By: Nikhil Jethava National Institute of Standards and Technology…beamdocs.fnal.gov › AD › DocDB › 0032 › 003294 › 001 › Fermilab... · 2009-01-30 · Nikhil Jethava

Nikhil Jethava Superconducting TES @ Fermilab January 20, 2008

Superconducting Transition Edge Sensors (TES)

By:

Nikhil Jethava

National Institute of Standards and Technology, Boulder, CO.


Outline

• Introduction

• Applications:

•Detectors for Astronomy

•Microcalorimeters for Gamma-ray Spectroscopy

• Optics Alignment Tool

• Conclusions


G Thermal conductance

E

C

Incident PhotonThermometer

Heat Capacity

T0 ≈ 80mK

Bulk Absorber

Introduction

• Thermometer and absorber are

connected by a weak thermal link

to a heat sink.

• Incoming energy is converted

to heat in the absorber:

ΔT = T – T0 = E/C.

• Temperature rise decays as

power in absorber flows out to

the heat sink

τ = C/G.


Voltage biased circuit: TES:

Introduction

The strong negative ETF maintains the transition temperature.

Sharp transition speeds up the detector so lower time constant.

Higher sensitivity.

SQUIDs and multiplexing of SQUID

electronics.

Re

sist

an

ceTemperatureT0

Working point

Tc

Rw

Strong Negative Electrothermal Feedback

T ⇒ R ⇒ PBias ⇒ PTotal ⇒ T

PTotal=PSignal+PBias where PBias=V02/R

G

C=0τ1

0

+=

L

ττ2) Faster bolometer response

1)


Detectors:

Thin film thermometers.

Bi-layer thermometers.

MPIfR Gold-Palladium (8 nm)/Molybdenum (60 nm)450±25mK

NIST Copper (0.1µm)/ Molybdenum (0.2µm)120 ±10mK

Introduction


Silicon

wafer

Thermister

Nb wiring

Si3N4 membrane

3.3 x 3.3 mm, ~1µm

thick

Au ring

Au-Pd cross

absorber

• Au-Pd / Mo bilayer structure

thermistor

• Transition temperature

Tc ≈ 450 mK

• Thermistor is mounted on silicon nitride (Si3N4) membrane.

Application: Astronomical detectors


AuAuAuAu----Pd cross absorberPd cross absorberPd cross absorberPd cross absorber

Ω/

•Gold-palladium alloy

•Surface resistance = 10

( ) ( ) 20

21

4

1

4

oZnR

nRZ

n

nA

+++=




•Surface resistance = 10 Ω/

Polarization sensitive absorbers




Advantages:

•Frequency selective absorber,

L=λ/2

•Polarization sensitive absorber


•Surface resistance = 10 Ω/




Siliconwafer

Thermister

Nb wiring

Si3N4

membrane3.3 x 3.3 mm, ~1µm thick

Au ring

Au-Pd cross absorber



1.5 K filter

1.5 K

Cryo-perm shield

4 SQUIDsat 1.5 K

1.5 K

Superconducting aluminiumHornarray/cavity at 0.3 K

Sorption pumpNiobium tube



TES equations:

)1(

1

)1(

1

ωτδδ

iL

L

VP

IS

BIASi +

⋅+

⋅−=≡ current response

)1()(

0ωταω

iGT

PL BIAS

+⋅= AC open loop gain

Finite Element Analysis

(WWW.COSMOSM.COM)

1) Structuring of Si3N4 membrane.

2) Estimation of G.



•The thermal conductance is tuned by

structuring the silicon nitride membrane.

Silicon nitride membraneSilicon nitride membraneSilicon nitride membraneSilicon nitride membrane

sensitivity1

thermal

conductance

∝


Gold ring

High-G Medium-G Low-G

100µmThermistor

Si3N4

300µm


•Thermal analysis using COSMOS

•Thermal conductivity (k ) values are obtained from Holmes et al.

