Download - 112-Pixel Arrays of High-Efficiency STJ X-ray Detectors

112-Pixel Arrays ofHigh-Efficiency STJ X-ray Detectors

Stephan FriedrichMatthew Carpenter

LLNL (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 Cantor

Star Cryo (Fabrication)

Jack HarrisBill Warburton

XIA (Electronics)

Synchrotron ScienceALS, SSRL

Superconducting Tunnel Junction Detectors

Al2O3

200×200 μm2

Nb

Ta AbsorberAl

SiO2 AlTa

X-ray Photon

Small energy gap (Δ ≈ 1meV) ⇒ (Comparably) high energy resolution (<10 eV FWHM)Short excess charge life time (~µs) ⇒ (Comparably) high count rate (>5,000 counts/s)

Energy resolution ∆EFWHM = 2.355√(εE(F+1+1/<n>)

Si Substrate

SiO2

STJ Operating Principle

06/26/2013 LTD-15, Pasadena

Signal = Current pulse

Al Al Ta TaAlOx

ΔAl

ΔTa

STJ Performance (as of LTD-14)


Single-pixel spectrum of MnO + Fe7(CN)18 on Al Resolution vs. Count Rate

At the Synchrotron, We Need Efficiency

Single Pixel


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

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.

RF

Rdyn Vbias

en

IX

Vout=IXRF

STJ


STJ Preamp Controller

Rdyn Vbias from DAC

en

IX

Vout=IXRF

New: 32 channelsOld: Single channel

Small, Cheap, Remote-Controlled Preamp

For details, ask Bill Warburton at XIA LLC06/26/2013 LTD-15, Pasadena

Simultaneous bias scan of all pixels:Average current provides I(V)… … rms fluctuations measure noise.

X-ray Spectra at LLNLWith 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):


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, PasadenaTa 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):

Sum Spectra


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

X-ray Absorption Spectroscopy with STJs

Electron yield:Sample surfacesModerate bgnd.

SynchrotronMonochromatic,intense X-ray beam

Sample xAbsorption µx(E)

DetectionThree options:

Monochromator

Transmission:Thin samplesHigh background

Fluorescence:Bulk samplesLow 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)


Sample

corelevels

valencelevels

vacuum

Organic Photovoltaics (“Plastic Solar Cells”)• Cheap, light, cheap, flexible, cheap… • Not as efficient yet, ~12% max in the lab• Efficiency depends on microstructure


Glass substrate

Ca/Ag electrode

ITO electrodePEDOT:PSS

P3HT - PCBM

Bulk hetero-jct.active layer

For details, ask Adam Moulé at UC Davis

Ca-L-edge Absorption Spectrumwith Ca electrode removed.

Organic Photovoltaics (oPV)Ca XAS of organic PV material (PCBM)


Ca diffuses from electrode into active area! Electrode materials can serve as dopants.

C XAS: Occupancy at EF changes: Doping!

S. Mauger et al., Adv. Funct. Mater. 23, 1935 (2013)

EV(oPV)=-6.1eV

EC(oPV)=-3.7eV

EF(Ca)=-2.9eV

Band

gap EF(Ag)=-4.6eV

Energy levels:

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)


Download - 112-Pixel Arrays of High-Efficiency STJ X-ray Detectors

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