Nuclear Instruments and Methods in Physics Research A 453 (2000) 84}88

Intermediate silicon layers detector for the CDF experiment
A. A!older , P. Azzi-Bacchetta, N. Bacchetta, G. Barker, A. Barbaro-Galtieri ,A. Basti, F. Bedeschi, D. Bisello, S. Blusk, W.P. Caskey, G. Chiarelli,A. Connolly , R. Demina, R. Ely , R. Field, M. Garcia-Sciveres , K. Giolo,
D. Goldstein , J. Goldstein, G.P. Grim, M. Guerzoni , R. Haas, C. Haber ,K. Hara , F. Hartmann, A. Heiss, C. Hill, M. Hrycyk, J. Incandela, Y. Kato ,D. Knoblauch, M. Kruse, R.L. Lander, C.M. Lei, G.L. Leonardi, S. Leone,Y. Miyazaki , A. Moggi, T. Muller, A. Munar-Ara, T. Okusawa , F. Palmonari ,M. Paulini , G. Piacentino , D.E. Pellett, F. Ra!aelli, F. Roederer, D. Saltzberg ,M. Shimojima *, D. Stuart, H. Suzuki , T. Takano , K. Takikawa , M. Tanaka ,Y. Taniguchi , P. Tipton, N. Turini, I. Volobouev , H. Wenzel, T.D. Wilkes,W. Yao , T. Yoshida , F. Zetti , S. Zucchelli
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
Universita% and INFN Sez. di Padova, I-35131 Padova, Italy
Universita( t Karlsruhe, 76148 Karlsruhe, Germany
Universita% and INFN Sez. di Pisa, I-56010 Pisa, Italy
University of Rochester, Rochester, NY 15627, USA
University of California at Davis, Davis, CA 95616, USAFermi National Accelerator Laboratory, Batavia, IL 60510, USA
University of Florida, Gainesville, FL 32611, USA
University of California at Los Angeles, Los Angeles, CA 90024, USA
Universita% and INFN Sez. di Bologna, I-40126 Bologna, Italy
University of Tsukuba, Tsukuba, Ibaraki 305, Japan
Osaka City University, Osaka 588, Japan
Universita% di Cassino, Cassino, Italy
Accepted 16 June 2000

Abstract
The Intermediate Silicon Layers (ISL) detector is currently being built as part of the CDF II detector upgrade project.
The ISL detector will signi"cantly improve tracking in the central region and, together with the Silicon Vertex detector,
provide stand-alone 3D track information in the forward/backward regions. In this article, we present the quality of theproduction sensors manufactured by Hamamatsu Photonics, which account for roughly half of the silicon sensors used in
the ISL detector.  2000 Published by Elsevier Science B.V. All rights reserved.

* Corresponding author.
E-mail address: mako@fnal.gov (M. Shimojima).
0168-9002/00/$ - see front matter  2000 Published by Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 6 1 0 - 0

A. Awolder et al. / Nuclear Instruments and Methods in Physics Research A 453 (2000) 84}88

1. Introduction
The CDF detector at Fermilab Tevatron Collider is currently being upgraded to CDF II [1] totake full advantage of 10-fold increase in luminosity. The Intermediate Silicon Layers (or ISL) detector is one of the three new silicon detectors. It isconstructed from "ve barrels in total, one central
barrel and a pair of inner and outer barrels inforward and backward regions, and covers the region "g"(2 and r"20}29 cm. Together with thenew Silicon Vertex detector (SVX-II) installed inside it, the ISL detector will provide stand-alone
3D track information in the forward/backward regions.
The ISL silicon sensors are double-sided AC
coupled microstrip detectors made from high-resistivity n-type silicon bulk material with atoll p-stops
to isolate strips on the n-side. Each sensor has 512
readout strips of 112 lm pitch on either side anda small stereo angle of &1.23. Sensors on thecentral and inner barrels are fabricated byHamamatsu Photonics KK (HPK) on 4 wafers [2]and have an active area of 5.7;6.7 cm per side,
while those on the outer barrels are produced byMicron Semiconductors Ltd., using 6 technology[4] and have an active area of 5.7;7.5 cm.
The ISL half ladder module is made of three suchsensors ganged together to form a single electricalunit and is glued on a carbon "bre support. The
readout hybrid is mounted o! silicon and is glued
on the edge of the support. Two half ladders makeup a full-ladder module, and 28, 24, and 36 of thesemodules are mounted on each of the central, inner,and outer barrels. The numbers therefore add up to148 ladders and 888 silicon sensors.
The overall design and some components of theISL detector have already been described in Refs.
[2}5]. In this article we review the quality of theHPK sensors. (Table 1)

2. Leakage current
While studying the prototype sensors [2] it wasnoted that the I}< characteristics of sensors vary
among production batches and in order to assurea wide range of stable operation voltages we re-85

