The micro-resistive WELL (µ-RWELL) detector is a compact, spark-protected, single amplification stage Micro-Pattern Gas Detector (MPGD). This new architecture exploits several solutions and improvements implemented in the last years for MPGDs, in particular for GEMs and Micromegas. The µ-RWELL, based on the resistive technology concept leading to efficient spark quenching, is a high reliable device. In addition, since it does not require any complex and time-consuming assembly procedures (neither stretching nor gluing), it becomes extremely simple to be assembled.
The detector is composed by only two elements, i.e. the readout-PCB embedded with the amplification stage (the core of the detector, named µ-RWELL_PCB) and the cathode. The amplification stage of the detector, realized by photolithography as a matrix of wells (with a pitch of 140 µm and a diameter of 60-70 µm) on a 50 µm thick polyimide substrate, is embedded through a resistive layer with the readout board.
The resistive layer can be realized by means DLC (Diamond Like Carbon) sputtering technology. The surface resistivity, typically ranging from tens to hundreds MΩ/square, is a crucial parameter that must be optimized as a function of detector performance. A cathode electrode, defining the gas conversion-drift gap, completes the detector mechanics.
Different resistive layouts have been studied: the most simple one, based on a single-resistive layer with edge grounding, has been designed for low-rate applications (up to tens of kHz/cm$^2$); while more sophisticated schemes are under study for high-rate purposes (up to few MHz/cm$^2$).
The R&D on single-resistive layer layout has been practically completed while different solutions for the high rate applications are still under studies.
The detector has been fully characterized on test bench with X-rays as well as on several beam test at CERN: the device operated in a safe mode at a gas gain >10$^4$ exhibits a space resolution better than 100 µm (for orthogonal tracks, B = 0T and charge-centroid method) and a time resolution of the order of 5 ns.
By combining the charge-centroid method with the new micro-TPC algorithm (based on the recording of the charge and arrival time of the ionization clusters produced along the track in the drift gap) a uniform space resolution in the range 100÷150 µm has been obtained, for non-orthogonal tracks in presence of a high magnetic field (up to 1 T).
A detailed description of the different resistive layouts proposed for the high rate version of the detector together with the discussion of their performance in terms of gain, efficiency and rate capability will be reported.
The µ-RWELL technology, under development with European industrial partners, is suitable for large area tracking devices and can be exploited as active device in digital hadron calorimetry in HEP experiments: the detector, proposed for the phase-2 upgrade of CMS and LHCb muon apparatus as well as for the neutrino detector of the SHIP experiment, is a technology suitable also for the muon apparatus at future colliders (CEPC, SppC and FCC – ee/hh).
A possible use in non-HEP applications as a detector for radioactive contamination of the environment in the framework of the Environmental Radiation Monitoring (ERM) networks for EURDEP is under investigation. Such an application requires for the development of large area/volume detectors to replace legacy Geiger-Müller and proportional counters which are typically used since about 50 years.