Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Performance of LGADs and AC-LGADs towards 4D tracking G. D’Amen 1 , W. Chen 1 , G. Giacomini 1 , L. Lavitola 2 , S. Ramshanker 3 , A. Tricoli 1 1 Brookhaven National Laboratory (US) 2 Universita’ degli studi Federico II (IT) 3 Oxford University (UK) CPAD INSTRUMENTATION FRONTIER WORKSHOP 2019 University of Wisconsin-Madison 9 December 2019 1 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Outline Time resolution - LGAD Introduction to LGADs I. LGAD response to 90 Sr β − II. Response to DT fast neutrons III. IV. Comparison with Geant4 simulation Response to 252 Cf fast neutrons V. LGAD wafer (BNL) Space & Time - AC-LGAD VI. The AC-LGAD concept Characterization with IR laser and 90 Sr VII. Conclusions and Future activities AC-LGAD matrix (BNL) 2 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Low Gain Avalanche Diode Introduction Low Gain Avalanche Diode (LGAD): highly doped layer of p-implant ( Gain layer ) near p-n junction creates a high electric field that accelerates electrons enough to start multiplication. ◮ Electric Field: ∼ 300 kV/cm in Gain Layer E field ◮ Silicon-based technology with low, Questions to be answered: adjustable gain (2 - 100) ◮ MIPs detection capabilities already proven, ◮ Breakdown Voltage ∝ Gain parameters fast neutron response to be characterized (dose, energy) ◮ How fast is the response to fast neutrons? ◮ High Signal/Noise ratio ◮ What are out limits of detectable neutron ◮ Ability to achieve fast-timing O (20-30) ps energy? in high radiation environments 3 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions LGAD structure Wafer structure (W1836,W1837,W1840) ◮ 500 µm substrate ◮ 1 × 1 mm 2 sensor size ◮ Aluminum thin layer ◮ 50 µm 28 Si p epitaxial layer, 10 B and 11 B doped (7 × 10 13 cm − 3 ) ◮ Silicon Oxide SiO 2 ◮ Different doping concentrations (3, 3.25 and 2.7 ◮ n++ layer, 31 P doped × 10 13 cm − 3 ) and gain layer thickness ◮ Gain p+ layer, 11 B doped 4 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions 90 Sr interactions Signal waveforms Waveforms from β − 90 Sr signals > W1836 , W1837 , W1840 show narrow Sensor Gain (X-Ray): peaks with widths O (1 ns) W1836: ∼ 15 > Sensors Gain for β − compatible to that of W1837: ∼ 20 W1840: ∼ 25 X-rays � dV � − 1 � ∼ 20 ps > σ j = � σ noise dt 5 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Deuterium-Tritium neutron generator BNL Thermo-Fisher MP 320 Neutron Generator (prototype) 3 T + 2 D → 4 He + n (14 . 1 MeV ) (1) Neutron energy spectrum very narrow σ E = O (10 − 2 MeV) and isotropic, with estimated neutron production of 6 × 10 7 neutrons/sec, with a flux of 7 × 10 4 neutrons/(cm 2 sec) at sensor position 6 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Fast Neutron interactions Signal waveforms Waveforms from neutron signals (V trig = 10mV) > W1836 , W1837 , W1840 show narrow Sensor Gain (X-Ray): peaks with widths O (1 ns) W1836: ∼ 15 > Sensor Gain for neutrons compatible to the W1837: ∼ 20 one measured with X-rays W1840: ∼ 25 � dV � − 1 � ∼ 20 ps > σ j = � σ noise dt 7 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Fast Neutron interactions Deposited Energy distributions Energy deposited by the neutron interaction computed as integral of each signal: 3 . 6 [ eV ] � E dep [ eV ] = Adt G n R fb q e wf Sensitive Range in deposited energy ( ∝ ( G n ) ), limited by trigger voltage and maximum signal amplitude in oscilloscope window. For a 10 mV trigger level and G n = 15, sensitivity to neutron signals with deposited energy as low as ∼ 30 keV . 