Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 8. DETECTOR GEOMETRIES 52
Figure 8.4: Left: The rst CVD diamond tracker (11cm 2 ) with a 100 m pitch, wire-bonded
to a VIKING readout chip. The strips are surrounded by a guard ring. Right: A24cm 2 CVD
diamond tracker, connected with two VA2 chips. The resistor and capacitor to the right form a
low pass lter for the bias HV line; the scale's major ticks represent centimeters.
both cases. With silicon detectors, for comparison, the spatial resolution strongly depends
on the SNR. It seems that certain limitations to the spatial resolution of CVD diamond
are implied by the polycrystalline, inhomogeneous structure.
In order to obtain two-dimensional particle track information, two strip detectors
can be used, one of which is rotated, as it is done in a beam telescope. However, this
method is entirely secure only with low particle rates, i.e., one single particle per amplier
time constant, resulting in one hit strip in each plane. Otherwise, the hits may become
ambiguous, and track reconstruction is no longer possible. One possible workaround to
diminish the probability of such \ghosts" is to use a third strip layer under a certain
angle. Theoretically, even more layers under dierent angles could be used, but the eort
of track recognition would be far too complicated. The safe solution, at the cost of a large
number of readout channels, is to use pixel detectors.
8.3 Pixels
A large number of small, equally shaped dots makes up a pixel detector. The dimensions
of the pixels are primarily limited by the readout electronics. In contrast to strip detectors,
here it is impossible to wire-bond the detector to a readout chip located nearby. Pixel
detectors require a readout chip with amplier cells of the same dimensions but mirrored,
which is then bump-bonded onto the detector, forming a \sandwich". This conguration