Tracking and Timing with Induced Current Detectors Ronald Lipton CPAD 2019 Dec. 10 2019
Introduction There has been increasing interest in fast timing as well as “intelligent” detector systems. I would like to present some ideas for alternate designs of such systems looking at how technology for silicon-based detectors might evolve. This is a talk about the future - next generation of collider experiments. We focus on capability enabled by new technologies that provide small pixels with low capacitance and sophisticated processing • 3D integration of sensors and electronics • Monolithic active devices • Semiconductor substrate engineering 12/10/2019 Ronald Lipton 2
Some Basics - time resolution • The rule of thumb for the time resolution of a system dominated by jitter is: Jitter Front end noise Time resolution 2 + t d ( ) 2 4 ktA ⎛ ⎞ 2 ∂ V ⎛ ⎞ t a C L Noise 2 = C L σ t ~ σ t ~ σ noise σ n ⎜ ⎟ ~ t r ⎜ ⎟ ⎝ ⎠ ∂ t ⎝ ⎠ Signal g m t a Signal g m t a • slew rate (dV/dt) is related to the inverse amplifier rise time, C L is the load capacitance t d and t a are the detector and amplifier rise times and g m is the input transistor transductance - related to input current, and A is a characteristic of the amplifier. • Fast timing -> large S/N, fast amp, small load capacitance • There are tradeoffs available 12/10/2019 Ronald Lipton 3
More Basics - Signal Development • Signal induced by moving charges ! E w × ! depends on work done by circuit. The i = − q v charge induced on an electrode depends ! d ! on the coupling between the moving ∫ ∫ Q s = idt = q E w x charge and the electrode (Ramo’s theorem) Q 1 → 2 = q ( V w 2 − V w 1 ) • We usually work with simple parallel plate systems • In a multi-electrode system the induced current on an electrode depends on the velocity of the charge and the value of the effective “weighting” field • Weighting field is calculated with 1 V on measuring elected, 0 V on others • There are fast transient induced currents on neighbor electrodes that integrate to zero - can we use them? 12/10/2019 Ronald Lipton 4
3D Integration and small pixels Fermilab has been involved the development of 3D sensor/ASIC integration for almost a decade and have demonstrated (with industrial partners): • Hybrid bonding technology • .5 mm Oxide bonding with imbedded metal sensor through silicon vias (TSV) (BNL) • Bond pitch of 4 microns 34 micron • high 2-tier First 3-tier electronics-sensor stack VICTR chip • Small pixels with ADC, TDC (24 microns) 500" • Small TSV capacitance (~7 ff) 450" Unbonded" 400" The noise in hybrid bonded VIPIC 3D • Bump"bonded" 350" Fusion"Bonded" assembly is almost a factor of two lower 300" Counts' 250" than the equivalent conventionally bump 200" 150" bonded parts due to lower C load 100" 50" 0" 25" 30" 35" 40" 45" 50" 55" 60" 65" 12/10/2019 Ronald Lipton 5 noise'(electrons)'
3D 9 pixel model Methodology We explore simple systems with various pixel sizes, detector thickness and pulse shapes • Build a (Silvaco) TCAD (2D or 3D) detector model • Inject a Q tot =4 fc pulse • Extract the capacitance and pulse shapes at the electrodes • Inject the resulting pulse into a SPICE model Pulses from “x-ray” at~100 μ 200 μ thick detector of a generic 65nm charge sensitive amplifier including noise TCAD Simulation • Analyze the characteristics of the 3 E-14 200 Micron Thick Detector Capacitance (farads) 2 .5E-14 Farads/micron resulting output pulses 2 E-14 • For angled track studies I use simple op amp 1 .5E-14 with defined bandwidth model with adjustable 1 E-14 5 E-15 bandwidth y = 2E-18x 2 + 1E-16x + 1E-15 0 0 20 40 60 80 100 120 Pixel Pitch (microns) 12/10/2019 Ronald Lipton 6
Simple Example - X-Rays Suppose an application requires fast timing on high energy x-rays • Usually we would like thin detectors for fast timing, but thin detectors imply low efficiency - can we use induced currents to achieve time resolution in a thick detector? Central pixel Initial Current Spike Edge neighbor (diffusion collected charge) Corner neighbor 0 collected charge 12/10/2019 Ronald Lipton 7
Pulse Shapes - 200 micron detector Χ -ray 2D Simulation Central Electrode z=10 z=10 z=100 z=190 2ns 2ns z=100 z=190 Central = n n+1 n+2 n+3 2ns 12/10/2019 2ns Ronald Lipton 8