Applied Physics letters 72, 18, 1998

( )LAkGso /=

Thermistor at 450 mK

Si3N4 at 300 mK

Thermal modeling



Bolometer response

to the periodic signal.

Thermal modeling

-COSMOS



Thermal conductance


10-1

100

10-10

10-9

10-8

10-7

Temperature (K)

G (

W /

K )

Thermal conductance vs Temperature

High G-100 µm squareMedium G-100 µm squareLow G-100 µm square



7-element array39-element array

Small Bolometer

CAmera (SABOCA)


12m - Submillimeter telescope APEX

The Atacama Pathfinder ExperimentAPEX



Latitude 23 deg south

Longitude 68 deg west

Altitude 5100 m=16700 feet

230 GHz 1.5THz

Chajnantor Plateau

Atacama, Chile



Siliconwafer

Thermister

Nb wiring

Si3N4 membrane3.3 x 3.3 mm, ~1µm thick

Au ring

Au-Pd cross absorber

Application: THz scanner


Without center Au ring With center Au ring

• FEA simulations showed

increase

in thermalization by

depositing the center ring

around radiation absorbing

area.

• Detectors successfully used

for Terahertz application.



Test scenario: a test person

hides a handgun mock-up

underneath its shirt, and the

THz scan reveals the threat

from 5 meter distance.

Human hand at 0.34 THz,

from 5 meter distance


Design of an

optical scanner

based on a

gyrating mirror


Microcalorimeters can provide

∆E < 50 eV FWHM at 100 keV !

State-of-art germanium = 500 eV

1 mm

0.25 mm

Sn

absorber

epoxy postthin-film TES

thermometer

To stop gamma-rays, a bulk absorber is required

Application: γ-ray spectroscopy

µcal Ge

50 eV

area 1-2 mm2 ~500 mm2

Γ

QE

500 eV∆E

~100 Hz ~50 kHz

25%(at 100 keV)

~95%


1 mm

0.25 mm

Sn

absorber

epoxy postthin-film TES

thermometer

Microcalorimeter arrays may perform better than Ge for some apps – Pu isotopics

Microcalorimeter arrays may enable new applications – Pu in spent reactor fuel


cal Ge

50 eV

area 1-2 mm2 ~500 mm2

Γ

QE

500 eV∆E

~100 Hz ~50 kHz

25%(at 100 keV)

~95%

256 ucal

50 eV

~500 mm2

~25 kHz

25%

Microcalorimeters can provide

∆E < 50 eV FWHM at 100 keV !

State-of-art germanium = 500 eV

To stop gamma-rays, a bulk absorber is required


• multi-post design

– better mechanical support for the absorber

– reduced mechanical and chemical stress on the TES thermometer

– reduced dependence of pulse height on interaction position

• larger absorber area for higher detection efficiency (2.25 mm2 vs. 1 mm2)

• larger dynamic range, better linearity

%Rn



0.4 mm

thin-film

Mo/Cu TES

epoxy post

1.5 mm

400 µm



Gamma-ray detectors

• 55 working detectors out of

total 66 detectors.

• 31 Multiplexing detectors.

• Linear from 60 KeV – 130 KeV

region.

Detector

Box




Time division multiplexing: SQUIDs

• Three stage SQUID wiring.

•Flux-locked loop.


Gamma-ray cryogenics

Nb shield

Cryoperm

shield

4 K stage

1 K stage

Heat Switch

~ 50mK stage

TeK cables

RF filters

Transmission lines Sealed

cryostat SMB cables

Digital

electronics

Lakeshore temperature

control

Source chest

• Configuration allowing 264 detectors.

• Typical base temperature=62mK, Temperature regulated at 100mK for 20 hours.

• No liquid cryogens; units working continuously at Los Alamos and NIST labs.

Detector

box- inside



Plutonium Spectrum:

240Pu/239Pu ratio > 0.075, then material is considered as ‘reactor grade’.