8 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Generated energy spectrum Distribution of energy deposited by DT neutron interactions as simulated by Geant4 shows good agreement with experimental data from W1836 in the sensor sensitive range E dep = [30, 450] keV Superimposing E dep distributions generated by neutrons with different energies can give us an estimate of minimum neutron energy sensitivity 9 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Neutron energy sensitivity Extrapolation of sensitivity to various neutron energies based on 14.1 MeV data W1836 sensitivity (according to 14.1 MeV W1836 sensitivity (according to 14.1 MeV deposited E distribution) to 300- and 500- keV deposited E distribution) to 20 MeV neutrons neutrons 10 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Californium 252 Decays 252 Cf decay scheme: - ∼ 96 % Alpha decay - ∼ 3 % Spontaneous Fission (SF) ( n, γ ) - < 1 % rare decays Energy spectrum (SF): > Neutrons : Landau( µ = 2 MeV, σ = 0.5 MeV) > Photons : Landau( µ = 400 keV, σ = 100 keV) > α : either 6.076 MeV or 6.118 MeV, entirely absorbed 11 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions LGAD sensitivity to 252 Cf Unshielded sensor ( Geant4 simulation) Lead shielding (2.5 cm) ( Geant4 simulation) Spontaneous Fission photon flux ∼ 8/3 neutron • E dep < 80/90 keV Photon dominated flux. Lead shielding should decrease γ • E dep = 90 - 200 keV Photon/Neutron population. population • E dep > 200 keV Neutron dominated 12 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions LGAD sensitivity to 252 Cf Distribution of energy deposited by 252 Cf neutron and photon interactions as simulated by Geant4 shows good agreement with experimental data from W1840 in the sensor sensitive range E dep = [15, 140] keV (photon dominated) Jitter from Cf signals ∼ 20 ps, compatible to DT and MIPs. Additional data covering mixed- and neutron- dominated regions are being collected as we speak. 13 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions 4D detectors: AC-LGAD tests with IR laser and 90 Sr > The AC-LGAD concept > LGAD vs AC-LGAD comparison > Cross-Talk studies > Timing performance 14 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions AC-LGAD concept LGAD limits: AC-LGAD goals: ◮ Dead volume (local gain ∼ 1) ◮ ∼ 100 % Fill Factor and fast timing information at a within the implanted region of the gain layer per-pixel level achieved ◮ Signal generated by drift of multiplied holes into the ◮ Pixels/strips (pitch ∼ 100 mm) with gain layer below the implant substrate but AC-coupled through dielectric have a Fill Factor «100 % ◮ Electrons collect at the resistive n + and then slowly ◮ Good for timing, hardly for 4D flow to a ohmic contact at the edge. reconstruction 15 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions AC-LGAD Signal comparison with LGADs ◮ Sensor wire-bonded to 16 channel Trans-impedance Amplifier board by FermiLab ◮ AC-LGAD: 3 × 3 pixel matrix, 200 µ m × 200 µ m AC-coupled pads bonded to TAs ◮ LGAD: same AC-LGAD device where the n ++ is read-out by the TA (same bias conditions and gain) ◮ Comparison of pulse amplitudes of betas from 90 Sr. ◮ Essentially equal distribution (same gain) for LGAD and AC-LGAD Amplitudes ◮ Is this signal well spatially localized? Need to estimate Cross-Talk between pixels/strips 16 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Cross-talk Strip Map Cross-talk measured as ratio between signal amplitude peaks in different strips Crosstalk ratio A2/A1 100 % ratio A3/A1 13 % ratio A4/A1 6 % ratio A6/A1 4 % Response of a single strip as a function of shining position of IR or red laser (TCT scan). Border effect: n ++ is a low resistance path that couples the signals back to the strip under measure. 17 / 21
Performance of LGADs and AC-LGADs towards 4D tracking Introduction Data Geant4 Simulation Californium AC-LGADs Conclusions Cross-talk Pixel Map Cross-talk measured as ratio between signal amplitude peaks in different pixels Dose n + 1/100 Dose n + 1/10 ratio A5/A1 7 % 9 % ratio A9/A1 11 % 16 % Response of a single pixel as a function of shining position of IR or red laser (TCT scan). Border effect: n ++ is a low resistance path that couples the signals back to the pixel under measure. 18 / 21
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