Design and Tests of the Silicon Sensors for the ZEUS Micro Vertex Detector

TL;DR

This paper details the design, fabrication, and testing of silicon micro-strip sensors for the ZEUS Micro Vertex Detector, including electrical measurements and irradiation tests to evaluate radiation hardness and performance degradation.

Contribution

It presents the design, production, and irradiation testing results of silicon sensors specifically developed for the ZEUS MVD upgrade.

Findings

Electrical measurements confirm sensor functionality.

Neutron irradiation results match empirical damage models.

Photon irradiation causes interface effects and mobility changes.

Abstract

To fully exploit the HERA-II upgrade,the ZEUS experiment has installed a Micro Vertex Detector (MVD) using n-type, single-sided, silicon micro-strip sensors with capacitive charge division. The sensors have a readout pitch of 120 micrometers, with five intermediate strips (20 micrometer strip pitch). The designs of the silicon sensors and of the test structures used to verify the technological parameters, are presented. Results on the electrical measurements are discussed. A total of 1123 sensors with three different geometries have been produced by Hamamatsu Photonics K.K. Irradiation tests with reactor neutrons and Co-60 photons have been performed for a small sample of sensors. The results on neutron irradiation (with a fluence of 1 x 10^{13} 1 MeV equivalent neutrons / cm^2) are well described by empirical formulae for bulk damage. The Co-60 photons (with doses up to 2.9 kGy) show the presence of generation currents in the SiO_2-Si interface, a large shift of the flatband voltage and a decrease of the hole mobility.