Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 1/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Simulation of new P-type strip detectors with trench to enhance the charge multiplication effect in the n-
type electrodes
Simulation of new P-type strip detectors with trench to enhance the charge multiplication effect in the n-
type electrodes
P. Fernández-Martínez, G. Pellegrini, J. P. Balbuena, D. Quirion, S. Hidalgo, D. Flores, M. Lozano
Centro Nacional de Microelectrónica (IMB-CNM-CSIC)
G. CasseLiverpool University
Work partially supported by RD50 collaboration
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 2/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Introduction
a. Irradiated detectors suffer displacement damage that change their charge
collection dynamics
• Defects induced by radiation increase the electric field at the junction
of the N+ diffusion
• The electric field increase leads to a multiplication of the collected
charge in irradiated devices
b. Project: fabricate a p-type strip detector with small gain ���� Similar signal
before and after irradiation
• Multiplication occurs at low bias voltage
• Gain should be limited between 2 and 10:
- Avoid Crosstalk
- Avoid exceeding the dynamic range of readout electronics
• Capacitance should not increase
- Higher capacitance ���� Higher noise
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 3/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Technological proposals
I. Trench filled with doped polysilicon along the centre of the strip pitch
− A N+ contact is created into the silicon bulk that modifies the
electric field in the collection region ���� multiplication
285µm
80µm
n+
p-
p+
32µm
5µm
5µm
20µm
8µm
p-stop
Poly trench
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 4/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Technological proposals
II. P-type diffusion along the centre of the strip pitch
− Under reverse bias conditions, a high electric field region is created
at the N+– P junction ���� multiplication
p-
p+
285µm
32µm
80µm
20µm
8µm
n+
5µmp-stop
P-type diffusion
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 5/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Simulation of the Electric Field
Strip Detector Poly Trench
P diffusionHigh Electric Field
region driven deep in the bulk
High Electric Field peak at the centre of the strip
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 6/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
0 10 20 30 40 50
102
103
104
105
Ele
ctr
ic F
ield
(V
/cm
)
Depth (µµµµm)
No Irradiated
ΦΦΦΦeq
= 1 x 1016
n/cm2
Strip Detector: Section @ Strip Center
High Electric Field peak at the junction
Simulation of the Electric Field
0 10 20 30 40 50
102
103
104
105
Ele
ctr
ic F
ield
(V
/cm
)
Depth (µµµµm)
Strip
Poly Trench
P Diffusion
Section @ Strip Center
High Electric Field region driven deep in
the bulk
Achieved Electric Field values are comparable with the irradiated devices
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 7/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Simulation of charge collection: MIP
A/cm2
Strip Detector Poly Trench P Diffusion
� We are developing a simulation procedure to obtain the gain value
� We are developing a simulation procedure to obtain the gain value
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 8/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Simulation of the Capacitance
p-
p+
n+
CBulk
CInterStrip
0 50 100 150
4
8
12
16
Bu
lk C
ap
ac
ita
nc
e (
pF
)
Applied Voltage (V)
Strip
Poly Trench
P Diffusion
0 50 100 1500
20
40
60
80
100
CIn
ter_
Str
ip (
pF
)
Applied Voltage (V)
Strip
Poly Trench
P Diffusion
Once Fully Depleted, the bulk capacitance is the same for all the
structures
Increment related with the depletion of the P
diffusion
� We need experimental results
to extract any conclusion
� We need experimental results
to extract any conclusion
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 9/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Variation over the basic proposals
I. P – type diffusion, implanted through a trench filled with oxide, along the
centre of the strip pitch
− N+/ P-type diffusion junction creates a high electric field region ����
multiplication
n+
p-
p+
285µm
32µm
80µm
5µm
5µm
20µm
8µm
p-stop
Oxide trench
P-type diffusion
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 10/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Variation over the basic proposals
• The deeper the trench, the
larger the volume of
multiplication
- We are considering trenches
of different depth
Electric FieldCharge Collection
0 50 100 1500
20
40
60
80
100
CB
ulk (
pF
)
Anode Voltage (V)
Strip
Oxide Trench
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 11/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Variation over the basic proposals
II. Large P-Type covering all the strip width
− N+/ P-type diffusion junction creates a high electric field region ����
multiplication
p-
p+
285µm
32µm
80µm
20µm
8µm
n+
30µmp-stop
P-type diffusion
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 12/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Variation over the basic proposals
DRAWBACK: If N+ and P diffusions are performed with
the same mask, a premature breakdown is expected
due to the curvature of the junction
- N+ diffusion should overlap P diffusion
���� One extra level of Mask
���� Optimisation of the overlap size
p-
p+
n+
Premature Cylindrical Breakdown
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 13/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Status of the Work: Fabrication
The fabrication run includes:
•Conventional Strip Detectors
•Poly Trench structures with
different trench depths:
− 5 µm− 10 µm− 50 µm
•Structures with small P layer
along the center of the strip
•Oxide filled trench structures
with a P layer implanted through
the trench:
− 5 µm− 10 µm− 50 µm
●Devices with large P layer along
the center of the strip
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 14/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Status of the Work: PAD Diodes
We have fabricated PAD diodes with a P layer diffused under the N+ diffusion
− N+/ P-type diffusion junction creates a high electric field region ����
multiplication
285 µµµµm
N+
P
High Electric Field region leading to multiplication
5000 µm
5000 µm
� First Measurements: Gain ~2
� First Measurements: Gain ~2
Simulation of new P-Type strip detectors RESMDD’10, Florence – 12-15.October.2010 15/15
Centro Nacional de Microelectrónica Instituto de Microelectrónica de Barcelona
Conclusions and Applications
11 We have presented several new designs to enhance the
multiplication process.
22 Presence of trenches or diffused P layers in the strips can
provide small gain values.
33 Capacitance value can be deteriorated. It will be better
established with the experimental results.
44 A run containing the discussed designs is being fabricated for
subsequent characterisation.
55 A PAD detector with small gain has been fabricated following
some of the procedures described in this work.
6 Applications:
- Radiation Hard Detectors
- Tracking Detectors- Charge multiplication permits the fabrication of thinner detectors