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Development of TES-microcalorimeter arrays and Frequency Domain Multiplexed read-out Henk Hoevers Division Sensor Research and Technology. Research Facilities for TES-microcalorimeter array and FDM development Two Kelvinox 100 dilution fridges 1 + 2 SQUID channels - PowerPoint PPT Presentation
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Netherlands Institute for Space Research
Development of
TES-microcalorimeter arraysand
Frequency Domain Multiplexed read-out
Henk HoeversDivision Sensor Research and Technology
Netherlands Institute for Space Research
Research Facilities for TES-microcalorimeter array and FDM development
Two Kelvinox 100 dilution fridges • 1 + 2 SQUID channels• moveable slit to position X-ray beam (micron resolution)• data-acquisition facilities: RT-, IV-curves, analog and digital pulse processing• X-ray sources: 5.9 keV and 1.5/2.2/3.0/3.3/5.9 keV
In-house clean room -> short turn-around times for detector research• class 10-100• processing on 4” wafers, sputter deposition, thermal evaporation, • spinners, mask aligners, wire bonders, inspection equipment
Staff• Physicists: 6 fte (senior) scientists• Electronics: 2.5 fte (senior) design engineers• Support staff: 2.5 fte (mechanical, electronical, lab assistant)• Clean room staff: 3 full-time persons
Netherlands Institute for Space Research
Funding of TES-microcalorimeter array and FDM development
SRON staff from NWO income (Dutch Organization for Scientific Research)
ESA TRP contract ‘Cryogenic Imaging Spectrometer’ (XEUS – NFI2)• SRON
TES-based arrays (thin film processing, testing), prime contractor• MESA+, Twente University, the Netherlands
micromachining development• VTT Automation Technology, Espoo, Finland
SQUID development • Space Research Center, Leicester, UK
detector packaging, pulse processing• University of Jyvaskyla, Finland
material parameters at sub-Kelvin temperatures• Metorex, Espoo, Finland
electrical crosstalk simulations (dense wiring)
SRON and partners will tender on X-10 (expected ESA TRP on array read-out)
Netherlands Institute for Space Research
Set-up of the talk
TES microcalorimeter array development
Status of Frequency Domain Multiplexing
Outlook area: energy resolution
Netherlands Institute for Space Research
Microcalorimeter array development for XEUS; approach
1) development of 5 x 5 pixel array with XEUS specification 2) address/investigate scalability from 5 x 5 array to 32 x 32 array
Production: fabrication of prototype 5 x 5 arrays following two routes• bulk micromachining• surface micromachining
Performance characterization of 5 x 5 pixel arrays• R(T), I(V) curves and their reproducibility• noise and energy resolution
Detector (re)design (5 x 5 -> 32 x 32) uses• performance (and understanding) of 5 x 5 arrays• additional measurements of all relevant low-temperature material parameters• development of a Finite Element Model of the 5 x 5 array (thermal design)
The Finite Element Model is also suited for performance analysis (time dependentpulse modeling) and investigation of other pixel sizes and/or geometries
Netherlands Institute for Space Research
Bulk and surface micromachining (SRON-MESA); the 5 x 5 arrays
TiAu TES (100 mK)and Cu absorber
on slottedSiN membrane
240 μm
Netherlands Institute for Space Research
R(T) and I(V) curves
