Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎

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

Detailed studies of full-size ATLAS12 sensors
L.B.A. Hommels c,n, P.P. Allport a, M. Baca a, J. Broughton a, A. Chisholm a, K. Nikolopoulos a,S. Pyatt a, J.P. Thomas a, J.A. Wilson a, J. Kierstead b, P. Kuczewski b, D. Lynn b, M. Arratia c,
C.T. Klein c, M. Ullan d, C. Fleta d, J. Fernandez-Tejero d, I. Bloch e, I.M. Gregor e,
K. Lohwasser e, L. Poley e, K. Tackmann e, A. Troﬁmov e, E. Yildirim e, M. Hauser f, K. Jakobs f,
S. Kuehn f, K. Mahboubi f, R. Mori f, U. Parzefall f, A. Clark g, D. Ferrere g, S. Gonzalez Sevilla g,
J. Ashby h, A. Blue h, R. Bates h, C. Buttar h, F. Doherty h, T. McMullen h, F. McEwan h,V. O'Shea h, S. Kamada i, K. Yamamura i, Y. Ikegami j, K. Nakamura j, Y. Takubo j, Y. Unno j,
R. Takashima k, A. Chilingarov l, H. Fox l, A.A. Affolder m, G. Casse m, P. Dervan m,
D. Forshaw m,1, A. Greenall m, S. Wonsak m, M. Wormald m, V. Cindro n, G. Kramberger n,
I. Mandić n, M. Mikuž n, I. Gorelov o, M. Hoeferkamp o, P. Palni o, S. Seidel o, A. Taylor o,
K. Toms o, R. Wang o, N.P. Hessey p, N. Valencic p, K. Hanagaki q,j, Z. Dolezal r, P. Kodys r,
J. Bohm s, J. Stastny s, M. Mikestikova s, A. Bevan t, G. Beck t, C. Milke u, M. Domingo u,
V. Fadeyev u, Z. Galloway u, D. Hibbard-Lubow u, Z. Liang u, H.F.-W. Sadrozinski u, A. Seiden u,
K. To u, R. French v, P. Hodgson v, H. Marin-Reyes v, K. Parker v, O. Jinnouchi w, K. Hara x,y,
K. Sato x, K. Sato x,y, M. Hagihara x, S. Iwabuchi x, J. Bernabeu z, J.V. Civera z, C. Garcia z,
C. Lacasta z, S. Marti i Garcia z, D. Rodriguez z, D. Santoyo z, C. Solaz z, U. Soldevila zaSchool of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
Brookhaven National Laboratory, Physics Department and Instrumentation Division, Upton, NY 11973-5000, USAc
Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United KingdomdCentro Nacional de Microelectronica (IMB-CNM, CSIC), Campus UAB-Bellaterra, 08193 Barcelona, Spaine
DESY, Notkestrasse 85, 22607 Hambrug, GermanyfPhysikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, D-79104 Freiburg, Germanyg
DPNC, University of Geneva, 24, Quai Ernest-Ansermet, CH-1211 Geneve 4, Switzerlandh
SUPA - School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdomi
Solid State Div., Hamamatsu Photonics K.K., 1126-1, Ichino-cho, Higashi-ku, Hamamatsu-shi, Shizuoka 435-8558, Japanj
Institute of Particle and Nuclear Study, KEK, Oho 1-1, Tsukuba, Ibaraki 305-0801, Japank
Department of Science Education, Kyoto University of Education, Kyoto 612-8522, Japanl
Physics Department, Lancaster University, Lancaster LA1 4YB, United KingdommOliver Lodge Laboratory, Department of Physics, University of Liverpool, Oxford St., Liverpool L69 7ZE, United Kingdom
nJožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, SloveniaoDepartment of Physics and Astronomy, University of New Mexico, MSC07 4220, 1919 Lomas Blvd. NE, Albuquerque, NM 87131, USAp
Nikhef, Science Park 105, 1098 XG Amsterdam, The Netherlandsq
Department of Physics, Osaka University, Machikaneyama-cho 1-1, Toyonaka-shi, Osaka 560-0043, Japanr
Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, Prague 8, Czech Republics
Academy of Sciences of the Czech Republic, Institute of Physics, Na Slovance 2, 18221 Prague 8, Czech RepublictSchool of Physics and Astronomy, Queen Mary University of London, London E1 4NS, United KingdomuSanta Cruz Institute for Particle Physics (SCIPP), University of California, Santa Cruz, CA 95064, USAv
Department of Physics and Astronomy, The University of Shefﬁeld, Hicks Building, Hounsﬁeld Road, S3 7RH Shefﬁeld, United Kingdomw
Institute of Science and Engineering, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-ku, Tokyo 152-8551, Japanx
Institute of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8751, JapanyCenter for Integrated Research in Fundamental Science and Engineering, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japanz
IFIC/CSIC-UVEG, Ed. Inst. Investigacion, PO Box 22085, 46071 Valencia, SpainbnCorresponding author.
E-mail address: lbah2@cam.ac.uk (L.B.A. Hommels).
1
Now at Syracuse University, USA.

