Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET)

Semiconductor device simulation of silicon radiation Semiconductor device simulation of silicon radiation

detectorsdetectors

R. H. Richter for the MPI Semiconductor LabR. H. Richter for the MPI Semiconductor Lab

Outline

Semiconductor equations

ExamplespnCCD

Depleted Field Effect Transistor (DEPFET)

Pixel detectors: field distribution in heavily irradiated silicon

Summary

R. H. Richter, 6th Hiroshima Symposium - STD6, Carmel, September 12th 2006

Continuity equationsContinuity equations

Simultaneous consideration of

Generation

Recombination

Drift

Diffusion

Drift due to electric field derived from Poisson Equation

Numerical simulation: simultaneous solution of diffusion and Poisson equation with boundary conditions

Equations


Boundary conditions and featuresBoundary conditions and features

Neumann b.c. (termination and symmetric continuation)

Direchlet b.c. (Ohmic contacts)

Gate b.c.

Schottky contacts

Simple networks with R,C,L possible

Sophisticated mobility models

Parametrization of impact ionization (avalanche)


Concept of PN-CCD with frame storeConcept of PN-CCD with frame store (Google-> pnCCD, XMM)(Google-> pnCCD, XMM)

backside illumination

pn-junctions instead of MOS gates

pn-junction (homogeneous)

full

y d

eple

ted

0

.5 m

m

transfer “deep” in bulk

anode +

JFET on chip

per channel

PN-CCD different from MOS-CCDs

p

n

p


pnCCD – simulation taskspnCCD – simulation tasks

WIAS-TeSCA2D-Simulation

charge transferbarriers to surfaceTransfer region + anode

charge transfer to anode Channel separation (perpendicular to transfer region)

Technology compatibility with on chip amplifiers (JFETs).

Challenges: large domain (50000 triangles), depletion state - electrons

How to verify?


MeshingMeshing

Triangulated grid (2D) often taken from the

technolgy simulator but additional programs

are also used (Gridgen, B. Heinemann)

20.000 – 40.000 points

potential

log(n)

Localized generation of e/h pairs simulate particle tracks or converted photons.

pn-CCD performancepn-CCD performance

• largest monolithic CCD

6 x 6 cm²

384 x 400 pixel

150 µm pixel

• fast, parallel readout

5 msec full frame

• low noise

4 el. rms

• high quantum efficiency

90 %

• radiation hard

400 Mp/cm²

XMM-Newton – first light (January 2000)XMM-Newton – first light (January 2000)

large Magellanic cloud

supernova remnant 1987A


Getting insight into a CCD - MeshGetting insight into a CCD - Mesh

Analysis of the charge collection process

Mesh experiment (Tsunemi, Yoshita, Kitamoto, Jpn J. Appl. Physics 36, 2906

N. Kimmel et al, Analysis of the charge collection process in pnCCDs , Proceedings of SPIE vol. 6276, p.


Mesh-results vs SimulationMesh-results vs Simulation

Charge distribution over the pixel Simulation: charge generation in steps of 5µm scanning the transfer direction


CTE degradation due to trapsCTE degradation due to traps

You can’t predict the real life completely. Even if you create ‘perfect’ transfer potential with a lot of headroom.

N. Krause et al, NIM A439, p228

Contamination in epitaxial layers (gas delivery, stainless steel)

Titanium contamination (ET about 0.26eV, several 1010cm-3) during epitaxy (also measured with DLTS)

Replace the epitaxial layer High energy implantation (P 20MeV)


pn-CCD – charge transfer efficencypn-CCD – charge transfer efficency

Replacing the epitaxial layerby a 20MeV HE P-impl.


p+

p+ n+

rear contact

drain bulksource

p

sym

met

ry a

xis

n+

ninternal gate

top gate clear

n -

n+p+

DEPFET-Principle of OperationDEPFET-Principle of Operation

FET-Transistor integrated in every pixel (first amplification)

Electrons are collected in „internal gate“ and modulate the transistor-current

Signal charge removed via clear contact

-

-

+

+

++

-

MIP

internal Gate

Potential distribution:

Drain

Source

Backcontact

[TeSCA-Simulation]

~1µm

50

µm

--- ---


p+

p+ n+

rear contact

drain bulksource

p

sym

met

ry a

xis

n+

ninternal gate

top gate clear

n -

n+p+

DEPFET-Principle of OperationDEPFET-Principle of Operation

FET-Transistor integrated in every pixel (first amplification)

