Charge Readout Research Articles

Prototype readout system for a multi Mpixels UV single-photon imaging detector capable of space flight operation

Our collaboration works on the development of a large aperture, high resolution, UV single-photon imaging detector, funded through NASA's Strategic Astrophysics Technology (SAT) program. The detector uses a microchannel plate for charge multiplication, and orthogonal cross strip (XS) anodes for charge readout. Our target is to make an advancement in the technology readiness level (TRL), which enables real scale prototypes to be tested for future NASA missions. The baseline detector has an aperture of 50×50 mm and requires 160 low-noise charge-sensitive channels, in order to extrapolate the incoming photon position with a spatial resolution of about 20 μm FWHM. Technologies involving space flight require highly integrated electronic systems operating at very low power. We have designed two ASICs which enable the construction of such readout system. First, a charge sensitive amplifier (CSAv3) ASIC provides an equivalent noise charge (ENC) of around 600 e−, and a baseline gain of 10 mV/fC. The second, a Giga Sample per Second (GSPS) ASIC, called HalfGRAPH, is a 12-bit analog to digital converter. Its architecture is based on waveform sampling capacitor arrays and has about 8 μs of analog storage memory per channel. Both chips encapsulate 16 measurement channels. Using these chips, a small scale prototype readout system has been constructed on a FPGA Mezzanine Board (FMC), equipped with 32 measurement channels for system evaluation. We describe the construction of HalfGRAPH ASIC, detector's readout system concept and obtained results from the prototype system. As part of the space flight qualification, these chips were irradiated with a Cobalt gamma-ray source, to verify functional operation under ionizing radiation exposure.

A pixelated charge readout for Liquid Argon Time Projection Chambers

Liquid Argon Time Projection Chambers (LArTPCs) are ideally suited to perform long-baseline neutrino experiments aiming to measure CP violation in the lepton sector, and determine the ordering of the three neutrino mass eigenstates. LArTPCs have used projective wire readouts for charge detection since their conception in 1977. However, wire readouts are notoriously fragile and therefore a limiting factor in the design of any large mass detectors. Furthermore, a wire readout also introduces intrinsic ambiguities in event reconstruction. Within the ArgonCube concept—the liquid argon component of the DUNE near detector—we are developing a pixelated charge readout for LArTPCs. Pixelated charge readout systems represent the single largest advancement in the sensitivity of LArTPCs. They are mechanically robust and provide direct 3D readout, serving to minimise reconstruction ambiguities, enabling more advanced triggers, further reducing event pile-up and improving background rejection. This article presents first results from a pixelated LArTPC prototype built and operated in Bern.

Radiation imaging with optically read out GEM-based detectors

Modern imaging sensors allow for high granularity optical readout of radiation detectors such as MicroPattern Gaseous Detectors (MPGDs). Taking advantage of the high signal amplification factors achievable by MPGD technologies such as Gaseous Electron Multipliers (GEMs), highly sensitive detectors can be realised and employing gas mixtures with strong scintillation yield in the visible wavelength regime, optical readout of such detectors can provide high-resolution event representations. Applications from X-ray imaging to fluoroscopy and tomography profit from the good spatial resolution of optical readout and the possibility to obtain images without the need for extensive reconstruction. Sensitivity to low-energy X-rays and energy resolution permit energy resolved imaging and material distinction in X-ray fluorescence measurements. Additionally, the low material budget of gaseous detectors and the possibility to couple scintillation light to imaging sensors via fibres or mirrors makes optically read out GEMs an ideal candidate for beam monitoring detectors in high energy physics as well as radiotherapy. We present applications and achievements of optically read out GEM-based detectors including high spatial resolution imaging and X-ray fluorescence measurements as an alternative readout approach for MPGDs. A detector concept for low intensity applications such as X-ray crystallography, which maximises detection efficiency with a thick conversion region but mitigates parallax-induced broadening is presented and beam monitoring capabilities of optical readout are explored. Augmenting high resolution 2D projections of particle tracks obtained with optical readout with timing information from fast photon detectors or transparent anodes for charge readout, 3D reconstruction of particle trajectories can be performed and permits the realisation of optically read out time projection chambers. Combining readily available high performance imaging sensors with compatible scintillating gases and the strong signal amplification factors achieved by MPGDs makes optical readout an attractive alternative to the common concept of electronic readout of radiation detectors. Outstanding signal-to-noise ratios and robustness against electronic noise allow unprecedented imaging capabilities for various applications in fields ranging from high energy physics to medical instrumentation.

