Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

Contents lists available at ScienceDirect

Nuclear Instruments and Methods inPhysics Research A
journal homepage: www.elsevier.com/locate/nima

Development of n-on-p silicon sensors for very high radiation environments
Y. Unno f,n, A.A. Affolder h, P.P. Allport h, R. Bates e, C. Betancourt m, J. Bohm l, H. Brown h, C. Buttar e,
J.R. Carter b, G. Casse h, H. Chen a, A. Chilingarov g, V. Cindro i, A. Clark d, N. Dawson m, B. DeWilde o,
Z. Dolezal k, L. Eklund e, V. Fadeyev m, D. Ferrere d, H. Fox g, R. French n, C. Garcia q, M. Gerling m,
S. Gonzalez Sevilla d, I. Gorelov j, A. Greenall h, A.A. Grillo m, N. Hamasaki p, K. Hara p, H. Hatano p,
M. Hoeferkamp j, L.B.A. Hommels b, Y. Ikegami f, K. Jakobs c, S. Kamada r, J. Kierstead a, P. Kodys k,
M. Kohler c, T. Kohriki f, G. Kramberger i, C. Lacasta q, Z. Li a, S. Lindgren m, D. Lynn a, M. Mikestikova l,
P. Maddock m, I. Mandic i, S. Marti i Garcia q, F. Martinez-McKinney m, R. Maunu o, R. McCarthy o,
J. Metcalfe j, M. Mikuz i, M. Minano q, S. Mitsui p, V. O’Shea e, S. Paganis n, U. Parzefall c, D. Puldon o,
D. Robinson b, H.F.-W. Sadrozinski m, S. Sattari m, D. Schamberger o, S. Seidel j, A. Seiden m, S. Terada f,
K. Toms j, D. Tsionou n, J. Von Wilpert m, M. Wormald h, J. Wright m, M. Yamada p, K. Yamamura raPhysics Department, Brookhaven National Laboratory, Bldg. 510A, Upton, NY 11973, USA
Cavendish Laboratory, Cambridge University, J J Thomson Avenue, UK-Cambridge CB3 0HE, United Kingdom
Physikalisches Institut, Universitaet Freiburg, Hermann-Herder Str. 3, D-79104 Freiburg i.Br., GermanydSection de Physique, Universite de Geneve, 24 rue Ernest Ansermet, CH-1211 Geneve 4, SwitzerlandeDepartment of Physics and Astronomy, University of Glasgow, UK-Glasgow G12 8QQ, United KingdomfInstitute of Particle and Nuclear Study, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0801, Japang
Physics Department, Lancaster University, UK-Lancaster LA1 4YB, United KingdomhOliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Oxford Street, UK-Liverpool L69 3BX, United KingdomiExperimental Particle Physics Department, Jozef Stefan Institute, Jamova 39, P.O. Box 3000, SI-1001 Ljubljana, SloveniajDepartment of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USAkInstitute of Particle and Nuclear Physics, Charles University in Prague, V Holesovickach 2, CZ-18000 Praha 8, Czech RepubliclInstitute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-18221 Praha 8, Czech RepublicmSanta Cruz Institute for Particle Physics (SCIPP), University of California Santa Cruz, Santa Cruz, CA 95064, USAn
Department of Physics & Astronomy, University of Shefﬁeld, Hounsﬁeld Road, UK-Shefﬁeld S3 7RH, United KingdomoDepartment of Physics and Astronomy, Stony Brook University, Nicolls Road, Stony Brook, NY 11794-3800, USAp
Institute of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba-shi, Ibaraki 305-8571, Japanq
Instituto de Fisica Corpuscular (IFIC), Centro Mixt Univ. de Valencia-CSIC, Apdo. 22085, ES-46071 Valencia, Spainr
Solid-State Division, Hamamatsu Photonics K.K., 1126-1 Ichino-cho, Higashi-ku, Hamamatsu-shi, Shizuoka 435-8558, Japanbca r t i c l e in f o

