Simulation of
Monolithic Active Pixel Sensors
for ILC ECAL

Y.Mikami, O.Miller, N.Watson, J.Wilson

University of Birmingham,

P.Dauncey, A-M.Magnan, M.Noy

Imperial College London,

J.Crooks, M.Stanitzki, K.Stefanov, R.Turchetta, M.Tyndel, G.Villani

CCLRC - Rutherford Appleton Laboratory

International Workshop on Silicon Sensors

for High Energy Physics and Astrophysics

16th December, 2006

Ewha Woman's University, Seoul, Korea

CALICE collaboration

Outline

MAPS (Monolithic Active Pixel Sensors) ECAL

Concepts

Design

Geometry modification in GEANT4 simulation

Demonstration of single e-/m- events using full detector simulation

Sensor simulation

Summary of status

Future prospects

MAPS ECAL concept

High granularity

Small cells

Digital calorimetry

Detecting individual particles after electromagnetic shower

Result in measuring a single particle in each cell

Binary readout

Higher spatial resolution

Better performance for particle separation inside jets

Cost saving

CMOS (Complementary Metal Oxide Semiconductor) silicon

Cheaper than higher resistive pure silicon

ZOOM

4mm X 4mm larger cells

50mm X 50mm smaller cells

Preliminary simulation with SLIC

MAPS Introduction

Analogue design

in Mokka simulation

1cm X 1cm cell

500mm Si sensitive thickness

Analogue readout

MAPS design

50mm X 50mm cell

15mm Si sensitive thickness

Binary readout

Si-W sandwich:

Si physical thickness and W thickness are the same for both default

design and MAPS design in LDC01.

Si physical thickness: 500mm

W thickness: 2.1mm for first 20 layers

4.2mm for last 10 layers

Physical detector slabs

Tungsten

1.4 mm

PCB

~0.8 mm

Embedded VFE ASIC

Physical Silicon

0.3mm

Analogue calorimeter

MAPS calorimeter

12mm

epitaxial layer

Charge collected mainly by diffusion:

(This is not yet modelled for the result of Geant4 simulation which I will show in later slides.)

- Optimization of the diode location

and size is necessary.

Mechanical structure is the same both for analogue and MAPS designs.

50mm

Geometry modification in
Geant4 full detector simulation

PCB

Lower PCB

Si Sensitive

Upper PCB

Default Mokka

Upper PCB

Si Non-sensitive

Si Sensitive

Lower PCB

MAPS (tentative)

800mm

485mm

15mm

Mokka 06-00, LDC01

Ecal02.cc (ECAL Geant4 driver) is modified.

Consistency checks:

Geant4 Adaptive GUI output is fine.

Energy deposit ratio agrees with expectation. (i.e. 15mm/500mm =3.0%)

Layer position shift agrees with expectation.

Linearity for sensitive thickness dependence is represented. (Please see next slide)

500mm

Tungsten

Tungsten

Tungsten

Tungsten

Tungsten

2.1 mm

Single e- simulation (1)
(Si sensitive thickness dependence)

Energy / Cell

v.s.

Si sensitive thickness

20 GeV single electron (from IP to zenith with 4T magnet on)

Cell size is 1cm X 1cm

No threshold is applied for energy of cell hits.

#Cell_hits / Event

(30 layers sum)

v.s.

Si sensitive thickness

Only a few % dependence

Single e-/m- simulation (2)
(Energy deposit of cell hits)

Single e-

Single m-

20 GeV single e-/m-

15mm Si sensitive thickness

50mm X 50mm cell size

No threshold and no noise is applied.

Before sensor level response is implemented.

Minimum Ionization Particles

Individual secondary particles are detected

after electromagnetic shower cascade !!

large cell

small cell

#Cell hits

Single e- simulation (3)
(Cell size dependence)

25mm x 25mm

50mm x 50mm

400mm X 400mm

100GeV single e-

15mm Si sensitive thickness

No threshold and no noise is applied.