Imaging Demonstration of a Glass Gas Electron Multiplier with Electronic Charge Readout

We have developed a Glass Gas Electron Multiplier (Glass GEM, G-GEM), which is composed of two copper electrodes separated by a photosensitive etchable glass substrate having holes arranged in a hexagonal pattern. In this paper, we report the result of imaging using a G-GEM combined with a 2D electronic charge readout. We used a crystallized photosensitive etchable glass as the G-GEM substrate. A precise X-ray image of a small mammal was successfully obtained with position resolutions of approximately 110 to 140 μm in RMS.

Performance of a MICROMEGAS-based TPC in a high-energy neutron beam

The MICROMEGAS (MICRO-MEsh GAseous Structure) charge amplification structure has found wide use in many detection applications, especially as a gain stage for the charge readout of Time Projection Chambers (TPCs). Here we report on the behavior of a MICROMEGAS TPC when operated in a high-energy (up to 800MeV) neutron beam. It is found that neutron-induced reactions can cause discharges in some drift gas mixtures that are stable in the absence of the neutron beam. The discharges result from recoil ions close to the MICROMEGAS that deposit high specific ionization density and have a limited diffusion time. For a binary drift gas, increasing the percentage of the molecular component (quench gas) relative to the noble component and operating at lower pressures generally improves stability.

Characterisation of large area THGEMs and experimental measurement of the Townsend coefficients for CF4

Whilst the performance of small THGEMs is well known, here we consider the challenges in scaling these up to large area charge readouts. We first verify the expected gain of larger THGEMs by reporting experimental Townsend coefficients for a 10 cm diameter THGEM in low-pressure CF4. Large area 50 cm by 50 cm THGEMs were sourced from a commercial PCB supplier and geometrical imperfections were observed which we quantified using an optical camera setup. The large area THGEMs were experimentally characterised at Boulby Underground Laboratory through a series of gain calibrations and alpha spectrum measurements. ANSYS, Magboltz and Garfield++ simulations of the design of a TPC based on the large area THGEMs are presented. We also consider their implications for directional dark matter research and potential applications within nuclear security.

Measurement of the directional sensitivity of Dark Matter Time Projection Chamber detectors

The Dark Matter Time Projection Chamber (DMTPC) is a direction-sensitive detector designed to measure the direction of recoiling $^{19}$F and $^{12}$C nuclei in low-pressure CF$_4$ gas using optical and charge readout systems. In this paper, we employ measurements from two DMTPC detectors, with operating pressures of 30-60 torr, to develop and validate a model of the directional response and performance of such detectors as a function of recoil energy. Using our model as a benchmark, we formulate the necessary specifications for a scalable directional detector with sensitivity comparable to that of current-generation counting (non-directional) experiments, which measure only recoil energy. Assuming the performance of existing DMTPC detectors, as well as current limits on the spin-dependent WIMP-nucleus cross section, we find that a 10-20 kg scale direction-sensitive detector is capable of correlating the measured direction of nuclear recoils with the predicted direction of incident dark matter particles and providing decisive (3$\sigma$) confirmation that a candidate signal from a non-directional experiment was indeed induced by elastic scattering of dark matter particles off of target nuclei.

PandaX-III: Searching for neutrinoless double beta decay with high pressure 136Xe gas time projection chambers

Searching for the Neutrinoless Double Beta Decay (NLDBD) is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments. PandaX-III (Particle And Astrophysical Xenon Experiment III) will search for the NLDBD of $^{136}$Xe at the China Jin Ping underground Laboratory (CJPL). In the first phase of the experiment, a high pressure gas Time Projection Chamber (TPC) will contain 200 kg, 90% $^{136}$Xe enriched gas operated at 10 bar. Fine pitch micro-pattern gas detector (Microbulk Micromegas) will be used at both ends of the TPC for the charge readout with a cathode in the middle. Charge signals can be used to reconstruct tracks of NLDBD events and provide good energy and spatial resolution. The detector will be immersed in a large water tank to ensure $\sim$5 m of water shielding in all directions. The second phase, a ton-scale experiment, will consist of five TPCs in the same water tank, with improved energy resolution and better control over backgrounds.

Characterization of the column-based priority logic readout of Topmetal-II− CMOS pixel direct charge sensor

We present the detailed study of the digital readout of Topmetal-II- CMOS pixel direct charge sensor. Topmetal-II- is an integrated sensor with an array of 72×72 pixels each capable of directly collecting external charge through exposed metal electrodes in the topmost metal layer. In addition to the time-shared multiplexing readout of the analog output from Charge Sensitive Amplifiers in each pixel, hits are also generated through comparators in each pixel with individually adjustable thresholds. The hits are read out via a column-based priority logic structure, retaining both hit location and time information. The in-array column-based priority logic features with a full clock-less circuitry hence there is no continuously running clock distributed in the pixel and matrix logic. These characteristics enable its use as the charge readout device in future Time Projection Chambers without gaseous gain mechanism, which has unique advantages in low background and low rate-density experiments. We studied the detailed working behavior and performance of this readout, and demonstrated its functional validity and potential in imaging applications.