a b s t r a c t

Available online 6 May 2010

We have developed a novel and highly radiation-tolerant n-in-p silicon microstrip sensor for very highradiation environments such as in the Super Large Hadron Collider. The sensors are designed for a
ﬂuence of 1  1015 neq/cm2 and are fabricated from p-type, FZ, 6 in. (150 mm) wafers onto which welay out a single 9.75 cm  9.75 cm large-area sensor and several 1 cm  1 cm miniature sensors withvarious n-strip isolation structures. By evaluating the sensors both pre- and post-irradiation by protons
and neutrons, we ﬁnd that the full depletion voltage evolves to approximately 800 V and that then-strip isolation depends on the p + concentration. In addition, we characterize the interstrip resistance,interstrip capacitance and the punch-through-protection (PTP) voltage. The ﬁrst fabrication batch
allowed us to identify the weak spots in the PTP and the stereo strip layouts. By understanding thesource of the weakness, the mask was modiﬁed accordingly. After modiﬁcation, the follow-up
fabrication batches and the latest fabrication of about 30 main sensors and associated miniature sensors
have shown good performance, with no sign of microdischarge up to 1000 V.
& 2010 Elsevier B.V. All rights reserved.

Keywords:
SiliconSensorMicrostrip
p-typen-in-pATLAS
SLHCRadiation damage

1. IntroductionnCorresponding author. Tel.: + 81 29 864 5791; fax: + 81 29 864 2580.
E-mail address: yoshinobu.unno@kek.jp (Y. Unno).

0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.nima.2010.04.080

The most eminent example of a very high radiation environment is the large hadron collider (LHC) and the future super LHC

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30(SLHC). The LHC collects collision data of about 700 fb 1 with anominal luminosity of 1034 cm 2 s 1. The silicon microstrip
tracker (SCT) in the inner detector (ID) of the ATLAS detector
was built to tolerate an integrated particle ﬂuence of 2  1014
(1-MeV neutron-equivalent (neq))/cm2 at a radius R 30 cm fromthe collision point. To maximize its research capabilities, the LHC
is to be upgraded to the SLHC, with the goal being to achieve overan order of magnitude higher luminosity ( 41035 cm 2 s 1) andover 4 times more integrated luminosity (3000 fb 1). Fig. 1 shows
an expected particle ﬂuence of  1015 neq/cm2 at R 30 cm withZ  150 cm (along the beamline), with a safety factor of 2 in theluminosity . The ratio of neutrons to charged particles is greaterthan unity for R430 cm. The neutron ﬂuence is 5  1014
neq/cm2 at R 30 cm and decreases slightly to  3  1014 at
R 90 cm. A large number of pile-up events per beam crossing isforeseen (300–400 compared with 20 at the LHC), so the particle
density in the ID will be 15–20 times larger than that at the LHC.
Radiation damage by hadronic particles (pions, protons,
neutrons, etc.) creates acceptor-like energy levels in the siliconbulk, causing n-type silicon to mutate into p-type, and increasing
the full depletion voltage (FDV) as ﬂuence is accumulated. As asilicon sensor using an n-implant readout in a p-type wafer, then-in-p sensor offers the following advantages: (1) n-in-p sensors
can be fabricated using a single-side lithography process, making
them more cost-effective than n-in-n sensors, which require adouble-side process. (2) They may be operated in the partiallydepleted state because the p–n junction is always on the signalcollecting side, making the sensor highly radiation-tolerant. (3) Bycollecting electrons, a faster signal is obtained and less charge
trapping is achieved than by collecting holes.
The surface of the silicon wafer is protected with a siliconoxide layer. At the silicon–silicon oxide interface, the built-in
defects and accumulated surface damage due to the ionizing dose
will create an excess positive charge leading to an inversion layerof electrons at the surface of the silicon, which shortens then-implant electrodes. Thus, the silicon surface requires a p + layer
to prevent the formation of the inversion layer so that the n-strip
implants remain isolated. The p + layer can be implemented by
implanting p-type ions in restricted areas, which is called
the p-stop method, or by covering the entire wafer surface witha p + layer, which is called the p-spray method. The high-bias
voltage required to operate the radiation-tolerant sensor
generates a high electric ﬁeld at the surface structures that willcause the onset of microdischarge, which is a sudden increase inleakage current when the electric ﬁeld strength exceeds theavalanche breakdown voltage for silicon (  30 V/mm).

Fig.1. Expected ﬂuences of particles in the inner tracker of the ATLAS detector at
SLHC. Values are taken from Ref. [1].