http://dx.doi.org/10.1016/j.nima.2016.03.042
0168-9002/& 2016 Elsevier B.V. All rights reserved.

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2

art ic l e i nf o

a b s t r a c t

Article history:
Received 20 November 2015
Received in revised form
11 March 2016
Accepted 11 March 2016

The “ATLAS ITk Strip Sensor Collaboration” R&D group has developed a second iteration of single-sidedn þ -in-p type micro-strip sensors for use in the tracker upgrade of the ATLAS experiment at the HighLuminosity (HL) LHC. The full size sensors measure approximately 97  97 mm2 and are designed fortolerance against the 1:1  1015 neq =cm2 ﬂuence expected at the HL-LHC. Each sensor has 4 columns of1280 individual 23:9 mm long channels, arranged at 74:5 μm pitch. Four batches comprising 120 sensors
produced by Hamamatsu Photonics were evaluated for their mechanical, and electrical bulk and strip
characteristics. Optical microscopy measurements were performed to obtain the sensor surface proﬁle.
Leakage current and bulk capacitance properties were measured for each individual sensor. For sample
strips across the sensor batches, the inter-strip capacitance and resistance as well as properties of thepunch-through protection structure were measured. A multi-channel probecard was used to measureleakage current, coupling capacitance and bias resistance for each individual channel of 100 sensors inthree batches. The compiled results for 120 unirradiated sensors are presented in this paper, includingsummary results for almost 500,000 strips probed. Results on the reverse bias voltage dependence ofvarious parameters and frequency dependence of tested capacitances are included for validation of theexperimental methods used. Comparing results with speciﬁed values, almost all sensors fall well within
speciﬁcation.
& 2016 Elsevier B.V. All rights reserved.

Keywords:
HL-LHCATLAS ITk
Micro-strip sensor
Leakage current
Depletion
Strip test

1. Introduction
The foreseen upgrade of the Large Hadron Collider (LHC) to theHigh-Luminosity LHC (HL-LHC) is scheduled to deliver collisions in
12022 [1]. To achieve a total cross-section of 3000 fb , theinstantaneous luminosity of the HL-LHC is expected to reach 5 1034 cm  2 s  1 at a centre of mass energy of 14 TeV. The increasein particle ﬂuence necessitates an upgrade of the ATLAS innerdetector: an all-silicon new inner tracker (ITk) [2] is proposed toreplace the current SemiConductor Tracker (SCT) and Transition
Radiation Tracker (TRT). The ITk layout as presented in the Letterof Intent [3] assumes silicon microstrip detectors to be used for7 endcap disks, and 5 barrel layers. From simulations veriﬁed byexperiments, the highest particle ﬂuence in the barrel short strip
layer is expected to be 5:3  1014 neq =cm2 [4]. Including a safety
factor of 2, candidate ITk sensors will have to be radiation hard up
to levels of 1:1  1015 neq =cm2 . The goal of the ITk Strip Sensor
collaboration is to develop a silicon microstrip sensor that is suitable for use in the new ITk. Results of detailed studies of properties of full-size sensor prototypes are presented in this paper,
whereas studies of radiation damage of 1  1 cm2 miniature sensors are reported in [5,6].

