Ultra Low Background Front End Electronics for the ...
Transcript of Ultra Low Background Front End Electronics for the ...
Ultra Low Background Front End Electronics
for the Majorana Demonstrator
Paul Barton
Applied Nuclear Physics Program, Nuclear Science Division
Lawrence Berkeley National Laboratory
14 May 2019
Conference on Science at SURF
P. Barton – 2CoSSURF
Semiconductor Detector Lab Activities at LBNL
Low Mass Front End (LMFE) for MajoranaLAr LMFE for LEGEND 0νββLDRD for LEGEND ASIC
CPG CdZnTe Module w/ depth sensingSpherical Coded Aperture / Compton Imager
HPGe double-sided strip detectorsfor gamma ray imaging
LBNL Scientific CCD for MeV Photon Beam Diagnostics
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Neutrinoless Double Beta Decay
in 76Ge
Is the neutrino it’s own antiparticle?
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Double-Beta Decay
(A,Z)
Nuclear
(A,Z+2)
2νββ-decay
Process
W−
W− e−
ν̄e ν̄e
e−
(A,Z)
(A,Z+2)
0νββ-decay
(“vanilla model”)
W−
e−
e−
Nuclear ν̄Process ν
W −
• 2νββ-decay: SM allowed and observed.• 0νββ-decay: Violates lepton number conservation (a requirement of
some neutrino mass models). Not yet observed.
• For 76Ge (Q = 2039 keV):
T2ν1/2
∼ 1021 y → Rare process.
T0ν1/2
> 1026 y → Search needs ultra-low background, large mass, and long
counting time. Good energy resolution helps distinguish from 2νββ-decay.
1/20ν 28e.g. T ∼ 10 y would give signal of ∼ 0.5
counts/ton/yr
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Ton-Scale Neutrinoless Double Beta Decay
(Out of 4 Ranked Recommendations)
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Next Generation 76Ge: LEGEND
Large Enriched Germanium Experiment for Neutrinoless ββ Decay
Mission: “The collaboration aims to develop a phased, Ge-76 based
double-beta decay experimental program with discovery potential at a half-life beyond
1028 years, using existing resources as appropriate to expedite physics results.”
Select best technologies, based on what has been learned from GERDA and the
Majorana Demonstrator, as well as contributions from other groups and experiments.
First phase:
• (Up to) 200 kg.
• Modification of existing
GERDA infrastructure at
LNGS.
• BG goal (×5 lower)
0.6 c/(FWHM·t·y)
• Start by 2021.
Subsequent stages:
• 1000 kg (staged).
• Timeline connected to U.S. DOE
down select process.
• BG goal (×30 lower)
0.1 c/(FWHM·t·y)
• Location: TBD.
Required depth (Ge-77m) under
investigation.
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The MAJORANA Demonstrator
Requires very low background front end electronics! (< 1 count in ROI per ton, per year!)
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Coaxial
Vb
C ~ 20 pF
Small Electrode
C ~ 1 pF
Vb
Detector Geometries
P. Barton – 9CoSSURF
Germanium Point Contact Detector
HV Bias
P. Luke, “Low Capacitance Large Volume Shaped-field Germanium Detector,” IEEE TNS 36 (1989) 926.
Point ContactElectrode
(~mm)
• Originally proposed as dark matter detector
• Discrimination of multi-site events
• Low capacitance → low noise
• Lower trapping from p-type (than n-type),hence the LBNL P-Type Point Contact (PPC) detector
HPGe
similar rise time, different drift timesMulti-Site EventIdentification
Lithium drifted contact(hole barrier)
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Resistive Feedback Pulsed Reset
Pro
- Simple
Con
- Johnson noise
- Excess noise
- Resistor mass/radioactivity
- Energy-rate limitation
- Pole-zero difficulties
Pro
- No feedback resistor
Con
- Reset crosstalk (multi-channel system)
- Dead time during reset
- Added input capacitance
- Added complexity
a-Ge
resistor
Increase Rf
Det. Det.
Preamplifier Configuration
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Resistive Feedback JFET Front End
Junction Field Effect Transistor (JFET) – a Voltage Controlled Resistor (tens of ohms)
HVgate
drain
source
feedback
pulser
Front End ElectronicsPPC
Moxtek JFET
example operating point
VdsVgs
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voltage current
1/f
Voltage (Series) Noise
ENC ~ Vn,FET (CFET + CDet + CF + Cstray + …)
Vn, FET ~ CFET-1/2
→ Min. noise: CFET ~ (CDet + CF + Cstray)
Current (Parallel) Noise
ENC ~ (2qIL + 4kT/Rp)1/2
IL – full shot-noise leakage current
1/f Noise
Lossy dielectric, trapping-detrapping, ...
