Collector Electrode Research Articles

The Topmetal-CEE prototype, a direct charge sensor for the beam monitor of the CSR external-target experiment

The Cooler-Storage-Ring External-target Experiment (CEE) which is being constructed since 2020 is a spectrometer to study the properties of nuclear matter at high baryon density region. We present the design and simulation results of a sensor named Topmetal-CEE which is being developed for an online beam monitor of the CEE. A prototype of the Topmetal-CEE has been designed in a standard CMOS 130 nm process and is being fabricated. The Topmetal-CEE prototype has 180 channels with a pitch of 100 μm. In each channel, electrons are collected by a charge collection electrode which is a top-most metal exposed to the surrounding media, amplified by a charge sensitive amplifier, and then fed into a discriminator. The output of the discriminator is split into two paths which record Time of Arrival (ToA) and Time over Threshold (ToT) of the collected signal, respectively. In order to reduce the dead time, 180 channels are split into two separate parts and then the information in each part is read out by a data-driving priority readout scheme independently. Each channel has its own address encoded by an address encoder. The ToA, ToT and address of each channel are framed and encoded, and then transferred off chip with a serial speed of 4.4 Gbps.

A novel front-end amplifier for gain-less charge readout in high-pressure gas TPC

This paper presents a novel low-noise front-end amplifier manufactured in a standard 130 nm CMOS process. The front-end amplifier is part of an integrated sensor, with an array of which, forms a charge readout plane in a high-pressure gaseous Time Projection Chamber (TPC) for 0νββ search. The novel front-end amplifier composed of a source-drain follower and a common-source amplifier is proposed. The potential of both the source and drain node of the input transistor follows its gate. Hence the effective input capacitance contributed by the input transistor is significantly reduced. A hexagon charge collection electrode with a diameter of 1 mm is connected to the input node of the front-end amplifier. The shielding technique is applied and the shielding metal is connected to the source or drain node of the input transistor. Therefore, the effective input capacitance contributed by the charge collection electrode is decreased. The extraction result shows that the input capacitance is decreased from the 4 pf down to 7.4 fF. A test chip has been designed and an equivalent noise charge of 33 e− is achieved from the simulations.

Easy fabrication of performant and broadband response SnS/Si photodetector

Broad response band photodetectors from ultraviolet (UV) to infrared (IR) range have attracted much attention in environmental monitoring, telecommunications, and thermal imaging. In this study, a simple method is proposed to fabricate photodetectors based on graphene/stannous sul-fide/silicon (Graphene/SnS/Si) heterojunction. The device was obtained by depositing SnS film on the Si substrate using the thermal evaporation technique. The graphene film is used as a transparent electrode for charge collection efficiently, and SnS/Si ensures that the device generates a uniform photocurrent under the light. The fabricated photodetector has a broad response band from visible to the near-infrared regime, high response speed with a fast-rising time of 11.0 ms at the bias of −5 V under 980 nm, and excellent responsivity up to 1.17 AW-1, and the responsivity for 1550 nm is as large as 17.31 mAW−1. Simultaneously, the self-powered characteristic can be realized. The gra-phene/SnS/Si heterojunction has a wideband and fast response, which may be used in future in-frared and even mid-infrared photoelectric detection.

Development and characterization of a DMAPS chip in TowerJazz [formula omitted] [formula omitted] technology for high radiation environments

The increasing availability of commercial CMOS processes with high-resistivity wafers has fueled the R&D of depleted monolithic active pixel sensors (DMAPS) for use in high energy physics experiments. One of these developments is a series of monolithic pixel detectors with column-drain readout architecture and small collection electrode allowing for low-power designs (TJ-Monopix). It is designed in a 180nm TowerJazz CMOS process and features a pixel size of 33μm×33μm. The efforts and improvements on the front-end electronics and sensor design of the current iteration TJ-Monopix2 increase the radiation hardness and efficiency while lowering the threshold and noise.

