Last updated 20 Jul. 1996
The four inner layers (called T2,T3,T4,T5) will be mounted within the magnet bore, while the outer layers (T1 and T6) will be just above (T1) and below (T6) the magnet bore.
Each layer is composed by several silicon ladders , that in turn are composed by several silicon sensors (7 to 15 depending on the ladder position) and the associated front-end electronics (You can get a drawing with the arrangement of the silicon wafers for the inner and the outer plane).
The two sides of the sensors measure the track position in the bending (y) and non-bending (x) directions. The strips in the bending direction, which run along the ladder length, are joined end to end from one sensor to the next for half the ladder length. In the non-bending direction, a kapton foil with diagonal traces connects the strips which run across the ladder from one sensor to another. For both directions, ie for both sensor sides, and for both ends of the ladder, the last set of strips or the traces on the end of the foil are connected to read out electronics. Because more precision is needed in the bending direction, every strip is read out at a pitch of ~100 um. In the non-bending direction only 1 out of 4 strips is read out for a pitch of ~200 um. Measurement of the energy deposition (dE/dx) in each silicon plane will also allow a determination of the absolute value of the charge (Z) of the particle.
There are in total 28 ladder on the inner layers and 34 ladders on the outer ones. All the ladders are read out at both ends with the exception of the shortest one on each layer that will be read out only at one end. In total there will be 168 "ladder end" equipped with the front end electronics ( TFE ).
The total weight of the tracker's supporting structure, the Silicon Tracker itself, the front-end electronics and cables to connect to the read out electronics (TDR) outside the magnet is budgeted at 110 Kg.
The 90 ladder will be built in four assembly line ,located at the University of Geneva, Perugia, Turku and ETH/Zurich.
Both the electronics unit are connected to the half-ladder end via a flexible kapton cable with a strip pattern. This allow the mounting of the electronics unit at 90 degree with respect to the half-ladder planes. This particular mounting allows to reduce the non active area inside the magnet bore.
On one side of the half-ladder the kapton cable has a length of only few centimetres to connect the hybrid to the half-ladder end. This is called the S-side of the half-ladder and the strips give the coordinate of the tracks hit in the bending plane. On the opposite side the kapton cable has the same length of the half-ladder itself and has a diagonal strips pattern to bring the signal from the silicon strips running orthogonal to the half-ladder length to the front-end electronics. This side is called the K-side and give information of the coordinate of the track hit in the non-bending plane.
As soon as they will be available you will get also a sequence of drawing showing the ladder assembly procedure.
A total of 1921 silicon sensor will be used for the Tracker. The silicon sensors, produced at C.S.E.M. (Neuchatel, Switzerland), are 41.360 mm long and 72.045 wide and made from 300 um thick high purity n-type silicon wafer (resistivity of the order of 10 kOhm cm). One side of the wafer has p+ implantation strips every 25 um and a read out pitch of 100 um. These strips run parallel to the ladder length and will be used to measure the tracks coordinate in the bending plane This side is the junction side of the silicon sensor and has two concentric guard ring around the strips. On the opposite side of the wafer, and orthogonal to the p+ strips, there are n+ implantation strips every 50 um intervaled with p+ blocking strips. (The p+ strips are needed in order to interrupt the accumulation charge layer between two adjacent n+ strips). This side is the ohmic side of the silicon sensor and has a single guard ring.
Before incorporation into a ladder, all silicon sensors are tested for total leakage current, single strip leakage current and inter-strip resistance. A sensor is accepted if it satisfies the following criteria:
This is the entry to the tracker database
AMS Note on the database:
title:
Preliminary study on the Tracker Construction Database
date: April 27, 1996
author: Michele Pauluzzi
pages: 5