Det. shaper
Electronic Noise & Equivalent Noise Charge (ENC)
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Mini-PPC
Low Mass Front End Test Cryostat
LMFE Test with Mini-PPC
Optimization of JFET operating temperature with thermally isolating glass PCB
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NoDetector
(preamp only)
LMFE Minimum Noise
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LMFE Minimum Noise
preamp & detector
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Am-241
Mini-PPC Spectral Performance
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BEGe Noise with Moxtek (MX11) JFET
150 eV-FWHM limited primarily by capacitance of crystal
…but OK for some large physics experiments →
~1 kg
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LBNL Low Mass Front End (for MAJORANA)
Front End Preamplifier
Cry
ost
at
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LBNL Low Mass Front End
Output
Front End PreamplifierLow Mass Front End
Cry
ost
at
200 µm thick Fused Silica
SputteredTi / Au Traces200A / 4000A
7 mm
~80 K
~200 K
• JFET experiences Joule heating from drain current
• Board thermally separated from LN temperatures
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LBNL Low Mass Front End
Output
Front End PreamplifierLow Mass Front End
Cry
ost
atEpoxiedMOXTEKMX-11RC Al(1% Si)
1 mil Wire Bonds
TRA-DUCT 2902 Silver EpoxyRoom temp cure, low outgassing0.001 ohm-cmCTE = 0.6e-6 cm/cm/K3.0 W/m/K
MOXTEK JFETMX-11RC (reduced capacitance)designed for x-ray detectorsCgs = 0.7 pFgm = 8en
2 = 1.5 nV/√Hz
DrainSource
Gate
GD
S
P. Barton – 21CoSSURF
LBNL Low Mass Front End
Front End PreamplifierLow Mass Front End
Cry
ost
atCp = 45 fF
Cf = 176 fF
3D Electrostatic SimulationSet voltages, Look for charge
Potential Electric Field
A
Capacitance = V-1∫Surface charge density
1
0 0 0 0
Feedback
F
P
Pulser
A
A
P. Barton – 22CoSSURF
LBNL Low Mass Front End
Output
Front End PreamplifierLow Mass Front End
Cry
ost
at
Sputtered Germanium, LBNL-B774000A24 hr pumpdown, 2 mTorr, 120 W, 90 A/min
a-Ge at low temperatures = low noise
Rf
P. Barton – 23CoSSURF
LBNL Low Mass Front End
Output
Front End PreamplifierLow Mass Front End
Cry
ost
at
Simple cascode design a la F. Goulding (1967)
To Buffer /Drive Stage
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Low Mass (~Radio-Pure) Materials
Ge Al(Si)
Ti / Au Epoxy FEP / CuSi
SiO2
Ultrasonically DrilledHoles (Bullen, Inc.)for MAJORANA
Preliminary Assay results courtesy J. Loach
Budget < 4.1 cnt/ROI-ton-yr
Goal = 3 cnt/ROI-ton-yr
715 nBq / LMFE → 0.3 cnt/ROI-ton-yr
P. Barton – 25CoSSURF
Majorana LMFE Design Layout
Ti / Au = 11.76 mm2 (x 200A / 4000A)
Ge = 0.71 mm2 (x 4000A)
1. Revision2. Lot3. Wafer4. Board
1/20th mil (1.27 µm) Laser Transparency
Layout 10 boards per 2 inch wafer
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Majorana LMFE Fabrication
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Majorana LMFE Fabrication
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Majorana LMFE Fabrication
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Majorana LMFE Fabrication
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↳ T & humidity control↳ dry boxes to store producHon parts under
LN boil-‐off atmosphere
↳ ionizer + HEPA filter bench
LMFE Production Facility
Class-100 clean room (with ESD flooring) @ LBNL
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Loading Electroformed Copper Clips
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mechanical QA electrical QA
↳ pressure corresponding to 650g applied on board
↳ full signal path + preamp test↳ check baseline
↳ pulser check of 1st and 2nd stages
Production: QA
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Majorana LMFE Assembly at SURF
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MJD Readout Block Diagram
a
HV LV
Detectorx5
Front-Endx5
Preamplifierx5
Controller Card
Mother Board 1
Mother Board 2
Digitizer Cardsx2
DAQ
DAQ Slow Control
interlock
cryostat
Detectorx5
Front-Endx5
DAC
ADC ADC
DAC DAC
DAC
FPGA
SPI interface
1st stage
2nd stage
Vds
pulsers
Power + digitizer Back-end electronics Front-end electronics
Low-noise LVpower supply
Controller card
Mother board
Front-end board
Preamp.
