Biomedical Engineering Reference
In-Depth Information
would be tedious. Therefore, the bottom glass of the sandwich is furnished with
nickel tracks with gold pads on top. The gold supplies the actual contact between
nickel conductors and silicon.
These metal structures are deposed via sputtering and patterned by wet chemical
etching. During anodic bonding the gold pads alloy with the silicon and form an
eutectic contact.
To minimize mechanical stress between the nickel conductors and the silicon, a
500 nm step, which corresponds to the height of the metal tracks, is etched into the
silicon before the wafers are bonded. Another 5 mm deep step is etched at areas,
which are to be removed, i.e., anodic bonding is to be prevented.
After the DRIE-process the second glass wafer is bonded on top of the silicon
structures to close the plasma and the ionization chamber. It also serves to mechani-
cally stabilize the system. To install the electrical contacts and the gas supply the
PIMMS chip is glued to a PCB and the gold pads of the chip are connected via wire
bonding to the PCB. After that, as described in Sect.
4
, capillaries are glued to the
plasma-/ionization-chamber inlet to connect the PIMMS to plasma and sample gas
supplies.
6
Hardware and Software
From the numerous and partly new functional principles as discussed in previous
sections the number and complexity of the peripheral components needed to operate
the PIMMS can be estimated. Besides the PIMMS-chip itself and the environment
providing an appropriate vacuum the electronic hardware is another very important
parameter, which determines the cost and size of the device. As the many subsys-
tems of the spectrometer and their interactions are not standard, in many respects
completely new electronic has to be generated to drive the system and read and
evaluate the measurements, respectively. To allow real-time applications, such as
online control, several hardware components have to work independently from a
central controller, which is another challenge for the firmware and software imple-
mentation. This section presents an overview on present state of the hardware,
firmware, and software infrastructure for the PIMMS and will outline the further
steps for industrialization.
6.1
Electronic Components
As a result of miniaturization several electrical extremes are concentrated on the
chip area of ca. 1 cm²: There are DC-voltage-sources in range of −2,000 to 200 V
driving electrodes and the MCP, the micro-plasma electron source is powered by a
RF-generator at 2.45 GHz, which is ignited by an arc discharge. For the ion separa-
tion steep pulse trains of several volts up to 270 MHz with a bandwidth of