Communication—Silicon Narrow-Band Solar-Blind Ultraviolet Detector Based on Ag-SiO2-Si Capacitor

Solar-blind narrow-band silicon ultraviolet photodetectors based on metal-oxide-semiconductor (MOS) capacitors with silver gate are presented. A very high selectivity was obtained using silver as the band-pass filter. An optimal relationship between the layer and silver film thicknesses was found to obtain a spectral response with a bandwidth of 20 nm at 320 nm and four/five orders rejection factor for the rest of the spectrum. Capacitors operate in non-equilibrium inversion mode that allows to obtaining an internal amplification of photocurrent, up to106, for a weak input optical signal due to a time compression between the charge storage and readout operating modes.

EXO-200 results and cosmogenic backgrounds

Status update and recent results from the double beta decay search experiment EXO-200 are presented. Detector is a liquid xenon TPC with charge and light readout located underground in low-background laboratory at 1600 m.w.e. depth. It contains 175 kg of xenon with 80.6% abundance of 136Xe, which acts as both the decaying nucleus and detection medium. Detector showed good performance and achieved remarkable results. The detector has demonstrated excellent energy resolution and background rejection capabilities and has set a lower limit on the 0νββ-decay half-life of 1.1 × 1025 years at 90% C.L. in early 2014. The EXO-200 collaboration has since published several papers on experimental backgrounds and searches for rare or exotic processes. After a two-year data interruption, EXO-200 is now back online with significant hardware improvements, including a radon reduction air system and a front end electronics upgrade for better energy resolution.

Directional dark matter detection with the DMTPC m3 experiment

Directional reconstruction provides a unique way to positively identify signal interactions induced by dark matter particles, owing to the motion of the Earth through the galactic dark matter halo. Directional information can additionally serve as a powerful discriminant against neutron (and neutrino-induced) backgrounds that have the same final-state signature as a signal interaction. The Dark Matter Time Projection Chamber (DMTPC) collaboration uses gas-based TPC technology, with both optical and charge readout, to measure the directional anisotropy of nuclear recoils induced by particles traversing the detector volume. Here, we present preliminary results from recent calibration runs of the DMTPC m3 detector in a surface laboratory, as well as a study of its projected directional sensitivity.

The DEPFET Sensor-Amplifier Structure: A Method to Beat 1/f Noise and Reach Sub-Electron Noise in Pixel Detectors.

Depleted field effect transistors (DEPFET) are used to achieve very low noise signal charge readout with sub-electron measurement precision. This is accomplished by repeatedly reading an identical charge, thereby suppressing not only the white serial noise but also the usually constant 1/f noise. The repetitive non-destructive readout (RNDR) DEPFET is an ideal central element for an active pixel sensor (APS) pixel. The theory has been derived thoroughly and results have been verified on RNDR-DEPFET prototypes. A charge measurement precision of 0.18 electrons has been achieved. The device is well-suited for spectroscopic X-ray imaging and for optical photon counting in pixel sensors, even at high photon numbers in the same cell.

KLauS: a low power Silicon Photomultiplier charge readout ASIC in 0.18 UMC CMOS

We present the development of a low power Silicon Photomultiplier charge readout ASIC for an imaging calorimeter at a future linear collider. The analog front-end is designed to achieve sufficient signal-to-noise ratio for single pixel signals using low gain SiPMs, while allowing charge measurements over the full dynamic range of the sensors. The front-end consists of an input stage, two charge measurement branches and a fast comparator. A SAR ADC with a resolution of 10 bit digitizes the pulse height information. An additional pipelined SAR stage allows to increase the quantization resolution to 12 bit for calibration measurements.

Gate-Sensing Coherent Charge Oscillations in a Silicon Field-Effect Transistor.