WARM COLD
P. Barton – 36CoSSURF
The MAJORANA Demonstrator (prelude to ton-scale)
Located at the 4850’ levelof Sanford Underground Research Facilityin South Dakota
Low background passive Pb and Cu shieldwith active muon veto
Ultraclean electroformedcopper cryostat
30 kg of87% enriched 76Ge
10 kg ofnatural Ge
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Noise performance
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Spectroscopic performance
Energy Resolution (FWHM)
2.4 keV FWHM at Q=2039 keV
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Silica substrate (radio-pure, electrical, thermal, mechanical)
1-100 GΩ Amorphous-Ge Rf (radio-pure, low excess noise)
200 eV-FWHM noise with large PPC detectors (Majorana)
150 eV-FWHM noise with BEGe detector
85 eV-FWHM noise with mini-PPC detector (55 eV w/o detector)
Low Mass Front End
Can we lower the noise?
Thank You…
This work was funded by: DOE {NP, NNSA {DNN R&D, NSSC}}
I gratefully acknowledge the support of my colleagues: Kai Vetter, Paul Luke, Mark Amman, Alan Poon, et al.
P. Barton – 41CoSSURF
Equivalent Noise Charge
222 2 2 2 24 4
4 28
dn na f d e d na
m F
Ce kT kTENC Q e A C q I i
g R
= = + + + + +
100:140
1.2 pF
3.0 pA
16 G
d
d
F
T
C
I
R
=
=
=
=
Voltage (series) Current (parallel)1/fsimple CR-RC Shaper
e2/8
T
gm
ena2
Cd2, Cd
2
τ, τ
Af
Id
T
Rf
ina2
from shaping filter (affects V/I differently)
JFET temperature
JFET transconductance (~gain)
preamp / amp voltage noise
detector (and other) capacitance
shaping time constant
fabrication-dependent factor
detector leakage current
feedback resistor temperature
feedback resistance
preamp / amp current noise
▪
▪
▪
▪
▪
▪
Front-End Related
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The Shaping Amplifier and Ideal Filters
CRRC
CR RC4
Semi-Gaussian Shaper: (tau * s) / (1 + tau * s)n
e.g. Canberra 2026 Spectroscopy Amplifier
Shaping Time
Preamp Out
Filter
Amp Out
Judicious choice of shaping filter can(de)emphasize Series vs. Parallel noise
less series noise
Frequency (Hz)
Time (s)
Vo
ltag
e (m
V)
Mag
nit
ud
e
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JFET Heating Affects Feedback Resistance
Preamp Output
36.8 %
(time after preamp turn-on)
Convert decay time into Rf by:
tau = Rf * Cf,
where Cf is known and constant
176 fF → 8-17 GΩ ( ~20 K range)
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JFET Heating Fights Feedback Resistor
1 mA
7 mA
(12 electrons-rms)
2009 – Mini PPC
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MOSFET Alternative to JFET
Investigating cold (<77 K) CMOS options:
XGLab CUBE ASICEntire Preamp-on-a-chipOriginally for SDDFunctional at 4 K
Pulsed-Reset0.75 x 0.75 mm2
3.4 el.rms alone
4.4 electrons-rmsfor Silicon Drift Detector
would be 24 eV-FWHM in Ge,
for a safe threshold of 70 eV!
P. Barton – 46CoSSURF
Cold CMOS Schematic
Trade feedback resistorfor Reset transistor
Preamp-on-a-chip
HV pulser for C-V
CMOS improves below LN2
Cin
Voltage 1 / f Current
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Microphonics during averaged 0.609 Hz pulser (100 K)
Microphonics from LN2 Boiling
And mechanical cryocoolers have significantly more vibrations
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Ultra-Low Vibration GM-Cycle Cryostat
Test HPGe and electronics at 10 – 100 K with GM CryocoolerNational Nuclear Security Consortium (NSSC) Supported
Additional vibration isolation used in optical systems for nm-scale vibration
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V_IO
V_SSS
OUT
I_BiasRST
GNDPulser
CUBE ASIC Printed Circuit Board
Test Pulse Capacitor
CP = 10.3 fF simulated
= 9.3 fF measured
PCB: Rogers 4000 – Low Dielectric Loss (low leakage current)
Power supply filters (RC surface mount) for Vio and Vsss
Minimal test pulse capacitor
3D Electrostatic Model
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From Pin to Wirebond
Existing Mini-PPC Dimple Lapped Off
1. Reduce capacitance
2. Streamline assembly
3. Improve reliability
4. Reduce microphonics
5. Minimize masswirebonding by Mark Amman
1. Wet etch to remove damage
2. Sputter Al on Li
3. Sputter a-Si on top
4. Evaporate 0.75 mm Al forpoint contact
5. Wirebond
Reprocessing Steps
Advantages
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Detector Characteristics
Detector Capacitance = 0.26 pF
Leakage Current = 20 fF (at 30 K)
2 mil Al
1 mil Al (1% Si)
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Be Window
241Am
Spectral Performance
Front View
P. Barton – 53CoSSURF
Ultra-Low Noise Ge (Neutrino) Detector Collaboration – ULGeN
First: Mechanically Cooled, Wirebonded PPC HPGe, with CMOS Front End
Atmospheric Pressure He GasProvides ultra-low vibration thermal link using standard GM cycle (10 – 80 K)→ Eliminates all vibrations
Ultra-Low CapacitanceSmaller point contact (0.26 pF)enabled by wire bonding→ Ultra-Low Electronic Noise
Preamp-on-a-ChipCMOS ASIC for SDD4 electrons-rms noise→ Better than JFET
at low temperatures
Low temperature and ultra-low capacitance of CMOS and Ge.Result: lowest noise HPGe detector: 39 eV-FWHM at 43 K.
