Nuclear Instruments and Methods in Physics Research A 731 (2013) 247–251

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

Beam test of novel n-in-p strip sensors for high radiation environment
T. Kubota a,n, T. Kishida a, O. Jinnouchi a, Y. Ikegami b, Y. Unno b, S. Terada b, S. Mitsui b,
A. Tamii c, T. Aoi c, K. Hanagaki d, K. Hara e, N. Kimura f, R. Takashima h, Y. Takubo b, J. Tojo i,K. Nagai e, I. Nakano g, K. Yorita fa

Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
Institute of Particle and Nuclear Study, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, Ibaraki 305-0801, Japanc
Research Center of Nuclear Physics (RCNP), 10-1 Mihogaoka, Ibaraki, Osaka 567-0047, JapandDepartment of Physics, Osaka University, Machikaneyama-cho, Toyonaka-shi, Osaka 560-0043, Japane
Institute of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba-shi, Ibaraki 305-8571, JapanfResearch Institute for Science and Engineering, Waseda University, Japang
Department of Physics, Okayama University, 3-1-1 Tshushima-naka, Kita-ku, Okayama-shi, Okayama 700-8530, JapanhDepartment of Education, Kyoto University of Education, 1 Fukakusa-Fujimori-cho, Fushimi-ku, Kyoto 612-8522, Japani
Department of Physics, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japanbart ic l e i nf oa b s t r a c t

Available online 17 June 2013

Highly radiation tolerant n-in-p strip sensors have been developed for the high-luminosity LHC (HLLHC). This paper reports the results of measurements with 392 MeV kinetic energy proton beam at RCNPin December 2011. The data was taken with a new DAQ system consisting of an universal read-out board‘SEABAS’ and beam tracking telescopes whose spacial resolution is better than 5 μm. The aim of thisbeam test is to evaluate the new 1 cm  1 cm n-in-p miniature sensors before and after 1015 neq cm−2irradiation. The median charge of un-irradiated sensor is 6.2 fC at full depletion voltage, while themedian charge after 1015 neq cm−2 irradiation of the sensor is 4.2 fC. The novel Punch-Through-Protection(PTP) has been implemented in these sensors. The length of active region of the sensor around PTP isobserved to be decreased by 12 μm in the irradiated sensors at 1015 neq cm−2.
& 2013 Published by Elsevier B.V.

Keywords:
Strip detector
SCTn-in-p
ATLAS
HL-LHC

1. Introduction
The LHC is planned to be upgraded to HL-LHC for new physics
at the high energy by improving the statistics. The goal ininstantaneous luminosity is 5  1034 s−1 cm−2 and the goal in
integrated luminosity is 3000 fb−1. The increase of the integrated
luminosity will make one order of magnitude larger radiation
damage to the ATLAS detector [4]. This particularly important for
the inner detectors. In order to keep the performance of semiconductor tracker (SCT) after the LHC upgrade, new structures ofsensor and read-out chip have been developed. In this paper, wepresent the result of the beam test carried out at the ResearchCenter of Nuclear Physics (RCNP) of Osaka University in December
2012 [3]. In this beam test, ‘n-in-p’ sensors with various irradiationlevel, 0 (un-irradiated), 5  1012, 1013, 1014 and 1015 neq cm−2 weretested. The n-in-p sensor has a number of advantages compared tothe ‘p-in-n’ sensor. In the ‘p-in-n’ sensors the type inversion occurs
at a few 1013 neq cm−2 irradiation. After the type inversion, thesilicon bulk is depleted from the back side. The type inversion does
not occur in the p-type silicon bulk and the depletion zone isalways formed from the strip side. This advantage means that then-in-p sensor is operational without full depletion after highirradiation. The n+-strips collect electrons for read-out while thep+-strips collect holes. These two features allow n-in-p sensors tohave high radiation tolerance and faster read-out. To read-out nin-p sensors for beam test, a dedicated DAQ system was developed. The system consists of new read-out chip ‘ABCN’ (ATLASBinary Chip Next) [1] and universal read-out board ‘SEABAS’ [2].
The beam telescope, whose spacial resolution is better than 5 μm,
was used with new DAQ to determine the precise track location atdetectors under test (DUTs).
The aims of beam test were Studying the charge collection efﬁciency of n-in-p strip sensors
with new read out chip ‘ABCN’.

 Studying the behavior of the PTP structure on active regions of
n-in-p strip sensors before and after irradiation.
In this paper, we describe the setup of beam test (Section 2),
the run plans (Section 3) and the analysis (Section 4).