Monolithic pixel sensor with 25 µm × 35 µm pixel size and high time resolution implemented in 180 nm technology

A monolithic pixel sensor with small collection electrode and partially depleted sensor diode named HVMAPS25 has been implemented in the 180 nm technology of TSI semiconductors. The pixel size is 25 µm × 35 µm. The pixel electronics contains a fast and low power charge sensitive amplifier, a comparator, a threshold tuning DAC and a digital block that measures the arrival time of the hit with 10 bit resolution and the signal amplitude (time over threshold) with 6 bit resolution. A deep p-well has been used for isolation of the pixel electronics from the sensor substrate. The building blocks of the chip, simulations and the measurement results will be presented.

The Tangerine project: Development of high-resolution 65 nm silicon MAPS

The Tangerine project aims to develop new state-of-the-art high-precision silicon detectors. Part of the project has the goal of developing a monolithic active pixel sensor using a novel 65 nm CMOS imaging process, with a small collection electrode. This is the first application of this process in particle physics, and it is of great interest as it allows for an increased logic density and reduced power consumption and material budget compared to other processes. The process is envisioned to be used in for example the next ALICE inner tracker upgrade, and in experiments at the electron-ion collider.The initial goal of the three-year Tangerine project is to develop and test a sensor in a 65 nm CMOS imaging process that can be used in test beam telescopes at DESY, providing excellent spatial resolution and high time resolution, and thus demonstrating the capabilities of the process. The project covers all aspects of sensor R&D, from electronics and sensor design using simulations, to prototype test chip characterisation in labs and at test beams. The sensor design simulations are performed by using a powerful combination of detailed electric field simulations using technology computer-aided design and high-statistics Monte Carlo simulations using the Allpix2 framework. A first prototype test chip in the process has been designed and produced, and successfully operated and tested both in labs and at test beams.

Corona discharge behavior in foggy environments with flat plate and fin plate electrodes

The corona discharge is widely used to charge fog droplets. However, there is a lack of an accurate description of the interaction between fog droplets and the corona discharge process. Discharge currents of the two wire-plate devices in two foggy environments were measured experimentally. It was found that fog droplets floating in the air restrained the corona discharge process, and the effect of fog droplets was more significant than that of humidity variation. The discharge current decreases with increasing fog concentration. In addition, the electrohydrodynamic flow enhances the flow near the collection electrode and prevents large droplets from hanging on the collection electrode. The experimental results demonstrate that the corona discharge behaviors for the two devices comprising two types of collection electrodes are similar. The numerical prediction agreed well with the experimental data when the contribution of the droplet charge to the voltage and ion charge density was considered.

Flexible porous Gelatin/Polypyrrole/Reduction graphene oxide organohydrogel for wearable electronics

Conductive hydrogel-based flexible electronics have attracted immense interest in wearable sensor, soft robot and human–machine interface. However, the application of hydrogels in flexible electronics is limited by the deterioration of mechanical and electrical properties due to freezing at low temperature and desiccation after long-term use. Meanwhile, flexible electronics based on hydrogel are usually not breathable, which has a great impact on wearing comfort and signal stability in long-term sensing. In this work, an adjustable porous gelatin/polypyrrole/reduction graphene oxide (Gel/PPy/rGO) organohydrogel with high breathability (14 g∙cm−2∙h−1), conductivity (5.25 S/m), mechanical flexibility, anti-freezing and long-term stability is prepared via the combination method of biological fermentation and salt-out toughening crosslinking. The sensor fabricated from the prepared porous organohydrogel exhibits excellent sensing sensitivity, fast response ability, and good endurance, which monitors both weak and intense human activities effectively like finger bending, elbow bending, walking and running, and tiny pulse beating. A pressure sensor array prepared from the porous organohydrogel detects pressure variation in 2D sensitively. Furthermore, the porous organohydrogel is utilized as flexible electrodes for the accurate collection and recognition of human physiological signals (EMG, ECG) and as an interface between human and machine.

