Development of pixel sensors with 25 $\times$ 500$\mu$m$^2$ pitch for the ATLAS HL-LHC upgrade

Upgrade of the ATLAS tracker detector for high-luminosity LHC conditions requires novel approaches to the pixel sensor design. Tests of different pitch layouts represent significant part of the ATLAS upgrade program. Better momentum resolution and multiple track reconstruction in the r–ϕ plane could be achieved with finer ϕ-segmentation. Changing the pitch from 50×250μm2 to 25×500μm2 in the outer pixel modules would improve the tracking performance of the upgraded ATLAS detector. The pixel sensors with 25×500μm2 readout by FE-I4 chips have been designed at the University of Liverpool. The sensors were measured in the laboratory and test-beam. Results of these tests will be presented together with geometry characteristics of other novel pixel layouts, compatible with the FE-I4 floor-plan, which have been designed and produced.