Development of one thousand pixel superconductingtunnel-junction array X-ray detectors toward EDX systems
with high energy resolution and high throughput
Go Fujii, Masahiro Ukibe, and Masataka Ohkubo
National Institute of Advanced Industrial Science and
Technology (AIST)
The STJs were fabricated in the clean room for analog-digital
superconductivity (CRAVITY) at AIST.
Outline
Motivation
Our present work of STJ spectrometer
Development of 1000 pixels STJ array
Summary
Motivation
Elemental mapping with sub-micrometer scale SEM
by scanning
electron
image of a heatsteel
microscopy (SEM) with energy dispersive X-ray resistant
spectroscopy
(EDX)
is widely applied in science, engineering, and technology


By using low acceleration voltage SEMs (LVSEMs), it is theoretically
possible to identify and quantify an elemental composition of a
sample with a nanometer-scaled lateral resolution [1]
However, in LVSEMs, emitted characteristic X-rays from samples are
only soft X-rays with a low intensity.
Soft X-ray spectrometers should have high throughput as well
as high energy resolution.
[1] R Wuhrer and K Moran, IOP Conf. Ser.: Mater. Sci. Eng., 109, 2016, 012019.
Comparison of soft X-ray spectrometers
Energy-dispersive type
Oxford instruments
High
Throughput
Silicon drift
Detector(SDD)
(10-1 sr, 50 eV)
Wave-dispersive type
Target
Superconductingtunnel-junction(STJ)
(10-3 sr, 5 eV)
Diffracting
crystal (WDS)
(10-4 sr, <10 eV)
Low
Bad
Energy resolution
JEOL Ltd.
Good
Our present work of STJ spectrometer
SEM-EDX system with developed STJ spectrometer
In order to demonstrate performances of the STJ
spectrometer, we have built up a prototype SEMEDX system combined with the STJ.
Developed 100-pixel STJ array
•
•
•
Detection area : 1 mm2
Mean energy resolution :
6.7 eV@400 eV
Max. counting rate :
100 kcps
SEM-EDX system with developed STJ spectrometer
x60
Analysis example: Heat-resistant steels
 The creep strength and creep life of heat-resistant steels (9Cr-Fe) can be
improved by adding small amounts of light elements such as B, C, and N
Measurement time:
0.5 hour
Elemental mapping (Sampling number: 128×128 pixels) ⇒ 8,000 hour
(~1 year)
Throughput of the analyzer ⇒ 1,000 times
Idea for improvement of the throughput
E-beam
Present
Polycapilary
“collimating” optics
E-beam
Throughput:
X1,000
Polycapilary
“focusing” optics
Input capture angle: 14°
Input capture angle: 5°
Photon flux
Requirement
Beam size
Present
New
> 100k photons/s
> 1M photons/s
~ 12 mm
~ 1 mm
Photon flux > 1000
Pixel number:
~ 100 photons/s/mm
density
New
2
~M photons/s/mm2
(max counting rate per one pixel less than kcps)
Detection area: >1 mm2, Max. counting rate: >1Mcps,
Filling factor:>50 %
Development of 1000 pixels STJ array
Development of one thousand pixels
Pixel number : > 1000
512-pixel STJ array
Low filling factor
in conventional STJ structure
which make the wiring beside
the STJs
Filling factor(FF): 7 %
In this work, we have developed new structure
to make close-packed STJ arrangement
STJ with three-dimensional structure (3D-STJ)
Top view
Cross-sectional view
STJ layer
Wiring layer
Si substrate
70 %
3D
12 times
Conventional
5.7 %
Fabrication of 3D-STJs
(1)
(5)
(8)
(2)
(6)
(3)
(4)
(7)
(9)
Rrms:0.3 nm
Summary
 We have developed SEM-EDX systems combined with the
100-pixel STJ array and have performed the analysis of
materials.
 We have developed 1024-pixel STJ array spectrometer
and evaluated the performances.
- Operation yield: ~ 95 %
- Mean energy resolution: 12.6 eV
 In the future, we will develop improved SEM-EDX systems
combined with the 1024-pixel STJ array spectrometer, and
the systems can achieve the high throughput of SDDs with
the high energy resolution of WDSs.
Thank you for your attention