2. ATLAS12 large area sensors
The ATLAS12 sensors are the second iteration of sensors
designed for the Upgrade ITk, superseding the ATLAS07 types [7].
To cope with the effects of radiation damage during the sensor
lifetime, operation in partial depleted mode is foreseen towards
the end of the detector lifetime. The sensor will need speciallydesigned structures between the strips to guarantee strip isolation
during its lifetime and mitigate radiation-induced surface damage
whilst retaining a low inter-strip capacitance. A single-sided n þ in-p sensor offers a trade-off between the above requirements andcost [8]. 120 full-size prototype sensors were manufactured byHamamatsu Photonics [9] on a 6 in. wafer process using p-type
ﬂoat zone silicon. Sensors were delivered in 4 batches: VPX12318,
VPX12518, and VPX12519, of 33, 32 and 35 sensors respectively
were shipped to the UK, and VPX14757 containing 20 sensors wasdelivered to the US.
The largest square sensor that can be cut from the wafer
measures 97:5  97:5 mm2 . This geometry is denoted “Outer Cut”.
Sensors with 462 μm reduced edge metal all around, denoted“Inner Cut”, were made available as well to allow for smaller
inactive regions in the ﬁnal detector layout. The sensor strip
implants are arranged in 4 columns of 1282 implants each, withthe top and bottom implant of each column serving as ﬁeld
shaping strips. The resulting strip pitch is 74:5 μm and the strip
length is 23:9 mm. All strips are connected to the bias rail by polysilicon resistors implanted in the sensor. For biasing the central
two columns, a bias rail runs through the centre of the sensor. Top
metal layer strips are AC-coupled to the strip implants, which havep-stop traces running in between along the full length for strip
isolation. The top metal layer is passivated, with openings forprobing and wirebonding. Fig. 1 contains a photograph showing
the sensor details.

3. ATLAS12A mechanical properties
The sensor mechanical speciﬁcations state the following: nominal thickness: 310 720 μm;
 thickness variation: 7 10 μm across the sensor. This means
some thickness variation is allowed between sensors, but not
across a sensor;
 sensor ﬂatness when unstressed: o 200 μm;
 outer cut dimensions: 97540 7 25 μm2 ; inner cut dimensions: 95; 692 7 25 μm2 ; and no cracks or chips at the dicing line to extend further inwards
than 50 μm.

Fig. 1. Picture of the corner of an Outer Cut ATLAS12 sensor, illustrating the layoutof the bias rail, guard ring, strip top metal and bias resistors. The dicing streets
intended for the Inner Cut sensors are clearly visible.

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3

VPX12519-W745
40
30

0

20

z(micron)z(micron)

-10
-20
-30

10
0
-10
-20

-40

-30

-50

-40

40
30

20
y(m 10 0m) -10
-20

-30
-40

-40

0

-20

40

20

40
30
20
10
y

(m

0

m) -10

-20
-30
-40

)

x(mm

-40

-20

0

40

20

)

x(mm

Fig. 2. Measured space points (left) and net bow interpolated plot (right) for sensor VPX12519-W745.

16

VPX12xxx
Entries
100
Mean
51.72
RMS
12.36

14
12
10
8
6
4
2
0

20

40
60
sensor bow (μm)

80

100

Fig. 3. Histogram of the maximum bow of the sensors from batches VPX12318,
VPX12518 and VPX12519.