1) Total: 38.9 million pulses. 2) ~18,700 240Pu counts for the first time using TES

detectors. 3) ∆E ~ 120 eV. Expected resolution: 70 eV



Plutonium Spectrum:

Things to improve:

• Number of pixels (can be achieved by circuit inductance and bandwidth

optimization).

• Energy Resolution.

Expected 70 eV, Achieved: 120 eV.

Thermal cross-talk between the pixels can degrade the energy

resolution.



100 mK

80 mK

90 mK

Au bond pads=80mK

SiO chip

0.5 µm Au1 µm Au

2 µm Au



Thermal Cross-talk determination

• 2% thermal cross-talk in neighboring pixel.

• Better thermalization of chip

should increase the resolution

by 8-10 %.

• New chip is fabricated and

is being tested at LANL.

IFFT Tsi(w).dTTES

dTSiO

.dI(w)dT(w)

T ( ρ ,t ) = 2.(e ( − t ' / τ F ) −∫ e ( − t ' / τ R ) ).E

c.e (− ρ 2 / 4D ( t − t ' )) .e ( −γ .( t − t ' ))

4πDc ( t − t ' ).dt '

Input heat pulse Heat flow in Si

Current across TES

(cross-talk)=



PSD 1

PSD 2

(x3,y3,z3)

(x4,y4,z)

Laser

(x1,y1,z1)

Horizontal Plane

Ver

tical

Pla

ne

Mirror surface aligned at45 degrees

Point on reflection

θ

X(x2,y2,z2)X1

X2

X3

X4

Non-Contact Surface Measurment

X = X1+(X2-X1) × S

X = X3+(X4-X3) × T

( ) ( ) ( )[ ]( ) ( )[ ]3412

341231

xxxx

xxxxxxD

−×−−×−⋅−

=

Skew Vector case:

Perform this procedure to obtain 15 to 20

measured points on mirror surface

PSD: Position Sensitive

Detector

Optics Alignment Tool


Pin hole 1

Pin hole 2



MATLAB LABVIEW

Linear Stage

Controller

PSD

Electronics

File Input/Output

Theoreticalmirror surface

Measured Mirrorsurface

Error measurmentsand calculations

Linear stagecontrol

PSD position

Define thetheoretical mirror

surface

Display Error

Save the Project

Reload theproject

-

Coordinates of linear stage

Laser beam centering

3 points to define thetheoretical mirror surface

Results



0.9

1

1.1

x 105

0.5

1

1.5

x 105

0.5

1

1.5

2

2.5

3

3.5

x 104

x

Data

y

z

0.9

0.95

1 x 105

1.4-1

0

1

2

3

4

5

6

x 104

0.9 1 1.1

x 105

0.5

1

1.5x 10

5

-1

0

1

x 105

x

Move camera target and zoom out

z

y

020

4060

80

0

20

40

60-4

-3

-2

-1

0

X- Axis

Ellipsoidal fit to points

Y- Axis

Z-

Axi

s

Theoretical curved mirror

0.5

1

1.5x 105

0.80.850.90.9511.051.11.151.21.25

x 105

4

5

6

7

8

9

10

11

12

x 104

X- AxisY- Axis

Ellipsoidal fit to points

Z-

Axi

s

Observed curved mirror



Conclusions:

• Superconducting TES are the most sensitive detectors for

millimeter-submillieter wavelength regime.

• Detectors successfully used for nuclear line forensics and

spectroscopy non-destructive analysis.

Personal gain:

• Ability to work on a project as a team member and individual.

• Knowledge of software and hardware.

• Lab-work, Cryostats, cryogens, instruments.

Everything has been very exciting and want to learn more.

Documents

By: Nikhil Jethava National Institute of Standards and Technology…beamdocs.fnal.gov › AD › DocDB › 0032 › 003294 › 001 › Fermilab... · 2009-01-30 · Nikhil Jethava