Tracking and Timing with Induced Current Detectors · 12/10/2019 Ronald Lipton Some Basics - time resolution • The rule of thumb for the time resolution of a system dominated by

Ronald LiptonCPAD 2019Dec. 10 2019

Tracking and Timing with Induced Current Detectors

12/10/2019 Ronald Lipton

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

2


Some Basics - time resolution

• The rule of thumb for the time resolution of a system dominated by jitter is:

• slew rate (dV/dt) is related to the inverse amplifier rise time, CL is the load capacitance td and ta are the detector and amplifier rise times and gm 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

3

σ t ~σ noise∂V∂t

⎛⎝⎜

⎞⎠⎟ ~ tr

NoiseSignal

⎛⎝⎜

⎞⎠⎟

σ n2 =

CL2 4ktA( )gmta

Front end noise

σ t ~CL

gmta

ta2 + td

2

Signal

Jitter Time resolution


More Basics - Signal Development• Signal induced by moving charges

depends on work done by circuit. The charge induced on an electrode depends on the coupling between the moving charge and the electrode (Ramo’s theorem)• 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?

4

i = −q!Ew ×

!v

Qs = i dt = q!Ew∫∫ d!x

Q1→2 = q(Vw2 −Vw1)


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 • Oxide bonding with imbedded metal

through silicon vias (TSV)• Bond pitch of 4 microns• First 3-tier electronics-sensor stack• Small pixels with ADC, TDC (24 microns)• Small TSV capacitance (~7 ff)• The noise in hybrid bonded VIPIC 3D

assembly is almost a factor of two lower than the equivalent conventionally bump bonded parts due to lower Cload

50"

50"

100"

150"

200"

250"

300"

350"

400"

450"

500"

25" 30" 35" 40" 45" 50" 55" 60" 65"

Coun

ts'

noise'(electrons)'

Unbonded"

Bump"bonded"

Fusion"Bonded"

.5mmsensor(BNL)

34micronhigh2-tierVICTRchip


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 Qtot=4 fc pulse• Extract the capacitance and pulse shapes at

the electrodes• Inject the resulting pulse into a SPICE model

of a generic 65nm charge sensitive amplifier including noise

• Analyze the characteristics of the resulting output pulses

• For angled track studies I use simple op amp with defined bandwidth model with adjustable bandwidth

6

3D 9 pixel model

Pulses from “x-ray” at~100μ200μ thick detector

y=2E-18x2 +1E-16x+1E-15

0

5E-15

1E-14

1.5E-14

2E-14

2.5E-14

3E-14

0 20 40 60 80 100 120

200MicronThickDetector

Farads/micron

TCAD Simulation

Pixel Pitch (microns)Ca

paci

tanc

e (f

arad

s)


Simple Example - X-RaysSuppose 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?

7

InitialCurrent Spike

Central pixel

Corner neighbor 0 collected charge

Edge neighbor (diffusion collected charge)


Pulse Shapes - 200 micron detector Χ-ray 2D Simulation

8

2ns 2ns

2ns2ns

z=10

z=190z=100

Central Electrode

z=10z=100

z=190

Central = n

n+1

n+2

n+3


hEntries 25Mean 104.5Std Dev 0.0204

/ ndf 2χ 0.4421 / 2Constant 2.457± 9.179 Mean 0.0± 104.5 Sigma 0.00445± 0.02177

104 104.2 104.4 104.6 104.8 1050

2

4

6

8

10h

Entries 25Mean 104.5Std Dev 0.0204

/ ndf 2χ 0.4421 / 2Constant 2.457± 9.179 Mean 0.0± 104.5 Sigma 0.00445± 0.02177

Timing histogram

E1

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

9

Edge pixel

Edge pixel σ~ 30ps

Central pixelCentral pixel σ~ 22ps

730 mV

850 mV

720 mV10 ns


Example - MIP in a 50 micron Detector

10


/ ndf 2c 0.6285 / 1Constant 3.24± 12.34 Mean 0.0± 102.3 Sigma 0.00311± 0.01657

102 102.1 102.2 102.3 102.4 102.5 102.6 102.70

2

4

6

8

10

12


/ ndf 2c 0.6285 / 1Constant 3.24± 12.34 Mean 0.0± 102.3 Sigma 0.00311± 0.01657

Timing histogram

σ~16ps

σ~25 micron pitch, 50 microns thick 200 V, sensor potential distribution Pulse on central pixel

2ns

Amplifier output with noise, 20ff load

Threshold


Comments

The 20-30 ps resolution will be degraded in a real systemHowever:• 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

11


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 signaturesTo get a feeling for this we use a 25 micron pitch electrode geometry in a ~300 micron thick sensor.

