page 1 science payload and advanced concepts office stjs as photon detectors

Science Payload and Advanced Concepts Office

STJs as Photon DetectorsSTJs as Photon Detectors


STJs: principle of operationSTJs: principle of operation

• photon with energy E breaks Cooper pairs quasiparticles

for Ta: ~0.7 meV N0 ~ 850 / eV

• multiple tunneling detected charge:

• resolving power limited by statistics of QP generation and tunneling:

Ta: E ~ 2.0 eV @ E=500eV

Additional resolution degradation:- electronics noise, infrared background- non-uniform detector response

Δ1.7E(E)

0N

(E)0

Nn N(E)tunnel

τloss

τn

n11F1.7EΔ2.355TδE


STJs: energy resolving powerSTJs: energy resolving power

10

100

1000

10000

1 10 100 1000 10000

photon energy (eV)

reso

lvin

g p

ow

er

20x100 micron Ta DROID

25x25 micron Ta STJfrom 6x6 array

50x50 micron Ta/Al STJ

Hf

Mo

Ta

Nb

Tc (K) gap (meV)Nb 9.2 1.55Ta 4.5 0.67Mo 0.92 0.14Hf 0.13 ~0.02


Ta-based STJs (for UV/visible)Ta-based STJs (for UV/visible)

• Ta layers: 100 nmBase: epitaxial (RRR~45)

• Al layers: 30 nm

• Nb wiring (QP out diffusion)

• AlOx barrier: ~1 nm tunnel time ~ 0.5-1 s low leakage: <0.1 pA/m2

• detector area: 10x10 - 100x100 m2

Al

Ta

Ta

Sapphire substrate

SiOx

Nb

Back-illumination

Front-illumination


S-Cam 3 Detector: 10x12 Ta/Al S-Cam 3 Detector: 10x12 Ta/Al STJsSTJs

371

m =

8.9

”

446m =

10.7”

S-Cam 3: 10x12 pixels ; 33x33 m2 FOV = 9x11 arcsec

top electrodecontact wires

25x25 m2

STJ

commonreturnwire

a)

170m = 4”

170m =

4”

S-Cam 2:


S-Cam 3 Detector S-Cam 3 Detector 120 pixels120 pixels

ALL subgap currents ~100 pA low noise operation

Uniform responsivity across array

Fiske modesResidual Jc

Bias region


S-Cam 3 image (9”x11”)S-Cam 3 image (9”x11”)


S-Cam 6: improved spectral resolutionS-Cam 6: improved spectral resolutionAluminium STJs:

• Tc=1.2K T<100mK (ADR)

• expected resolution 2x better than Ta

• Measured resolution ~ Ta

(mechanism and solution

under investigation)

Next step:

molybdenum STJs:

• Tc=0.9K

• better efficiency than Al


Distributed Read Out Imaging Devices Distributed Read Out Imaging Devices (DROIDs)(DROIDs)

absorber with 2 STJs for readout:

• Position sensitivity: S1 - S2• Photon energy: S1 + S2

sapphire substrate

SiOx

Al (65 nm) AlOx

Nb contacts

Ta top electrode

200 m50 m

- - -- - - - - - - Ta absorber


100x20 m2 absorber with 20x20 m2 STJs

E=2.4 eV (FWHM) at E=500 eV

DROIDs as X-ray detectorsDROIDs as X-ray detectors


100x100 m2 absorber

with 20x20 m2 STJs

2D DROIDs as X-ray detectors2D DROIDs as X-ray detectors

10 keV diffraction pattern

from 5 m pinhole

with 2-D DROID


Detection efficiency for 500nm thick Detection efficiency for 500nm thick DROIDsDROIDs

0

0.2

0.4

0.6

0.8

1

10 100 1000 10000photon energy (eV)

eff

icie

nc

y

Ta

Mo


Possible detector layout for NFI1 on XEUSPossible detector layout for NFI1 on XEUSArray of DROIDs

0.5x1.7 arcmin

FL=30m 4.4x15mm

750x75 micron DROIDs 6x200 DROIDs

1.7’ = 15mm = 200 DROIDs

0.5’ = 4.4mm

= 6 DROIDs


Latest Ta/Al STJs for opticalLatest Ta/Al STJs for optical

• Ta layers: 100 nmBase: epitaxial (RRR~30)

• Al layers: 30 nm

• Nb wiring (QP out diffusion)

• AlOx barrier: ~1 nm tunnel time ~ 0.5-1 s low leakage: <0.1 pA/m2

• detector area: 10x10 - 100x100 m2


Latest Ta/Al STJs for opticalLatest Ta/Al STJs for optical

0 1 2 3 4

IR ~2 micron

lambda=500nm R~23

30x30 micron


Latest Ta/Al STJs for optical: resolving Latest Ta/Al STJs for optical: resolving powerpower

MUL169.D3 #6 (30x30) FIR=9.0kHz, w=0.85

0

5

10

15

20

25

30

35

40

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Photon Energy (eV)

Re

so

lvin

g P

ow

er

bulk Ta 0.70meV, G=1

Ta 0.50meV, G=0.45

Ta 0.50meV, G=1

Ta 0.50meV, G=0 (Fano)

page 1 science payload and advanced concepts office stjs as photon detectors

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