For visual inspection and evaluation of the above properties, a
non-contact optical Coordinate Measurement Machine (CMM) wasused, with a precision better than 2 μm in x; y, and 4 μm in z. A
coordinate system is deﬁned, with the origin ð0; 0; 0Þ at the centreof the sensor, with the axes in right-handed orientation with the zaxis pointing upwards, and the scratch pad located in the bottom
right. For measuring outer and inner cut sensors within a reasonable timespan, measurements were taken on a 11  11 gridwith 9:440 mm spacing. To compensate for tilt of the freely suspended sensor, a ﬂat plane is ﬁtted to, and subtracted from thespace points measured. The measurement points and an interpolated net bow result for a typical sensor are plotted in Fig. 2. The
difference between the highest and lowest points from the net
bow is taken as the maximum bow. A histogram of the maximum
bow of sensors from batches VPX12318, VPX12518 and VPX12519
is plotted in Fig. 3, the resulting average is 51:7 μm, with an RMS
deviation of 12:4 μm, which is well within speciﬁcation.

4. Bias voltage and frequency dependence of parameters4.1. Leakage current
Development of the leakage current against bias voltage ðV bias Þ
for all 120 sensors is plotted in Fig. 4. The data was taken at
T ¼ 21 1C, and at a relative humidity (RH) of 40 7 10%. Since the
ATLAS12 sensors are very sensitive to the ambient humidity, theinitial batch VPX12318 was tested in a dry N2 environment. As canbe observed from the graphs on VPX12318 however, aFig. 4. Leakage currents versus V bias for ATLAS12 sensors at 21 1C, grouped
per batch.

considerable number of sensors exhibit early, soft breakdown. The
two subsequent batches were stored in dry atmosphere, andmeasured in standard cleanroom conditions at T ¼ 21 1C, and 40
710% RH, and fewer soft breakdowns occur. Measurements werecarried out using Keithley 2410 and 6517 Source Measure Units(SMUs), with 10 V step increases with a 10 s delay from 0 V to
 1000 V unless the compliance limit of 100 μA was exceeded. In
some cases, the sensors were trained by increasing the bias voltage very slowly, after which a normal IV measurement wasrecorded.
With a 2 μA=cm2 speciﬁcation for leakage current, and the area
inside the bias ring spanning 91:8 cm2 , the maximum allowedleakage current at  600 V bias and T ¼ 21 1C, is 184 μA. Two
sensors exhibited early breakdown, and were excluded from all
further measurements. A histogram containing the leakage currents at V bias ¼  600 V of the remaining 118 sensors is plotted inFig. 5. It shows that the sensors examined sit well below 1 μA cm2 ,comfortably within speciﬁcations.

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4

VPX12xxx
Entries
118
Mean
14.62
RMS
59.35

25

0.08
[1/nF ]

20

0.1

C

15
10

VPX12519
W701
W706
W709
W712
W717
W722
W727
W733
W738
W742
W746
W749

0.06
0.04
0.02

5

W702
W707
W710
W713
W719
W723
W730
W734
W739
W744
W747

W705
W708
W711
W715
W721
W724
W731
W736
W741
W745
W748

0
0

0
1

2

10

10
I(nA/cm2) at V

100

200

300

3

10

V

400

500

600

700

[-V]

Fig. 7. Plot of 1=C 2bulk versus V bias for the sensors of batch VPX12519.

=-600V

Fig. 5. Histogram of the normalised leakage current at V bias ¼  600 V, at T ¼ 21 1C.

Entries
Mean
RMS

14

4.2. Bulk capacitance12

The sensor bulk capacitance ðC bulk Þ was measured as a functionof bias voltage to determine the sensor depletion, and versus
frequency to verify the validity of the measurement. Using a
Wayne-Kerr 6440B LCR meter in R–C series network mode, thefrequency dependence of C bulk for various V bias values of sensor
VPX12519-W748 is plotted in Fig. 6. As can be observed, C bulk isconstant between 0.5 and 6 kHz for a wide range of V bias . C bulk
measurements were carried out with frequencies between 1 and2 kHz.
Fig. 7 contains plots of 1=C 2bulk versus V bias for 33 sensors ofbatch VPX12519. As can be seen from the plot, behaviour is very
consistent within the batch. The full depletion voltage ðV FD Þ isdetermined by taking the intersection point of straight line ﬁts tothe sloped, and ﬂat region. Histogrammed V FD for 98 sensors ofbatches VPX12318, VPX12518 and VPX12519 are plotted in Fig. 8:
the distribution is narrow, with an average of V FD ¼ 365 V, and a
RMS of 8.6 V.
Assuming a parallel plate capacitor model for the sensor, withthe area deﬁned as the inside of the bias ring, the active thickness
is estimated at 301 μm. With the area and thickness known, thedoping concentration can be calculated both from the sloped
region and the saturated region of the C bulk data. For both methods, the calculated doping concentrations are plotted with blue
and red lines respectively in Fig. 9. The resulting values of 5:3 7
0:12  1012 cm  3 are consistent with a wafer bulk resistivity of
2:5 kΩ cm, which is, although V FD is higher than the desired valueof o 300 V, in accordance with speciﬁcation.

