration of Ion/Electron Multiplier
The presently used amplifier in the system is a hybrid-integrated MCP. This hybid
integration is disadvantageous for a mass production, since it makes an individual
handling of each system necessary to insert the MCP. To allow for an integrated
amplification, a MCP-type device is not the optimum choice. Instead a “classical”
dynode arrangement appears to be appropriate, since it can be fabricated in the same
way and processes as the rest of the PIMMS and is less sensitive to higher pressures
than an MCP, as they are intended in the PIMMS. Such a secondary electron
amplifier is presently under investigation.
8.2
Pressure Stage in Silicon
Despite the miniaturized size of the PIMMS, the way gases are fed into the system
is not optimum for total system integration. Capillaries have to be glued to each
system individually, which in addition to tedious handling decreases the manufac-
turing yield due to defects such as blocked capillaries and/or chambers. Furthermore,
according to pressure analysis, the quadratic pressure drop dependence versus
length is critical when the vertex of the parabola is approached. A slight variation in
the capillary length (in the sub-mm range) causes a pronounced variation in the