2. SetupnCorresponding author. Tel.: +81 3 5734 2388.
E-mail address: kubota@hep.phys.titech.ac.jp (T. Kubota).

0168-9002/$ - see front matter & 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.nima.2013.06.005

This beam test made use of the proton beam line facility in RCNP.
The 392 MeV kinetic energy proton beam with approximately

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T. Kubota et al. / Nuclear Instruments and Methods in Physics Research A 731 (2013) 247–251

2  3 cm2 beam spot size was used. The setup of this beam test,
illustrated in Fig. 1, consists of scintillation counters for trigger,
beam telescopes and detector under the test (DUT).

2.1. Beam telescopeThe beam telescope was used for beam tracking. One telescope
module consists of two silicon strip sensors, and each provides Xand Y space point. The strip pitch of the sensor is 50 μm and thenumber of strips is 384. The strip signals are multiplexed by Viking
Analog chip [6] and read-out by VME ﬂash ADC modules. The
analog read-out enables the beam telescope to achieve better than
5 μm spacial resolution when the high momentum beam isinjected. The dead time of the telescope is 10 ms. In this beamtest, two telescope modules were used, one before DUTs andanother one after DUTs shown in Fig. 1.

3. Run plans
We operated three run plans in this beam test. The beam
injection frequency was adjusted for the each run plan to matchwith the test condition, e.g., 10 kHz. The summary of the tested
Table 1Features of miniature sensor.
Sensor type
Size
Number of strips
Bonded strips
Strip pitch
Strip length
Thickness

FZ4D5
1 cm2  1 cm2
103
34
74:5 μm
8050 μm
320 μm

2.2. DUTs
The n-in-p strip sensors are manufactured by Hamamatsu
Photonics (HPK) in collaboration with KEK. The miniature sensors,shown in Fig. 2, were also manufactured for the evaluation. Thesensors were irradiated in various levels by 70 MeV proton at
CYRIC (CYclotron and RadioIsotope Center). The speciﬁcation ofminiature sensors is shown in Table 1.
The miniature sensors have PTP (Punch Through Protection)
structure on the end of the strip as shown in Fig. 5. The PTP
structure routes the large induced current to the bias ring toprotect the AC coupling capacitors. Each sensor is mounted on
sensor-board as shown in Fig. 3 and connected to Single Chip Card(SCC) as shown in Fig. 4. In this beam test, only 34 strips out of 103
strips are connected to the read-out pads by wire-bondingtechnology. The new read-out chip ‘ABCN’ is mounted on theSCC. The ABCN chip has been developed for operating with theshort strip, and is compatible with both signal polarities, thus theSCC can be used with both n-in-p and p-in-n sensors. The ABCNchips are read-out via TCP/IP connection by the DAQ system using
the SEABAS universal read-out board. Up to eight SCCs are readout simultaneously, and the maximum DAQ rate operating withthe beam telescope is about 10 kHz while that with beam
telescope is about 100 Hz.

Fig. 3. Photograph of the sensor-board. The 34 strips are wire-bonded to the readout pads.

Fig. 4. Photograph of the single chip card.

Fig. 1. The setup of beam test. The setup consists of three parts, the scintillation
counters, the beam telescopes and the DUTs.

Fig. 2. Photograph of the miniature sensor. The miniature sensor contains 103
strips with 74.5 μm pitch.

Fig. 5. Left: The schematic view of the pads position of DUT. Right: The schematic
view of the strip end. The scale of length is μm.

T. Kubota et al. / Nuclear Instruments and Methods in Physics Research A 731 (2013) 247–251

DUTs and characteristics of them for each run plan are shown inTable 2.

Plan1. The threshold scan of un-irradiated n-in-p and p-in-n sensors
without the beam telescope.
Plan1 was operated with two n-in-p sensors and threep-in-n sensors, aimed to measure the hit efﬁciencies andthe collected charges of un-irradiated n-in-p sensors. Forthe sake of efﬁcient data collection, beam telescope wasexcluded from the DAQ because of slow read-out. The unirradiated p-in-n sensors were used as a reference insubstitute of the telescope for beam tracking. In this plan,
two parameters, the threshold voltage and the sensor biasvoltage, were varied during the data acquisition. Thethreshold voltage was varied in order to measure thecollected charge as the ABCN chip does not have ADC
function. The median charge value is estimated by thethreshold voltage whose hit efﬁciency is 50%. In order toconvert threshold voltages (mV) into charges fC, calibrations were performed with injected charges from ABCN
chip. Sensor bias voltages were varied to measure therelation between bias voltage and collected charge. Threshold voltages were varied between 96 and 800 mV in 110steps. Bias voltages were varied between 15 and 400 V ineight steps.
Plan2. The threshold scan of irradiated n-in-p sensors without thebeam telescope.
Plan2 was operated with four irradiated n-in-p sensors andone un-irradiated p-in-n sensor. This plan was aimed tomeasure the hit efﬁciency and the collected charge ofirradiated n-in-p sensors. The irradiation levels, 5.7  1012,
1.1  1013, 1.2  1014 and 1.2  1015 neq cm−2 were tested. Inorder to suppress leak currents of irradiated sensors at coldtemperatures, this run was operated in cold temperature
between −30 and −601C. The measurement menu weresame as plan1, i.e., threshold scan and bias scan. Thresholdvoltages were varied between 96 and 800 mV in 110 steps.
Bias voltages of 5.7  1012, 1.1  1013, 1.2  1014 neq cm−2
were varied from 50 to 500 V while 1.2  1015 neq cm−2
was from 400 to 950 V in 10 steps.
Plan3. The hit efﬁciency map of un-irradiated and irradiated n-in-psensors with the beam telescope.
Plan3 was operated with un-irradiated and 1.2  1015 neq cm−2
irradiated n-in-p sensors. This plan was aimed to measure thelength of active region especially the side which has PTP
structure by mapping the hit efﬁciency for precise spacepoints. The beam telescope was used to measure the particlepositions at their intercept with the DUTs. In order to retain
higher position resolution than 10 μm with the low beamenergy, only two DUTs were set-up. Threshold voltages were249

