1. Microwave Kinetic Inductance Detectors for X-ray Science
Antonino Miceli
FNAL Research Techniques Seminar
April 24, 2012

2. Outline Overview of MKIDs MKID activities at Argonne
Why Superconducting Detectors?
Detector Requirements
Applications
Overview of MKIDs
MKID activities at Argonne
MKID resonator readout

3. Acknowledgements Tom Cecil (XSD Staff) Orlando Quaranta (Post-doc)
Lisa Gades (XSD Staff)
Outside Collaborators:
Professor Ben Mazin (UCSB)
MSD/UChicago TES Team (Novosad et al)
CNM Cleanroom Staff

4. Superconductors Detectors for X-ray Detector R&D
Energy dispersive semiconductor detectors have almost reached their theoretical limits
e.g., Silicon Drift Diodes have energy resolution ~ 150 eV at 6 keV
Limited R&D on spectroscopic detectors
Only effort is Silicon array detector of Peter Siddons (BNL) and Chris Ryan (Australia)
Using silicon arrays to achieve large collection solid angles for fluorescence experiments.
Leverages local facilities and existing projects.
ANL’s Center for Nanoscale Materials for device fabrication
Many groups with thin film deposition experience
Superconducting Transition Edge Sensors for UChicago’s SPTpol
ANL’s Material Science Division

5. Detector Requirements
Solid angle coverage
Pixel area and sample-detector distance
Count-rate
Need lots of pixels (i.e. multiplexing) if you going to deal with superconducting detectors, which tend to be slow
Peak-to-background ratio
Maximize charge collection
Minimum of 1000:1
Limits overall sensitivity
Energy resolution
Depends on applications (1-50eV at 6 keV)

6. Applications for superconducting x-ray detectors?
X-ray Inelastic Scattering
Access wide range of excitations.
Superconducting detectors allows broadband and efficient measurement compared to crystal analyzers (i.e., wavelength dispersive spectrographs).
X-ray Fluorescence
Fluorescence line overlap in complex biological samples
Fluorescence Tomography
Needs pixelated energy-dispersive detectors
White-Beam Diffraction (ED-XRD)
Versus angle-dispersive diffraction
Using monochromatic incoming beam and area detector
Complex sample environments (e.g., high-pressure cells)

7. Competing with x-ray spectrographs (like astronomers…)

8. Quasiparticle detectors
Use small Superconducting Energy Gap
Break Cooper Pairs
Use Cooper Pairs as detection mechanism (like electron hole pairs in a semiconductor)
Cooper Pair
Semiconductor Energy Gap: ≈ 1 eV
Superconductor Energy Gap: ≈ 1 meV
How to measure change in quasiparticle number?

9. Microwave Kinetic Inductance Detectors
Quasiparticle generated by x-ray causes an inductance increase (i.e., “kinetic inductance”)
Measure inductance change in a LC resonating circuit
DLs
DRs
Observables….
Multiplexing: Lithographically vary geometric inductance/resonant frequency…
1024 pixels demonstrated in 2011
People are contemplating 10k pixels now
Limited by room temperature electronics

10. What has been shown already for x-rays?
62eV
Mazin et al 2006
Material
Atomic Number Z
Transition Temperature
Theoretical Energy Resolution at 6 keV
Attenuation Length at 6 keV
Lead 82
7.2 Kelvin
3.53 eV
1.86 mm
Tantalum 73
4.5 Kelvin
2.79 eV
1.79 mm
Tin 50
3.7 Kelvin
2.53 eV
2.60 mm
Indium 49
3.4 Kelvin
2.43 eV
2.77 mm
Rhenium 75
1.7 Kelvin
1.72 eV
1.31 mm
Molybdenum 42
.92 Kelvin
1.26 eV
2.94 mm
Osmium 76
.66 Kelvin
1.07 eV
1.18 mm

11. MKIDs @ Argonne for synchrotrons
The goal is moderate energy resolution (< 20eV) with good count rate capabilities (> 200kcps) (i.e., ~ pixels)
Leverages Argonne’s micro/nano-fab facilities (CNM) and superconductivity expertise (MSD); Astronomical TES bolometer program(MSD & UChicago).
Three Main Aspects:
Device Fabrication
Fabrication is completely in-house
Relatively “simple”… patterning of metal (deposition, photolithography, etching)
Film quality is very important!
Initially aim a simple device, then progress to more complex designs (e.g., membrane-suspended)
Dedicated deposition system on order.
Cryogenics and Device Characterization
We are mostly limited by how fast we can test devices.
Readout electronics
Initially the analog readout for characterization.
Digital FPGA-based array readout in the near future.