98
365.2
8.61

10
8
6
4
2
0

340

350

360

370

380

390

VFD [-V]
Fig. 8. Histogram of V FD determined from C bulk , see text.

35

N (depletion)
Entries
98
Mean
5.235
0.1234RMS

30

N (slope)
Entries
98
Mean
5.336
0.1235
RMS

25
20
15
10
5
0

4.5

5

5.5

6

N [× 1012 cm-3]
Fig. 9. Histogrammed doping concentrations, N eff , extracted from the data plottedin Fig. 7. The blue line histogram is extracted from the ﬂat region and the red line
histogram is from the sloped region. (For interpretation of the references to colourin this ﬁgure caption, the reader is referred to the web version of this paper.)4.3. Strip coupling capacitance

Cbulk [pF]104

VPX12519-W748
3

10-50V bias-100V bias

-150V bias

-200V bias

-250V bias

-300V bias

-350V bias

-400V bias

-450V bias

-500V bias
3

104

10

Frequency [Hz]Fig. 6. Plot of C bulk versus the measurement frequency.

105

The capacitance and resistance of the R–C network formed by
the strip implant resistance ðRimplant Þ and the capacitance between
the implant and the top metal readout strip ðC coupling Þ are plotted
as a function of measurement frequency for various bias voltagesin Fig. 10. It has been measured directly between the strip implant
and top metal using an LCR in R–C series network mode. As can beseen from the plots, the behaviour of the capacitance and implant
resistance both show little variation across a 2–100 kHz range. At
higher frequencies, the resistance and capacitance drop, as
expected from the implant resistance and the transmission line
formed between the strip implant and top metal. The nominal
value of C coupling is 25:7 pF=cm, which is well within the speciﬁcation of 4 20 pF=cm. More results are presented and discussed in
Section 5.

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1
−1

10

-50V bias-100V bias

-150V bias

-200V bias

-250V bias

-300V bias

-350V bias

-400V bias

-450V bias

-500V bias

1
Cis [pF/cm]

Rimplant [MΩ*cm]

1.2

VPX12519-W746

10

5

10−2

0.8
0.6

VPX12519

0.4

W746-Seg1

W746-Seg2

0.2

W746-Seg3

W746-Seg4

10−3
103

104

105

0
0

106

50

100

150

200

Frequency [Hz]

300

350

400

450

500

Vbias [-V]2

10

Ccoupling [pF/cm]

250

Fig. 11. Inter-strip capacitance C is result for a few sample strips versus V bias .

Cis [pF/cm]

1

VPX12519-W746

10-50V bias-100V bias

-150V bias

-200V bias

-250V bias

-300V bias

-350V bias
-450V bias

VPX12519-W746-50V bias-100V bias

-150V bias

-200V bias

-400V bias

-250V bias

-300V bias

-500V bias

-350V bias

-400V bias

-450V bias

-500V bias

103

−1

10

104

105

106

Frequency [Hz]Fig. 10. Frequency dependence of Rimplant (top plot), and C coupling (bottom plot), forvarious V bias values.

4.4. Bias resistance

4

10

5

10

6

10

Frequency [Hz]Fig. 12. Behaviour of the inter-strip capacitance C is versus measurement frequency
for various V bias values.