12

CMS “Pt module”


Charge Motion Visualization

13

.1 ns

2 ns1.5 ns

1.0 ns.5 ns

2.5 ns

electrons

holes

30 degree track, n on n, maximum field at bottom.


MIPs at various angles

14

0 Deg

30 Deg20 Deg

10 Deg

10ns

10ns10ns

10ns

Cur

rent

(Arb

. Uni

ts)

Cur

rent

(Arb

. Uni

ts)

Cur

rent

(Arb

. Uni

ts)

Cur

rent

(Arb

. Uni

ts)

Transient time. Transient time.


Time resolution and Pattern Recognition

15

E2

0.00E+00

2.00E-06

4.00E-06

6.00E-06

8.00E-06

1.00E-05

1.20E-05

1.40E-05

0.00E+00 2.00E-09 4.00E-09 6.00E-09 8.00E-09 1.00E-08 1.20E-08 1.40E-08

E4

1ns

Iin

2ns

0.00E+00

2.00E-07

4.00E-07

6.00E-07

8.00E-07

1.00E-06

1.20E-06

1.40E-06

1.60E-06

1.80E-06

2.00E-06

0.00E+00 2.00E-09 4.00E-09 6.00E-09 8.00E-09 1.00E-08 1.20E-08 1.40E-08

Electrode 6

Iin

2ns

1ns

Long drift• some collected charge• dominated by induced current• difficult to measure secondary peakMedium drift• Dominated by collected chargeShort drift• collected charge similar

to induced current• Induced and collected

signals merge

E4 E6

•


A look at angular resolution• To try to get a feeling for what time and pulse

height resolution is needed we look at 10 and 20 degree tracks

• 1 nanosecond rise time is assumed• Lowest threshold defines time resolution and

provides induced current t0

• Other thresholds provide time structure and shape of secondary peak

16

-1.00E-06

0.00E+00

1.00E-06

2.00E-06

3.00E-06

4.00E-06

5.00E-06

6.00E-06

0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08

Sig

(Arb

Uni

ts)

Time (sec)

20 Deg TrackE2E3E4E5E6

-1.00E-06

0.00E+00

1.00E-06

2.00E-06

3.00E-06

4.00E-06

5.00E-06

6.00E-06

0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08

Sign

al (A

rb U

nits

)

Time (Sec)

10 Degree TrackE2

E3

E4

E5

E6

0.00E+00

2.00E-07

4.00E-07

6.00E-07

8.00E-07

1.00E-06

0.00E+00 5.00E-09 1.00E-08 1.50E-08 2.00E-08

Sig

(Arb

Uni

ts)

Time (sec)

20 Degree TrackE2E3E4E5E6

ToT end Threshold

ToT start Threshold


Time over Threshold• This simple case seems to work, time stamps reflect pulse shape• Slope indicates difference in charge drift among electrodes• Clear cutoff in signal for 10 degree track• Consistent start times (particle impact at 1 ns)

17

• 300ps error bars to guide the eye

0

1E-09

2E-09

3E-09

4E-09

5E-09

6E-09

7E-09

8E-09

9E-09

-60 -40 -20 0 20 40 60

Tim

e (S

ec)

Electrode Position (microns)

Time over threshold20 Deg Tend20 Deg, Tstart10 Deg, Tstart10 Deg Tend


Comments

Patterns of hits on pixels in “thick” detectors can provide a wealth of information - but the devil is in the details• S/N and bandwidth are crucial• Information is in the first 10 ns• This means power • The more information about the waveforms the better• Time over Threshold (TOT) with multiple threshold points• Requires transresistance amplifier

• Simple diode arrays are more radiation hard than LGADs, but radiation will affect internal fields and charge collection

