The Intermediate Silicon Layers Detector at
CDFII
Design and Progress
Proceedings of VERTEX '98
P. Azzi-Bacchetta j, N. Bacchetta j, A. Basti k, F. Bedeschi k,
D. Bisello j, S. Blusk `, K. Bockjoo k, M. Chertok m,G. Chiarelli k, R. Demina e, S. Donati k, R. Field f , L. Galtieri h,
J. Goldstein e, G. Grim b, M. Guerzoni a, C. Haber h, K. Hara n,
F. Hartmann g, A. Heiss g, C. Hill b, M. Hrycyk e, J. Incandela e,Y. Kato i, D. Knoblauch g, M. Kruse `, C.M. Lei e, S. Leone k,G. Martignon j, P. Mcyntire m, Y. Miyazaki i, A. Moggi k,T. Muller g, A. Munar-Ara k, T. Okusawa i, F. Palmonari d,
D. Pellett b, G. Piacentino d, F. Ra aelli k, D. Saltzberg c,
E. Sanders c, M. Schilling g, M. Shimojima n, D. Stuart e,T. Takano i, K. Takikawa n, P. Tipton `, N. Turini k, H. Wenzel g,T. Yoshida i, F. Zetti h, S. Zucchelli aa Universita' and INFN Sez. di Bologna, Italyb University of California at Davis, USAc University of California at Los Angeles, USAd Universita' di Cassino, Italye Fermilab, Batavia IL, USAf University of Florida, USAg Institut fur Experimentelle Kernphysik Universitat Karlsruhe, Germanyh Larwence Berkeley Laboratory, USAi Osaka City University, Japanj Universita' and INFN Sez. di Padova, Italyk Universita' and INFN Sez. di Pisa, Italy` University of Rochester, USA

mTexas A&M University, USAn University of Tsukuba, Japan

Corresponding author Frank Hartmann g hartmann@fnal.gov
Preprint submitted to Elsevier Preprint

29 October 1998

AbstractThe Intermediate Silicon Layers Detector is presently being built as part of theCDF upgrades to prepare for the next Tevatron data taking run, scheduled to startin the year 2000. The ISL will be located in the radial region between the SiliconVertex Detector and the Central Outer Tracker. It will add tracking in the forward
region and signi cantly improve tracking in the central region. Together with theSVX II, the ISL forms a standalone, 3D silicon tracker. In this article we present
the design of the ISL and the current status of its construction.

1 IntroductionThe Fermilab Tevatron Collider and its two multipurpose detectors CDF[1]and D0[2] are preparing for the next data taking run, starting in the year
2000II). The goal is the accumulation of 2fb;1 of pp-collisions atps =(RUN
2:0 TeV , with instantaneous luminosities of up to 2  1032 cm;2s;1 .
The modest increase from 1.8 TeV to 2.0 TeV in the Tevatron center of massenergy leads to a signi cant increase in cross section of all phenomena, withhigh mass nal states; e.g the tt cross section is increased by 40%. The increase in luminosity, on the other hand, will lead to a 20 fold increase in event
statistics and requires a signi cant upgrade of the CDF detector.
The CDF II is a general purpose solenoid spectrometer which combines charged
particle tracking with projective calorimetry and muon detection. The tracking system is optimized for pattern recognition, momentum resolution, andb-tagging up to pseudo rapidity jj  2. Combining tracks with informationfrom electromagnetic calorimetry or muon chambers provides ecient electronand muon identi cation.

2 Motivation
The Intermediate Silicon Layers Detector (ISL) is an integral part of theCDF II tracking system, which consists of three concentric detector systems.
Closest to the beampipe is the Silicon Vertex Detector (SVX II), consisting of
5 silicon layers at radii between r=2.45 cm and 10.60 cm. The ISL is a silicondetector with a length of almost 2 m, with one central layer (jj < 1) at radial
position r=22 cm and two layers in the forward region (1 < jj < 2) at radial positions r=20 cm and 28 cm respectively. The third detector, the Central
Outer Tracker (COT), is a large drift chamber with a length of 3 m, covering aradial span beginning at 40 cm and ending at 137 cm. The ISL provides one or2

Fig. 1. Elevation view of one half of the CDF II detector.
The tracking system is located inside a superconducting solenoid, which generates
a 1.4 T magnetic eld parallel to the beam axis. Calorimetry and muon systems are
all outside of the solenoid. The Intermediate Silicon Layers detector (ISL) is locatedbetween the inner Silicon Vertex Detector (SVX II) and the Central Outer Tracker(COT).