The bias resistance ðRbias Þ for a small sample of channels wasmeasured directly, as part of the DC measurement of the PunchThrough Protection circuit behaviour, see Section 4.7. The current
between the implant and the bias rail was monitored while thevoltage was increased from 0 V to 10 V in 0.25 V steps. The results
lie within 1:5 7 0:03 MΩ, which is well within the speciﬁcation of
Rbias ¼ 1:5 7 0:5 MΩ. More results on many individual strips probed are presented and discussed in Section 5.

developed across its bias resistor V S . V M is applied in 1 V steps inthe interval [  5 V, þ 5 V]. Even though instruments with highinput impedance and excellent isolation were used (Keithley 6517,
Keithley 2000), it is likely that above 10–20 GΩ the accuracy islimited due to setup systematics. Nonetheless, from the plot of V S
against V M in the top plot in Fig. 13, it shows that there is a clear
linear dependence of the two properties. The bottom plot contains
summary results on extracted Ris for sample strips for a range ofV bias .

4.5. Inter-strip capacitance

4.7. Punch-through protection

The inter-strip capacitance ðC is Þ dominates the input capacitance contributions to the front-end electronics, and determines
the noise levels of the detector. Its value is one of the main input
parameters to the design process of new revisions of the front-end
preampliﬁer, and should be kept as low as possible. The speciﬁcation states that it should be o 0:8 pF=cm, measured at 100 kHz
with both neighbouring strips grounded. For ATLAS12 sensors
with 23:9 mm strip length, C is o 1:91 pF. The development of C isversus V bias for 4 sample channels is plotted in Fig. 11. The C is value
is largely determined by the strip metal geometry, and sensor
surface layout. Its frequency dependence is plotted in Fig. 12,
results suggesting that the measurement frequency should lie inthe 50 kHz to 1 MHz range. The average value measured is0:77 pF=cm, conﬁrming ﬁndings from other institutes.
4.6. Inter-strip resistance
The inter-strip resistance ðRis Þ was measured by applying amaster voltage ðV M Þ to a strip implant, and measuring the induced
current ðic Þ on the neighbouring strip by sampling the voltage

To protect the strip implants and front-end electronics fromexcessive charge liberated in the bulk, for example as the result ofa beam splash, a Punch-Through Protection (PTP) structure isincorporated in the sensor. It embodies an elongation of the strip
implant under the bias resistor, leaving a 8 μm gap to the bias rail.
Soft breakdown will occur across this gap as soon as a threshold
potential is exceeded. The PTP structure is of the “fully gated”
design, where the bias rail implant extends over the gap, covering
the PTP gap entirely, see [5].
A static measurement to determine the threshold voltage
consists of monitoring the current whilst increasing the voltage
imposed on the strip implant. To limit the power dissipation,
voltage and current are limited to 50 V and 50 μA respectively.
Typical results for sample channels of the differentiated dV/dI plot
showing the resistance against applied voltage are plotted inFig. 14. A threshold at 13 V is clearly visible, with the apparent
resistance dropping sharply from the 1:5 MΩ bias resistance totens of kΩ. As expected, the sharper drops are observed when thevoltage is applied on the implant end nearer to the PTP structure.

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6

0.1
0
Vi [mV]z-height is recorded and a pre-deﬁned probestation chuck
overdrive is applied to ensure a good contact between the probecard needles and the sensor. This procedure was repeated forevery touchdown, providing uniform and consistent contact
quality across the entire sensor. In contrast, for the single-needle
measurement such functionality does not exist, resulting in variable contact quality due to the non-planarity of the prober chuck,
jig or sensor.

VPX12518-W745−0.1

20V bias

40V bias

60V bias

80V bias

100V bias

120V bias

140V bias

160V bias

−4

−2

−0.2
−0.3

5.2. Strip test description

− 0.4
−6

0

2

4

6

Vm [V]

43

 Connect to the strip metal using a probe needle.
 Connect an SMU set to 10 V to the strip metal through a 1 MΩ42
41
Ris [GΩ]A “Full Strip Test” refers to the following sequence for testing asingle strip on a sensor that is biased at  150 V to achieve full
strip isolation:

current-limiting series resistance, and measure the current.

