Biomedical Engineering Reference
In-Depth Information
restrict available geometries, features, and also electrical functions—e.g., highly
conductive metal or silicon structures, which may cause large RF-losses
(Radiofrequency) due to capacitive coupling, and limitations in applying appropri-
ate electrical potentials. In addition complex and mostly individualized 3D-assembly
procedures are finally necessary to fix the systems. This opposes the principle
advantage of micromachining on fine machining processes. On the other hand,
however, mostly positive results with respect to system performance of such not
real microsystem mass spectrometer designs can be demonstrated rather quickly,
also because most of the periphery including the electronics is standard.
Unfortunately such designs are far off the performance a full microsystem approach
would allow, since interfaces between micro- and macrodesigns are problematic
with respect to size accommodation, dead volumes, and adjustment, the vacuum as
well as electric and electronic. Furthermore, volume requirements are hardly
improved and the cost of a complete mass spectrometer keeps the same or is even
higher due to the microcomponent, since the effort for its fabrication, assembly,
and integration is comparable to or even larger than that of fine machined parts and
lot size is low.
The intention of this contribution is to demonstrate that such a micro-mass spec-
trometer can be realized with features which in part resemble that of state-of-the-art
spectrometers for standard applications closely and that the state of the art of this
system is at the verge to make it a commercial, easily to handle analytical system.
To allow the reader to understand the philosophy behind this development and
the physical and technological challenges and already obtained results, the text is
divided into the following subsections: Sect.
2
shortly overviews the basic system
design. In Sect.
3
the simulation and derived design of the different subsystems of
the micro-mass spectrometer are presented and how they entwine to form the com-
plete mass spectrometer. The subsystem to manage the sample and plasma gas pres-
sure and flow is discussed in Sect.
4
. After a description of the applied basic
microsystem technologies and the process flow to fabricate the system in Sect.
5
,
Sect.
6
summarizes the main features of the electronics in hardware and software to
drive and control the system automatically, extract the raw data, and evaluate them
to generate calibrated spectra. In Sect.
7
experimental results for operating param-
eters, mass resolution and spectral width, selectivity, sensitivity, and characteristic
time constants are given and typical spectra are presented and compared to the sim-
ulations. The contribution ends with a summary and outlook for work presently in
progress and still to do in Sect.
8
and finishes with an acknowledgment.
2
The Planar Integrated Micro-mass Spectrometer
In order to avoid the limitations of macro scale mass spectrometers and those where
just single subsystems of such standard systems are exchanged for microdesigns, as
mentioned in the introduction, a fully integrated mass spectrometer containing all
the necessary subsystems was designed. It can be fabricated “in one step,” i.e., all