two additional spacepoints in the intermediate region (r=10.6 cm up to 40 cm),
which improves the linking probability between SVX II tracks and COT tracks,and its ne granularity helps to resolve ambiguities in dense track environments. The complete tracking system, consisting of SVX II, ISL and COT,
provides high momentum resolution for jj < 1 (P =PT2 = 0:09%(GeV=c)
at PT = 10 GeV=c [1]). In addition, SVX II together with the ISL forms astandalone, 3D silicon tracker, with up to 7 axial and 7 stereo measurements
extending the tracking capabilities out to jj  2. The 3D tracking performance and the momentum resolution of the SVX II is largely improved bythe ISL and enables good b tagging in the forward region. By increasing theacceptance the ISL has a signi cant impact on the double b-tag eciency (seeTable 2). Figure 2 shows a reconstructed tt event in SVX II and ISL (MonteCarlo).
Detector
Con guration
SVX'+CTC 1
SXV II+COT
SVX II+ISL+COTSingle tage .(%)
37:6  1:0
46:7  1:1
60:1  1:0

Double tage .(%)
6:9  0:58:7  0:6
15:1  0:8

Table 1
Eciency for single and double b-tagging[1] in tt Monte Carlo events for di erent detector con gurations. The results are from a parametric study, including geometry,acceptance cuts and tracking eciencies.

3Fig. 2. An eventdisplay of a tt event; Monte Carlo.
This picture shows two views of a Monte Carlo simulation of a tt event reconstructedin SVX II and ISL.

3 Conceptual Design Considerations
The ISL project started in October 1996, the short time available until theinsertion scheduled for late 1999 required a quick yet innovative design andaggressive construction schedule. To minimize R&D and to allow easy integration into CDF, the ISL uses the same readout electronics and data acquisition(DAQ) as the SVX II [1,4]. The design takes advantage of the large radialposition; radiation damage occurs more slowly and the hit occupancy is lower,
it is therefore possible to use longer strips and a large readout pitch to reduce the number of readout channels and subsequently the cost of frontend
electronics and data acquisition. The mechanics of the ISL called for an innovative design. Given the large volume between SVX II and the COT, it waspossible to design a light-weight yet robust support structure (see section 4.2).
estimate 1:5% radiation length in the central region and 2% radiation length
in the forward region, including 1% radiation length due to hybrids, endcaps,cooling.
The result is a detector with 888 large area, double-sided silicon microstrip
sensors with a total of 303104 channels. The basic ISL unit is the ladder,composed of three silicon sensors bonded together and their readout electronics located on a hybrid at the end. The support structure is built in carbon
ber 2 . 296 ladders are paired to form 148 modules of 55 cm length each. The
1 SVX' Silicon Vertex Tracker of CDF for the running period of '92 - '96 (RUN I);

CTC Central Tracking Chamber of RUN I
2 Testbeam results showed that additional crosstalk with the conductive ber support and additional capacitance e ects can be avoided by isolating the carbon ber

4modules are mounted on carbon ber rings to form barrels, which are thenassembled into a spaceframe (see section 4.2).

Fig. 3. SVX to SVX II + ISL.
SVX was a 4 layer, 51 cm long detector in RUN I providing r information. It will
be replaced by the SVX II-ISL combination; a 5 layer, 87 cm long detector (SVX II)
providing stereo information plus one additional central layer and two additional
layers in the forward region (ISL), 195 cm long. All sensors are double sided withstereo readout, 4 layers with a stereo angle of 1:2o and 3 with a 90o stereo angle.

4 Mechanical components
4.1 Ladders and ModulesThe most crucial aspect of the construction is the exact alignment of the individual silicon sensors inside the support spaceframe. The internal alignment ofa ladder has to be much better than the intrinsic hit resolution of 25 m (seesection 5.1). We achieve this high precision with one rotating stage, holding
the hybrid, and a row of 3 X-,Y-,rotating-stages, holding the sensors (Figure4 right). The hybrid and the 3 sensors are held in position by applying a vacuum. The te on surfaces of the vacuum chucks on top of the towers have anaccuracy in planarity of 5 m. The carbon ber support is placed on a metal
bridge underneath the te on vacuum chucks, led by high precision bearings toprovide good planarity. The mounting is done on a coordinate measurement
machine (CMM) with a precision along the strips of about 1 m. The hybrid
is mounted rst, rotated with respect to the carbon ber ladder, the 3 siliconsensors are then positioned with respect only to the precision hole on the hybrid. The glue-laden ladder is then elevated to the sensors. The structure isladder from the sensors and grounding the carbon ber ladder [5].

5

released when the glue has fully settled. This procedure ensures an internal
module precision only depending on the CMM precision for construction. It
ensures an internal precision independent of the carbon ber ladder. The wirebonding to connect the sensors is done after mounting, therefore the bonding areas have to be fully accessible after gluing (Figure 4 left). Finally thetwo ladders are glued together on a similar mounting xture. The precision iscontrolled by a CMM.

