| The discovery of Higgs boson opens a new era of particle physics.The precision measurements of Higgs boson will be one of the most important themes of the experimental particle physics in the next decades.The new physics goal gives higher requirements on particle detectors,tracking devices especially.For example,the Circular Electron Positron Collider(CEPC)program,proposed in 2012,gives requirements on spatial resolution,better than 3μm,and on material budget,less than 0.9%X0,for vertex detector in the baseline detector design.For inner silicon tracker,the values are 7μm and 3.9%X0.A CMOS pixel sensor,named Supix-1,is developed in Shandong University to explore the feasibility of CMOS pixel sensor with large pixels for CEPC silicon tracker.The chip has been designed and taped out.The simulation and test work also have been carried out.Supix-1 is fabricated on Tower Jazz 180 nm CMOS Image Sensor process with pixel pitches up to 21 μm × 84μm.In order to investigate the detection capability of the sensor,3D Technology Computer Aided Design(TCAD)simulations have been performed to extract the depletion zone profile,the diode leakage and the diode capacitance of Supix-1.3D transient simulations have also been carried out to study the charge collection and charge sharing of pixels.Furthermore,the non-ionizing energy loss(NIEL)effects on Supix-1 under the fluence of 1 × 1013 1 MeV neq/cm2 has been conducted.The geometry of the pixel diode has been optimized according to the simulation.Supix-2 is another CMOS pixel sensor with large pixels based on SMIC 0.18μm process.Pixels in Supix-2 are designed to be full-filled by the collecting diode according to the technology.The properties of Supix-2 on diode leakage and capacitance have been studied carefully via TCAD simulations.The sensor has been designed and taped out,in which the geometries of the diodes were optimized via TCAD.Supix-1 has been tested.with the radioactive source of 55Fe.This article will focus on the test system and on the offline analysis.The test system consists of the readout electronics based on FPGA and the data acquisition system which is based on ROOT framework.The sensor gain of Supix-1 has been calibrated using the radioactive source of 55Fe.The pixel-wise equivalent noise charge,the charge collection efficiency and the signal-to-noise ratio are then measured.Besides,a cluster reconstruction algorithm has been developed and the cluster properties have been studied.The test results demonstrate that it is feasible to use the enlarged pixels for charged particle tracking.The radiation hardness performance is essential for the CMOS pixel sensor in a colliding environment.In order to study the bulk damage scaled by Non-Ionizing Energy Loss on Supix-1,the sensor has been irradiated under the total fluence of 1.16 ×1013 1 MeV nep/cm2 at China Spallation Neutron Source.The irradiated sensor has been tested again with 55Fe under the same condition as that before irradiation.Though suffering degradations on sensor performance,Supix-1 is still potential for tracking on a future collider.The radiation hard design of Supix-1 is optimized according to the TCAD simulation and the radioactive source test.The upgrade of BESⅢ inner chamber based on ultra-thin(50μm)CMOS pixel sensor has been proposed by Shandong University and Institute of High Energy Physics Chinese Academy of Science.The simulation and reconstruction on the pixelated inner chamber with the ultra-thin CMOS pixel sensor are conducted,based on the BESIII software framework.Simulations and reconstructions for the CGEM detector,the traditional CMOS pixel sensor(350μm)and the existing Main Drift Chamber are also carried out,for comparison.The ultra-thin CMOS pixel sensor performs best both in position and momentum resolution.The pixel pitch for the ultra-thin CMOS pixel sensor is 30 × 200μm2 considering the readout and power consumption.The geometry of the pixel has been optimized,via TCAD,to improve the charge collection efficiency for such large configuration. |
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