Low-noise Readout Electronics Research Articles

Advances in High-Energy-Resolution CdZnTe Linear Array Pixel Detectors with Fast and Low Noise Readout Electronics.

Radiation detectors based on Cadmium Zinc Telluride (CZT) compounds are becoming popular solutions thanks to their high detection efficiency, room temperature operation, and to their reliability in compact detection systems for medical, astrophysical, or industrial applications. However, despite a huge effort to improve the technological process, CZT detectors' full potential has not been completely exploited when both high spatial and energy resolution are required by the application, especially at low energies (<10 keV), limiting their application in energy-resolved photon counting (ERPC) systems. This gap can also be attributed to the lack of dedicated front-end electronics which can bring out the best in terms of detector spectroscopic performances. In this work, we present the latest results achieved in terms of energy resolution using SIRIO, a fast low-noise charge sensitive amplifier, and a linear-array pixel detector, based on boron oxide encapsulated vertical Bridgman-grown B-VB CZT crystals. The detector features a 0.25-mm pitch, a 1-mm thickness and is operated at a -700-V bias voltage. An equivalent noise charge of 39.2 el. r.m.s. (corresponding to 412 eV FWHM) was measured on the test pulser at 32 ns peaking time, leading to a raw resolution of 1.3% (782 eV FWHM) on the 59 keV line at room temperature (+20 °C) using an uncollimated 241Am, largely improving the current state of the art for CZT-based detection systems at such short peaking times, and achieving an optimum resolution of 0.97% (576 eV FWHM) at 1 µs peaking time. The measured energy resolution at the 122 keV line and with 1 µs peaking time of a 57Co raw uncollimated spectrum is 0.96% (1.17 keV). These activities are in the framework of an Italian collaboration on the development of energy-resolved X-ray scanners for material recycling, medical applications, and non-destructive testing in the food industry.

Optimization of low-noise read-out electronics for high energy resolution X-ray strip detectors

Semiconductor strip sensors applied as solid-state radiation or particle detectors can be used in radiation detection and measurement for various applications in particle physics experiments, X-ray imaging (e.g. medical), or material science. The X-ray imaging devices with spectroscopic and position resolution features are a very important research topic at many institutes and companies worldwide. Short strip silicon detectors are good candidates for X-ray spectroscopy, because of their relatively small capacitance and leakage current. If additionally, strip pitch is below 100 μm, then the high spatial resolution is also possible. In this paper, the analysis and noise optimization of the read-out electronics for short silicon strip detectors with Charge Sensitive Amplifier (CSA) and shaping amplifier (shaper) is presented. The CSA is optimized for the detector capacitance of around 1.5 pF, and the shaper nominal peaking time is about 1 μs (controlled by the sets of switches). We take into account the sources of noise in a radiation imaging system (current parallel noise, voltage series noise, and 1/f or flicker series noise) both internal (related to the front-end electronics itself) but also external, stemming from a sensor, interconnect, or printed circuit board parasitic components. We target the noise level below 40 el. rms, considering low power consumption (a few mW) and limited channel area.

Cherenkov Radiation–Based Coincidence Time Resolution Measurements in BGO Scintillators

Bismuth germanate oxide (BGO) scintillators can be re-introduced in time-of-flight positron emission tomography (TOF-PET) by exploiting the Cherenkov luminescence emitted as a result from 511 keV interactions. Accessing the timing information from the relatively few emitted Cherenkov photons is now possible due to the recent improvements in enhanced near-ultraviolet high-density (NUV-HD) silicon photomultiplier (SiPM) technology, fast and low noise readout electronics, and the development of efficient data post-processing methods. In this work, we aim to develop a scalable detector element able to achieve excellent coincidence time resolution (CTR) required for TOF-PET using BGO scintillator elements of various lengths. The proposed detector element is optically coupled to 3.14 × 3.14 mm2 NUV-sensitive SiPMs mounted on a custom design circuit board. In particular, we have evaluated the CTR performance of BGO crystal elements of dimensions 3 × 3 × 3 mm3, 3 × 3 × 5 mm3, 3 × 3 × 10 mm3, and 3 × 3 × 15 mm3, with chemically etched surfaces and wrapped in Teflon tape. To achieve excellent CTR performance, we apply state-of-the-art post-processing methods during data analysis. Best values of 156 ± 6 ps, 188 ± 5 ps, 228 ± 8 ps, and 297 ± 8 ps CTR FWHM have been achieved for the 3, 5, 10, and 15 mm length BGO crystals, respectively. These values improve to 105 ± 6 ps, 127 ± 8 ps, 133 ± 4 ps, and 189 ± 8 ps CTR FWHM, when only considering the Cherenkov component of the timing signal, which is extracted by considering the events with the fastest rise time (20% of the total data). The accurate classification of the events based on their rise time is possible; thanks to the implementation of a dual threshold approach that sets the lower threshold below one light photon equivalent level and the upper one above the signal amplitude of a single photon avalanche diode (SPAD).