Quantum mechanical effects induced by the miniaturization of complementary metal-oxide-semiconductor (CMOS) technology hamper the performance and scalability prospects of field-effect transistors. However, those quantum effects, such as tunneling and coherence, can be harnessed to use existing CMOS technology for quantum information processing. Here, we report the observation of coherent charge oscillations in a double quantum dot formed in a silicon nanowire transistor detected via its dispersive interaction with a radio frequency resonant circuit coupled via the gate. Differential capacitance changes at the interdot charge transitions allow us to monitor the state of the system in the strong-driving regime where we observe the emergence of Landau-Zener-Stückelberg-Majorana interference on the phase response of the resonator. A theoretical analysis of the dispersive signal demonstrates that quantum and tunneling capacitance changes must be included to describe the qubit-resonator interaction. Furthermore, a Fourier analysis of the interference pattern reveals a charge coherence time, T2 ≈ 100 ps. Our results demonstrate charge coherent control and readout in a simple silicon transistor and open up the possibility to implement charge and spin qubits in existing CMOS technology.

Developing LAr scintillation light collection ideas in the Short Baseline Neutrino Detector

Scintillation light is becoming the most rapidly developing feature of Liquid Argon Time Projection Chamber (LArTPC) neutrino detectors due to its capability to enhance and expand their physics reach traditionally based on charge readout. The SBND detector, set to be built on the Booster Neutrino Beam Line at Fermilab, is in a unique position to test novel liquid argon scintillation light readout systems in a detector with physics neutrino events. The different ideas under consideration by the collaboration are described, including an array of PMTs detecting direct light, SiPM coupled lightguide bars and a setup which uses PMTs/SiPMS and wavelength shifter covered reflector foils, as well as their respective strengths and physics foci and the benchmarks used to compare them.

A low-noise CMOS pixel direct charge sensor, Topmetal-II-

We report the design and characterization of a CMOS pixel direct charge sensor, Topmetal-II-, fabricated in a standard 0.35μm CMOS Integrated Circuit process. The sensor utilizes exposed metal patches on top of each pixel to directly collect charge. Each pixel contains a low-noise charge-sensitive preamplifier to establish the analog signal and a discriminator with tunable threshold to generate hits. The analog signal from each pixel is accessible through time-shared multiplexing over the entire array. Hits are read out digitally through a column-based priority logic structure. Tests show that the sensor achieved a <15e− analog noise and a 200e− minimum threshold for digital readout per pixel. The sensor is capable of detecting both electrons and ions drifting in gas. These characteristics enable its use as the charge readout device in future Time Projection Chambers without gaseous gain mechanism, which has unique advantages in low background and low rate-density experiments.

Recent R&D results on LAr LEM TPC and plans for LBNO demonstrators

The double phase Liquid Argon (LAr) Time Projection Chamber (TPC) is the state-of-art technology for neutrino detection thanks to its superb 3 Dimensional (3D) tracking and calorimetry performance. Based on this technology, the Giant Liquid Argon Charge Imaging ExpeRiment (GLACIER) is proposed to be the far detector for the Long Baseline Neutrino Oscillation (LBNO) experiment aiming at studying neutrinos 2300 km away from their production point. We report recent R&D results on the charge readout system for GLACIER and the plans to build the GLACIER demonstrators at CERN.

Fast probe of local electronic states in nanostructures utilizing a single-lead quantum dot.

Transport measurements are powerful tools to probe electronic properties of solid-state materials. To access properties of local electronic states in nanostructures, such as local density of states, electronic distribution and so on, micro-probes utilizing artificial nanostructures have been invented to perform measurements in addition to those with conventional macroscopic electronic reservoirs. Here we demonstrate a new kind of micro-probe: a fast single-lead quantum dot probe, which utilizes a quantum dot coupled only to the target structure through a tunneling barrier and fast charge readout by RF reflectometry. The probe can directly access the local electronic states with wide bandwidth. The probe can also access more electronic states, not just those around the Fermi level, and the operations are robust against bias voltages and temperatures.

Measurement of the Cosmic Ray spectra by the ARGO-YBJ experiment

Exploiting the features and location at high altitude (the Cosmic Ray Observatory of Yangbajing in Tibet, China, at about 4,300 m a.s.l.) of the ARGO-YBJ detector, the study of several aspects concerning cosmic ray physics in the primary energy region 1012–1016 eV has been performed. Here, the preliminary results of the measurement of all-particle and light-component (i.e. protons and helium nuclei) energy spectra between few tens TeV and ∼5 PeV will be reported, as obtained from the data of RPC (Resistive Plate Chamber) analog charge readout. The study of such energy region is particularly important to better understand the so called knee of the energy spectrum and its origin, as well as for a powerful cross-check among very different experimental techniques, like balloon/space-borne spectrometers and surface air shower detectors. It also allows to test the hadronic interaction models currently used for investigating particle and cosmic ray physics up the highest energies. Finally, the precise measurements of the cosmic ray energy spectrum and composition make possible a more reliable estimation of the atmospheric neutrino flux, which is crucial for any extra-terrestrial neutrino search.