40

 If the current exceeds 1 μA, the strip is marked as having a short,39

and the measurement proceeds to the next strip.

 The SMU voltage is increased to 100 V, and the current is38

recorded after a short time delay.

37

 The strip is connected to GND, and subsequently to the

36
0

20

40

60

80

100

120

140

160

Vbias [-V]

LCR meter.

 The LCR meter measures the R–C series network formed by Rbias
and C coupling , and results are recorded.

Fig. 13. Top plot: measured voltage induced by ic against the applied voltage V M forvarious values of V bias (see text). Bottom plot: extracted Ris against bias voltage.

 The strip metal is connected to GND and the measurement
proceeds to the next strip.
5.3. Strip test results summary

3

10

VPX12518 PTP
W648
W648
W621
W621
W606
W606
W644
W644

2

10

0

5

10

15

Vstrip(-V)
Fig. 14. Plot showing the apparent resistance ΔV =ΔI against the voltage applied tothe strip implant V strip .

5. Strip scan results

Histograms of accumulated data of strip metal current (topplot), C coupling (middle plot), and Rbias (bottom plot) are plotted inFig. 15. Data from almost 500,000 channels from 97 sensors frombatches VPX12318, VPX12518, and VPX12519 is included. One
sensor exhibited high leakage current and was excluded from themeasurement. Ignoring defective channels, the measured values
fall well within speciﬁcation, see Table 1.
A geometrical map of accumulated defective channels is displayed in Fig. 16. There seems to be no obvious correlation withsensor geography, although segment 3 seems to have signiﬁcantly
more defects than the other segments. Of the 132 recorded faulty
channels across 97 sensors probed, 79 have a short or pinhole, 10
fail the C coupling requirement, and of 43 strips the Rbias is out ofrange. The total fraction of good strips is 99.97%, comfortably
exceeding the 98% requirement.

5.1. Measurement techniques
To evaluate properties of individual strips, study the uniformityof electrical characteristics over the entire sensor surface, andcompare against other sensors, full scans of individual sensor
channels were made. A relatively simple Strip Test protocol, see
Section 5.2, was used to check for strip shorts and pinholes, andmeasure the C coupling and Rbias for each individual strip. A single
probe needle was used for probing the initial 31 sensors in batch
VPX12318, after that a custom 32 channel probecard and associated multiplexing equipment were used, reducing the sensor
measurement time from 14 to under 3 h.
During the test, the sensor was held in place by a low-force
spring rather than a vacuum jig to minimise stress and strain on
the sensor that could lead to early breakdown or inﬂuence strip
test results, with the bias provided by wirebonded contacts to theedge metal and bias rail. Additional needles on the probecard
provide a edge-sense feature, breaking a contact as soon as theneedles touch the sensor surface. After detecting touch-down, the6. Summary and conclusion
Detailed studies on ATLAS12 sensors produced by Hamamatsu
Photonics have been presented in this paper. Results from theevaluation are summarised in Table 1, and compared to the speciﬁcations set out in the ATLAS12 Technical Speciﬁcation Document. 118 of 120 sensors tested satisfy the speciﬁcations for nonirradiated sensors for maximum bow, leakage current. Only 0.03%
of probed strips were measured as defective; all other strips
satisﬁed the requirements for C coupling and Rbias . The values of theInter-Strip Capacitance and Resistance measured for sample
channels are well within speciﬁcation. The conclusion of examination of 120 sensors is that they are of high quality, have goodconsistency between sensors in three different batches, andexcellent uniformity across channels on a sensor. They satisfy therequirements, and are considered suitable for use in the barrel ofthe ATLAS Upgrade ITk.