Microdosimetry in low energy proton beam at therapeutic-equivalent fluence rate with silicon 3D-cylindrical microdetectors

In this work we show the first microdosimetry measurements on a low energy proton beam with therapeutic-equivalent fluence rates by using the second generation of 3D-cylindrical microdetectors. The sensors belong to an improved version of a novel silicon-based 3D-microdetector design with electrodes etched inside silicon, which were manufactured at the National Microelectronics Centre (IMB-CNM, CSIC) in Spain. A new microtechnology has been employed using quasi-toroid electrodes of 25 μm diameter and a depth of 20 μm within the silicon bulk, resulting in a well-defined cylindrical radiation sensitive volume. These detectors were tested at the 18 MeV proton beamline of the cyclotron at the National Accelerator Centre (CNA, Spain). They were assembled into an in-house low-noise readout electronics to assess their performance at a therapeutic-equivalent fluence rate. Microdosimetry spectra of lineal energy were recorded at several proton energies starting from 18 MeV by adding 50 μm thick tungsten foils gradually at the exit-window of the cyclotron external beamline, which corresponds to different depths along the Bragg curve. The experimental values in silicon cover from (5.7 ± 0.9) to (8.5 ± 0.4) keV μm−1 in the entrance to (27.4 ± 2.3) keV μm−1 in the distal edge. Pulse height energy spectra were crosschecked with Monte Carlo simulations and an excellent agreement was obtained. This work demonstrates the capability of the second generation 3D-microdetectors to assess accurate microdosimetric distributions at fluence rates as high as those used in clinical centers in proton therapy.

Estimating the biological effects of helium, carbon, oxygen, and neon ion beams using 3D silicon microdosimeters

In this study, the survival fraction (SF) and relative biological effectiveness (RBE) of pancreatic cancer cells exposed to spread-out Bragg peak helium, carbon, oxygen, and neon ion beams are estimated from the measured microdosimetric spectra using a microdosimeter and the application of the microdosimetric kinetic (MK) model. To measure the microdosimetric spectra, a 3D mushroom silicon-on-insulator microdosimeter connected to low noise readout electronics (MicroPlus probe) was used. The parameters of the MK model were determined for pancreatic cancer cells such that the calculated SFs reproduced previously reported in vitro SF data. For a cuboid target of 10 × 10 × 6 cm3, treatment plans of helium, carbon, oxygen, and neon ion beams were designed using in-house treatment planning software (TPS) to achieve a 10% SF of pancreatic cancer cells throughout the target. The physical doses and microdosimetric spectra of the planned fields were measured at different depths in polymethyl methacrylate phantoms. The biological effects, such as SF, RBE, and RBE-weighted dose at different depths along the fields were predicted from the measurements. The predicted SFs at the target region were generally in good agreement with the planned SF from the TPS in most cases.

Performance evaluation of a new 30 μm thick GaAs x-ray detector grown by MBE

A circular mesa (400 μm diameter) GaAs p+-i-n+ photodiode with a 30 μm thick i layer was characterized for its performance as a detector in photon counting x-ray spectroscopy at 20 °C. The detector was fabricated from material grown by molecular beam epitaxy (MBE). An earlier MBE-grown detector fabricated using a different fabrication process and material from a different area of the same epiwafer was shown to suffer from: relatively high leakage current at high temperatures; a high effective carrier concentration that limited its depletion layer width; and material imperfections (butterfly defects) [Lioliou et al 2019 Nucl. Instrum. Methods Phys. Res. A 946 162670]. However, the new detector has better performance (lower leakage current and effective carrier concentration within the i layer). Using the new detector and low noise readout electronics, an energy resolution of 750 eV ± 20 eV Full Width at Half Maximum (FWHM) at 5.9 keV was achieved at 20 °C, equal to that reported for high quality GaAs detectors made from high quality material grown by metalorganic vapour phase epitaxy [Lioliou et al 2017 J. Appl. Phys. 122 244506]. The results highlight the substantially different performances of detectors made from the same epiwafer when the wafer qualities are not uniform and the effects of different fabrication processes.