Electrons are collected in „internal gate“ and modulate the transistor-current

Signal charge removed via clear contact

internal Gate

Potential distribution:

Drain

Source

Backcontact

[TeSCA-Simulation]

~1µm

50

µm

--- ---

0V

+15V

0V


DEPMOS Technology on high ohmic 6” waferDEPMOS Technology on high ohmic 6” wafer

(DIOS-ISETCAD-Simulation)(DIOS-ISETCAD-Simulation)

DEPMOS pixel array cuts through one cell

Along the channel Perpendicular to the channel

Metal 2

Metal 1

Oxyd Poly 2

Metal 2

Metal 1

Poly 2

Clear Gclear Channnel

pDeep n

n+Deep p

Poly 1

Double poly / double aluminum process on high ohmic n- substrate

Low leakage current level: < 200pA/cm² (fully depleted – 450µm)


Potential of the Potential of the emptyempty Internal Gate Internal Gate

L = 4 (3) µm

L= 5 (4) µm

L = 6 (5) µm

L = 7 (6) µm

L = 10 (9) µm ToSCA – 2D device simulation


Comparison with simulation – Comparison with simulation – internal amplification vs channel lengthinternal amplification vs channel length

Simulation @ 50µA drain current

Assuming an under-etching of 1.2µm

Measured by S. Rummel

measured at 100µA

measured at 50µA

nice illustration of the DEPFET scaling potential


DEPFET 3D-SimulationDEPFET 3D-Simulation

ILC layoutK. Gärtner, R.R., DEPFET sensor design using an experimental 3d device simulator, accepted for publication in NIM


Simulated signal responseSimulated signal response

Charge reaches the interface -> slow diffusionIn reality: charge loss due to trapping and smallpotential barriers

Introduction of:buried channel implantationlateral drift fields by inclined deep p implantations


Auslese-knoten #1 Transfer-

gate

Clear #1 Auslese-knoten #2

Clear #2

Bias

Gate #1 Gate #2

RNDR principleRNDR principle(repetitive non destructive readout )(repetitive non destructive readout )

By measuring the charge multiple (n) time the noise can be reduced by 1/ sqrt(n) Because the collected charge is stored during readout in the DEPFET-RNDR, the very same charge can be measured multiple times.


gate


Clear #2

Bias

Gate #1 Gate #2


gate


Clear #2

Bias

Gate #1 Gate #2


gate


Clear #2

Bias

Gate #1 Gate #2


gate


Clear #2

Bias

Gate #1 Gate #2


gate


Clear #2

Bias

Gate #1 Gate #2


Investigated Structure: 4x4 MinimatrixInvestigated Structure: 4x4 Minimatrix(G. Lutz)(G. Lutz)

ILC-Type RNDR

Realised as a four by four Minimatrix


Laser spectra Laser spectra (S. Wölfel)(S. Wölfel)

Measurement:

Charge injection with laser during integration time

180 Loops for the readout (duration: 9.18 ms) -45 °C

Measured leakage current:

ca. 0,4 e- in 180 loops


Double trap model for heavily irradiated siliconDouble trap model for heavily irradiated silicon

V. Chiocia et al (accepted for Proceedings of Wildbad Kreuth (NIM A))

see also Eremin, Verbitskaja, Li, NIM A476, p.556


Charge collection profile by grazing angle techniqueCharge collection profile by grazing angle techniqueon a CMS pixel detector (testbeam measurement)on a CMS pixel detector (testbeam measurement)


Simulated and measured chargeSimulated and measured charge

0.5 x 1014 neq

2 x 1014 neq

10V 20V15V

25V 150V50V 100V


Electric fieldsElectric fields0.5 x 1014 neq unirradiated2 x 1014 neq


SummarySummary

Developing state of the art detectors there is no way around a thorough

numerical simulation.

Primary task: Prediction of the device behavior and finding optimal operation states and process parameters

Provides insight into the potential and limits of a device concept.

For a full understanding of complicated pixel detectors 3D-simulation is a must!

Investigation of radiation induced defects by the ‘grazing angle technique’ together with simulations is a promising way.

Outline Semiconductor equations Examples pnCCD Depleted Field Effect Transistor (DEPFET)

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