Bulk MMThree pixels in the same array
Bulk MMThree pixels in different arrays/chips
Surface MMThree pixels in the same array
Netherlands Institute for Space Research
Bulk micromachining; pulse performance/energy resolution
Effective time constant: τeff = 300 to 400 μs• This is 3 - 4 times lower than expected (and what was designed for)• Thermal conductance of SiN/Si(110) is 3 - 4 times lower than of SiN/Si(100)
Measured energy resolution ∆E = 6 - 7 eV at 6 keV• Resolution not understood; from the measured noise 4 - 5 eV is expected• Note: the best single pixels have ∆E = 3.9 eV and τeff = 85 μs
Netherlands Institute for Space Research
In progress: Bi-absorber arrays (7 μm thick with Cu bottom/thermalisation layer)
Mushroom shaped absorbers: thermal evaporation and lift-off
Problems encountered for XEUS sized pixels (240 x 240 μm2) in 5 x 5 arrays:lift-off edges, particle-like anomalies, μ-cracks in Bi
5 x 5 arrayBi absorbersHat: 240 x 240 μm2
Stem: 100 x 100 μm2
Single pixelBi-absorberHat: 160 x 160 μm2
Stem: 100 x 100 μm2
Netherlands Institute for Space Research
Advanced detector design through Finite Element Modelling (2D, 3D)
Basic layout of a sensor pixel Measured and modelled thermal transport
• el-ph coupling in TES and absorber• Kapitza coupling between TES - SiN• conductance silicon nitride membranes• conductance Si support beams• thermal coupling of Si chip to heat bath
5 x 5 pixel array 32 x 32 pixel array
Material parameters and Finite Element Modeling
Netherlands Institute for Space Research
Thermal coupling of detector pixels to heat bath• Bare Si chip Tchip = 187 mK TSi beam = 200 mK
• Cu coating back-side Si-chip Tchip = 41 mK TSi beam = 140 mK
• Cu coating on Si beams and chip Tchip = 41 mK TSi beam = 47 mK
Finite Element Model of the XEUS array (1000 pixels of 10 pW each)
Improvement of coupling to heat bath and a small thermal gradient in Si beam: proper heat bath
Improvement of coupling chip to bath
Future XEUS 32 x 32 pixel array
SiN
Si-beamBeam with Cu
side view Si(110) beam
Si-beam with Cu
SiN
Uncoated Si
Netherlands Institute for Space Research
Array development - summary
• Array production based on bulk and surface micromachining• The pixel to pixel performance in BMM and SMM arrays is quite good (R(T), I(V))
• Thermal conductance of SiN on Si(110) is lower than expected -> τeff too high To be measured: pixels with redesigned thermal support • Improvement of ΔE from 6 - 7 eV to values smaller than 5 eV needed Working on reduced sensitivity of set-up for EMI Working on more fundamental issues of the energy resolution
• Development of large mushroom-shaped absorbers is critical and has high priority
• The XEUS detector chip and pixels can be adequately cooled• Detailed Finite Element Model is available for thermal design, all relevant low-temperature material parameters measured
Netherlands Institute for Space Research
Frequency Domain Multiplexing - Motivation for multiplexed read-out
Thermal aspects related to the read-out and biasing of one pixel• Power dissipation: 10 pW/pixel• Power dissipation; 100pW/shunt resistor• Power dissipation: 1 nW/SQUID current amplifier• Heat input through wiring (5 at minimum, 4 twisted-wire pairs preferred)
Available cooling power XEUS ADR: 5.5 μWh @ 35 mK • 32 x 32 pixel array without multiplexing: only ~4 hours of operation!
