Technical Design Report Super Fragment Separator

DRAFT
material is post processed, i.e. lapped down from 1 mm EG thick wafers by removing several
hundreds of micrometers from the bad substrate side. These much more homogeneous
DG-PC-CVDD films with a charge collection efficiency ≈ 65 % are available between 300 µm and
600 µm thickness. In the next 2-3 years, (10 x 10) mm 2 SC-CVDD samples have been announced
for sale. Intense R&D is going on to achieve areas as large as 2 inch wafers. All those prices
mentioned above are forced at the time being by decisions which do not correspond to real production
costs. It has been demonstrated that PC-CVD-DD operating with low-noise
low-impedance broadband amplifiers are able to measure linearly heavy ion rates in a broad range
from 1 Hz up to > 500 MHz by single particle readout of one detector channel. This value has been
obtained with a detector of large capacitance of 8 pF and a scaler which limited the measurement
due to its 500 MHz bandwidth. The s-p rate capability is higher for reduced strip capacitance and
GHz electronics signal processing [21]. If two-dimensional position resolution on thin detectors is
needed, crossed strips can be applied on opposite sides of the diamond substrate. Note, that although
this type of detector is of high interest for different experimental groups and the expectations
for a successful realization are good, no such a detector has been developed up to now at GSI.
Thus, joined R&D e.g. with the Atomic Physics and R³B collaborations is foreseen. Figure 2.4.81
shows the microscopic image of a pixel structure, which has been processed by sputtering a 1000 Å
Si3N4 layer on a metallized surface. PC-CVDD micro-strip and micro-pixel detectors have been
developed (Figure 2.4.82) and excessively tested by the RD42 Collaboration at CERN [22] (GSI is
a member), striving for MIP tracking at high luminosity colliders.
Figure 2.4.81: Pixel readout by Si3N4 - isolated micro tracks. Microscopic image of a pixel structure on a 1.3
µm thick diamond membrane. The small pixels are (110 x 290) µm 2 and the large ones (400 x 400) µm 2 . The
width of the tracks is 15 µm and their pitch is 30 µm.
For fast micro-electrode readout providing a large dynamic range as needed for HI measurements
no suitable ASIC exists yet. For CBM at FAIR solutions to readout the diamond start detector,
which will be a (20 x 20) mm 2 micro-strip detector of a pitch of 50 µm at a strip width of 25 µm, are
currently developed. The electronics would fit also for beam monitoring and tracking at Super-FRS.
84