CMOS sensors in 90Â nm fabricated on high resistivity wafers: Design concept and irradiation results

The LePix project aims at improving the radiation hardness and the readout speed of monolithic CMOS sensors through the use of standard CMOS technologies fabricated on high resistivity substrates. In this context, high resistivity means beyond 400Ωcm, which is at least one order of magnitude greater than the typical value (1-10Ωcm) adopted for integrated circuit production. The possibility of employing these lightly doped substrates was offered by one foundry for an otherwise standard 90 nm CMOS process. In the paper, the case for such a development is first discussed. The sensor design is then described, along with the key challenges encountered in fabricating the detecting element in a very deep submicron process. Finally, irradiation results obtained on test matrices are reported.