A New Improved
Silicon Drift Detector (SDD) for Microanalysis and
X-Ray Mapping Applications
Shaul Barkan*, Valeri D. Saveliev*, Jan S. Iwanczyk**, Liangyuan
Feng*, Carolyn R. Tull**, Bradley E. Patt**, Dale E. Newbury***
and John A. Small***
* SII NanoTechnology USA Inc,
19355
Business Center Drive, Suite 8, Northridge, CA 91324
** Photon Imaging, Inc.
*** National Institute of Standards and Technology
A new class of silicon drift detectors (SMCD)
has been developed for microanalysis and X-ray mapping applications
[1,2]. The SMCD has a large active area (~0.5 cm2), high
energy resolution, and high count rate capability. The detector
utilizes novel structures that have produced very low dark current,
high electric field, uniform charge collection, low noise and high
sensitivity to low energy X-rays [3,4]. A custom designed spectrometer
package has been built with a long probe to fit a JEOL 840 scanning
electron microscope (SEM). In bench-top measurements with an 55Fe
radioisotope source, an energy resolution of 129 eV FWHM was repeatably
measured with the 0.5 cm2 SMCD (at 5.9 keV, 6 - 12
µs peaking time, cooled to -70 oC).
The spectrometer package, shown in Figure 1, contains
a 0.5 cm2 SMCD detector, cooled by using a
small Peltier element. The spectrometer model shown in Figure
1 was designed specifically to use with a JEOL 840 scanning
electron microscope (SEM) at the National Institute of
Standards and Technology (NIST). The probe diameter is ¾” and
its length is 12”. An atmospheric thin window (ATW) from
Moxtek (Orem, UT) is placed at the window edge and allows good
transmission of very low energy X-rays while the detector is
kept in a high vacuum condition. An electron trap is placed on
the window to deflect electrons scattered from the
sample.
The detector spectral response was evaluated using
an 55Fe radioisotope source, as well as by fluorescing
materials with an X-ray source. Figure 2 shows an 55Fe
spectrum showing an energy resolution of 129 eV FWHM at 5.9 keV
(collected at 12 µs peaking time, -70 oC). To
evaluate the high count rate X-ray performance, which is very
important for fast X-ray mapping, a Cu sample was fluoresced
using a Rh anode X-ray tube. Figure 3 shows the Cu spectra
collected at: (a) 3000 cps input, with 206 eV FWHM at 8.04 keV
(0.5 µs peaking time), and (b) at > 1 Mcps with an energy
resolution of 214 eV FWHM and output count rate exceeding 350
kcps. The photopeak position and energy resolution are
virtually independent of count rate.
The detector is
scheduled to be assembled on a JEOL 840 SEM at NIST at the end
of February 2004. We will measure the X-ray energy resolution
and count rate performance under microanalysis conditions. In
addition, we will evaluate the spectral response to very low
energy X-rays, including C and B. The SEM results will be
presented.
References:
[1] S. Barkan, et al., "Vortex® - A new
high performance silicon drift detector for XRD and XRF Applications",
Advances in X-Ray Analysis, Vol. 46 (2003) 332-337.
[2] L. Feng, et al., "A New High Performance Silicon Drift
Detector for XRD and XRF Applications", Hard X-ray and Gamma-ray
Detector Physics V, Proceedings of SPIE, International Society of
Optical Engineering, Vol. 5198, (2004) 103-110.
[3] J. S. Iwanczyk, et al, "Large Area Silicon Drift Detectors
for X-Rays- New Results", IEEE Trans. Nucl. Sci. vol. 46 (1999)
284-288.
[4] U.S Patent #6,455,858 B1 "Semiconductor Radiation Detector",
2002.
Acknowledgements:
This work was supported in part by NIST.
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Figure 1.
Photograph of the first generation
prototype, spectrometer designed
for the JEOL
840 SEM. Probe length is 12”.
Figure 2. Spectral response of
SMCD to 55Fe
(12 µs peaking
time)
Figure 3 (a).
Spectrum of Cu sample at low count rate
(206 eV FWHM at 8 keV, 0.5
µs peaking time and 6%
dead time)
Figure 3 (b).
Cu spectrum at high count rate
(>1 Mcps
input, 350 kcps output, 214 eV FWHM at
8 keV, 0.5 µs peaking time,
68% dead time).
VORTEX® - A New High Performance Silicon Drift
Detector for XRD and XRF Applications
J. Liangyuan Feng, Shaul Barkan and Carolyn R. Tull
SII NanoTechnology USA
Inc., 19355 Business Center Drive,
Suite 8, Northridge, CA 91324
Jan S. Iwanczyk and Bradley E. Patt
Photon Imaging, Inc., 19355
Business Center Drive, Suite 8, Northridge, CA
91324 ABSTRACT
Vortex®, a high performance silicon
drift detector, has been developed and extensively tested
for potential X-ray diffraction (XRD) and X-ray fluorescence (XRF)
applications. As a type of silicon drift detector, it utilizes our
patented structure design [1] and achieves very low capacitance
and very low leakage current with a relatively large active area
(~50 mm2). The detector operates at near room temperature
with thermoelectric cooling and is thus very compact in size. These
features make it ideal for many XRD and XRF applications. Results
will be presented to demonstrate its superior performance over conventional
cryogenic Si(Li) detectors, especially with respect to energy resolution
and throughput at short amplifier peaking times.
Keywords: Vortex®, Silicon Drift Detector,
Silicon Drift Detector, FET, Peltier Cooler, X-ray
Diffraction, X-ray Fluorescence, Multi-channel Analyzer,
Single-channel Analyzer, Digital Pulse Processor, Sealed
Proportional Counter, Graphite Monochromator, SMCD, SDD, XRD,
XRF, Si(Li), SCA, MCA, DPP, SPC, FWHM, ICR, OCR
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High Efficiency Silicon X-Ray Detectors
C. R. Tull, Member IEEE, J. S. Iwanczyk, Senior Member
IEEE , B. E. Patt, Senior Member IEEE, S.
Barkan, and L. Feng
ABSTRACT
Thick silicon drift detectors (SMCD) for high efficiency
X-ray detection have been designed, fabricated and tested. These
thick detectors (up to 1.5 mm thick) extend the practical X-ray
detection range from the current level of ~20 keV, up to ~40 keV,
while still maintaining the low noise and high count rate performance
of the thinner (~0.3 mm) SMCD technology. The increase in X-ray
detection efficiency at higher energies will have a significant
impact on practical uses of these detectors in a wide variety of
X-ray fluorescence (XRF) applications. In addition to increasing
the detection efficiency for X-rays, the thick silicon detectors
will offer improved efficiency for high energy electrons, alphas
and other light particles in nuclear physics and astrophysics applications.
Very high resistivity float zone material was used for the substrates
to minimize the operating voltages required. Multiguard ring structures
were designed to prevent the premature breakdown of the devices
at the voltages required to fully deplete the thick detectors. We
have measured 172 eV and 158 eV FWHM energy resolution at 5.9 keV
(at 4 µs and 12 µs peaking time, respectively, -55 oC)
on 1 mm thick prototype detectors. Spectral performance, energy
resolution, efficiency and count rate performance are presented.
Index Terms: X-ray detector, silicon, drift
detector, synchroton.
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