1The CDF Intermediate Silicon Layers detector

P. Azzi-Bacchettaa, N. Bacchettaa, A. Bastie , F. Bedeschie, D. Biselloa, S. Bluskb, K. Bockjooe, M.
Chertokc, G. Chiarellie, R. Deminad , S. Donatie  , R. Fieldf , L. Galtierig , J. Goldsteind , G. Grimh , M.
Guerzonii, C. Haberg , K. Haraj, F. Hartmannk , A. Heissk , C. Hillh , M. Hrycykd, J. Incandelad, Y.
Katol, D. Knoblauchk, M. Kruseb, C. M. Leid, S. Leonee, G. Martignona, P. Mcyntirec , Y. Miyazakyl,A. Moggie, T. Mullerk , A. Munar-Arae, T. Okusawal, F. Palmonarie, D. Pelletth, G. Piacentinoe, F.
Ra aellie, D. Saltzbergm, E. Sandersm, M. Schillingk , M. Shimojimaj , D. Stuartd, T. Takanol, K.
Takikawaj, P. Tiptonb , N. Turinie , H. Wenzelk , F. Zettie , S. Zucchelliia Universita di Padova, Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italyb University of Rochester, Rochester, New York 15627
c Texas A&M University, College Station, Texas 77843
d Fermi National Accelerator Laboratory, Batavia, Illinois 60510
e Universita di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56010 Pisa, Italy
f University of Florida, Gainesville, Florida 32611
g Lawrence Berkeley Laboratory, Berkeley, California 94720
h University of California at Davis, Davis, California 95616
i Universita di Bologna, Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, I-40126 Bologna, Italyj University of Tsukuba, Tsukuba, Ibaraki 305, Japank Institut fur Exeperimentelle Kernphysik, Universitat Karlsruhe 76148 Karlsruhe, Germanyl Osaka City University, Osaka 588, Japanm University of California at Los Angeles, Los Angeles, California 90024
The Intermediate Silicon Layer (ISL) detector is presently being built as part of CDF upgrades. The ISL is alarge radius (30 cm) silicon tracker with a total active area of about 3.5 m2 . The challenge is to build a device
which provides precise 3D points introducing a minimal amount of material for the supporting structure. The
conceptual design and the status of the project are reviewed.

1. INTRODUCTION
The Tevatron pp Collider and the CDF detector
are presently being upgraded for Run II operation(to begin in early 2000). The Tevatron center-ofmass energy will be increased from 1.8 TeV to 2.0
TeV and the istantaneous luminosity by almost
one order of magnitude, to reach 1-21032 cm;2
 Corresponding author

sec;2 . The bunch spacing will be reduced from
3.7 s, rst to 396 ns and then, during the second
part of the Run, to 132 ns. CDF goal for Run II
is to take 2 fb;1 of data [1].
The CDF will have two mechanically separate
silicon detectors: the Silicon Vertex (SVX II)[2]and the Intermediate Silicon Layers detector(ISL), both using double-sided sensors. SVX II
has ve layers located between the minimum dis-2tance of 2.5 cm and the maximum distanceof 10.6 cm from the beamline. With a total
length of 1 m, it covers the pseudorapidity region j  j<2. The ISL is located between SVX II
and the Central Outer Tracker (COT), with one
central layer (6 C) at 23 cm from the beamline
and two forward/backward layers (6 and 7 F/B)
respectively at 20 and 29 cm from the beamline. Layer 6C covers the region j  j<1, whilelayers 6 and 7 F/B cover the region 1<j  j<2.
The total length of the detector is 2 m (Fig. 1).
The measurement of 5+1 3D points matchedto the COT information provides a strong tracking in the central region. In the forward region,
where the acceptance of the COT rapidly decreases, silicon-only tracking will be experienced
using the measurement of 5+2 3D points. Simulations show that the silicon-only tracker hasp  0:4 %/p2t . The ISL increases the eciencyand the purity of single and double b tagging in
the forward region and its ne granularity helps
to resolve tracking ambiguities within sti jets,often produced in tt events.
The ISL is a challenging project: 900
large area double-sided silicon detectors will bemounted on 296 ladders, for a total of 3.5 m2
total active area (300,000 channels). The designfor the support structure (spaceframe) foresees asystem of hollow carbon ber anges connectedby hollow carbon ber rods. Carbon ber waschosen to minimize material and maximizes rigidity. The readout electronics and DAQ already designed for the SVX II will be used. The request
is to operate in deadtimeless mode at the rate of
50 MHz. A severe problem is posed by the heatload: the cooling system has to dissipate 1.2
kW produced by the readout electronics.