ﬁxed at 96 mV. The bias voltages were also ﬁxed to full
depletion voltage, to 350 V for un-irradiated, to 900 V for
irradiated sensors.

4. Analysis
4.1. Plan1
In Plan1, threshold scan and bias scans were performed.
Approximately 30,000 triggered events were collected for eachthreshold. The hit efﬁciencies of n-in-p sensors were calculatedusing beam tracks which were reconstructed by two reference pin-n sensors (DUT0 and DUT3). The single hit clusters in all planes
are required in order to reconstruct the beam track. The eventswere collected based on the selection criteria on the cluster size
and the hit window size. The cluster size is the number of adjacentstrips which had hits, the events with the clusters whose size wasone and two were selected. The alignment is performed in X, Y andZ shift and rotations. The threshold curves of various bias voltages
are shown in Fig. 6. Threshold curves are ﬁtted by complementary
error function, Erf, which takes into account the effect of thelandau distribution shown as follows:ErfðqÞ ¼ p3 ð1−erfðT  f ðTÞÞð1Þ

f ðTÞ ¼ 1 þ 0:6  tanhð−p4  TÞ

ð2Þ

pﬃﬃﬃ

T ¼ ðq−p1 Þ= 2  p2

ð3Þ

In these functions, p1, p2, p3 and p4 express the median, thewidth, the saturation and the skew, respectively.
The threshold voltage (fC) of 50% hit efﬁciency is deﬁned as
median charge. The median charges of various bias voltages areshown in Fig. 7. The saturation of the median charges of unirradiated n-in-p sensors is measured around 6.2 fC above 250 V.
4.2. Plan2
Plan2 was aimed to compare the median charge of n-in-psensors before and after the irradiation. The measurement andanalysis methods were same as Plan1. Two lower irradiation levelsensors were used as a reference to reconstruct beam tracks:(1) DUT0 (un-irradiated p-in-n) and DUT1 (5.7  1012 neq cm−2

Table 2
The DUT IDs of each plan.
DUT ID

Plan1

Plan2

Plan3

DUT0p-in-nunirradn-in-p
unirradn-in-punirradp-in-nunirradp-in-nunirradn-in-p5.7  1012 neq cm−2n-in-p1.1  1013 neq cm−2n-in-p1.2  1014 neq cm−2n-in-p1.2  1015 neq cm−2n-in-punirradn-in-p1.2  1015 neq cm−2

DUT1
DUT2
DUT3
DUT4Fig. 6. The threshold curves of DUT1 in various bias voltages. The threshold voltageof 50% hit efﬁciency is deﬁned as the median charge.

250T. Kubota et al. / Nuclear Instruments and Methods in Physics Research A 731 (2013) 247–251irradiated) and (2) DUT0 (un-irradiated p-in-n) and DUT2
(1.1  1013 neq cm−2 irradiated). In the DUT3, DUT4 and DUT5
analysis, these two track reconstruction methods, (1) and (2),were used. The median charges of various irradiated level DUTs asa function of the bias voltage are shown in Fig. 8. The bias voltage
where the median charges are saturated as a function of theﬂuence are shown in Fig. 9. The decreases of median charges wereobserved after irradiation. About 4.2 fC was collected after1.2  1015 neq cm−2 irradiation above 600 V and charge collection
efﬁciency is about 67.7%, compared to the median charge of theunirradiated sensor which was 6.2 fC.
4.3. Plan3
Plan3 was aimed to study the length of the active region before
and after irradiation. About 2M triggered events were collected forthis plan. The beam tracks are reconstructed by the beam
telescopes. In this analysis, the single track events, in which only
one hit exists in one beam telescope plane, are used. The X, Y and Z
shift and rotations are aligned to the position where the position
resolution is minimized. The track positions are estimated to scat
about 10 μm by the multiple Coulomb scattering [5] due to a low
momentum beam. The hit efﬁciency was calculated for each
5 μm  5 μm space point in order to study the position dependence of the hit efﬁciency. The collected events were categorized

