A New Multiplexable Superconducting DetectorKinetic Inductance DetectorsTitle Here A New...
Transcript of 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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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∆
Title HereKinetic Inductance Detectors
• 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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
S-Cam (ESTEC - Rando et al., RSI, 2000)
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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 !
Title HereKinetic Inductance Detectors
Surface Impedance of Superconductors• Surface resistance drops exponentially as temperature is lowered• Surface reactance (kinetic inductance) increases near Tc
Title HereKinetic Inductance Detectors
Measure variations in kinetic inductanceδXs , Rs, nqp all decrease exponentially with temperatureδXs , Rs have nearly constant response to changes in nqp
Title HereKinetic Inductance Detectors
CPW Resonator Measurements
Title HereKinetic Inductance Detectors
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)
Title HereKinetic Inductance Detectors
Analysis of Resonance Data
• derive properties of the superconductors and resonators
• use Mattis-Bardeensurface impedance
Title HereKinetic Inductance Detectors
Quarter-wavelength resonator: Al on sapphire
Note:resonator hasposition-dependentresponse, ~ cos2(πx/2L)
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
Responsivity: phase shift vs. number of thermal quasiparticles
0 4 8 12Number of thermal quasiparticles (millions)
0
50
100
150P
hase
(de
gree
s)
Title HereKinetic Inductance Detectors
It works !!!
Rise time: resonator bandwidth
Fall time: quasiparticledecay
Nyquistsampled readout
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
Pulse Fitting
Title HereKinetic Inductance Detectors
Pulse tail decay time
0.0 0.2 0.4Temperature (K)
10
100
1000
Dec
ay ti
me
(µs)
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
Noise, continued…
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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 ?
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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)
Title HereKinetic Inductance Detectors
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)
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
32-channel, 2 Msa/s, Σ−∆ ADC VME board
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
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
Title HereKinetic Inductance Detectors
UV-Optical KID Array
Title HereKinetic Inductance Detectors
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 ?
Title HereKinetic Inductance Detectors
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