22-26 January 2018
Bormio, Italy
Europe/Berlin timezone

The micro-RWELL technology: status and perspectives

23 Jan 2018, 18:05
Bormio, Italy

Bormio, Italy

Short Contribution Applications and Instrumentations Tuesday Afternoon


Dr Gianfranco Morello (Laboratori Nazionali di Frascati dell'INFN)


The micro-Resistive-WELL (μ-RWELL) has been conceived as a compact, simple and robust Micro-Pattern Gaseous Detector (MPGD) for large area HEP applications requiring the operation in harsh environment. The detector amplification stage is realized with a polyimide structure micro-patterned with a blind-hole matrix, embedded through a thin Diamond Like Carbon (DLC) resistive layer in the readout PCB. The DLC surface resistivity, typically in the range 10÷200 MOhm/square, affects the detector performance. The introduction of the resistive layer, mitigating the transition from streamer to spark, gives the possibility to achieve large gains (> 10$^4$). Different detector 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 30-40 kHz/cm$^2$); while more sophisticated schemes are under study for high-rate purposes (up to 2-3 MHz/cm$^2$). The single-resistive layer scheme has been extensively tested and validated and it is substantially ready for applications in HEP (CMS, LHCb, SHiP), as well as for non-HEP applications (ERM network for EURDEP). In this review of the R&D activity, after an introduction on the principle of operation of the detector we will give an overview of the performance mainly measured with single-resistive layer detectors: gain, space and time resolution, rate capability, aging studies. In particular concerning the space performance of the detector we will discuss the preliminary results of a recent analysis based on the micro-TPC mode, that combined with the classical charge-centroid method will lead to a uniform space resolution in the range 100÷150 µm, for non-orthogonal tracks and/or in presence of an high magnetic field (up to 1 T). An overview of the different architectures under study for the high rate version of the detector will be eventually presented.


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.

Primary author

Dr Giovanni Bencivenni (LNF-INFN)


Prof. Atsuhiko Ochi (Kobe Univeristy) Dr Gianfranco Morello (Laboratori Nazionali di Frascati dell'INFN) Dr Marco Poli Lener (LNF-INFN) Dr Maurizio Gatta (LNF-INFN) Dr Rui de Oliveira (CERN-CH)

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