At the HERA collider in Hamburg an experiment (ZEUS) has been built to study electron-proton collisions. For the near future an upgrade of this experiment is foreseen. One of the main improvements will be a new detector close to the collision point. This vertex detector is designed to measure the tracks of charged particles. The design is based on the use of silicon strip sensors.

In the centre of the experiment the proton and the electron collide with such high energy that new particles can be formed. Most of these particles decay immediately and only the decay products are measured. Some particles travel up to a millimetre before they decay. This can be concluded from the secondary vertex that is measured. The vertex detector consists of three concentric layers around the interaction point.

The detector consists of 800 separate sensors: thin slices (0.3 mm) of silicon. When a particle traverses the silicon it creates charge. This charge is collected at the surface where an array of diodes is implanted. When the signal is carefully analysed the position of the track can be determined with an accuracy of 5 micrometer!

Secondary vertex produced by decay of a particle.

A LADDERThe support structure for the silicon modules is made off carbon fibres. The ladder holds five modules. The fast analog readout chip (Helix) is visible as it is mounted on the hybrid. To ensure operation at a stable temperature the chips are water cooled.

Carbon fibre structure

Kapton connection to sensorsCooling pipe

Connector

A MODULESilicon sensors of 6 x 6 cm are used with an array of 512 readout strips each. A module is constructed with four sensors providing measurements in 2 orthogonal directions. Fast preamplifiers are mounted on hybrids. The connection to the sensors is made with thin kapton foils covered with copper lines.

silicon

hybrid

kapton

Helix chips

Before series production is started, prototypes are being carefully tested.

The ladder is made out of 0.35 mm thick carbon fibre sheets.

The cylinder supporting the ladders is a sandwich of two 0.5 mm carbon fibre sheets filled with a honeycomb structure.

Each silicon strip is connected to a channel of the readout chip. In this picture you can see the aluminium wires connected to the input pads of the readout chip. These wires have a diameter of only 30 micrometer.

The chip has 128 input channels and consists of a preamplifier, a shaper and multiplexer part. In this picture a small part (1 x 1 mm²) of the components can be seen.