a new multiplexable superconducting detectorkinetic inductance detectorstitle here a new...

Title HereKinetic Inductance Detectors

A New Multiplexable Superconducting Detector

Caltech Jet Propulsion Laboratory

Anastasios Vayonakis Peter DayBen Mazin (at this workshop) Rick LeDucPeter MasonJonas Zmuidzinas

Jonas ZmuidzinasCalifornia Institute of Technology

Supported by: NASA Code R, A. Lidow – Caltech Trustee,

Caltech President’s Fund, JPL DRDF


Why Superconducting Detectors ?• Astrophysics

– Millimeter-wavelength arrays• CMB polarization (CMBPOL)

– Submm/far-IR arrays• imaging and spectroscopy of dusty high-z

galaxies (SAFIR)– Energy resolved photon counting

• Extract more information from every photon !

• UV/optical (NHST ?)• X-rays: imaging spectroscopy of galaxy

clusters, AGN, … (Con-X )• Dark matter searches, neutrino mass

experiments• X-ray microanalysis

SAFIR

Con-X


Pair-breaking Detectors (e.g. STJ)• Analogous to

photoconductors, with meV gap (tunable)

• Photon-counting with energy resolution in optical/UV/X-ray

• How to measure quasiparticles ?

Must separate from Cooper pairsCan use tunnel junction as a “filter” (STJ)Can trap quasiparticlesinto TES (zero gap energy)

ener

gy

Cooper pair (2∆~meV)

quasiparticles (N ~ hν/∆)

photonhν

2∆


• Operate well below Tc, not at phase transition– physics should be simpler (n.b. HEB/TES not fully understood)

• Finite gap energy– Thermal quasiparticle density scales as nqp ~ exp(- ∆/kT) – Heat capacity ~ nqp

• can use much larger detector volume– Quasiparticle lifetime τqp ~ 1/nqp

– Fundamental sensitivity set by quasiparticle generation-recombination noise

• Sensitivity scales as (nqp / τqp)1/2 ~ exp(- ∆/kT)

Advantages of pair-breaking detectors

NEP =

√Nqp

τqp

2∆

η ∆EFWHM = 2.355

(∫ ∞

0

4

NEP2(2πν)dν

)− 12


Energy resolution: Fano limit

• Ultimate resolution set by quasiparticle creation statistics– Energy resolution: ∆E = 2.35 [F ε E]1/2

– F = 0.2 is the Fano factor– Photon energy per quasiparticle: ε = 1.7 ∆– ∆E = 0.04 eV [E/1eV] 1/2 for Ta (R = 28 at 1 eV ⇒ 1.2 µm)– ∆E = 0.02 eV [E/1eV] 1/2 for Al (R = 56 at 1 eV)

• STJ’s have extra “tunnel” noise


S-Cam (ESTEC - Rando et al., RSI, 2000)


High quantum efficiency over a broad band(Peacock et al., ESTEC, A&A Suppl., 1998)

Wavelength (nm)

0 500 1000 1500

Eff

icie

ncy

(%

)

0

20

40

60

80

100

Quantum Efficiency

Reflectivity

Magnesium Fluoride Substrate + Tantalum Film


Problems with STJ quasiparticle readout

• Junction fabrication is very challenging !– Need ultra-low leakage current– Only certain materials combinations have been successful

• e.g. Nb/AlOx/Nb, Al/AlOx/Al, Ta/Nb/Al-AlOx-Al/Nb/T

• STJ detectors need uniform magnetic field– Fiske modes…

• Each STJ needs separate low-noise amplifier– Fairly high impedance devices– Use JFET amplifiers– Noise margin is small– Efficient multiplexing not possible


New concept: microwave readout of quasiparticles

• quasiparticles change the kinetic inductance (surface reactance) of superconductor

• use a thin-film microwave resonant circuit• kinetic inductance influences the resonant frequency • quasiparticles can change resonant frequency• Measure microwave transmission amplitude and phase• Use low-noise HEMT amplifier• Frequency domain multiplexing !