S25

There are several issues involved in developing a highly
radiation-tolerant silicon microstrip sensor. A silicon material isneeded that has the smallest possible FDV and, especially, an FDV
that increases least as a function of ﬂuence. The operational bias
voltage must be found that results in the required signal strength.
The surface structures must be optimized so that the electric ﬁeld
is minimized, and the necessary concentration of p-type ions inthe surface must be determined so that the onset voltage formicrodischarge exceeds the operation bias voltage, and yet then-implant strips remain isolated.
An n-in-p sensor was prototyped for the LHC [2], andsigniﬁcant research has been devoted to the SLHC [3]. For ourdevelopment [4,5], we have evaluated 4 and 6 in. (100 and
150 mm) silicon wafers, silicon materials incorporating ﬂoat-zone(FZ) and magnetic Czochralski (MCZ) materials and the wafer
orientations of /1 0 0S and /1 1 1S. Most recently, we havefabricated about 50 large-area sensors in a sequence of batches
using 6 in. (150 mm) FZ wafers with an orientation of /1 0 0S.

2. n-in-p R&D sensors
2.1. Large-area main sensor
The mask layout for the 6 in. wafer is shown in Fig. 2. The
layout contains a large-area main sensor of dimensions
9.75 cm  9.75 cm, which is the maximum size square possible
in the usable area deﬁned by the vendor [6]. In addition,
miniature 1 cm  1 cm sensors with various strip and isolation
structures are included in the layout, as well as 4 mm  4 mm
miniature diodes, which are ﬁt into the space remaining on thewafer. The main sensor is an R&D sensor designed for a high track
density environment that has four segments of short strips(2.39 cm each). The top two segments are made with ‘‘axial’’
strips where the strips are parallel to the sensor edge. The bottom
two segments are made with ‘‘stereo’’ (i.e., inclined) strips where
the strips are rotated by 40 mrad with respect to the sensor edge.
The stereo strips are intended for development and veriﬁcation of
the sensor design for a full-area stereo-strip sensor. The strip
isolation structure of the main sensor is the one equivalent to theZone3 of the miniature sensors.
2.2. Miniature sensors
Each miniature sensor (1 cm  1 cm) has one out of six
different surface structures for strip isolation. The cross-sectionsof the surface structures, Zone 1–Zone 6 (Z1–Z6), are shown in
Fig. 3. Z1 has no p-stop structure, Z2 has individual p-stops
independently encircling each n-strip and Z3–Z6 have one
continuous, common p-stop in between n-strips that are 6 mm
wide. The Z1 miniatures become ‘‘p-spray-only’’ if p-spray isapplied. The sensors are made with an integrated AC-coupling
structure consisting of a sandwich of an insulating layer withaluminium-metal and implant strips. For all the zones except Z5,
the metal is wider than the n-strip implant, so that the wider
metal functions as a ﬁeld plate to reduce the electric ﬁeld strength
at the n-strip implant edge when the potential of the metal andthe n-strip implant is the same. For comparison, the metal widthfor Z5 is narrower than the implant. The major features of the R&D
sensors are summarized in Table 1.
The fabrication of the sensors was split into a sequence ofbatches. The ﬁrst three batches X1–X3 were small in quantity, andthe fourth, S1, was the ﬁrst large-quantity batch. For each batch,
we tried the p-stop (P), p-spray (R), or combined isolation
methods with p + surface-density concentrations ranging fromS26

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

Fig. 2. The layout of the mask for the latest sensors (ATLAS07) for a 150 mm wafer. The central piece is the 9.75 cm  9.75 cm main sensor and P1–P24 are the miniature
sensors of 1 cm  1 cm.

Fig. 3. Cross-sections of the strip (n + ) and the isolation structures (e.g., p-stop) in the surface of the miniature sensors. Six structures, named Zone 1–Zone 6, areimplemented—one structure per miniature sensor. The dimensions are in mm.

1011 to 1013 ions/cm2. We are foreseeing a batch of p-spray infuture. The p-stop and p-spray densities, and the number ofwafers delivered for testing are summarized in Table 2. Eachbatch is named after the sequence and the isolation, e.g., X1R2P8
denotes the ﬁrst batch with a p-spray density of 2  1012 and ap-stop density of 8  1012 ions/cm2, combined. The batches with
only p-spray (R) were fabricated by skipping the p-stop process,i.e., there are no p-stop structures in either the main sensor or in
any of the miniature sensors in the wafers of the batch.