Table 1
Some important electrical speci"cations for the HPK siliconsensors
Full depletion voltage
Leakage current at 203CI at < "140 V *I (< "100}130 V) No. of dead channels
TotalPer side(100 V(4 lA(1 lA(2%(3%Fig. 1. Number of leaky strips in Grade B sensors.

quire a plateau in the region above the full-depletion voltage. This is speci"ed as the di!erence inleakage current *I between < "100 and 130 
V and was initially set to 300 nA (Grade A sensors).
However, the yield of the HPK Grade A sensors
was not as high as we hoped and we revised thespeci"cation in January 1999, when we had received about 10% of the production sensors fromHPK. We have examined some of the production
sensors using a semi-automatic probe station at theUniversity of Tsukuba to investigate the problem
and found that the large leakage current increase isdue entirely to only a few bad strips that develop
micro-discharge at an early stage. As Fig. 1 shows,the number of leaky strips (de"ned as strips drawing more than 200 nA at < "140 V) is not large } only one or two isolated strips contribute to the4. SILICON VERTEX DETECTORS86

A. Awolder et al. / Nuclear Instruments and Methods in Physics Research A 453 (2000) 84}88

Fig. 2. Number of dead channels.

increase. We have decided to count these leaky
strips as dead and accept sensors (as Grade B sensors) if their *I values are less than 1 lA, provided
they pass all other speci"cations including thenumber of dead channels.
After the speci"cation was loosened a little, theproduction yield went up by as much as 38%  andat the time of the conference 78% of the sensors had
been delivered to Fermilab.

3. Dead channels

shown in Fig. 2 in four categories: faulty coupling
capacitors (i.e., pinholes), shorts on Al traces, open
Al traces, and bad poly-Si bias resistors. Most of
the dead channels are due to faulty coupling
capacitors and contributions from bad Al traces
are quite small. Bad poly-Si bias resistors include
both faulty resistors (large R) and bad isolation to
the implant strips nearby (small R). Measurements
for bias resistors are only available on the p-side
where we can bias the n-strips from the p-side
through a dedicated n-electrode implanted on thep-side.

The statistics of dead channels (excluding leaky
strips for Grade B sensors de"ned in Section 2) is4. Coc irradiation

 In the end Grade B sensors came out to be about 20% of thetotal.

Three Grade B sensors were irradiated withc rays from a Co source to 0.2 Mrad. The electrical characteristics of the sensors were measured

A. Awolder et al. / Nuclear Instruments and Methods in Physics Research A 453 (2000) 84}88

Fig. 3. Leakage current at < "140 V before (䢇) and after (*) 0.2 Mrad Co c irradiation.

before and after the irradiation. Fig. 3 shows
the leakage current of one of the sensors foreach strip before and after the irradiation. The
current of good strips increased from 1 to 50 nA
and that of leaky strips remained leaky but noadditional radiation-induced increase was observed. Moreover, there was no obvious e!ect onneighbouring strips.
The ISL sensors will not receive more than
0.1 Mrad of radiation for an integrated Tevatron luminosity of 10 fb\, so we do not expect
them to undergo type inversion throughout theirlifetime.

5. Long-term stability
A total of seven sensors of varying I}< characteristics were burned at 120 V for 3 months at 203C
to see the long-term stability of these sensors as wellas the possible di!erences between them. Thesesensors all fail the criteria on the number of deadchannels but sensors 199, 200, and 201 are otherwise good to be Grade A while sensors 195 and 202

87

Fig. 4. I}< on day 5 (top) and day 66 (bottom).

are good to be Grade B. Even sensors 203 and 204,which failed the *I criteria on day 0, are quitestable after a few days of burn-in.
Fig. 4 shows the I}< curves of these seven sensors measured on day 5 and day 66. Both Grades
A and B sensors show no noticeable di!erence
between the two measurements.

6. Detector assembly
At the time of the conference, ladder assemblies
had just been started at the two sites, Fermilab for
the HPK sensors and Pisa for the Micron sensors.
Right now, we have more than 100 half-ladders
assembled and both half- and full-ladders productions are very well on schedule.

7. Conclusion
ISL silicon sensors are fabricated by Hamamatsu
Photonics using 4 technology and MicronSemiconductors using 6 technology. We have

4. SILICON VERTEX DETECTORS88

A. Awolder et al. / Nuclear Instruments and Methods in Physics Research A 453 (2000) 84}88

examined the quality of the HPK production sensors. Using Grade B sensors we have evaluated theperformance of the sensors under radiation environment as well as their long-term stability.
ISL detector should be ready for SVX installation in June 2000, and for physics run in March2001.

References[1] CDF II Collaboration, FERMILAB-Pub-96/390-E (1996).
[2] K. Hara et al., Nucl. Instr. and Meth. A 435 (1999) 437.
[3] A. A!older et al., Nucl. Instr. and Meth. A 435 (1999) 44.
[4] G. Bolla et al., Nucl. Instr. and Meth. A 435 (1999) 51.
[5] P. Azzi-Bacchetta et al., Nucl. Phys. Proc. Suppl. 78 (1999)
307.