Before sensor level response is implemented.

Charge sharing effects

at cell boundary

Multi MIPs increase Landau tail

50mm x 50mm cell size is good working assumption.

Cell hit energy distributions:

50 mm

25 mm

100mm

1mm

shower particles

100mm x 100 mm

#Cell hits

0 10 keV

Single e- simulation (4)
(Incoming electron energy dependence)

1 GeV single e-

40 GeV single e-

180 GeV single e-

15mm Si sensitive thickness

50mm X 50mm cell size

No threshold and no noise is applied.

Before sensor level response is implemented.

Similar cell hit energy distributions except for number of cell hits.

-> One MIP per cell -> Digital calorimetry

Cell hit energy distributions:

Longitudinal shower shapes in 30 layers:

180 GeV e-

40 GeV e-

1GeV e-

#Cell hits

0 10keV

0 10keV

Nweight = S Nhit + 2 S Nhit

Linearity for energy measurement

W thickness: 2.1mm for first 20 layers

4.2mm for last 10 layers

layer# =1

layer# =21

20

30

Weighted #cell hits

v.s.

Incoming e- energy

180GeV e-

with no weight

180GeV e-

with weight

Energy proportional to counting number of cell hits.

4T B field (1GeV e- is injected just in front of ECAL, other energy e- is from IP.)

No threshold and no noise is applied for cell hit energy.

Before sensor level response is implemented.

Counting number of cell hit in a event without clustering.

Weighted number of cell hits is used for different W thickness layers.

Very preliminary linearity plots:

Full 3D device simulation

Injected 1 MIP charge at 21 separate positions on a grid of 5 mm pitch.

Using the symmetry the collected charge in the rest of the device is extrapolated

Pixel layout

3.5x3.5 m2

1.8x1.8 m2

Epitaxial thickness: 12 m

0V (Substrate)

1.5 V

3.3 V

N-well

Diodes

Capacitor

Resistor

1

21

Cell size: 50 x 50 m2

Charge collection simulation (1)

Adding realism: Including sensor level response

Charge collection simulation (2)

Charge lost in the N-well

e-

Charge collected by diodes

Collected charge on the diodes v.s. MIP impact position

e-

~50% of the charge collected when a MIP hits the N-well

Collected charge increases with the diode size

e- (0.1)

Collected charge on the diodes and on the N-well

v.s. MIP impact position

Sensor layout example









10 mm

Readout

Control

Pad & Power Ring

Pixels

Test Bump Pads

Test Structures

36 pixels

36 pixels

1800 mm

200 mm

1800 mm

4000 mm μ

4000 mm

80 pixels

10mm

Sensors from foundry arrive at RAL July 2007

200mm dead area in every 2mm in test structure -> will be reduced.

Actual test structure design

Summary of status

MAPS geometry is implemented in full detector simulation.

Each cell has only one secondary particle in most cases.

50mm X 50mm cell size is reasonable starting assumption.

Other ongoing studies

Sensor level simulation

Noise and digitization

MAPS Electronics

MAPS DAQ

Future Prospects

First sensors fabricated in August 2007

Second sensor fabrication run, delivery July 2008

Comparison between data and simulation

MAPS geometry (After 2007 MAPS sensor is available.)

Energy resolution study with sensor response

Clustering algorithm development

Spatial resolution study

Physics studies

Back up(1)
Single e- simulation (3.b)
(Cell size dependence)

#Cell hits / Event

v.s.

Cell size

In small cell case (less than ~ 100 mm X 100 mm):

Only one secondary particle pass each cell in most case.

One MIP's energy deposit is sharing by neighbour cell.

Energy / Cell

v.s.

Cell size

100GeV e-

15mm Si sensitive

No threshold and no noise is applied.

Before sensor level response is implemented.

50 um

25 um

100um

1mm

Total energy / Event

v.s.

Cell size

3% bias:

Minimum step size effect ?

yoshi mikami

2006-10-13T18:36:51