2.3. Punch-through protection structure
In the Zone 4 (Z4) miniature sensor, we developed a structure
for the AC coupling insulator to protect against accidents such as abeam splash into the sensors. When a large amount of charge isdeposited in the sensor by a beam splash, a large current ﬂows
through the bias resistor and drops the potential of the n-strip
implants toward the backplane bias voltage, thus generating a
voltage spike across the AC coupling insulator [8]. When the

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

S27

3. Evaluation

Table 1Features of the R&D sensors.
Silicon wafer diameter
Type
Orientation
Resistivity (kOcm)
Thickness (mm)Sensor dimension (dicing center–center)
Number of strip segments
Number of strips per segment
Strip pitch (mm) (y: stereo angle)
Strip length (cm) (y: stereo angle)
Stereo angle, y of ‘‘axial’’/‘‘stereo’’
segments (mrad)
Strip width, implant/metal (mm)Distance between bias rail and n-strips
implants (mm)Sensor dimension (dicing center–center)
Number of strips, Z1–Z5 (Z6)
Strip pitch, Z1–Z5 (Z6) (mm)Strip length (cm)Strip width, implant/metal (Z1–Z6), (Z5)Distance between bias rail and n-strips
implants(Z1)/(Z2–Z6)/(Z4) (mm)Sensor position

Interstrip capacitance (one-neighbourboth) (pF/cm)
Body capacitance per strip (pF/cm)
Bias resistance (Polysilicon) (MO)Signal readout
AC coupling breakdown voltage (V)

6 in. (150 mm)
p-type FZ (high grade)/1 0 0S
 6.7
320
9.75 cm  9.75 cm
4
1282
74.5  cos(y)2.39/cos(y)
0/40
16/22
70
1 cm  1 cm
104 (77)74.5 (100)0.80
16/22, 22/16

3.1. Proton and neutron irradiations
We characterize the R&D sensors both pre- and postirradiation. Irradiations were made with 70 MeV protons at the
Cyclotron and Radioisotope Center (CYRIC) of Tohoku University,
Japan [9], and with neutrons with energies below approximately
3 MeV at the TRIGA reactor, at the Jozef Stefan Institute, Slovenia[10]. Typical ﬂuences are 1012, 1013, 5  1014 and 1015 neq/cm2.
The low ﬂuences are to evaluate the effect of surface damage, e.g.,charge-up in the silicon–silicon oxide interface before bulk
damage becomes imminent. The high ﬂuence is to evaluate thebulk and surface damage at the ultimate SLHC ﬂuence. Unlessotherwise mentioned, the irradiated samples were annealed for
80 min at 60 1C.
3.2. Bulk damage

12/70/20
Z1:(P7,19)
Z2:(P2,5,8,14,17,20),
Z3:(P1,3,6,9,13,15,18,21)
Z4:(A-P4,B-P10,C-P16,D-P22),
Z5: (P11,23), Z6:(P12,14)
 0.80 [7] 0.27 [7] 1.5
AC coupling4100

A study of the bulk damage is presented in Ref. [11]. Evolutionof the FDV as a function of ﬂuence is evaluated for the FDVs thatare derived from the measurement of the body capacitance C as afunction of bias voltage V (C–V) and the measurement of thecharge collection as a function of bias voltage using beta rays from90
Sr (CC-V beta). In an ideal semiconductor, 1/C2 increases linearlywith V. In irradiated sensors, 1/C2 exhibits a nonlinearity (i.e., akink). The FDV estimated from the low bias voltage range isconsistent with the FDV estimated from the CC-V(beta) method.
The FDVs of proton and neutron irradiations are 700 V at
1015 neq/cm2 and  800 V at 5  1014 neq/cm2, respectively.
3.3. Surface damage

Table 2
Summary of delivered sensors for testing.
Batch name

X1R2P8
X1P10
X2R2P8
X2P2
X2P4
X2R2
X3R2P2
X3R2P8
X3P1
X3P2
X3P4
X3R1
X3R2
X3R4
S1P4
S1P10
S1P20
a

P-spray (R)(ions/cm2)

12

2  10–2  1012––
2  1012
2  1012
2  1012–––
1  1012
2  1012
4  1012–––

P-stop (P)(ions/cm2)

12

8  101  1013
2  1012
2  1012
4  1012–
2  1012
8  1012
1  1012
2  1012
4  1012–––
4  1012
1  1013
2  1013

No. of wafers
Main

Miniaturea

Wafer range

9
–
–
–
–
–
–
1
1
6
2
2
1
1
28
1
1

14
9
1
1
1
1
3
2
1
4
2
1
1
2
15
2
2

1–22
23–36
1
25
31
35
1–11
46–47
12–13
14–31
32–39
40–41
42–43
44–45
1–41
42–45
46–49

Only those tested by testing sites.

distance between the bias rail and the n-strip implants isappropriate, this voltage between the bias rail and the n-strip
implants can be limited by inducing a surface current like thesource-drain current of a MOSFET. The protection structure iscalled the punch-through protection structure (PTP). In the p-stop
method, we have investigated a few variations in PTP structures,as shown in Fig. 4. The structure X1Z4 is the ﬁrst PTP structure
implemented in X1, and Z4A–Z4D are the improved designs inbatches X2 and later. The reason for the improvement is discussed
in Section. 4.