Figure 1. The ISL detector. The four anges 7
and one every second module are drawn. In thelower part some rods connecting the two externalanges 6 and 7 can be recognised. In the central
part layer 6 C modules are visible.

t

2. ISL COMPONENTS
The ISL ladder is made of three silicon detectors ganged together to form one single electricalunit and glued on a carbon ber support. The
readout hybrid is mounted o silicon and glued
on the edge of the support. Two ladders buttedhead to head form the modules (55 cm long)mounted on the spaceframe.

2.1. Silicon detectors

The ISL uses double-sided AC coupled microstrip detectors made from high resistivity ntype silicon bulk material. Detectors have 512
strips/side with a pitch of 112 micron and a stereo
angle of 1.2o. The active area is 5.77.5 cm2for layer 7 detectors, produced by Micron Semiconductors on 6" wafers[3], and 5.76.7 cm2 forlayer 6, produced by Hamamatsu Photonics on 4"wafers. Although more challenging, the 6" technology has the convenience of accomodating twodetectors on each wafer. Both Micron and Hamamatsu detectors have polysilicon bias resistors on
both sides and common p-stops on the n+ side.
The design is to have a depletion voltage
40 V, with a breakdown voltage of coupling capacitors >120 V. This allows to follow the increasing of depletion voltage with radiation damage,which anyway is expected to be rather low for
the ISL. Since the total ladder length is >20 cm,
the interstrip capacitance/cm is kept at a level<1.0-1.2 pF/cm in order to reduce the total capacitance load to the readout chip ampli er andconsequently the noise. Electrical tests show that
prototypes delivered by Micron are now meeting speci cations and nal production has begun.
The measured value of coupling capacitance (be-3Figure 2. The ISL ladder. The holes on the bodyof the support are for the assembly jig towers
and for the microbonding machine. The hybrid isglued and microbonded on one edge of the ladder.
tween the single strip and the backplane) is 150
pF both on the p-side and on the n-side, with abias resistance of 4-6 M and an interstrip resistance > 2 G . The level of broken capacitors andleaky strips is better than the requested 3 %.
Micron prototypes performance was also tested
during 1997 testbeam at Fermilab[4]. The resolution is 25 m, with an average signal/noise ratioof 21, measured using SVX electronics, and a cluster size of 1.7 strips (with no magnetic eld). No
signi cant signal loss is observed as a function ofincoming particle interstrip position. This simplies the development of reconstruction programs.

2.2. Frontend electronics

Signals from the silicon detectors are read out
by the SVX3 chips[5], which perform signal integration, analog pipelining to provide the delay required by Level 1 trigger, digital conversion, and data sparsi cation for each of the 128
channels per chip. The SVX3 chip continuosly
performs the analog data acquisition during digitization and readout, which allows operation forLevel 1 rates up to 50 kHz.
The ISL DAQ system is basically identical tothat used for SVX II, with the only di erence ofthe hybrid design and placement. The ISL hy-brid is made of Aluminum Nitride and hosts four
SVX3 chips. Since the SVX3 chip has been designed to match the pitch of the SVX II detectors (60 m), a pitch adapter is mounted on thehybrid to match the 112 m pitch of the ISL detectors. The cables connecting the hybrids to theportcards are about 1 m long and, to avoid problems in signals amplitude and sincronization, atranceiver chip is mounted on the ISL hybrid. Aprecision hole is drilled in order to x the hybrid
to the assembly jig and give a point of reference
to the Coordinate Measuring Machine. This holeis also used to x the module to the spaceframewith a pin.