into single-hit and multi-hit events by cluster size. Unfortunately
the tracks in the region of one side of strip edge (other side of thePTP structure) was not reconstructed at all, due to the technicalproblems in beam telescope during the beam test. In order todetermine the precise position in Y, the multi-hit events are used.
The hit efﬁciency of multi hit events is computed as the number ofmulti-hit events dividing by the number of all tracks. The multiple
strips were overlaid on top of the one strip in order to improve thestatistics. As shown in Fig. 10, the strip structure, e.g., the positionof AC pads, is visible as blank area in the map, which can be usedas landmarks. The double-Gaussian function, Fdouble(x) shown inEq. (4), is applied on the projection of efﬁciency in Y in order todetermine the position of the pad centerF double ðxÞ ¼ a1 Gðp0 −p1 ; s1 Þ þ a2 Gðp0 þ p1 ; s2 Þ þ b1
ðx−pÞ2Gðp; sÞ ¼ pﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ exp −s2
2πs2

ð4Þ!
ð5Þ

In these functions, p, p0, p1, a1 (a2) and b express the median,
the position of the pad center, the design length between the padcenter and the AC pads, the amplitude and the offset, respectively.

Fig. 7. The median charge vs bias voltage of un-irradiated n-in-p sensors.
The behavior of DUT1 and DUT2 are almost same as expected.

Fig. 9. The saturated median charge as a function of ﬂuence. Median charge of
un-irradiated sensor is pointed as 1011 neq cm−2.

Fig. 8. The median charge as a function of sensor bias voltage. The median charges of
un-irradiated sensors are about 6.2 fC while that of after 1015 neq cm−2 irradiation isabout 4.2 fC.

Fig. 10. Left: The hit efﬁciency map of multi-hit events of DUT1. Both axes areshown as the pixel number. The size of all pixel 5 μm  5 μm. Right: The design ofpad patterns of three strips. Comparing both ﬁgures, the AC pads are visible asblank area and the positions of pads are consistent with the design.

T. Kubota et al. / Nuclear Instruments and Methods in Physics Research A 731 (2013) 247–251

Table 3The positions of AC pads center. Positions are calculated by applying doubleGaussian function and expressed as a pix number.

# 1 & # 3 [pix number]# 2 [pix number]
Combined
Position of active edge
Length of active region
Length of active region ½μmDUT0DUT11292.00 7 1.38
1290.10 7 1.37
1291.05 7 0.98
1555.46 7 0.58
264.98 7 1.14
1322.05 7 5.68

1264.51 7 0.40
1264.88 7 0.47
1264.70 7 0.31
1526.67 7 0.69
261.98 7 0.76
1309.88 7 3.78

The pad design of strips # 1 and 3 is same so that Fdouble(x)applied on two patterns, # 1 & 3 and # 2. The position of the edgeof the active region is calculated by ﬁtting the projection of the hit
efﬁciency map of all events in Y with the error function. The active
length is estimated as the length from the AC pads center to theedge of the active region. The location in the design of the end ofthe strip and the edge of PTP gate are shown in Table 3. The design
length of strip end and the edge of PTP gate is 1325 and 1316:5 μm
from the pads center, respectively. A decrease in the length of theactive region by 12 μm is observed. The measured active lengths
are 1322.1 75.7 and 1309:9 7 3:8 μm in the un-irradiated and theirradiated samples, respectively.
5. SummaryA beam test was carried out with 394 MeV kinetic energy proton
beam at RCNP in order to evaluate the n-in-p strip sensors for HL-251

LHC. The n-in-p miniature sensors are manufactured by HPK andsensors with various irradiation levels were tested. The new DAQ
which consist of ABCN chip and SEABAS board was used in order toread-out the n-in-p sensors. The median charge of the un-irradiatedn-in-p sensor saturated around 6.2 fC at 250 V, while the mediancharge of 1.2  1015 neq cm−2 irradiated sensor saturated around
4.2 fC at 600 V. This result shows that the charge collection efﬁciencyof n-in-p sensors is 67.7% after 1.2  1015 neq cm−2 irradiation. The
length from AC pads center to the edge of active region of unirradiated sensor is 1322 μm, while the length of 1.2  1015 neq cm−2irradiated sensor is 1310 μmð1309:9 μmÞ. A decrease of the active
length by 12 μm is observed. The active regions run till close to theend of the strip in the un-irradiated and to slightly before the edge ofPTP gate.

Acknowledgment
The authors would like to acknowledge the staff of RCNP for theoperation of the beam and the staff of KEK for technical support.

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