X-Ray With Noise at 185/200 micron depth • Apply a constant threshold of E1~10 mV, E4~130 mV • Tabulate time at threshold crossing including noise • Edge pixel can provide a “start” time stamp if needed Edge pixel E1 Edge pixel σ ~ 30ps 730 mV 720 mV 10 ns Timing histogram Central pixel h h 10 25 25 Entries Entries 104.5 104.5 Mean Mean Central pixel 0.0204 0.0204 Std Dev Std Dev χ χ 2 2 / ndf / ndf 0.4421 / 2 0.4421 / 2 Constant Constant 9.179 9.179 ± ± 2.457 2.457 Mean Mean 104.5 104.5 ± ± 0.0 0.0 Sigma Sigma 0.02177 0.02177 0.00445 0.00445 ± ± 8 σ ~ 22ps 6 850 mV 4 2 12/10/2019 Ronald Lipton 9 0 104 104.2 104.4 104.6 104.8 105
Example - MIP in a 50 micron Detector σ ~25 micron pitch, 50 microns thick 200 Pulse on central pixel V, sensor potential distribution 2ns Amplifier output with noise, 20ff load Timing histogram h h Entries Entries 26 26 Mean Mean 102.3 102.3 12 Std Dev Std Dev 0.01593 0.01593 c c 2 2 / ndf / ndf 0.6285 / 1 0.6285 / 1 ± ± Constant Constant 12.34 12.34 3.24 3.24 ± ± Mean Mean 102.3 102.3 0.0 0.0 ± ± Sigma Sigma 0.01657 0.01657 0.00311 0.00311 10 σ ~16ps 8 Threshold 6 4 2 12/10/2019 Ronald Lipton 10 0 102 102.1 102.2 102.3 102.4 102.5 102.6 102.7
Comments The 20-30 ps resolution will be degraded in a real system However: • All pixels with spacing small compared to depth will have similar signals ~ 16 pixels for a 25x200 micron sensor x 4 in (uncorrelated) time resolution • The central pixel will see a large signal within a few ns of the leading edge - initial thresholds can be set low and signals latched only if a central pixel fires at a higher threshold • The pattern of pixels will provide depth and slope information • Multiple thresholds or more sophisticated processing can give a time walk correction • These results are for n-on-p with maximum field at the top. n-on-n sensors have a maximum field at the bottom. The field profiles can be adjusted to suit the application by varying the applied bias 12/10/2019 Ronald Lipton 11
CMS “P t module” Pattern Recognition Collider based experiments have to deal with increasingly complex events • HL LHC with ~200 interactions per crossing • The CMS experiment is addressing this with stacked sensor arrays to distinguish low from moderate momentum tracks • Can we do this in a single sensor? • Muon collider experiments with huge decay backgrounds • Muon collider studies use timing - fall x 100 short • Backgrounds are from various absorber surfaces/angles • We can use the pattern of electrode signals to distinguish between signal and background tracks signatures To get a feeling for this we use a 25 micron pitch electrode geometry in a ~300 micron thick sensor. 12/10/2019 Ronald Lipton 12
Charge Motion Visualization 30 degree track, n on n, maximum field at bottom. electrons holes .1 ns .5 ns 1.0 ns 1.5 ns 2 ns 2.5 ns 12/10/2019 Ronald Lipton 13
MIPs at various angles Current (Arb. Units) Current (Arb. Units) 0 Deg 10 Deg 10ns 10ns Transient time. Transient time. Current (Arb. Units) Current (Arb. Units) 20 Deg 30 Deg 10ns 10ns 12/10/2019 Ronald Lipton 14
Time resolution and Pattern Recognition 1.40E-05 E4 E4 E2 E6 1.20E-05 1ns Iin 1.00E-05 2ns • 8.00E-06 6.00E-06 4.00E-06 2.00E-06 0.00E+00 0.00E+00 2.00E-09 4.00E-09 6.00E-09 8.00E-09 1.00E-08 1.20E-08 1.40E-08 Long drift 2.00E-06 • some collected charge Electrode 6 1.80E-06 • dominated by induced current Iin 1.60E-06 • difficult to measure secondary peak 2ns 1.40E-06 Medium drift 1ns 1.20E-06 • Dominated by collected charge 1.00E-06 Short drift 8.00E-07 • collected charge similar to induced current 6.00E-07 • Induced and collected 4.00E-07 signals merge 2.00E-07 0.00E+00 0.00E+00 2.00E-09 4.00E-09 6.00E-09 8.00E-09 1.00E-08 1.20E-08 1.40E-08 12/10/2019 Ronald Lipton 15
A look at angular resolution 6.00E-06 10 Degree Track E2 5.00E-06 • To try to get a feeling for what time and pulse E3 E4 height resolution is needed we look at 10 and 20 4.00E-06 E5 degree tracks E6 Signal (Arb Units) 3.00E-06 • 1 nanosecond rise time is assumed 2.00E-06 • Lowest threshold defines time resolution and provides induced 1.00E-06 current t0 0.00E+00 • Other thresholds provide time structure and shape -1.00E-06 of secondary peak 0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08 Time (Sec) 6.00E-06 1.00E-06 20 Deg Track 20 Degree Track E2 E2 5.00E-06 E3 E3 E4 8.00E-07 E4 E5 E5 4.00E-06 E6 E6 6.00E-07 Sig (Arb Units) 3.00E-06 Sig (Arb Units) 2.00E-06 4.00E-07 ToT end Threshold 1.00E-06 2.00E-07 0.00E+00 ToT start Threshold -1.00E-06 0.00E+00 0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08 0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08 Time (sec) Time (sec) 12/10/2019 Ronald Lipton 16
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