CUBE - XGLab

High rate X-Ray spectroscopy with Silicon
Drift Detectors coupled with “CUBE” front-end
electronics
L. Bombelli(1,2), R. Alberti(2), C. Fiorini(1), T. Frizzi(2), R. Quaglia(1)
(1) Politecnico di Milano, Dip. Elettronica e Informazione, Piazza L. da Vinci 32, I-20133, Milano, Italy
(2) XGLab SRL, via Moretto da Brescia 23, I-20133, Milano, Italy, ph. +390249660460, info@xglab.it
Summary
The development of radiation detectors for high-resolution X-ray spectroscopy is a research field of continuously growing interest, for its application either in
scientific research (e.g. in synchrotron experiments) or in industrial applications like X-ray fluorescence, X-ray diffraction and microanalysis with SEM, just to make
few examples. In most of the applications, especially when a mapping analysis is required, the general trend is to increase the count-rate. This reduces the
measurement time or increases the accuracy thanks to the higher statistics. As a consequence, the performances of the system at short processing time are of
primary concern.
In this work, we compare the performances of our CUBE circuit with respect to the typical performances of the external JFET transistor. We will show that CUBE
enables to get superior energy resolution at short shaping time. These CUBE characteristics lead to practical advantages in several industrial applications already
cited, like the possibility to get high-rate spectroscopy still preserving enough energy resolution to identify light elements.
CUBE’s main features
Preamplifier design to replace the front-end JFET
Advantages
High signal level at the output of the module.
No sensible loop outside the module.
Possibility to drive “long” connection.
Very low series noise. Superior performance
respect to all the front-end JFET available at
short shaping time.
cooler
Erengy resolution FWHM [eV]
peaking time
0.5 us
170
1 us
160
2.2us
150
140
130
120
1
10
100
1000
30
Input Count rate [kcps]
Mn-Ka shift [eV]
Measures shows the possibility to have
contextually close-to-optimum energy
resolution and the highest counting rate.
The shift of the Mn-Ka lines contains both potential
changes of CUBE gains and gain/offset variation on
the DPP.
1
10
170
160
0.1us
1
2
3
4
5
6
7
8
100
1000000
XRF measurement at
Elettra synchrotron
Sample: Zn
deposition with
trace of Ga
Same detector type
and assembly
The CUBE
advantages
become evident in
applications where
a very fast analysis
is required, like in
XRF mapping
applications.
0
-30
180
XRF applications
2.2 us
-20
A Stable operation up to 1.5Mcps has been
measured
190
Peaking time [us]
1 us
-10
200
0
0.5 us
10
210
120
peaking time
20
JFET-based
preamplifier
220
130
In application where an high flux of photons
is available. The classical trade-off is the
maximum output-count rate Vs. energy
resolution.
CUBE makes possible to readout the detector
with a very short peaking time with an
excellent energy resolution, in the past only
possible with longer peaking times.
25mm2 SDD @ -30°C
DPP with Trapezoidal filter
The performances has been confirmed by testing
CUBE with different SDD area, different SDD
manufacturer and measurement conditions.
The figure on the left report a comparison of the
energy resolution at the Mn-Ka line measured
with the same type of SDD (a circular 25mm2 SDD
at -50° C) with CUBE and a more standard JFET
readout.
A commercial digital pulse processor with
trapezoidal filter has been used.
CUBE
230
140
High count-rate measurements with CUBE
180
0.2us
240
150
The possibility to have a small, low-power and
monolithic preamplifier enable the readout of
multi-channel detector even in 2-D pixelated
detector.
CUBE
250
1000
Measurement condition (A)
Peaking time= 1us
Input count rate = 100 kcps
Output count rate = 73 kcps
Dead time = 27%
Energy resolution
CUBE: 132eV @ Mn-ka
JFET: 152eV @ Mn-ka
CUBE
Zn-Ka
JFET
100000
Ga-Ka
Zn-Kb
10000
Counts
SDD
260
Escape
Ga-Kb
1000
100
Primary
Fe
Ar
Ca
Al
10
1
1000
3000
5000
Measurement condition (B)
Peaking time= 0,3us
Input count rate = 800 kcps
Output count rate = 360 kcps
Dead time = 54%
Energy resolution
CUBE: 138eV @ Mn-ka
JFET: N/A
7000
ADU
1000000
9000
Zn-Ka
Zn-Kb
JFET
100000
11000
Ga-Ka
CUBE
Escape
Ga-Kb
Primary
10000
Counts
radiation entrance window
750um x 750um x 250um
<6mW
3.4el ENC
4.4el ENC
7ns
<30ns
<125eV @ 6keV
FWHM Mn-Ka
Physical size
Power Consumption
Measured Noise (no SDD)
Measured noise (with SDD)
Rise time (no SDD)
Rise time (with SDD)
Best energy resolution
Design TO8 Compatible
Simulation shows that CUBE is a suitable CMOS preamplifier for SDD with external front-end readout.
The best energy resolution achievable with a standard SDD is close to the state-of-the-art
performances.
The energy resolution at short shaping time is one of the best results reported so far for a SDD
(147eV at 100ns peaking time)
Fe
1000
Ar Ca
Al
100
In collaboration with XAFS Beamline
ELETTRA Trieste Dr. Olivi
10
1000
Input Count rate [kcps]
3000
5000
7000
9000
11000
ADU
SDD operation with CUBE at warm temperature....
165
155
150
145
T=-10°C
140
T=-30°C
135
T=-35°C
T=-50°C
130
125
Advantages of full CMOS readout
It is known that the operation of bipolar or JFET transistor is affected by extremely low temperature.
The CMOS technology in intrinsically more robust respect to low temperature.
The measured energy resolution below shows that CUBE work perfectly even when cooled down to
a temperature of 50 K.
Not only, the optimal resolution gets better due to the evident reduction of SDD leakage current.
Also the CUBE performances improve with lower temperature due to an increase in the Mosfets
trasconductance.
160
120
Square area SDD with 60 mm2 active area
The SDD in not collimated.
155
0,5
1
1,5
2
2,5
3
3,5
4
4,5
Peaking Time (us)
152 eV resolution
with large area SDD
Cooled at only –10 °C
with 0.5us peaking time.
Fe spectrum
60 mm2 SDD
SDD/CUBE at 50 K
220
55
210
Fe Energy resolution for a
80 mm2 collimated detector
55
200
190
180
T=-10 °C
170
T=-20 °C
160
T=-30 °C
150
T=-35 °C
140
130
150
Resolution FWHM (eV)
0
Resolution FWHM (eV)
Resolution FWHM (eV)
Advantages of very-low series noise
Possibility to operate large-area SDDs with
no resolution penalty.
Higher thermal budget.
Better high count-rate measurements.
In handheld applications: less sensitive to
room temperature, faster operation settling
time, low-power Peltier required.
55
Fe Energy resolution for a 30 mm2
collimated detector
160
...and at cryogenic temperature
145
240 K
140
200 K
160 K
110 K
135
50 K
130
125
120
120
0
0
0,5
1
1,5
2
2,5
Peaking Time (us)
3
3,5
4
4,5
0,5
1
1,5
2
2,5
3
3,5
4
Peaking time [us]
The CUBE is suited for operation in Liquid Nitrogen in application with Ge detectors.
to contact us
info@xglab.it