Netherlands Institute for Space Research
Frequency Domain Multiplexing
AC-biasing of TES microcalorimeter• TES acts as AM-modulator• LC noise blocking filters• One SQUID per column
Netherlands Institute for Space Research
Need for loop gain
Large dynamic range required (current pulse vs current noise)DR = 8.106 = Φ0/(2ΦSQUID) (1+LFLL); low-noise VTT SQUID: LFLL > 1.4
Common impedance (SQUID input coil) leads to cross talk (from f1 to f2) CT = 0.001 = [Lc/(1+LFLL )/L]2; LFLL > 10
The SQUID is an non-linear component -> mixing products (from f1 to f2) CT = 0.001 requires LFLL > 15
Netherlands Institute for Space Research
Limitations of the achievable loop gain
• Phase rotation due to cable delay imposes: tdelay.foperation < 0.11/LF;
For an optimized cryostat with 20 cm distance between SQUID andwarm electronics (t delay = 3 ns)
• Phase rotation of the amplifier (simulation performed for a 200 MHz amplifier with one pole zero compensation)
Standard FLLCombining 32 channels (with 100 kHz seperation) requires 3 MHz• LFLL ~ 10 @ 3 MHz It requires very close packing and the available low loop gain is low; it implies an appreciable fraction of mixing products
Baseband feedbackThe carrier is deterministic and carries no information (use it in the feedback)In principle, only the signal bandwidth (200 kHz) is relevant; it allows for high loop gains• LFLL ~ 200 @ 200 kHz
Netherlands Institute for Space Research
Standard FLL
Pro: Con:FLL proven concept - A-linearity in SQUID introduces crosstalk at 0.2% level
- Common impedance leads to crosstalk at 0.4% level- Bandwidth limited to ~3 MHz, 32 close packed channels
Netherlands Institute for Space Research
Pro: Con:• L > 200 results in: Complex demux/mux electronics A-linearity in SQUID: crosstalk at < 0.01% level Idle-current cancellation not required Available bandwidth is up to ~10 MHz; allows for well-spaced carriers -> cross-talk due to common impedance is no longer a problem
Baseband feedback
Netherlands Institute for Space Research
Experimental status Frequency Domain Multiplexing (biasing of detectors)
Biasing of microcalorimeterAC-bias measurements at 500 kHz to study potential switch-off behavior
Microcalorimeter can be biased over the whole transition provided that the there is a small impedance in the biasing circuit <-> low dielectric loss in C
Set-up for 250 kHz FLL operational and optimizedElectronic resolution of FLL electronics, bias sources and mixers/de-mixers, and SQUID for detector biased in normal state is at present 2 eV
Tests with a TES microcalorimeter with 5 eV resolution @ 6 keV (DC) AC-bias experiment at 50 kHz with 6.5 eV @ 6 keV
Baseline noise 5 eV (~sensor dominated resolution)AC-bias experiment at 500 kHz with 8.8 eV @ 6 keV
SQUID back-action noise (LSQUID) limits resolution of 8-9 eVAC-bias experiment at 250 kHz with 7 eV @ 6 keV
Baseline noise 5 - 6 eV (sensor dominated resolution)
Netherlands Institute for Space Research
Status Frequency Domain Multiplexing (noise blocking filters)
LC filters required with Q ~2500 (depends on carrier frequency)
Washer-type superconducting coilsMinimize dimensions (reduce intercoil cross-talk)
Superconducting capacitorsHigh dielectric constant (small components)Low dielectric losses (tan δ < 0.001; introduces resistance)
Si3N4 (VTT): Q = 2800 (compatibility of Si3N4 process)Al2O3 (SRON): Q = 300 (limited by critical current)
Test structures: 2.4 to 240 nF; size up to 4 x 4 mm2 Low leakage, R ~ 1 mΩ
L = 100 nH
500 m
Netherlands Institute for Space Research
Outlook area: energy resolution
ΔE = 2.35 ξ [kBT2C]1/2
Microcalorimeter physics Low heat capacity absorbers
What motivates the improvement of ΔE?• there is still very limited margin on ΔE with respect to the specification for XEUS and other applications• the development of large area pixels with a good ΔE requires that ξ and/or C are as low as possible (and under control)
Netherlands Institute for Space Research
Outlook – summary
Detector physics – improvement of energy resolution (design: 1 – 1.5 eV) Typical energy resolution (measured) 4 - 5 eV• Possible improvement pulse filtering factor 1.5 – 2 (Fixsen method)• Possible improvement by ITFN reduction factor 1.5 – 2 (TES with lower RN)Device testing (single pixels and arrays)
Large area pixelsLow C materials: Bi, Sn Compatibility with large arrays?Design optimization, thermalization issues: ΔE and ΔE_xy (position dependence)ProductionDevice testing (single pixels and arrays), E < 6 keV
Absorber development