Development of Large-Area LGADsFor Space Application

A. Bisht 1,2 † G. Borghi2 M. Boscardin2 M. Centis Vignali2 F. Ficorella2

O. Hammad Ali2 G. Paternoster2

†ashish.bisht@unitn.it

1Universita degli Studi di Trento, Italy

2Fondazione Bruno Kessler, Italy

38th RD50 Workshop, 2021

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 1 / 15

Introduction: Requirements of Time Resolving Tracking in space Experiments

Velocity resolution crucial forisotopic measurements:

δM

M=δp

p+ γ2

(δβ

β

)

• d and anti-d

• 3He/4He

• 6Li/7Li

Advantages of 4D tracking• Identification of back-scattered

hits from calorimeters.

• Ghost hits in “Si-MicroStrip”detectors.

• Time-of-flight (ToF) measurement

• Improved e/p identification

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 2 / 15

Space LGADs: Need for large channel?

• Rate is not as high as in HEP

• Power Issue→ Reduce the number of channels

• “Typical” Silicon sensor: strip, ∼ 100µm pitch, 50-60 cm long (∼ 1 cm2)

• Timing (∼ 50-60 ps) is desired.

• Low Earth Orbit Experiments→Radiation is not an Issue

Solution?

LGADsExcellent Timing resolution!!

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 3 / 15

Specification of the DUT

LGAD Pads

• Pads with different area: 1 ×1 mm2, 2.5 × 2.5 mm2, and 5× 2.5 mm2

• Metal frame

1 × 1 mm2 2.5 × 2.5 mm2 5 × 5 mm2

4 cm3.5 cm

LGAD Strips

• 3.5 cm long, 192 µm pitch(Total 16 strips)

• Strip 15 is with single longopening

• Strip 13 is with multi openings

• The metal openings are 8.5mm apart

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 4 / 15

MoVeIT Production

Standard LGAD Technology Active Thickness: 45 µm

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 5 / 15

Experimental Setup: TCT

• Particulars TCT setup

• Particulars broadband amplifier (53 dB)

• IR and Red Laser

• Beam Monitor

• 3 channel passive readout board

• V(t).

• Baseline Correction.

• Non measuring strips are terminatedusing 50Ω termination.

• Collected charge is given as:

Q =

∫ tf

t0

I(t)dt,

• Normalization of charge/amplitude.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 6 / 15

Gain Comparison

Gain Definition:

Gain =QLGAD

QPIN

0 50 100 150 200

(V)biasV

0

5

10Gai

n

MoveIT Wafer-13 Pads, IR

2 1 mm×1

2 2.5 mm×2.5

2 5 mm×5

MoveIT Wafer-13 Pads, IR

2 1 mm×1

2 2.5 mm×2.5

2 5 mm×5

0 50 100 150 200

(V)biasV

0

5

10Gai

n

MoveIT Wafer-14 Pads, IR

2 1 mm×1

2 2.5 mm×2.5

2 5 mm×5

MoveIT Wafer-14 Pads, IR

2 1 mm×1

2 2.5 mm×2.5

2 5 mm×5

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 7 / 15

1 × 1 mm2 2.5 × 2.5 mm2 5 × 5 mm2

Charge at Vbias = -200 V

Amplitude at Vbias = -200 V

Significant non-uniformity of amplitude in pad with large area.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 8 / 15

Big Pad Anomaly

Amplitude Map

0 1000 2000 3000 4000 5000 6000

m)µX-Axis (

0

1000

2000

3000

4000

5000

6000

m)

µY

-Axi

s (

2

4

6

8

10

12

Am

plitu

de (

mV

)

Rise-Time Map

0 1000 2000 3000 4000 5000 6000

m)µX-Axis (

0

1000

2000

3000

4000

5000

6000

m)

µY

-Axi

s (

0

0.2

0.4

0.6

0.8

1

1.2

1.4

(ns

)ris

eτ

• Significant decrease in amplitude towards center in non metallized big pads.

• Increase in rise-time towards center for the same data.

• This might be a resistive effect of the implant.

• It needs to be studied in a systematic way with some modelling and simulations.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 9 / 15

Resistance Modelling

• Resistance of implant with metal frame.

• Maximum resistance at the center of the pad as seen by the signal.

• Similar shape observed in the experimental data.

Need more in depth study to fit experimental data.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 10 / 15

Hit Map of Strip (single opening)

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 11 / 15

Charge and Amplitude v/s Strip Length

0 10 20 30Strip Length (mm)

50

55

Nor

m. C

harg

e (a

rb.)

MoveIT Wafer 13 LGAD IR

Strip 15

Strip 13

0 10 20 30Strip Length (mm)

14

16

18

20

22

Nor

m. A

mpl

itude

(ar

b.)

MoveIT Wafer 13 LGAD IR

Strip 15

Strip 13

• Non uniformity in charge collection.

• Both strips shows similar trend

• Non-uniformity in the gain layer (sensors in the outer edge of wafer)

• Amplitude increases with increase in distance from readout

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 12 / 15

Strip 15: Ratio & Rise Time

• Ratio of amplitude and charge shows a linear rise along the strip length.

• Read-out is from the left pad for both strips.

• Decrease in rise time along the strip length for both strips.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 13 / 15

Ratio (Amplitude/Charge)

0 10 20 30Strip Length (mm)

0.25

0.3

0.35

Am

plitd

ue/C

harg

e (a

rb.)

MoveIT Wafer 13 LGAD IR

Strip 15

Strip 13

Reflection

• The ratio increases as we move away from the readout pad.

• The ratio of amplitude and charge shows consistent behaviour for both strips.

• Change in signal shape.

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 14 / 15

Summary and OutlookThe single channel big pads and long strips from the standard LGAD technology werestudied using the IR-TCT.

• Change in signal shape has been observed in the big pads.→ Resistive effect of implant

• Significant change in the amplitude along the strip.

• The rise time changes in both big pads and long strips.→ Signal reflection might be a cause for different signal shape. We need to study theeffect of reflection in more detail and find an optimal solution to corrected it (ifnecessary).

• New production batch devoted to space application.→ Will be used to study these effects and other parameters.

• Upcoming Timing setup (90Sr).

Acknowledgment: We would like to thank MoVeIT group.

Thank you for your attention

Ashish Bisht (UniTn-FBK) Development of Large-Area LGADs 22nd June 2021 15 / 15