28th International Workshop on Vertex Detectors, 13-18 Oct, 2019 @Lopud Island, Croatia

Design of a Segmented LGAD Sensor for
Development of 4-D Tracking Detector
University of Tsukuba~10cm

WADA Sayaka，ONARU Kyoji，HARA Kazuhiko，

KEK-INPS

4D Tracker

Low-Gain Avalanche Detector (LGAD)

Should we add time information to the hits,
Identify vertices otherwise difficult using position
information only
Effective in forward regions where vertexing
precision is limited(Δt=10ps ⇄ Δz=3mm)

Add p+ layer underneath the n+ readout electrodeHigh E-field induces avalanche multiplicationthin (50μm) substrate is effective forsignal creation
short charge collection time with fast
signal shape→ good time resolution O(10ps)

collision points
centralAdding timeinformation

forwardwith superior position resolution O(10μm) achievable with semiconductor,
LGAD is a good candidate for realizing 4-D tracker．

Tracks reconstructed by ATLAS(event with 17 interactions)

HPK LGAD samples➡ Expect 200/crossing at HL-LHC

Should we add time information to each hit,
Reconstruct tracks using proper time differences
Help reduce wrong hit combinations and effective in
reducing the track reconstruction CPUhits

UNNO Yoshinobu, NAKAMURA Koji

Adding time
information

Pad type

Strip type

window：1mmD

strip pitch：80μm

Active thickness：50 or 80μm (150μm physical)
p+ layer concentration：4 steps (A<B<C<D)→ Innovation in tracking

Evaluation of Timing Precision in High-Energy BeamFeb 20-Mar 4, 2018
@FNAL FTBF

Signal readout
LGAD signal is amplified (usinghigh-speed amps) and digitizedusing DRS4 flash ADCs (5GS/s)
Pulse height：12bit, 1Vpp
(1V/4096 ~ 0.25mV)Time bins：10bit, 5GS/s(200ps*1024~200ns F.S.)

120GeV protons

Stacked 3
LGAD sensors

Pulse height① noise only
② beam hit the gain=1 region③ beam hit the LGAD region

CAENV1742

evaluation③ → timing resolution evaluatedgain > 1
LGAD signal

gain = 1

Flash ADC data are fitted to a polynomial
function to extract the time when thesignal exceeds f×(signal peak), where fis an arbitral coefficient.
Extract the timing resolution from themeasured time differences for the twosensors．

noise

Two LGADs aresame active
thickness (50mm)

results
Better timing precision achieved
for thinner active thickness
50μm : ~30ps @340V (f=0.9)80μm : ~40ps @500V (f=0.3)
at lower temperature
22℃ : ~35ps @330V (f=0.5)
8℃ : ~28ps @330V (f=0.5)
as expected for higher LGAD gain

TCAD SentaurusTM(synopsys)

TCAD Simulation for Segmented LGADs
actual device(response to IR laser)

TCAD

TCAD

Gain non-uniformity of strip is
also reproduced by TCAD
TCAD with parameters tuned toreproduce the measurements is used tosimulate new segmented devices withleast non-uniformity

actualdevice

actualdevice

candidate：deep trench

p+conc:D>C>B>A

Measured IV and CV are reproduced by TCAD
at a precision reasonably well
Impact ionization map

at 100V, E-field in the junction is
not high and multiplication is notlarge．
at 300V, E-field in the junction ishigh but too large at the ends ofthe multiplication layers, causing
sensor breakdown．

Summary

300V 200V 100V

To separate electrodes physical by deep and thin trenches

Uniform gain~10 is obtainable in wider
region except a few μm around trenches

IV特性IVIV characteristics is more stable than inthe strip type
Gain uniformityTRENCHImpact ionisation(enlarged)

E-field concentration around thetrenches causes the breakdown．
Needs optimization of neutralisation
process around the trenches

dotted：strip
solid：trench
p+conc：R>G>B→ trench is a good candidate for the LGAD segmentation, butneed further process optimisation

We are developing LGAD sensors to realise 4-D tracking detector➡ Time precision better than 30 ps is obtained from test beam measurements➡ TCAD simulation tuned to reproduce measured characteristics is used to design segmented LGADsensors. Trench is a good candidate. Continue to optimize the electrode structure and trench process

Acknowledgement