5 Solid State Detectors
167
Fig. 5.26 On-chip single sided junction FET coupled to the readout node of a cylindrical silicon
drift detector
Having only one surface structured allows using the unstructured surface of
the fully depleted device as radiation entrance window. Not having to take other
functions into considerations, this radiation entrance window can be made very thin
and uniform [22]. The circular geometry with a very small charge-collecting anode
in its centre reduces the capacitive load to the amplifier and therefore the noise.
Having the first transistor integrated into the device [23], the capacitance of the
detector-amplifier system is minimized by eliminating bond wires between detector
and amplifier. In this way stray capacitances between the readout node and ground
are avoided, which makes the system faster and less noisy. Further advantages
are evident as electrical pickup is significantly reduced and microphony i.e. noise
introduced by mechanical vibrations, is excluded. In order to work on the lowly
doped and fully depleted substrate, a non-standard “Single Sided Junction Field
Effect Transistor” (SSJFET) has been developed [24].
Drift detectors with an integrated transistor are commercially available. They can
also be obtained as modules assembled with a Peltier cooler in a gas-tight housing
with a thin radiation entrance window (Fig. 5.27). To demonstrate the excellent
spectroscopic performance achieved with such devices a spectrum obtained with an
55 Fe source and the quantum efficiency are presented in Fig. 5.28 for a cylindrical
SDD with a sensitive area of 5 mm 2 . The detector temperature, important for the
leakage current, was set to −20 ◦ C and the signal shaping time to 1 μs. The Mn Kα
line at 5.9 keV and the Mn Kβ line at 6.5 keV are clearly separated and their widths
are only slightly above the intrinsic Fano limit given by the pair generation process
in silicon.
Cylindrical silicon drift diodes with integrated SSJFETs have been manufactured
with sensitive areas in the range from 5 mm 2 to 1 cm 2 .
167
Fig. 5.26 On-chip single sided junction FET coupled to the readout node of a cylindrical silicon
drift detector
Having only one surface structured allows using the unstructured surface of
the fully depleted device as radiation entrance window. Not having to take other
functions into considerations, this radiation entrance window can be made very thin
and uniform [22]. The circular geometry with a very small charge-collecting anode
in its centre reduces the capacitive load to the amplifier and therefore the noise.
Having the first transistor integrated into the device [23], the capacitance of the
detector-amplifier system is minimized by eliminating bond wires between detector
and amplifier. In this way stray capacitances between the readout node and ground
are avoided, which makes the system faster and less noisy. Further advantages
are evident as electrical pickup is significantly reduced and microphony i.e. noise
introduced by mechanical vibrations, is excluded. In order to work on the lowly
doped and fully depleted substrate, a non-standard “Single Sided Junction Field
Effect Transistor” (SSJFET) has been developed [24].
Drift detectors with an integrated transistor are commercially available. They can
also be obtained as modules assembled with a Peltier cooler in a gas-tight housing
with a thin radiation entrance window (Fig. 5.27). To demonstrate the excellent
spectroscopic performance achieved with such devices a spectrum obtained with an
55 Fe source and the quantum efficiency are presented in Fig. 5.28 for a cylindrical
SDD with a sensitive area of 5 mm 2 . The detector temperature, important for the
leakage current, was set to −20 ◦ C and the signal shaping time to 1 μs. The Mn Kα
line at 5.9 keV and the Mn Kβ line at 6.5 keV are clearly separated and their widths
are only slightly above the intrinsic Fano limit given by the pair generation process
in silicon.
Cylindrical silicon drift diodes with integrated SSJFETs have been manufactured
with sensitive areas in the range from 5 mm 2 to 1 cm 2 .