Signal Readout Electronics for LEGEND-200

LEGEND (Large Enriched Germanium Experiment for Neutrinoless Double-Beta Decay) is a ton-scale experimental program to search for neutrinoless double beta (0vββ) decay using high-purity germanium detectors enriched in the isotope 76Ge. An observation of 0vββ decay would unequivocally prove the existence of lepton number violation and provide insight into the nature of neutrino masses.On-site construction for the first 200-kg phase (LEGEND-200) of the experiment will start at the Gran Sasso underground laboratory (Laboratory Nazionali del Gran Sasso, Italy) in mid-2020. In order to achieve a sensitivity of 1027 years on the 0vββ half-life, ultra-clean low-noise signal readout electronics are essential as they impact both the background budget of the experiment and the efficiency of background rejection. In this contribution, the current status of the signal readout electronics for LEGEND-200 is presented.

Data fusion methods for improving resolution from a gamma-ray scintillator network

Abstract Enhancements in gamma-ray spectral resolution have been realized through hardware development, including low-defect scintillation materials, solid-state detector technology, and low-noise read-out electronics. Enhanced resolution has also been provided by deconvoluting hardware response through the application of spectral unfolding techniques. However, fusing data from multiple independent measurements, both before and after spectral unfolding, to obtain more information than exists from a single measurement represents a largely unexplored path. This work provides a statistical foundation from which data acquired from an arbitrary number of independent gamma-ray spectra can be fused to yield higher resolution than the constituent measurements yield in isolation. Specifically, three data fusion techniques are considered: (i) pulse-height spectrum fusion, (ii) unfolded fluence linear opinion pool, and (iii) unfolded fluence logarithmic opinion pool. We explore the qualitative characteristics of these methods. We then apply them to spectra of thallium-doped sodium iodide [NaI(Tl)] and bismuth germanate (BGO), where all spectra are provided by MCNP simulations. Our results demonstrate improved resolution, thus establishing the methods as an inexpensive alternative to hardware upgrades. Moreover, our results demonstrate that these results have the potential to expand the capability of cutting-edge technology to provide currently unachievable resolution.

Wide Band Low Noise Love Wave Magnetic Field Sensor System

We present a comprehensive study of a magnetic sensor system that benefits from a new technique to substantially increase the magnetoelastic coupling of surface acoustic waves (SAW). The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top. The velocity of these so-called Love waves follows the magnetoelastically-induced changes of the shear modulus according to the magnetic field present. The SAW sensor is operated in a delay line configuration at approximately 150 MHz and translates the magnetic field to a time delay and a related phase shift. The fundamentals of this sensor concept are motivated by magnetic and mechanical simulations. They are experimentally verified using customized low-noise readout electronics. With an extremely low magnetic noise level of ≈100 pT/sqrt{{rm{Hz}}}, a bandwidth of 50 kHz and a dynamic range of 120 dB, this magnetic field sensor system shows outstanding characteristics. A range of additional measures to further increase the sensitivity are investigated with simulations.

Stand-Alone Stretchable Absolute Pressure Sensing System for Industrial Applications

A stand-alone stretchable absolute pressure sensing system has been proposed and demonstrated. This is the first step towards the development of an absolute pressure distribution monitoring system for industrial applications. The pressure sensing network can be fabricated in a cost-effective manner on silicon wafers and utilizes the advantages of microelectromechanical system technology. The sensor network possesses great stretchability, capable of being expanded to 10 000% times its original dimensions. Pressure sensing elements in the network have a sensitivity of about –0.14 mV/V/kPa. In addition, low-noise readout electronics, designed for signal conditioning, power management, and wireless communication, were implemented to realize the stand-alone absolute pressure sensor network. Furthermore, the stand-alone pressure sensing system prototype has been tested by measuring pressure at different locations in real time. Experimental measurements show good agreement with simulations and a commercial reference sensor. The sensor system can measure real-time mapping profiles of absolute pressure and has great potential for a variety of industrial applications.

Graphene-based tunable SQUIDs

The superconducting proximity effect in graphene can be used to create Josephson junctions with critical currents that can be tuned using local field-effect gates. These junctions have the potential to add functionality to existing technologies; for example, superconducting quantum interference device (SQUID) magnetometers with adaptive dynamic range and superconducting qubits with fast electrical control. Here, we present measurements of graphene-based superconducting quantum interference devices incorporating ballistic Josephson junctions that can be controlled individually. We investigate the magnetic field response of the SQUIDs as the junctions are gated and as the device is tuned between symmetric and asymmetric configurations. We find a highest transfer function ≈ 300 μV/Φ0, which compares favorably with conventional, low temperature DC SQUIDs. With low noise readout electronics and optimised geometries, devices based on ballistic graphene Josephson junctions have the potential to match the sensitivity of traditional SQUIDs while also providing additional functionality.

