Tunnel Junction Refrigerators Cooling From 300 mK to 112 mKwith Large Cooling Power

Galen O'NeilFor Peter Lowell(his knee )

NIST Boulder NIS TeamPeter LowellDan Schmidt

Jason UnderwoodJoel Ullom

NIS Refrigerator

Si

Al-MnAl-MnSiO2

AlAl(Al-Mn)Ox

Superconductor(Al)

Normal Metal (AlMn)

Junc

tion

Substrate (Si)

10 um

I

I

hot

hothot

hot

hot

cold

cold

More options for refrigeration below 300 mK

Dilution refrigeratorMost expensive10 mK

2-stage 3He

ADRModerate price50 mK

NIS refrigerator cooling detectors 100 mK

cheapest~ 300 mK

+

Previous State of the Art

hot

S N

A.M Clark, et al, Appl Phys Lett 86, 1734508 (2005)N.M. Miller, et al, Appl Phys Lett 92, 163501 (2008)

-NIS cooled X-Ray detector hasbest 6keV resolution with cryostat above 200mK:9.4 eV @ 6keV-Representative of a class sensors that operate near 100mK

230 mK

320 mK

160 mK

rest of chip = 260mK

cold

Tc=185mKDissipating 22 pW

How does it work?Vbias=.5Δ/e

eVbias

2

BCS DOS BCS DOSBCS DOS

Hot Electrons TunnelVbias=.9Δ/e

eVbias

2

BCS DOS BCS DOS

Normal Metal Cools - Superconductor HeatsVbias=.9Δ/e

eVbias

2

BCS DOS BCS DOS

Vbias=.9Δ/e

eVbias

2

BCS DOS BCS DOS

no bias on heatsinkjunction

Add a Heatsink (Quasiparticle Trap)

NIS Refrigerator Geometry

Si

Al-MnAl-Mn

SiO2

AlAl(Al-Mn)Ox

I

hot

hot

cold

Al-Mn

Old Thermal Model

normal metalelectrons

substrate/normal metalphonons (fixed at bath temperature)

superconductor(fixed at bathtemperature)

NIS Junction CoolingFunction of Tn

Electron-Phonon Coupling

IV Power

I2R

PayloadPower

Quasiparticle Return(Small Fraction of IV,Empirical)

New Thermal Model with Heatsink

normal metalelectrons

substrate/normal metalphonons (fixed at bath temperature)

superconductor(QP Density vsPosition)

NIS Junction CoolingFunction of Tn,Ts

Electron-Phonon Coupling

IV Power

I2R

normal metaltrap electrons(T vs Position)

Quasiparticle Trapping/(Heatsink)

Electron-Phonon Coupling

QuasiparticleRecombination

PayloadPower

Inside The Thermal Model

Si

Al-MnAl-MnSiO2

Al-Mn

x

Al

quasiparticle:

Si

Al-MnAl-MnSiO2

AlAl(Al-Mn)OxI

hot

hot

cold

Al-Mn

Predictions of Model

Previous 50nm

Target 25nm

Predictions of Model

Previous OverlayerOxide(no overlayer trap)

Target for overlayer10 m2

Si

Al-MnAl-MnSiO2

AlAl(Al-Mn)OxI

hot

hot

cold

Al-Mn

Measured Cooling to 112 mK

Record NIS Cooling(Large Junction)

T NIS=T ADR

Sat July 30 2010

2008

300 mK ↓

112 mK

Next Step:NIS Cooled Cryogenic Stage

•3mm chip -> 0.1uW @ 100 mK•10 uW dissipated at 300mK

NIS Junction Cooling Function of Tn