Surface damage is presented in Ref. [12]. Strip isolation isevaluated in the miniature sensors of the batch X3 with p-stop
only, p-spray only and p-spray and p-stop combined. The
pre-irradiation samples all show good isolation resistance of
410 GO. The post-irradiation samples show degraded isolation
resistance. The isolation resistance of samples irradiated byprotons to 1.14  1013 neq/cm2 is characterized by the total p +concentration. It is in the 1 MO range for 1012 ions/cm2 and in the
10 MO range for 2  1012 ions/cm2 and it grows to the 100 MO
range for 4  1012 ions/cm2 and is greater than 10 GO for1  1013 ions/cm2. The interstrip capacitance changes little after
irradiation and is very similar among the various structures andisolation methods. The exception to this ﬁnding is the Z5
structure that exhibits an increase in capacitance after irradiation.
The punch-through voltage (PTV), deﬁned as the voltage where
the PT resistance RPT is equal to the bias resistance Rbias, depends
on the total p + concentration and the fabrication method. For thesame distance, higher PTV is observed for p-spray than for p-stop.
The PTV of non-irradiated samples is in the range of 10–30 V, but
it decreases by 5–10 V for low ﬂuences of 1012–1013 neq/cm2
before increasing again for high ﬂuence (1015 neq/cm2) to thesame level as for the non-irradiated samples.

4. Mask design improvement
4.1. Onset of microdischarge
With the mask designed for the ﬁrst batch, X1, we observed
the onset of microdischarge in the non-irradiated X1R2P8
samples at bias voltages of 200–400 V. We identiﬁed threeprominent hot spots using a hot-electron microscope [13]. One

S28

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

Fig. 4. Punch-through protection structures. Z4A–Z4D are in the improved mask, and X1Z4 is in the original mask.

Fig. 5. Hot spot in the X1R2P8 Z4 miniature sensor observed using the
hot-electron equipment.

hot spot was in the miniature sensors of X1Z4 at the PTP
structure, as shown by spot (1) in Fig. 5. The other two hot spots
were in the main sensor in the structure of the ‘‘stereo’’ strip
segments. Speciﬁcally, hot spot (2) shown in Fig. 6 was at thecorner of the bonding pads facing the bias rail, and hot spot (3)was at the end of alternating strips, as shown in Fig. 7. For
clariﬁcation, graphical drawings of the layout corresponding to

Fig. 6. Hot spots at the corner of the bonding pads of the stereo strips in the
X1R2P8 main sensor observed using the hot-electron equipment.

the regions of hot spots (2) and (3) are shown in Fig. 8 (a) and (b),respectively. We used a TCAD simulation program [14] todetermine the large electric ﬁeld needed to induce such a
microdischarge. A brief conclusion of the study is that multiple
p-stops in the p-bulk function more like a wide single piece,

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

S29

Fig. 9. Mask patterns after modiﬁcation to eliminate the hot spots in Figs. 6 and 7.

Fig. 7. Hot spots at the end of the stereo strips in the X1R2P8 main sensor
observed using the hot-electron equipment.

Fig. 8. Mask patterns before modiﬁcation to eliminate the hot spots in Figs. 6 and 7.

Fig. 10. Leakage currents of the 29 main sensors of the batch S1P4 as a function ofbias voltage, measured at room temperature.

a wider p-stop leads to higher electric ﬁeld, and a more
asymmetric positioning of the p-stop leads to higher electric ﬁeld.