Surface Impedance of Superconductors• Surface resistance drops exponentially as temperature is lowered• Surface reactance (kinetic inductance) increases near Tc


Measure variations in kinetic inductanceδXs , Rs, nqp all decrease exponentially with temperatureδXs , Rs have nearly constant response to changes in nqp


CPW Resonator Measurements


CPW Resonator Measurements

5.3703 5.3703 5.3703 5.3703 5.3703 5.3704 5.3704

x 109

−30

−25

−20

−15

−10

−5

0

5020204.1, −85dbm, 60mK

f (Hz)

S12

log

mag

f0 =5.370322e+009, Q =1042039

S21 Data and Model Fit for D020204.1

-0.6 -0.4 -0.2 -0.0 0.2 0.4 0.6-1.0

-0.5

0.0

0.5

1.0

Fit to Resonator Data - Magnitude

5.37028•100 5.37030•100 5.37032•100 5.37034•100 5.37036•100

GHz

-50

-40

-30

-20

-10

0

|S21

|2 (dB

)

Fit to Resonator Data - Phase

5.37028•100 5.37030•100 5.37032•100 5.37034•100 5.37036•100

GHz

-200

-100

0

100

200

Phas

e (d

egre

es)

Q = 2 x 106 !(Al on sapphire)


Analysis of Resonance Data

• derive properties of the superconductors and resonators

• use Mattis-Bardeensurface impedance


Quarter-wavelength resonator: Al on sapphire

Note:resonator hasposition-dependentresponse, ~ cos2(πx/2L)


Resonance vs. Temperature (Qc ~ 50,000)

10.586 10.589 10.591Frequency (GHz)

10

8

6

4

2

0T

rans

mis

sion

(dB

)320 mK

260 mK

120 mKI

Q


IQ readout of amplitude and phase

V cos(ωt - φ) = V cos φ cos ωt + V sin φ sin ωt

= V cos φ

= V sin φ


Responsivity: phase shift vs. number of thermal quasiparticles

0 4 8 12Number of thermal quasiparticles (millions)

0

50

100

150P

hase

(de

gree

s)


It works !!!

Rise time: resonator bandwidth

Fall time: quasiparticledecay

Nyquistsampled readout


5.9 keV X-ray produces 2.5η x 107 thermal qp

0 200 400 600 800Time (µs)

0

50

100

150

200

Pha

se (

degr

ees)

70 mK

300 mK


Pulse Fitting


Pulse tail decay time

0.0 0.2 0.4Temperature (K)

10

100

1000

Dec

ay ti

me

(µs)


Phase Noise• Can measure I,Q noise• Calculate phase noise power spectrum Sθ (ω)• Gives NEP and expected energy resolution:

NEP2(ω) = Sθ(ω)

(ητ0

∆

dθ

dNqp

)−2

(1 + ω2τ 20 ),

oContributions to phase noise:oHEMT amplifieroMicrowave synthesizeroReference frequency oDevice noise (ultimate limit: GR noise)

∆EFWHM = 2.355

(∫ ∞

0

4

NEP2(2πν)dν

)− 12


Noise-Equivalent Power: ∆E ~ 10 eV

101 102 103 104 105

Frequency (Hz)

10−2010−19

10−18

10−17

10−16

10−1510−14

NE

P (

W/H

z1/2 )

Total

Amplifier

Synthesizer


Noise, continued…


What is currently limiting Q ?• X-ray pulse device is limited by coupling• Test resonator Q increases as width of CPW is decreased

– inconsistent with ohmic loss or dielectric loss– consistent with radiation loss

• Calculated and measured Q reasonably consistent, within factor of 2– but radiation Q calculation highly idealized

• Significant increases in Q are likely– Q of 107 or 108 ?