12. Anatomy of an MKID – Our work (one design)
1 pixel
1 micron WSi2 (XSD)
Inductor/Absorber
Capacitor
15 pixels
2 mm
First x-ray pulses at APS in January 2012!
Fe-55 and Cd-109

13. Detector Testing Cryostat Cryostat Microwave Electronics
Be window (x-ray transparent)
Cryostat
Microwave Electronics
Cryostat
Cryogen Free ADR
T = 100 mK for 2 days
3-4 hour recycle time
Microwave Electronics
Vector Network Analyzer
IQ mixing
Control & Data Analysis Software

14. NbTi (superconducting)
Inside the cryostat…
Attenuator
60 K stage
m-metal shield
NbTi (superconducting)
coax
0.5K stage
LNA
Stainless Steel
coax
Sample box
@ 60 mK
4 K stage

15. VNA Measure the transmission through the device (S21)
Wide range of frequency: GHz
Easily identify resonators:
Resonance frequencies, Quality Factors (Qr, Qc, Qi)
Cannot measure pulses nor noise
VNA

16. IQ mixing (Pulses and Noise)
Homodyne mixing
Demodulate to 0 Hz (DC) and monitor for changes in Re(S21) and Im(S21) (i.e., I & Q)
Amplitude = sqrt(I2 + Q2)
Phase= arctan(Q/I)
Signal
Generators
IQ Mixer
IQ Mixer
Variable
attenuator

17. IQ Fitting and parameter extraction
Frequency (GHz)
Real (S21)
Imag (S21)

18. Pulses I &Q Amplitude Phase Pulse fitting Time (ms)
Decay Time -> Quasiparticle life time
Phase pulse height -> Energy of the incident photon
The signal in phase is larger than amplitude

19. Tungsten Silicide MKIDs
We have been searching for dense materials for x-rays.
WSix is a material with low Tc, high kinetic inductance fraction and good quality factors.
Similar to Titanium Nitride
Maybe also be interesting for optical MKIDs.
arXiv: v1

20. Optical MKIDs (Mazin et al) -- Spectrophotometry
R=E/ΔE=16 at 254 nm
Limited by LNA/power handling/Q
Mazin et al., Optics Express 2012

21. A readout for large arrays of Microwave Kinetic Inductance Detectors (McHugh, Mazin et al, arXiv: v1)
How to readout 1024 MKIDs….

22. Another technology – Transition Edge Sensors
TES have the best energy resolution (not Fano limited)
However, TES require relatively complex cryogenic electronics which makes multiplexing difficult.
Limited to 200 pixels right now.
Also, larger pixel means slower response….

23. TES are evolving towards MKID/resonator readout
“Microwave SQUIDs”
Eventually would like a wideband, quantum-limited LNA for MKIDs (i.e., don’t need SQUID anymore)
Josephson parametric amp (J. Gao et al)
arXiv: v1
Kinetic Inductance parametric amp (P. Day et al)
arXiv: v1
B. Mates et al ApL 2008 (NIST)
Superconducting microwave resonant circuits for the detection of photons from microwaves through gamma rays, Irwin, K.D., et al. Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International , vol., no., pp.1-4, 5-10 June 2011

24. Conclusions
Superconducting detector development has started at the APS.
Testing infrastructure (cryo, electronics, analysis software) is complete.
Now focusing on device fabrication and iterating on designs
MKIDs are a path towards high count rates and higher solid angle coverage.
Has the potential to provide a very unique capability (detector/instrument) for the APS.
MKIDs are a relatively young technology and there is room for R&D.
Thank you!

25. The End

26. Extra Slides

27. + Comparison of Silicon Drift Diode, MAIA, TES and MKID Area 5mm 1 cm
Sensor-Window Distance
Energy 6keV
Max Count rate (per pixel)
P/B ratio
Energy Range
State of maturity
Silicon Drift Diode
40mm2
5mm
250eV
250kHz
5000:1 (?)
< 20keV
Commercially
Available
175eV
100kHz
MAIA
1mm2 x 384
20kHz per pixel
Semi-commercial??
NIST TES
0.14 mm2 per pixel (256+ pixels)
1 cm
6keV
40keV
100keV
Hz/pixel (256+ pixels) ??
300eV – 100keV
Semi-commercial
MKIDs
0.14 mm2 per pixel
60eV (2006)
2eV is theoretical limit
4000Hz/pixel
(256+ pixels)
300eV-100keV
R&D +

28. Silicon Drift Diodes Commercially available
E.g., Vortex 4-pixel SDD (4 x 40mm2)
Performance of single pixel SDDs (measured)
Mn Ka FWHM ~ 250 eV (Max Count rate ~ 250 kHz per pixel)
Mn Ka FWHM ~ 175 eV (Max Count rate ~ 100 kHz per pixel)
SDD have reached their limits of energy resolution.
Only improvement to be made is more pixels to increase total count rate throughput and solid angle collection.
Thus, the MAIA detector (BNL/Australia)!

