Charge sensing properties of monolithic CMOS pixel sensors fabricated in a 65 nm technology

In this work the initial performance studies of the first small monolithic pixel sensors dedicated to charged
particle detection, called CE-65, fabricated in the 65 nm TowerJazz Panasonic Semiconductor Company are
presented. The tested prototypes comprise matrices of 64 × 32 square analogue-output pixels with a pitch of
15 μm. Different pixel types explore several sensing node geometries and amplification schemes, which allows
for various biasing voltage of the detection layer and hence depletion conditions and electric field shaping.
Laboratory tests conducted with a 55Fe source demonstrated that the CE-65 sensors reach equivalent noise
charge in the 15 to 25 e− range and excellent charge collection efficiencies. Charge sharing is substantial for
standard diodes, but can be largely suppressed by modifying their design. Depletion of the thin sensitive layer
saturates at a reverse diode bias of about 5 V.