• We also need to process and transmit that information - this implies “intelligent” pixels where the information in a field of pixels can be processed and decisions made

18

σ t ~CL

gmta

ta2 + td

2

Signalf ~ gm gm ∼ Id


More Work (for someone …)

This work is very much at a conceptual stageDetails will need to be understood to validate the concept and understand it’s range of application

To Do: • Define an overall toy->serious algorithm• What is the angular resolution as a function of bandwidth?• How do Landau fluctuations affect the reconstruction?• What is the overall time resolution?• Implement a realistic transimpedance amplifier in 65 nm and access power

requirements• Re-acquire hybrid bonding technology for sensor/readout integration• Access optimal detector thickness and depletion fields

Build something

19


Prospects

Fast timing in small pixels and thin detectors - most technologies have been demonstrated• Thin sensors (8” wafers)• Time of arrival (demonstrated with LGADs)• fine pitch bonding (3D hybrid bonding)• Chip to wafer bonding (dead regions?)The use of induced currents• Small signal/noise, large bandwidth• Power consumption• Assembly geometry and size• Data processing - intelligent pixels to

select hits around a central core• Data bandwidth

Vendors - The basic hybrid bonding technology is now licensed to several foundries (inc MIT-LL, Sandia, IZM), used in cell phone cameras many

20

VICTR& VIP&VIP&

VIPIC& VIPIC&


Conclusions

I have discussed some possible applications of small pixels enabled by emerging technologies.• It is one way of addressing some of the extreme challenges of future

experiments (FCC, Muon Collider, EIC …)• Fast timing• Radiation hard• Complex event topologies • I have presented toy models without engineering detailTo do more, a specific application and real engineering is needed• What power is needed? Cooling mass? Support geometry• Amplifier/discriminator design• Design of the digital tiers• Area to be deployed? Coverage? Cost? - What Experiment?

21


Chip to Wafer

22

DBIbondingofROICs(VICTR,VIPIC,VIP)toBNLsensorwafer

ExposeTSVs,patternTopaluminum

Wafer-wafer3DBond

OxidebondHandlewafer

ExposesensorsideTSVs, patternDBIstructures

DBIbondROICchipstosensorwafer(RTpick+Place)

Grindandetchtoexposetopconnections


Integrator Circuit

23


Implementation

24

25µ

Digitaltierprocesses afieldofpixels

Analogelectronicstierwithdiscriminatorstimingandmemory


Time resolution of a thick detector

• We use the TCAD/SPICE simulation chain to model an x-ray in the thicker detector going into a 65nm charge sensitive amplifier

25

Electrode1– smallpulse, butfastriseDepositatZ=185– notescalesarenotequal

Electrode3– DepositatZ=25

Edge pixel peak at 25 mV, 2 ns 0 total charge collected

Central pixel peak at 1V, 12 ns

100ns110ns


Pixel Capacitance

A detector with low capacitance can provide excellent time resolution:

Before this improvement is realized other effects will dominate including charge deposition variations. Power considerations will limit front-end current which will reduce transistor transductance However with “spare” margin we can become more adventurous

26

y=2E-18x2 +1E-16x+1E-15

0

5E-15

1E-14

1.5E-14

2E-14

2.5E-14

3E-14

0 20 40 60 80 100 120

200MicronThickDetector

Farads/micron

σ t ,pixel

σ t ,LGAD

∼Cpixel

CLGAD

× 1GainLGAD

≥102 × 120∼ 5

σ t ∼1gm, gm ∼ Id

α(α ~ 1)

TCAD Simulation

TSV Test Structure

Pixel Pitch (microns)

Cap

acita

nce

(fara

ds)


Hybrid Bonding Vendors (2019)

27

Vendor Wafer Diam Wafer-Wafer Die-Wafer TSV

Sony -

NHanced 8” ✓ ✓ ~1 um?

Teledyne Dalsa 6”, 8” ✓ ~5 um

Sandia 6”->8” developing ✓ no

IZM 12” ✓ no ~5 um

Raytheon 8” ✓ -

Documents

Tracking and Timing with Induced Current Detectors · 12/10/2019 Ronald Lipton Some Basics - time resolution • The rule of thumb for the time resolution of a system dominated by