Fluctuations in the collected charge in integrating photoconductive detectors under small and large signals: the variance problem

Charge collection efficiency (CE) η 0 under small signal conditions, corresponding to a uniform field in the detector medium, has been widely used in evaluating the performance of photoconductive detectors. The present paper answers the question, ‘What is the variance of the collected charge in an integrating detector as a function of photoinjection level and what are the errors if we continue to use the small signal equations?’ The variance in η 0 under small signals has been theoretically derived in the literature and has been a key factor in the detective quantum efficiency modeling of integrating detectors based on various semiconductors. is a noise source and can degrade the detector performance under incomplete charge collection. The statistical variance in the CE η 0, under small signals and the variance in the CE ηr under an arbitrary injection level r (injected charge divided by charge on the electrodes) have been studied using the Monte Carlo simulation model developed in this work to evaluate the difference between and from small to large signals. Initial injection of electron and hole pairs and their subsequent transport and trapping in the presence of an electric field, which is calculated from the Poisson equation, is used to calculate the photocurrent. Each injected carrier is tracked as it moves in the semiconductor until it is either trapped or reaches the collection electrode. Trapped carriers do not contribute to the photocurrent but continue to contribute to the field through the Poisson equation. The instantaneous photocurrent i ph(t) is calculated from the drift of the free carriers through the Shockley–Ramo theorem. i ph(t) is integrated over the duration of the photocurrent to calculate the total collected charge and hence the CE ηr . The variance in ηr is found from multiple simulations of ηr . The ηr and have been generated over varying charge injection ratios r, the electron and hole ranges μτ, mean photoinjection depths δ and drift mobility ratios b. At full injection, the deviation of the CE variance from the uniform field case ( = may be as much as 40% larger or 20% lower than the small signal model prediction. This study provides the extent of errors involved in the variance of the CE in non-uniform fields and quantifies the increase in errors that can occur in high injection cases. In practice, typical injection ratios are less than 0.2, which means that the magnitude of percentage error is less than 5%.

Heating-insulating and semitransparent inorganic perovskite solar cells

Heat-insulating semitransparent solar cells, with power-generating and energy-saving functions, have attracted wide attention due to their potential applications in building and automobile integrated photovoltaics. However, it is challenging to simultaneously improve the power conversion efficiency (PCE) and average visible transmittance (AVT) in the wavelength of 400–800 nm for multifunctional semitransparent solar cells. Moreover, as an essential requirement for practical application, the thermal stability is still lacking. In this work, CsPbI2Br inorganic perovskite with high bandgap and superior thermal stability is selected as absorber, combined with ultrathin silver top electrodes for charge collection and infrared reflector, composing the heat-insulating and semitransparent perovskite solar cells (PSCs). By virtue of dual-function ultrathin silver top electrodes, combined with high-index MoOx to further improve visible transmittance, the semitransparent PSCs exhibit PCE of >11% with high AVT of >21%, as well as an outstanding infrared ray energy rejection of >72%. Moreover, the semitransparent inorganic PSCs exhibit superior thermal stability than the organic-inorganic counterparts, remaining 75% and 65% of initial PCE after aging at 85 °C for 200 h in N2 and 105 h in air, respectively. This work paves the way toward realizing high-performance and thermal stable heat-insulating semitransparent solar cells, which greatly enhances their integration into various further applications.

A 1-μW Radiation-Hard Front-End in a 0.18-μm CMOS Process for the MALTA2 Monolithic Sensor