4.2. Mask modiﬁcation
In accordance with our understanding of the electric ﬁeld as per
Ref. [14], the PTP structure of X1Z4 was modiﬁed to form thestructures Z4A–Z4D. For these structures, the n–n distance wasincreased from 12 to 20 mm. For the Z4A and Z4B structures, thecircle of p-top was enlarged towards the p-stops between the
n-strips. Thus, the multiple p-stops were placed closer together. For
the Z4C structure, the multiple p-stops were compacted into a single
continuous p-stop. Finally, for the Z4D structure, the n-island
implant was eliminated, making the Z4D structure simple. Although
we do not observe a dramatic difference in performance(see Section. 3.3), we investigate further to see if there is a subtle
but systematic difference between these structures.
In the main sensor mask, the source of the high electric ﬁeld isthe widely spaced p-stops near the n-strips and the bias rail. This
design was only used in the layout of the stereo strips, and we
observed no hot spots in the similar corners of the axial strip
segments. The mask was modiﬁed to eliminate the outermost
p-stop near the bias rail and to modify the shape of the bias rail togo along the n-strip edge, so that the distance between the bias
rail and the n-strip edge is uniform and the same as in otherstrips. Drawings of the modiﬁed layout for the Fig. 8 (a) and (b)are shown in Fig. 9 (a) and (b), respectively. No n-strip or otherp-stop was modiﬁed.

Fig. 11. Leakage currents of 48 miniature sensors from 2 wafers of the batch S1P4
as a function of bias voltage, measured at room temperature. The low current
below 100 V in a few samples is an artifact of the measurement device.

4.3. Results after the mask modiﬁcation
The second batch X2 and later batches were fabricated using
the modiﬁed mask. We observed good performance and noS30

Y. Unno et al. / Nuclear Instruments and Methods in Physics Research A 636 (2011) S24–S30

microdischarge in the small quantity fabricated, e.g., in batch
X3P4 [4]. The I–V characteristics of 29 non-irradiated main
sensors from the latest batches S1P4 and S1P10, measured at
approximately 26 1C, are shown in Fig. 10. Microdischarge is notobserved up to the bias voltage of 1000 V. The leakage current is
low at less than 0.5 mA or 5 nA/cm2. The 29 main sensors areequivalent to 2756 miniature sensors of 1 cm  1 cm in area. The
I–V characteristics of 48 miniature sensors from the two wafers of
S1P4 are shown in Fig. 11. All miniature sensors, including themodiﬁed Z4 sensors, exhibit no microdischarge up to 1000 V.
Further characterization results of the main sensors are reported
in Ref. [7].

5. Summary
We have developed a novel and highly radiation-tolerant n-inp silicon microstrip sensor for very high radiation environments
such as in the SLHC. The sensor is designed for a ﬂuence of1015 neq/cm2. The goals for this project are also to establish thenecessary technological elements to develop a large-area sensor
for use in a large-area tracker. We have established a fabrication
sequence for fabricating a single 9.75 cm  9.75 cm large-area
sensor with two axial segments and two stereo strip segments
and 24 pieces of 1 cm  1 cm miniature sensors with various
n-strip isolation structures. These structures are all laid out on asingle p-type, FZ, 6 in. (150 mm) wafer.
We evaluate the sensors both pre- and post-irradiation by
protons and neutrons and ﬁnd that the n-strip isolation depends
on the p + concentration and that the full depletion voltages
evolve to about 800 V. We also report the characterization of theinterstrip resistance, interstrip capacitance, the punch-throughvoltage, etc.
The ﬁrst fabrication batch allowed us to identify the weak
spots in the PTP and in the stereo strip layouts that cause theonset of microdischarge at low bias voltages of 200–400 V. With
the help of TCAD simulation, the origin of the weakness was
identiﬁed and the mask was modiﬁed accordingly. The batches
after the modiﬁcation and the latest fabrication of about 30 main
sensors with p-stop 4  1012 ions/cm2 and associated miniature

sensors have shown good performance, with no microdischarge
up to 1000 V.

Acknowledgments
We express our thanks to the team from CYRIC at the Tohoku
University and from the TRIGA reactor at the Jozef Stefan Institutefor conducting excellent irradiations. The research was partly
supported by Ministry of Education, Youth and Sports of the Czech
Republic, the German Federal Ministry of Education and Research,
the Japan Grant-in-Aid for Scientiﬁc Research (A) (Grant no.
20244038), Researh (C) (Grant no. 20540291) and Research on
Priority Area (Grant no. 20025007), the Slovenian Research
Agency, the Spanish National Program for Particle Physics, the
UK Science and Technology Facilities Council (under Grant PP/
E006701/1), the US Department of Energy and the US National
Science Foundation (under Grant PHY0652607).
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