2.3. Supports and assembly procedure

The geometry and the openings made on thebody of the ladder carbon ber supports allow
an easy assembly and microbonding (Fig.2). Fulltorsional rigidity of the ladder is reached after
sensor gluing. Tests show that there is no additional noise due to the electromagnetic coupling
between silicon and supports (antenna e ect) in
the region of gluing, where the two surfaces areseparated only by 100 m of glue[4]. To reduceany possible e ect, also a layer of insulating kapton is inserted.
For assembly, the support is positioned on theAl bridge of the jig and the hybrid and the threesilicon detectors are mounted on four independent rotating towers. After having aligned thedetectors to the hole on the hybrid, gluing is performed. The residual interstrip misalignement
has been measured to be <5 m, with a detector aplanarity <30 m. The bowing of the entire
module is of the order of 100 m.

3. ISL SPACEFRAME
3.1. Design

The spaceframe is made of eight hollow carbon
ber rings ( anges) connected by carbon berrods. It is supported and anchored to the COT
endplates by two extensions xed to the externalanges 7. The design foresees also a carbon berouter screen which will give an enormous rigidity
to the whole structure. The ISL spaceframe will
also hold the SVX II detector.

4
sonable con dence that no stresses will be present
in the real spaceframe. Finally, this model wasused to study the routing of the cooling pipes.

4. COOLING

Figure 3. The aluminum prototype of the ISL
spaceframe fully assembled.
The lamination of the components of theanges uses 4 layers of carbon ber, each 125 mthick, assembled with a stardard manual lay-up
technology. This technology has the advantageof reliability and low cost. Lamination of anges
and rods production is done by two italian companies, Monfrini S.R.L. and Reglass S.p.A.
The desired precision of 50 m in the positionof the modules cannot be reached if the modules are directly xed on the anges, because theanges can be positioned only with a precision of
100 m. Thin layers of berillium (ledges) arexed on the ange using dedicated tooling, whichallows to compensate for the global misalignemntof the ange, and the modules are then mounted
on the berillium ledges.

3.2. Aluminum prototype

A full size Aluminum prototype of the spaceframe was built in order to test the alignement
and mounting procedure (Fig. 3). This prototype
was also used to optimize the routing of cables
connecting hybrids to the portcards, which are
xed to the ISL extension. Cables run parallel tothe detector axis and to the magnetic eld. Thisavoids possible interactions with the currents running on the cables. No residual stresses between
aluminum anges and carbon ber rods were
found after the glue had settled. This gives a rea-The challenge is to dissipate the heat producedby the 2,400 readout chips (0.5 W/chip) and mantain the silicon below 20o C and the hybrid below
25-30o C. The idea is to ux a low temperatureliquid in a aluminum pipe glued to the berillium
ledges which act as heat sinks. To have a low pressure and temperature drop along the pipes, thedesign foresees to divide each of the three(two)layer 6(7) barrels into three(four) identical sectors and to have an independent cooling circuit
for each sector. Tests show that a ux of 0.6 l/mof a 30 % mixture of water and glycole at 4.5o C
keeps the desired temperature. The external diameter of pipes is 4.5 mm, which is large enoughto allow an easy bending. To avoid liquid losses,
liquid is uxed at a pressure below 1 atm.

5. CONCLUSION
The conceptual design and the status of theproject of the CDF Intermediate Silicon Layers
detector have been reviewed. R&D has been completed and production of components is beginning. The expectation is to have all the components tested during the year 1999 and the detector
assembled for CDF Run II in early 2000.

REFERENCES
1. CDF II Collaboration, Technical Design Report, FERMILAB-Pub-96/390-E 1996.
2. J. Valls, The CDF Silicon Vertex Detector,
these Proceedings.
3. G. Bolla, Silicon microstrip detectors on 6"
technology, Proceedings of the Conference\Vertex 98", Santorini (Greece), September
1998, to be published on NIM A.
4. F. Bedeschi et al., Detector prototype tests for
ISL, CDF Internal Note 4450.
5. M. Garcia-Sciveres, The SVX3D Integrated
Circuit, Proceedings of the Conference \Vertex 98", Santorini (Greece), September 1998,
to be published on NIM A.