31. Speed and resolution are inverse proportional.
Controllable  thermal conductance to bath (“G”)
SiN membrane geometry

32. Phonon-Coupled MKIDs -- Single Photon Emission CT -- SPECT
SPECT Imaging (for animals)
Patrick La Riviere thinks phonon-coupled MKIDs might be good for this.
Also interesting for high-energy x-ray applications
Sunil Golwala et al

33. Current Status of MKID Research at APS II
Exploring various detector configurations
Quasiparticle Trapping  Tradition Configuration
60eV resolution and 4000cps per pixel proven in 2006
30eV should be “easily” possible
More is understood about noise sources
2eV is theoretical limit at 6keV
Lump-element design (WSix) No charge diffusion  High Peak-to-Background
Phonon-Coupled  Large pixels and thick silicon (or other dielectric material for absorption
Inductor/Absorber
Capacitor
Silicon Absorber (1mm)
SiN membrane
Resonator

34. Pump-probe XAS w/o mono
3eV at 7keV
80Hz with 40 pixels (256 possible today)
80Hz * 256 = 20kHz (TDM)
80Hz * 1000 = 80kHz (CDM) This starts to be very interesting for RIXS/XES/XANES

35. MKIDs – Readout Scheme Should be able to readout ~4000 pixels
Multiplexing is main advantage of MKIDs over STJs and TES
Should be able to readout ~4000 pixels

36. FPGA- based IQ demodula tion (Xilinx SX95T RF Engines Channel Core)
MKID Array readout
Room temperature electronics
Transfer complexity from cryogenic electronics (TES & SQUIDs) to room temperature.
Scalable system
Array size limitation is room temperature electronics (512 is practical today)
Riding on Moore’s Law for room temperature microwave integrated circuits developed for the wireless communications industry. X
IQ Mixer
Low Pass Filters
16-bit D/A
14-bit A/D
FPGA- based IQ demodula tion (Xilinx SX95T RF Engines Channel Core)
GHz Synthsizer

37. Quasiparticle Generation – A Cascade Process
Incoming Photon  absorbed, ionizing atom and releasing inner-shell electron
First Stage: Rapid energy down-conversion (electron-electron interactions  secondary ionization and cascade plasmon emission)
e.g. 10keV photoelectron down-conversion to a thermal population of electrons and holes at a characteristics energy ~ 1eV takes ps (Kozorezov et al )
1st stage ends when electron-phonon inelastic scattering rate dominates electron-electron interactions.
Second Stage: ~ 1eV down-convert to large number of Debye energy phonons
Energy of phonon distribution exceeds energy of electron distribution
Debye energy of superconductors is larger than SC gap energy
Phonons with energy > 2 D will generate quasiparticles.
Finally, we have a mixed distribution of quasiparticle and phonons:
Nqp ~ Ephoton/D
But scaled down because large percentage of photon energy stays in the phonon system
For Tantalaum, 60% energy resides in qp system. (Kurakado) (Efficiency  h)
Nqp = hhn/D
At 6keV and Ta absorber, D = 0.67 meV  5 Million qp!!

38. Phonon Trapping Thus thicker films or membrane-suspended absorbers.
Dominant phonon loss mechanism for Ta and Al is through the substrate.
Copper Pair breaking phonons Mean Free path ~ 50nm
Effective quasiparticle lifetime is lengthened by phonon trapping.
Acoustic match between superconducting film and substrate.
Thus thicker films or membrane-suspended absorbers.

39. Two major classes of Superconducting Detectors
Thermal Detectors (i.e., Transition Edge Sensors)
Quasiparticle Detectors

40. Transition-Edge Sensors (TES)
1/e response time = 100 μs - 1 ms
Kent Irwin, NIST

41. Transition-Edge Sensors (TES)
TES have the best energy resolution (not Fano limited)
However, TES require relatively complex cryogenic electronics which makes multiplexing difficult.
Limited to 200 pixels right now.
Also, larger pixel means slower response….
Irwin & Ullom, NIST

42. TES array at NSLS (NIST U7A)
Commissioned at NSLS this year…. Waiting for results…

43. Gamma-Ray TES Array (NIST + Los Alamos)
Resolution
25 eV at 100 keV for 1 mm2
20eV at 40keV for 1 mm2
70 eV at 100 keV for 2 mm2
Count Rate
10Hz/pixel (now)
25Hz/pixel (soon)
Pixels
256 (now)
1024 (soon)