In this article, a low-power, radiation-hard front-end circuit for monolithic pixel sensors, designed to meet the requirements of low noise and low pixel-to-pixel variability, the key features to achieve high detection efficiencies, is presented. The sensor features a small collection electrode to achieve a small capacitance (<5 fF) and allows full CMOS in-pixel circuitry. The circuit is implemented in the 180-nm CMOS imaging technology from the TowerJazz foundry and integrated into the MALTA2 chip, which is part of a development that targets the specifications of the outer pixel layer of the ATLAS Inner Tracker upgrade at the LHC. One of the main challenges for monolithic sensors is a radiation hardness up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> 1-MeV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {n}_{\text {eq}}/\text {cm}^{{2}}$ </tex-math></inline-formula> non-ionizing energy loss (NIEL) and 80 Mrad total ionizing dose (TID) required for this application. Tests up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${3} \cdot {10}^{15}$ </tex-math></inline-formula> 1-MeV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {n}_{\text {eq}}/\text {cm}^{{2}}$ </tex-math></inline-formula> and 100 Mrad were performed on the MALTA2 sensor and front-end circuit, which still show good performance even after these levels of irradiation, promising for even more demanding applications such as the future experiments at the high-luminosity large hadron collider (HL-LHC).

Progress in DMAPS developments and first tests of the Monopix2 chips in 150 nm LFoundry and 180 nm TowerJazz technology

Depleted Monolithic Active Pixel Sensors (DMAPS) are monolithic pixel detectors with high-resistivity substrates designed for use in high-rate and high-radiation environments. They are produced in commercial CMOS processes, resulting in relatively low production costs and short turnaround times, and offer a low material budget. LF-Monopix1 and TJ-Monopix1 are large DMAPS prototypes produced in 150 nm LFoundry and 180 nm TowerJazz technology, respectively, that follow two different design concepts regarding the charge collection electrode. Prototypes of both development lines have been extensively tested and characterized over the last years. The second-generation Monopix prototypes, Monopix2, were recently produced. They were designed to address the shortcomings of their predecessors, in particular related to radiation hardness and cross talk, and further improve upon their performance. The latest measurements with LF-Monopix1 and TJ-Monopix1 concerning hit efficiency, depletion, and radiation hardness as well as the initial test results of the new Monopix2 prototypes are presented.

Radiation hardness and timing performance in MALTA monolithic pixel sensors in TowerJazz 180 nm

The MALTA family of depleted monolithic pixel sensors produced in TowerJazz 180 nm CMOS technology target radiation hard applications for the HL-LHC and beyond. Several process modifications and front-end improvements have resulted in radiation hardness >1015 1 MeV neq/cm2 and time resolution below 2 ns, with uniform charge collection and efficiency across the pixel of size 36.4 × 36.4 µm2 with small collection electrode. This contribution will present the comparison of samples produced on high-resistivity epitaxial silicon with Czochralski substrates, before and after neutron irradiation, and results from MALTA2 with a new cascoded front-end flavour that further reduces the RTS noise.

Transient Monte Carlo simulations for the optimisation and characterisation of monolithic silicon sensors

An ever-increasing demand for high-performance silicon sensors requires complex sensor designs that are challenging to simulate and model. The combination of electrostatic finite element simulations with a transient Monte Carlo approach provides simultaneous access to precise sensor modelling and high statistics. The high simulation statistics enable the inclusion of Landau fluctuations and production of secondary particles, which offers a realistic simulation scenario. The transient simulation approach is an important tool to achieve an accurate time-resolved description of the sensor, which is crucial in the face of novel detector prototypes with increasingly precise timing capabilities. The simulated time resolution as a function of operating parameters as well as the full transient pulse can be monitored and assessed, which offers a new perspective for the optimisation and characterisation of silicon sensors.In this paper, a combination of electrostatic finite-element simulations using 3D TCAD and transient Monte Carlo simulations with the Allpix2 framework are presented for a monolithic CMOS pixel sensor with a small collection electrode, that is characterised by a highly inhomogeneous, complex electric field. The results are compared to transient 3D TCAD simulations that offer a precise simulation of the transient behaviour but long computation times. Additionally, the simulations are benchmarked against test-beam data and good agreement is found for the performance parameters over a wide range of different operation conditions.