Qradiation = 3.4 (L/s)2


What sensitivity can we expect ?• Understand and eliminate apparent excess noise• Improve amplifier noise from 50 K to 5 K• NEP ~ 2 10-18 W Hz-1/2, ∆E ~ 0.3 eV• Responsivity given by

dθ/dNqp = 4× 10−7 αcenterγQV −1 [µm3 rad/qp]

o Agrees quite well with measured responsivityo Already demonstrated Q up to 2 106

o Decrease volume (film thickness)o Obtain NEP below 10-19 W Hz-1/2 ? Fano-limited ∆E ?


Frequency-domain multiplexing

• Lithographically tune each detector to a slightly different frequency• Use a single HEMT amplifier to simultaneously read out many (103-

104) detectors• Two microwave (coax) cables to sub-K stage – eliminates wiring

problem• No complex readout electronics inside cryostat !• Phase noise of HEMT amplifier, frequency reference are common to all

detectors (can reduce or eliminate)• RF signal processing electronics can take advantage of rapidly

advancing semiconductor technology for wireless communications


Frequency-domain multiplexing

10.55 10.60 10.65 10.70 10.75 10.80Frequency (GHz)

−40

−30

−20

−10

0

Tra

nsm

issi

on (

dB)


RF Prototype Board Block Diagram

Phillips SA8028 PLL

Cryostat & HEMT

Honeywell HRF-AT4521

Digital Attenuator

Analog AD8347IQ Mixer

SPI MultiplexerAndLogic Level Converter

Programming from PC

Analog DAC AD8347 Amplifier Gaincontrol

I Q

Small, low power RFICs readily available (used in cell phones)


Prototype RF Board

1) Phillips SA8028 PLL: 0.5-2.5 GHz, –101 dBc/Hz phase noise

2) Analog Device AD8247 IQ Mixer: 0.8-2.7 GHz, Includes 69.5 dB of Gain

3) Voltage Controlled Oscillator

4) Honeywell HRF-AT4521 RF Digital Attenuator (1-31 dB of programmable attenuation)

1

34

2


32-channel, 2 Msa/s, Σ−∆ ADC VME board


X-ray absorber with KID readout• Similar in concept to X-ray STJs developed at Yale• Simultaneous low-noise pulse readout of both CPW resonators• Absorber, resonator design need optimization


New Mask Design

• Optical and X-ray Devices

• 3 Layer Design (Absorber, Sensor, and Protect)

• Resonant Frequencies of 1.8, 6, and 10 GHz

• Devices with up to 1024 pixels

• Design Q’s Range from 100,000 to 20,000,000

• Various trapping geometries and test structures are included.

32x32 Optical Array, 50 µm square pixels, Q=2х106, f0 = 6 GHz


UV-Optical KID Array


Future Prospects• Straightforward to increase format to Nx32 (N > 32)• Larger formats also possible

– Need to reduce area used by resonator.– E-beam lithography ?– Use resonator as absorber ? Already position sensitive.– Use microstrip resonator on top of absorber ?– Use phonon coupling to resonator underneath absorber ?

• Readout electronics with 104 channels conceivable.• Gain factor of 10-100 with position-sensitive readouts.• Array formats of 105 – 106 spatial pixels ?


Invented and demonstrated a new superconductingdetector concept:

• very simple to fabricate• compatible with a wide variety of materials• simplifies instrument design• leverages wireless communications technology• high SNR single photon X-ray detection demonstrated• 2-way multiplexing demonstrated

A wide range of NASA SEU/Origins applications:• Millimeter-wave detectors (CMBPOL)• Submillimeter & far-IR arrays (128 x 128; SOFIA, SAFIR) • Optical/UV energy resolving arrays (NHST ?)• X-ray spectroscopy

Not commercial – needs NASA support

SUMMARY

a new multiplexable superconducting detectorkinetic inductance detectorstitle here a new...

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