A. Mochizuki

Radiation resistance of SOI pixel devices fabricated with OKI 0.15μm FD-SOI technology

Silicon-on-insulator (SOI) technology is being investigated for monolithic pixel device fabrication. The SOI wafers by UNIBOND allow the silicon resistivity to be optimized separately for the electronics and detector parts. We have fabricated pixel detectors using fully depleted SOI (FD-SOI) technology provided by OKI Semiconductor Co. Ltd. The first pixel devices consisting of 32×32 pixels each with 20 μm square were irradiated with 60Co γ’s up to 0.60 MGy and with 70-MeV protons up to 1.3×1016 1-MeV n eq /cm2. The performance characterization was made on the electronics part and as a general detector from the response to RESET signals and to laser. The electronics operation was affected by radiation-induced charge accumulation in the oxide layers. Detailed evaluation using transistor test structures was separately carried out with covering a wider range of radiation level (0.12 kGy to 5.1 MGy) with 60Co γ’s.

Total dose effects on 0.15μm FD-SOI CMOS transistors

The silicon-on-insulator (SOI) CMOS technology has a number of advantages over the standard bulk CMOS technology such as negligible latch-up probability, high speed and low power dissipation. The fully depleted SOI (FD-SOI) CMOS technology provided by OKI Electric Industry Co., Ltd. is realizing the full features of the advantages. Although the total dose response of SOI devices is more complex due to the presence of the buried oxide, high radiation tolerance is expected for a very thin silicon layer. We investigated the total dose effects on transistors fabricated using the OKI 0.15 mum FD-SOI CMOS process. Assuming a radiation environment at the super LHC experiment, we have irradiated with 70 MeV protons three chips each to 6.4 times1013, 5.8 times1014, and 5.5 times 1015 neq/cm2. In this paper we report the latest results in comparison with the data taken in a 2006 exposure test.

Evaluation of contact resistance of silver-loaded epoxy with aluminized backplane of silicon microstrip sensors

Some modules of the ATLAS silicon strip detector (SCT) exhibited a significantly higher effective bias resistance than we had expected. About 20 % of the barrel modules, for instance, showed such a resistance of 40 Omegak or higher. We have tried to identify causes of this high resistance as well as to find a remedy if necessary. As for the SCT modules, the bias connection is made with silver-loaded epoxy to the aluminized backplane of the silicon sensors. It was identified that the contact of the silver-loaded epoxy to the surface of the aluminized backplane sometimes provoked the high resistance. Fortunately, however, it automatically cures in practice by applying a usual bias voltage, to become harmlessly small of a few ten ohms.