Development of a radiation tolerant fine pitch planar pixel detector by HPK/KEK

In the recent development of pixel detectors for the inner part of the ATLAS detector upgrade of the High Luminosity LHC, a thin, typically 150 μm, planar pixel detector has been developed. To reduce hit occupancy, the pixel size is smaller compared to the currently operating pixel detector in ATLAS and the 2 pitch options, 50 μm×50μm and 25μm×100μm, are readout by the same 50μm×50μm pitch readout ASIC. To evaluate the performance of the fine pitch pixel detector, two methods are tested, a) emulated using the current ASIC (FE-I4) using non-uniform size of pixel, where two 50μm×250μm pixels are spitted to 50μm×50μm and 50μm×450μm, (b) used new ASIC (FE65p2) with full 50μm×50μm pitch. The FE65p2 is the prototype ASIC produced by TSMC using 65 nm CMOS process, with an expected lower noise than FE-I4. In this paper, basic devices performance and testbeam results before and after irradiation are presented.