ATLAS17LS – A large-format prototype silicon strip sensor for long-strip barrel section of ATLAS ITk strip detector

The ATLAS experiment is going to replace the current Inner Detector with an all new inner tracker (ITk) in the ATLAS detector for HL-LHC at CERN. Silicon strip detectors cover the outer layers of the barrel and the endcap sections. We have designed and fabricated a prototype single-sided n + -in-p AC-coupled silicon strip sensor for the outer barrel layer with long strips (LS), ATLAS17LS. It is of the maximum allowable size to fit in a 6-in. silicon wafer, with an outer dimension of 9.80 (width) × 9.76 (length) cm$^2$. The sensor features two rows of LS strip segments, 4.83 cm strip length per segment, a strip pitch of 75.5 μm , and a slim edge design. We have implemented technology for high voltage operation of up to 1000 V, with a good signal collection after irradiation fluence of 5.6 × 10$^{14}$ n$_{eq}$∕cm$^2$ at the end of HL-LHC operation. We had two objectives for the ATLAS17LS fabrication: qualification of the sensor design and fabrication quality, and providing an adequate number of the sensors for prototyping the building blocks of the strip detector. The sensors were fabricated in 3 batches by HPK with standard wafers from the foundry (320 $\mu m$ physical thickness). Additional 10 sensors were fabricated with a thinner active thickness of 240 $\mu m$ to investigate the influence of active thickness on charge collection. Another additional 5 sensors, with special passivation to investigate the influence of passivation on humidity sensitivity. The visual inspection of fabricated sensors revealed an inadequacy that the designed metal width of 10 $\mu m$ was too narrow. The initial measurements by the vendor showed that the sensors fulfilled the specifications: onset voltages of Microdischarge $V_{MD}$ above the operation voltage $V_{OP}$ (700 V for the 1st and 2nd batches; 500 V for the 3rd batch, which has improved the yield), leakage currents of < 0.1 $\mu$A/cm$^2$ at $V_{OP}$, full depletion voltages $V_{FD}$ < 330 V, and rates of bad strips << 1%