Development of cryogenic CMOS Readout ASICs for the Point-Contact HPGe Detectors for Dark Matter Search and Neutrino Experiments

The paper presents the developments of two cryogenic readout ASICs for the point-contact HPGe detectors for dark matter search and neutrino experiments. Extremely low noise readout electronics were demanded and the capability of working at cryogenic temperatures may bring great advantages. The first ASIC was a monolithic CMOS charge sensitive preamplifier with its noise optimized for ∼1 pF input capacitance. The second ASIC was a waveform recorder based on switched capacitor array. These two ASICs were fabricated in CMOS 350 nm and 180 nm processes respectively. The prototype chips were tested and showed promising results. Both ASICs worked well at low temperature. The preamplifier had achieved ENC of 10.3 electrons with 0.7 pF input capacitance and the SCA chip could run at 9 bit effective resolution and 25 MSPS sampling rate.

The XGS instrument on-board THESEUS

Consolidated techniques used for space-borne X-ray and gamma-ray instruments are based on the use of scintillators coupled to Silicon photo-detectors. This technology associated with modern very low noise read-out electronics allows the design of innovative architectures able to reduce drastically the system complexity and power consumption, also with a moderate-to-high number of channels. These detector architectures can be exploited in the design of space instrumentation for gamma-spectroscopy with the benefit of possible smart background rejection strategies. We describe a detector prototype with 3D imaging capabilities to be employed in future gamma-ray and particle space missions in the 0.002-100 MeV energy range. The instrument is based on a stack of scintillating bars read out by Silicon Drift Detectors (SDDs) at both ends. The spatial segmentation and the crystal double-side readout allow a 3D position reconstruction with ∼3 mm accuracy within the full active volume, using a 2D readout along the two external faces of the detector. Furthermore, one of the side of SDDs can be used simultaneously to detect X-rays in the 2-30 keV energy range. The characteristics of this instrument make it suitable in next generation gamma-ray and particle space missions for Earth or outer space observations, and it will be briefly illustrated.

Vertical nano superconducting quantum interference device based on Josepshon tunnel nanojunctions for small spin cluster detection

The ultra high sensitivity exhibited by Superconducting Quantum Interference Device (SQUIDs) could be the key to explore new field of nanoscience such as the investigation of small cluster of elementary magnetic moments. In this paper, an ultra high sensitive niobium nanoSQUID based on submicron Josephson tunnel junction is presented. It has been fabricated in a vertical configuration by using a three-dimensional focused ion beam sculpting technique. In such a configuration, the nanosensor loop (area of 0.25μm2) is perpendicular to the substrate plane allowing to drastically reduce the spurious effects of the external magnetic field employed to excite the nano-objects under investigation. Main device characteristics have been measured at T=4.2K by using a low noise readout electronics. Due to high voltage responsivity, the nanosensor has exhibited a spectral density of the magnetic flux noise as low as 1.6μΦ0/Hz1/2.

Capacitive detection of micrometric airborne particulate matter for solid-state personal air quality monitors

A novel microsensor for capacitive detection of particulate matter (PM) directly in air is presented. The feasibility of detecting single PM10 particles (calibrated 10μm polystyrene beads) by means of ad-hoc designed coplanar microelectrodes (4μm gap), a PDMS air deposition system, and a low-noise (∼2aF capacitive resolution) readout electronics is experimentally demonstrated. Finite element numerical simulations have been performed to optimize the design of the microelectrodes, investigate the detection limit and validate the experimental results. The real-time deposition on the sensor surface of sequences of single industrial talc particles (average diameter of ∼8μm, corresponding to a signal of ∼12aF) has been successfully tracked with 10ms temporal resolution and, subsequently, validated by microscope inspection. This CMOS- and MEMS-compatible capacitance detection technique enables radical miniaturization of next generation air quality monitors, paving the ways to their embedment in personal portable devices for pervasive mapping of air pollution.

