Professor Tony Weidberg

Abstract:

We study the radiation hardness and the lifetime of Light Emitting Diodes (LEDs) and Vertical Cavity Surface Emitting Laser diodes (VCSELs) in the context of the development of the optical readout for the ATLAS SemiConductor Tracker (SCT) at LHC. About 170 LEDs from two different manufacturers and about 130 VCSELs were irradiated with neutron and proton fluences equivalent to (and in some cases more than twice as high as) the combined neutral and charged particle fluence of about 5×1014 n (1 MeV eq. in GaAs)/cm2 expected in the ATLAS inner detector. We report on the radiation damage and the conditions required for its partial annealing under forward bias, we calculate radiation damage constants, and we present post-irradiation failure rates for LEDs and VCSELs. The lifetime after irradiation was investigated by operating the diodes at an elevated temperature of 50 °C for several months, resulting in operating times corresponding to up to 70 years of operation in the ATLAS SCT. From our results we estimate the signal-to-noise ratio and the failure rate of optical links using LEDs developed specifically for application at LHC.

Abstract:

Two kinds of photodiodes have been investigated for the ATLAS SCT readout. We present in this paper the results of irradiating bulk and epitaxial Si PIN diodes with 1 MeV-equivalent neutrons and 24 GeV protons. The devices were biased during some of the tests. They were exposed to a fluence of around 2.5×1014 n cm-2 followed by a fluence of approximately 2.5×1014 p cm-2.

Abstract:

A full study of the optical readout package for the ATLAS SCT/Pixel detector data transmission is presented. Radiation hardness studies of VCSEL emitters, Epitaxial Silicon PIN diodes receivers and their associated chips have been carried out with fluences higher than 10(15)n.cm(-2) 1 MeV neutron equivalent and total ionising doses of 10 Mrad. The reliability was assessed by testing a large number of devices and accelerated ageing tests were also pursued over a period equivalent to more than the LHC operation time. Single Event Upset and magnetic field studies up to 6T have also been done on a new optical package design with positive results.