Please cite this article as: L.B.A. Hommels, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/
j.nima.2016.03.042i

L.B.A. Hommels et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎×10

50

VPX12xxx defective strips map
4966401.019
1.737

Entries
Mean
RMS

40

1200

30

1000

Strip Number

20
10
0

7

0

5
I

10
[nA/cm]×10
Entries
Mean
RMS

25
20

496640
27.23
0.622

800

600
400
200

15

0

10

1

5

3

4

Segment

0

26

28
C

30

[pF/cm]×10
25

Entries
Mean
RMS

20

4966401.49
0.1114

15
10
5
0

2

1

1.5
R

2

[MΩ]

Fig. 15. Accumulated strip test results for 97 sensors from batches VPX12318,
VPX12518, and VPX12519.
Table 1Comparison of ATLAS12 speciﬁcation and summarised measurement values forvarious sensor properties.
Sensor property

Speciﬁcation

Measured values

Maximum bow
Leakage current at
V bias ¼ 600 V
Depletion voltage

o 200 μm
o 2 μA=cm2

51:77 12:4 μm
o 1 μA=cm2 for 118 of 120
sensors
365 7 8:6 V

Bias resistor value
Coupling capacitanceInter-strip capacitanceInter-strip resistance
Percentage good strips

o 300 V, wafer resistivity allowing
1:5 7 0:5 MΩ
420 pF=cm at
V bias ¼ 300 V
o 0:8 pF=cm
415 7 5 MΩ498% per segment

1:497 0:111 MΩ
27:27 0:62 pF=cm
0:77 pF=cm
4 30 GΩ
4 99:97

Acknowledgements
The Irradiations were performed: with protons at the University of Birmingham MC40 cyclotron, supported by the H2020
project AIDA-2020, GA number 654168, and the UK's Science andTechnology Facilities Council, at Cyclotron and Radioisotope Center(CYRIC), Tohoku University, with Y. Sakemi, M. Ito, and T. Wakui, atthe Karlsruhe Institute of Technology (KIT) by A. Dierlamm, supported by the Initiative and Networking Fund of the Helmholtz
Association, Contract HA-101 (Physics at the Terascale) and theEuropean Commission under the FP7 Research Infrastructures
project AIDA, Grant agreement no. 262025, and at the LANSCE
facility, Los Alamos National Laboratory; with neutrons at JSI

Fig. 16. Map of 132 faulty strips accumulated from 97 measured sensors. Strips
failing from Rbias , C coupling , and strip current are plotted in red, green and blue
respectively. (For interpretation of the references to colour in this ﬁgure caption,
the reader is referred to the web version of this paper.)

TRIGA reactor in Ljubljana supported by the H2020 project AIDA2020, GA no. 654168; with pions at Paul Scherrer Institut (PSI);
and with γ's at Brookhaven National Laboratory (BNL). The
research was supported and ﬁnanced in part by the Ministry of
Education, Youth and Sports of the Czech Republic (Grant no.
LG13009), the German Federal Ministry of Education and Research,and the Helmholtz Association, the European Social Fund and by
the Ministry of Science, Research and Arts, Baden-Wuerttemberg,
Germany, the Japan Society for Promoting Science KAKENHI-A
Grant number 20244038 and KAKENHI-C Grant number
20540291, the Ministry of Education, Culture, Sports, Science andTechnology-Japan, KAKENHI for Research on Priority Area Grant
number 20025007 and for Scientiﬁc Research on Innovative
AreasGrant no. 23104002, the Slovenian Research Agency, theSpanish Ministry of Economy and Competitiveness through theParticle Physics National Program (refs. FPA2012-39055-C02-01
and FPA2012-39055-C02-02) and co-ﬁnanced with FEDER funds,
the ﬁnancial support of the State Secretariat for Education,
Research, and Innovation, the Swiss National Science Foundationand the Canton of Geneva, Switzerland, the UK Science andTechnology Facilities Council (Grant ST/M006409/1), CONICYT
Becas Chile 72140349 and Cambridge Trust, and the United States
Department of Energy, Grant DE-FG02 13ER41983.

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Please cite this article as: L.B.A. Hommels, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/
j.nima.2016.03.042i