Development of novel n⁺-in-p Silicon Planar Pixel Sensors for HL-LHC

We have been developing highly radiation-tolerant n⁺-in-p planar pixel sensors for use in the high-luminosity LHC. Novel n⁺-in-p structures were made using various combinations of the bias structures (punch-through or polysilicon resistor), isolation structures (p-stop or p-spray), and thicknesses (320μm or 150μm). The 1-chip pixel modules with thin FE-I4 pixel sensors were evaluated using test beams, before and after 2×10^15neq/^cm2 irradiation. The full depletion voltages were estimated to be 44±10 V and 380±70 V, in the non-irradiated and the irradiated modules, respectively. A reduction of efficiency was observed in the vicinity of the four pixel corners and underneath the bias rail after the irradiation. The global efficiencies were >99% and >95% in the non-irradiated and the irradiated modules, respectively. The collected charges were uniform in the depth direction at bias voltages well above the full depletion voltages. The encapsulation of vulnerable edges with adhesive or parylene prevented HV sparking. Bump bonding with the SnAg solder bumps was performed at HPK with 150μm- and 320μm-thick sensors and chips. No disconnection of bumps was observed after 10 thermal cycles between -40 and +50 °C, with a temperature slew rate of >70K/min.