Toward VIP-PIX: A Low Noise Readout ASIC for Pixelated CdTe Gamma-Ray Detectors for Use in the Next Generation of PET Scanners

VIP-PIX will be a low noise and low power pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) detectors. The proposed pixel will be part of a 2D pixel-array detector for various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. Each pixel will include a SAR ADC that provides the energy deposited with 10-bit resolution. Simultaneously, the self-triggered pixel which will be connected to a global time-to-digital converter (TDC) with 1 ns resolution will provide the event's time stamp. The analog part of the readout chain and the ADC have been fabricated with TSMC 0.25 μm mixed-signal CMOS technology and characterized with an external test pulse. The power consumption of these parts is 200 μW from a 2.5 V supply. It offers 4 switchable gains from ±10 mV/fC to ±40 mV/fC and an input charge dynamic range of up to ±70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 e- RMS at room temperature.

Specific HEMTs for deep cryogenic high-impedance ultra low low-frequency noise read-out electronics

For decades, high-impedance and low-frequency readout electronics with the lowest noise level is based on silicon JFETs (Junction Field-Effect Transistors) with an equivalent input noise voltage level of about 1 nV/Hz1/2 at 1 kHz. But their operating temperature is limited to be higher than 100 K due to their intrinsic structure. It is well known that HEMTs (High Electron Mobility Transistors) are intrinsically available for very low temperature operation, but conventional HEMTs suffer high gate leakage current and large channel low-frequency noise under cryogenic condition. In order to overcome these two major issues, we have extensively investigated the conventional HEMTs at 4.2 K by the bias-cooling method. At a given working point, the dependence of the channel low-frequency noise on the gate leakage current has been found out and this has allowed us to devise a new transistor structure. Specific AlGaAs/GaAs HEMTs have then been fabricated. At 4.2 K, our HEMTs can attain a noise level lower than 0.8 nV/Hz1/2 at 1k Hz with an intrinsic gain Aint of 26 and an input gate-source capacitance of 46 pF, and their gate leakage current can be limited about 1 pA This result shows that our specific HEMTs may be a suitable transistor for future ultra-low noise deep cryogenic high-impedance and low-frequency readout electronics.

Development of a bioinspired MEMS based capacitive tactile sensor for a robotic finger

This paper presents the development of a MEMS based capacitive tactile sensor intended to be incorporated into a tactile array as the core element of a biomimetic fingerpad. The use of standard microfabrication technologies in realising the device allowed a cost efficient fabrication involving only a few process steps. A low noise readout electronics system was developed for measuring the sensor response. The performance of both bare and packaged sensors was evaluated by direct probing of individual capacitive sensor units and characterising their response to load–unload indentation cycles.

Readout ASICs for silicon drift detectors

Semiconductor drift detectors (SDDs) are widely used in X-ray spectroscopy due to their excellent performances in terms of energy resolution and detection-rate. Suitable low noise readout electronics have to be designed in order to exploit the SDD intrinsic performances. The integration of this electronics in custom application specific integrated circuits (ASICs) is mandatory when the compactness of the detection system (detector and electronics) and the need to read out multi-elements SDDs are primary requirements. This work describes the development of three circuits for SDDs, which are a charge sensitive preamplifier operating in the pulsed reset regime, a fast shaping amplifier for high-count rates applications and a multi-channel ASIC that provides the whole analog processing and multiplexing of the signals from SDD arrays. The ASICs have been tested with SDDs with on-chip JFET and the results are presented here.

Charge Collection Efficiency Measurements of Heavily Irradiated Segmented n-in-p and p-in-n Silicon Detectors for Use at the Super-LHC

The planned luminosity upgrade of the Large Hadron Collider at CERN (Super-LHC) will provide a challenging environment for the tracking and vertexing detector systems. With a proposed nearly 10-fold luminosity increase to 1035 cm2 middot s-1, the innermost devices will have to be able to withstand a hadron dose on the order of 1times1016 1 MeV neutron equivalent per square centimeter over the anticipated five year lifetime of the experiments. Planar, segmented silicon detectors with n-strip readout are one of the radiation tolerant technologies under consideration for use for the Super-LHC tracking detectors in either pixel or strip geometries. This paper details measurements made with n-strip (n-in-p) and p-strip (p-in-n) planar devices that have been irradiated to doses as high as 1times1016 neq cm-2 with reactor neutrons and fast protons. The doses under study cover the expected range of final fluences for the different tracking systems of the ATLAS and CMS experiments at the Super-LHC. The charge collection measurements have been carried out using analogue, high-speed (40 MHz) electronics and a Strontium electron source. These measurements show that p-in-n sensors are not radiation tolerant enough for the requirements of the micro-strip detectors at the SLHC; whereas, the charge collection properties exhibited by the n-in-p strip devices may be sufficient for all tracker regions (pixels and strips) of the SLHC assuming that appropriate low noise and threshold readout electronics are designed and adequate bias voltage can be routed to the sensors.