HighEfficiency STJ Xray Detectors Stephan Friedrich Matthew Carpenter LLNL Detector Testing This work was funded by DOE grants DESC0006214 DESC0002256 and SC0002256 This work performed under the auspices of the US Department of Energy by Lawrence ID: 243681
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Slide1
112-Pixel Arrays ofHigh-Efficiency STJ X-ray Detectors
Stephan FriedrichMatthew CarpenterLLNL (Detector Testing)
This work was funded by DOE grants DE-SC0006214, DE-SC0002256 and SC-0002256.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
John HallRobin CantorStar Cryo (Fabrication)
Jack HarrisBill WarburtonXIA (Electronics)
Synchrotron Science
ALS, SSRLSlide2
Superconducting Tunnel Junction Detectors
Al
2
O
3
2
00×
200 μm
2
Nb
Ta Absorber
Al
SiO
2
Al
Ta
X-ray Photon
Small energy gap (Δ
≈ 1meV)
⇒
(Comparably) h
igh energy resolution (<10 eV FWHM)
Short excess charge life time (~µs)
⇒
(Comparably) high count rate (>5,000 counts/s)
Energy resolution ∆E
FWHM
= 2.355√(ε
E(F+1+1/<n>)
Si Substrate
SiO
2
STJ Operating Principle
06/26/2013
LTD-15, Pasadena
Signal = Current pulse
Al
Al
Ta
Ta
AlOx
Δ
Al
Δ
TaSlide3
STJ Performance (as of LTD-14)
06/26/2013
LTD-15, Pasadena
Single-pixel spectrum of MnO + Fe7(CN)18 on Al
Resolution vs. Count RateSlide4
At the Synchrotron, We Need Efficiency
Single Pixel
06/26/2013
LTD-15, Pasadena
36 Pixels200 x 200 µm2
112 pixels of 200 x 200 µm2 STJs
For details on fabrication, ask Robin Cantor at the STAR Cryoelectronics booth.
⇒ Matt Carpenter
(Monday talk)
Options: 1) Increase area/pixel 2) Thicker Ta absorber 3) Arrays: Detectors, readout Slide5
Scalable 32-Pixel STJ Preamplifier
New preamp has same noise, but is small,
cheap ($25 in parts), and remote-controlled.
Existing preamp works fine, but is too big, too expensive (~$1k) and bias is manual.
R
F
R
dyn
V
bias
e
n
I
X
V
out
=I
X
R
F
STJ
06/26/2013
LTD-15, Pasadena
STJ
Preamp Controller
R
dyn
V
bias
from DAC
e
n
I
X
V
out
=I
X
R
F
New: 32 channels
Old: Single channelSlide6
Small, Cheap, Remote-Controlled Preamp
For details, ask Bill Warburton at XIA LLC
06/26/2013
LTD-15, Pasadena
Simultaneous bias scan of all pixels:Average current provides I(V)… … rms fluctuations measure noise.Slide7
X-ray Spectra at LLNL
With old single-channel preamp:
27 of 32 pixels tested have high resolution (rest is either open or shorted).
With new 32-channel XIA preamp(and 32-pixel digitizer / DSP board):
06/26/2013
LTD-15, PasadenaSlide8
More X-ray Spectra from Same 112 Pixel array
26 of 32 pixels tested have high resolution (rest is either open or shorted).
06/26/2013
LTD-15, Pasadena
Ta STJs seem to trap flux more easily than Nb STJs.
With old single-channel preamp:
With new 32-channel XIA preamp
(and 32-pixel digitizer / DSP board):Slide9
Sum Spectra
06/26/2013
LTD-15, Pasadena
With old setup, rise time discrimination can be used to veto bottom layer events.⇒ a) Implement veto in XIA DSP, or b) Make STJs with thicker Ta absorber
53 pixels of 112-pixel STJ array, 165 nm Ta absorber Slide10
X-ray Absorption Spectroscopy with STJs
Electron yield:
Sample surfacesModerate bgnd.
SynchrotronMonochromatic,intense X-ray beamSample xAbsorption µx(E)
DetectionThree options:
Monochromator
Transmission:
Thin samples
High background
Fluorescence:
Bulk samples
Low background
Fluorescence-detected XAS provides highest sensitivity,
if
the detector used can separate the fluorescence of interest with high efficiency.
Scan energy of X-ray beam, measure absorption (by transmission, e-yield or X-ray yield)
06/26/2013
LTD-15, Pasadena
Sample
core
levels
valence
levels
vacuumSlide11
Organic Photovoltaics (“Plastic Solar Cells”)
• Cheap, light, cheap, flexible, cheap…
• Not as efficient yet, ~12% max in the lab• Efficiency depends on microstructure
06/26/2013
LTD-15, Pasadena
Glass substrate
Ca/Ag electrode
ITO electrode
PEDOT:PSS
P3HT - PCBM
Bulk hetero-jct.
active layer
For details, ask Adam Moulé at UC Davis
Ca-L-edge Absorption Spectrum
with Ca electrode
removed
.Slide12
Organic Photovoltaics (oPV)
Ca XAS of organic PV material (PCBM)
06/26/2013
LTD-15, Pasadena
Ca diffuses from electrode into active area! Electrode materials can serve as dopants.
C XAS: Occupancy at E
F changes: Doping!S. Mauger et al., Adv. Funct. Mater. 23, 1935 (2013)
E
V
(oPV)=-6.1eV
E
C
(oPV)=-3.7eV
E
F
(Ca)=-2.9eV
Band gap
E
F
(Ag)=-4.6eV
Energy levels:Slide13
112-Pixel Ta-STJ X-ray Detector Arrays
• ~5 to ~10 eV FWHM below ~1 keV, ~5000 counts/s per pixel
• 112-pixel arrays have high uniformity, 8-9 eV FWHM, ~75% yield (STAR Cryo)• Computer-controlled 32-channel pre-amplifier and digitizer cards (XIA LLC)• Chemical analysis of dilute samples (e.g. organic solar cells with UC Davis)
06/26/2013LTD-15, Pasadena