Tuesday, October 11, 2022

10 μm-thick four-quadrant transmissive silicon photodiodes for beam position monitor application: electrical characterization and gamma irradiation effects


Silicon photodiodes are very useful devices as X-ray beam monitors in synchrotron radiation beamlines. Owing to Si absorption, devices thinner than 10 µm are needed to achieve transmission over 90% for energies above 10 keV. 

In this work, new segmented four-quadrant diodes for beam alignment purposes are fabricated on both ultrathin (10 µm-thick) and bulk silicon substrates. Four-quadrant diodes implementing different design parameters as well as auxiliary test structures (single diodes and MOS capacitors) are studied. An extensive electrical characterization, including current-voltage (I-V) and capacitance-voltage (C-V) techniques, is carried out on non-irradiated and gamma-irradiated devices up to 100 Mrad doses. Special attention is devoted to the study of radiation-induced charge build-up in diode interquadrant isolation dielectric, as well as its impact on device interquadrant resistance. 

Finally, the devices have been characterized with an 8 keV laboratory X-ray source at 108 ph/s and in BL13-XALOC ALBA Synchrotron beamline with 1011 ph/s and energies from 6 to 16 keV. Sensitivity, spatial resolution and uniformity of the devices have been evaluated

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(a) Front and (b) back side pictures of a processed Si wafer showing the final devices

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