Speaker
Sonia Fernandez Perez
(CERN)
Description
Silicon-on-insulator (SOI) technologies have been developed for applications which require radiation hardness since many years. However, for its use as particle detector the total ionizing dose response of SOI devices is more complex than bulk silicon devices due to the buried oxide (BOX). A significant influence of radiation damage in the BOX on the transistor characteristics due to the so-called back gate effect has been observed and published in SOI technologies.
We have fabricated and tested a new 0.18 um SOI CMOS monolithic pixel sensor using the XFAB process. In contrast to most SOI technologies, this particular technology provides a double well structure, which shields the thin gate oxide transistors from the Buried Oxide (BOX). This in addition with the particular geometry between transistors and BOX makes the technology promising against back gate effects mentioned before. The process further allows the use of high voltages (up to 200V), which are used to partially deplete the substrate. Thus the newly fabricated device in the XFAB process is especially interesting for applications in extremely high radiation environments, such as LHC experiments.
We have carried out a validation program of the technology and the fabricated monolithic pixel sensor in a two stages approach. The first targets the characterization of the charge collection in the silicon bulk below the BOX, the second investigates the radiation hardness of the transistor characteristics, with focus on possible influences of the BOX.
The mentioned prototype has been irradiated with X-rays up to 700MRad under two different bias conditions. This presentation summarizes the promising results of the total ionizing dose hardness after this extreme dose of various transistor types - both, standard transistors with different geometries and enclosed transistors. The radiation performance is characterized by transistor threshold voltage shifts, leakage current shifts and transconductance shifts. Results obtained under different bias conditions are compared. Leakage current measurements on the monolithic pixel sensors at different temperatures are used to characterize the silicon bulk behavior and will be presented. To verify the function as pixel sensor we have also tested the device using 55Fe source.
Author
Sonia Fernandez Perez
(CERN)
