Development of a Technology needed for the PIXel particle detectors – DoTPIX

For future particle detectors it will be necessary to integrate internal sub-detectors, which will allow the precise reconstruction of the trajectories of charged particles very close to the interaction point. In e+e- colliders (e.g. the ILC), we propose to simplify the proposed MAPS (Monolithic Active Pixel Sensors) pixel detectors, which are based on three transistors and a photodiode, by reducing them to 1T (one transistor). Additionally drastic improvements in spatial resolution can be made by reducing the pixel size to less than 1 µm2. The other advantage is the ability to resolve multiplicities, multiple hits in a single pixel that may occurs in larger pixels. For this purpose, we want to realize a Ge quantum box in a 1T pixel, which collects the charges generated by the charged particle tracks and modulates the readout current of the 1T device. With the bottom-up project, in 2020-2021 (now finished) we studied UHV/CVD epitaxy of Ge on Si as a first step for an NMOS structure. 2D Ge growth on silicon substrate was obtained, with a final Ge layer of 20 nm presenting a very low roughness (0.25 nm), despite the presence of dislocations at the Si/Ge interface generating defects stacking in the thickness of the layer. Recently, the C2N SEEDs team also demonstrated the feasibility of Si (25nm)/Ge (21 nm)/Si sandwich structures with a Ge composition up to 95% and with a decrease in the density of defects in the Ge layer. Intermixing studies due to thermal anneal are also necessary to assess the compatibility of the buried Ge with CMOS processes. We also plan to use gate dielectrics like HfO2 to reduce the thermal budget. R&D on the technology and materials necessary for the realization of this device should prove the practical feasibility of this pixel simulated as a device five years ago. Prototype pixel arrays fabricated at C2N for the substrate and LAAS for the MOS process will be characterized in order to know their performance as charged particle and X-photon detector at the final step of this development.