Fig. 4. ISL Ladder Design & Mounting Jig.
The picture on the left shows the design of an ISL ladder; the expanded view shows
the cut-out designed for easy access for microbonding. On the right you see the ISL
Mounting Jig.

4.2 Spaceframe

The spaceframe was designed with respect to weight, sti ness and material
budget, which led to a carbon ber structure. Carbon ber rings are connectedwith hollow carbon ber rods. The total weight of the structure is about 6 kg
before mounting the modules. Finite element analysis predicts a maximum
gravitational sag of less than 30 m in the center. We expect the structure
to be even sti er after mounting the modules, with a nal precision of 50 mover the whole length of 2 m. The internal module precision is ported to thenal position precision in the spaceframe by only connecting the hybrids, notthe carbon ber ladders. The position of each silicon sensor is measured by aCMM. The nal alignment precision will be achieved with tracks.
6

Fig. 5. Mechanical Design of the Carbon Spaceframe.
The geometrical concept of the single additional layer in the central region and thetwo additional layers in the forward direction can be seen.

Fig. 6. Picture of the aluminium prototype.
One forward prototype barrel is displayed with the nal hollow carbon ber rods.
Some dummy modules are mounted to check the assembly procedure.

4.3 Assembly

The spaceframe was designed in Pisa, and carbon ber parts are laminatedby Monfrini S.R.L. (Italy). The gluing of single parts into the whole structure
will be done in Pisa under a CMM using precision gluing masks to obtain7

the needed accuracy. Struts are custom-made by Reglass S.p.A. (Italy). Thespaceframe is designed in such a way that it can be disassembled into 3 partsand shipped to Fermilab. The SVX II and the ISL will be assembled together
on the adapted rail system, previously used to install the SVX' in RUN I.
We make use of one single CMM by placing one granite table on both ends.
SVX II and ISL will then be placed on the rail system, resting on this set ofgranite tables (see Figure 7). We will begin to assemble the SVX II on theCMM, then move it to one side to make room for the ISL. After assembling
both detectors, we will mount the SVX II in the ISL. The same rail system
will also be used to insert the ISL and SVX II into the COT. All parts rest onthe same rail from the beginning of assembly until nal insertion into CDF II.
Adapted railsystem of SVX

SVX IIISL
3 meter CMM

Granite Table

Granite Table~10 meters
Fig. 7. Assembly of the SVX II and the ISL on one CMM.
We use 3 granite tables, with a CMM on the inner one to support a rail system
supporting both ISL and SVX II. Everything will be assembled on a rail system,
which itself will be used to insert both detectors into the COT.

5 Electrical components
5.1 Silicon detectors [6{8]The sensors are 7:4  5:5 cm2 silicon microstrip detectors, AC coupled with512 axial strips on the p-implant side and 512 stereo strips (1:2o) on the nimplant side; both sides have a strip pitch of 112 m. The sensors consist ofhigh resistivity n-bulk silicon. We use a conventional design: bias is applied via
polysilicon resistors, one guardring for eld shaping and for the n-side a p-stop
design is used. Detectors will be produced by Micron Semiconductors on 6\wafers. A slightly shorter version (6:7  5:7 cm2) of the same detectors will
be manufactured by Hamamatsu Photonics on 4\ technology, with the stereostrips (1:2o) on the p-implant side. The performance of Micron prototypes wasmeasured in a testbeam. Using the SVX electronics, we measured a resolutionof 25 m with an average signal/noise ratio of 21 for an average cluster sizeof 1.7 strips (with no magnetic eld) [5]. The prototype phase is nished and8

Micron has started production. Each sensor is sent to Karlsruhe for quality
control, before the nal ladder assembly in Pisa. The quality control checks
for pinholes and strips with a high leakage current. We require less than 3%
bad channels in total and less than < 2% on each side.
5.2 The SVX3 chip [1,4]The silicon sensors are read out by the SVX3 chip, a radiation hard CMOS
custom integrated circuit. Each chip has 128 parallel input channels. The chip
consists of two separate parts: the frontend for the analog functions and thebackend part for the digital functions. The input ampli ers, integrators, the46 cell pipelines needed for deadtimeless operation and the pipeline acquisition logics are located in the frontend. Up to 4 groups of cells can be queued
for digitization and readout at one time. The backend consists of an 8 bit
Wilkinson ADC, a readout FIFO and di erential output drivers. The chip isable to work with positive and negative signals to handle double sided silicondetectors. It has a sparsi cation mode, a calibration input and is capable ofpedestal subtraction on chip level. The chip is programmable to adjust for different Tevatron running conditions. e.g bunch-spacings (132 - 396 ns). It canhandle strip capacitances from 10 to 35 pF. Also the pipeline depth, thresholdlevel and bandwidth limit is adjustable. The chip has been irradiated with a
Co60 source up to 4 Mrad and was found to perform well 3 [9]. The amplication is 15 mV=fC , which corresponds to 60 mV for a minimum ionizing
particle.The chip provides deadtimeless readout with Level-1 trigger rates up
to 50 kHz. The maximum delay between Level-1 trigger decision and readout
without overwriting the pipeline cell content is 5:5 s at 132 ns between beamcrossings.