P. Barton – 54CoSSURF
A Common Theme
1. the ASIC!
2. die attach (e.g. epoxy)
3. substrate
4. traces
5. bond wires
6. bypass capacitor(s) + passives
7. passives’ attachment
8. connector
ASIC Front End Elements
Remember:• Electrical• Mechanical• Thermal• (Radiopurity)
P. Barton – 55CoSSURF
LBNL internal LDRD funding for a more suitable preamplifier ASIC
1. Optimized for operation in liquid argon
2. Optimized for large mass 1.5 kg HPGe detectors (1-3 pF?)
3. Single power supply (reducing the cabling needs)
4. Integrated feedback resistor (reduce external a-Ge)
5. Built-in power supply capacitor and filter (eliminate external cap)
6. Differential output for >10 m cable to DAQ
Coupled with silicon MEMS capacitors for off-chip PS decoupling
Silicon (radiopure) PCB, with wirebonds to detector
Next Steps for L-1000
Thank You…
This work was funded by: DOE {NP, NNSA {DNN R&D, NSSC}}
I gratefully acknowledge the support of my colleagues: Kai Vetter, Paul Luke, Mark Amman, Alan Poon, et al.
P. Barton – 57CoSSURF
A tale of two experiments
Majorana Demonstrator (SURF)
Detectors (29.7 kg enr76Ge) in 2 vacuum
cryostats.
Surrounded by passive shield. Ultra-
clean materials used.
GERDA (LNGS)
• Detectors (37.6 kg enr76Ge) in
liquid argon (LAr).
• LAr an active shield: Backgrounds
tagged with scintillation light.
detector arrays have demonstrated the lowest
backgrounds and best energy resolution of all 0νββ
experiment technologies.
P. Barton – 58CoSSURF
LEGEND Discovery Potential
10−3 10−2 10−1 10 102 1031Exposure [ton-years]
1024
1025
2610
1027
1028
1029
1030
T1
/2 3
DS
[years
]
IO mmin range
Background free
0.1 counts/FWHM-t-y
1.0 count/FWHM-t-y
10 counts/FWHM-t-y
76Ge (88% enr.)
MJD/GERDA
LEG
EN
D-
200
LEG
END
-1000
• Reduction of backgrounds is crucial to achieve good discovery potential.
• Majorana and GERDA technologies combined with new R&D to accomplish this.
P. Barton – 59CoSSURF
Broad LEGEND Methodology:
Use best radiopurity elements from Majorana
Use LAr shielding from GERDA
Ongoing Tasks
Test LMFE in LAr
Modify a-Ge resistor on LMFE
Choose JFET (MX11,SF291)
Modify Preamp (GERDA | Majorana)
Current Front End Steps for L-200
High Mass Front End surrogate w/ modified GERDA preamp
P. Barton – 60CoSSURF
LEGEND-200
• Initial 200 kg phase permits early science with a world-leading experiment.
• Exposure 1 ton·yr, sensitivity > 1027 yr
• Keeps young people involved and maintains skilled workers.
• Reduces risk for a future ton-scale phase. Reuse of GERDA infrastructure and
• Majorana/GERDA detectors (60 kg) permits possible data taking in 2021-2022.
• Room in GERDA cryostat for 200 kg of enriched detectors.
Jordan Myslik (LBNL) July 7,201860/ 14
water
(Ø 10m,
lock
Ge detector array
LAr veto
cryostat
(Ø 4m, 64m
PMT of muon
floor of clean
roof of clean
plastic muon
glove box
Required reduction in background for LEGEND-200 has already been demonstrated as feasible in the Majorana Demonstrator, GERDA, and dedicated test stands.