6 The Online Alignment System [11,12] and Active Alignment
The Silicon Vertex Trigger (SVT) will use impact-parameter information inthe trigger to detect secondary vertices. In order to obtain impact-parameter
information in the Level-2 trigger, the SVX II is read out after each Level-1trigger. The SVT combines this data with the Level-1 tracking informationfrom the COT, reconstructed with the XFT (eXtremely Fast Tracker) trigger[1]. The SVT computes track parameters in the transverse plane (0; pT , andimpact parameter) with resolution and eciency comparable to full oine
3 During RUN II the chip will be exposed to about 7  1013 minimum ionizing
particles per cm2 over a period of two years, corresponding to an absorbed dose of

2 Mrad at the inner layer of SVX II [10]9analysis. This trigger needs the beam axis to be parallel to the tracking system.
Small tilts can be corrected for by adjusting the Tevatron beam. For this it
is necessary to feed back the beam position to the Tevatron control room. To
adjust for larger tilts an active alignment system is foreseen. It allows to moveand tilt the SVX II/ISL with respect to the beam. The movement is achievedby mounting the system on rods. Micro motors (so called \inchworms" basedon piezo crystals) move along the rods with high precision and so vary theposition of the SVX II/ISL system. The relative positions of SVX II, ISL andCOT will be continuously monitored by the so called Rasnik system 4 andcontrolled. A system of a light source, consisting of an array of 9 infraredLEDs, a distinctive pattern, a lens and a CCD camera will be mounted inthe detector. The pattern is continuously projected on the CCD. Any relative
movement of LED-array and CCD will be noticed as a shift of the pattern. APC with pattern recognition software will calculate the movement and rotation
with a precision in the submicron range. In Figure 8 you can see the Rasnik
components positions in the system; relative shift of ISL to SVX II, ISL toCOT, twists in the SVX II and the global tracking system to end ange position
can be monitored.

Fig. 8. The Online Global Alignment System.
This picture displays the spaceframes of SVX II, ISL, COT and eight Rasnik systems. With this arrangement the relative positions of the 3 subdetectors can bemonitored. One control unit consists of an array of infrared LEDs as source, a projected pattern, a lens to focus the light and the CCD as receptor. Each change ofposition of source or camera will be observed as a shift of the pattern.

7 Conclusion
The ISL project started in late 1996, as part of the CDF upgrade for RUN II.
The ISL-SVX II combination forms a standalone silicon tracking system andextends the tracking region from jj < 1 up to jj  2. Adding the ISL in thecentral area jj < 1 improves the tracking precision, it also helps to resolve
4 A similar system was used in the CHORUS experiment.

10

ambiguities in dense track environments. The spaceframe design is nished anda prototype has been built. The mounting xtures have been manufactured
and exceed the expected precision. The silicon sensors passed the design andprototype phase and production started. The hybrids are designed and therst hybrids were produced. The rst prototype ladder has been built and isworking. We expect the ISL-SVX II tracking system to be ready for installationin November 1999.

References[1] CDF II Collaboration, Technical Design Report,
FERMILAB-Pub-96/390-E (1996).
[2] D0 Collaboration, Nucl. Instr. and Methods, A338, 185 (1994),
FERMILAB-PUB-93/179-E .
[3] Maurice Garcia-Sciveres, The SVX3D Integrated Circuit, These proceedings.
[4] Maurice Garcia-Sciveres, The SVX3D Integrated Circuit, These proceedings.
[5] Detector prototype test for ISL, CDF INTERNAL NOTE 4450.
[6] Frank Hartmann et al., Evaluation of the ISL prototypes,
CDF INTERNAL NOTE 4627.
[7] Gino Bolla, Silicon microstrip detectors on 6" technology, These proceedings.
[8] K. Hara et al., 4" prototype Si microstrip sensors for the CDF ISL,
CDF INTERNAL NOTE 4506.
[9] Maurice Garcia-Sciveres et al., Radiation E ects on the SVX3 Chip, CDF
INTERNAL NOTE 4461.
[10] Barnett et al. (Particle Data Group). Phys. Rev. D54 p. 1268 (1996).
[11] D. Saltzberg et al., The Optical Alignment Monitoring System of CHORUS(RASNIK), CERN-PPE/96-179[12] Eddie Sanders, Rasnik Relative Alignment Monitor
for the CDF II SVX II-ISL-COT, CDF INTERNAL NOTE 4510.

11