2-Dimensional Resistivity Imaging of Inyi Coal-Field, Anambra Basin, Nigeria

2-Dimensional resistivity imaging of Inyi coalfield has been carried out with a view of imaging the coal field for possible location and future exploitation of the coal seam in the area and to carry out detailed geological mapping aimed at producing the geologic map of the area and to provide recommendations for managing the exploitation and exploration of solid minerals in the area. ABEM Terrameter SAS 1000 was used for resistivity data collection and Wenner-Schlumberger array electrode configuration was used because of its sensitivity to both horizontal and vertical structures. 2-D imaging was targeted at determining the lateral extent of the coal seam, the depth to the coal seam and the thickness of the coal seam. 50 VES points was conducted to help in delineating lithology and to be used in correlating 2-D results. Result reveals a resistivity values ranging from 600Ωm to 45000Ωm around the surveyed area. It also show that the coal in the area occurred at varying depth between 4m to about 14.3m which could be extensive below this depth and the thickness ranging from 1m to 3m. Twenty one (21) points of coal seams was identified using VES at various depths ranging from about 0.9m to 23m. The thickness of the coal seams found in the area ranges from about 0.2m to 4m. The coal in the study area is disseminated and occurred at shallow depth hence it’s not in economic quantity but the coal can be mined locally.

A composite electrode model for lithium-ion batteries with silicon/graphite negative electrodes

Silicon is a promising negative electrode material with a high specific capacity, which is desirable for commercial lithium-ion batteries. It is often blended with graphite to form a composite anode to extend lifetime, however, the electrochemical interactions between silicon and graphite have not been fully investigated. Here, an electrochemical composite electrode model is developed and validated for lithium-ion batteries with a silicon/graphite anode. The continuum-level model can reproduce the voltage hysteresis and demonstrate the interactions between graphite and silicon. At high states-of-charge, graphite provides the majority of the reaction current density, however this rapidly switches to the silicon phase at deep depths-of-discharge due to the different open circuit voltage curves, mass fractions and exchange current densities. Furthermore, operation at high C-rates leads to heterogeneous current densities in the through-thickness direction, where peak reaction current densities for silicon can be found at the current collector–electrode side as opposed to the separator–electrode side for graphite. Increasing the mass fraction of silicon also highlights the beneficial impacts of reducing the peak reaction current densities. This work, therefore, gives insights into the effects of silicon additives, their coupled interactions and provides a platform to test different composite electrodes for better lithium-ion batteries.

Performance of the FASTPIX Sub-Nanosecond CMOS Pixel Sensor Demonstrator

Within the ATTRACT FASTPIX project, a monolithic pixel sensor demonstrator chip has been developed in a modified 180 nm CMOS imaging process, targeting sub-nanosecond timing measurements for single ionizing particles. It features a small collection electrode design on a 25 micron thick epitaxial layer and contains 32 mini matrices of 68 hexagonal pixels each, with pixel pitches ranging from 8.66 to 20 micron. Four pixels are transmitting an analog output signal and 64 are transmitting binary hit information. Various design variations are explored, aiming at accelerating the charge collection and making the timing of the charge collection more uniform over the pixel area. Signal treatment of the analog waveforms, as well as reconstruction of time and charge information, is carried out off-chip. This contribution introduces the design of the sensor and readout system and presents the first performance results for 10 μm and 20 μm pixel pitch achieved in measurements with particle beams.

Reduced graphene oxide nanofluidic electrolyte with improved electrochemical properties for vanadium flow batteries

Development of the Vanadium Redox Flow Battery (VRFB) has been widely reported but typically only focuses on one part of the cell (e.g. electrode, electrolyte, or membrane). Improvement to a single part of the cell may cause side effects on other parts during long-term cycling leading to an overall drop in the performance of the battery. To avoid this, the use of nanofluidic electrolyte seems to be a promising approach to enhance the performance of both electrode and electrolyte simultaneously. This paper aims to investigate the electrochemical performance of a newly prepared reduced graphene oxide (rGO) nanofluidic vanadium electrolyte, applicable for Vanadium Redox Flow Batteries (VRFB). Herein, we report for the first time a stable rGO/vanadium nanofluidic electrolyte with improved electrochemical performance. Benefiting from the low degree of oxidation as compared to GO, the rGO can provide high electrical conduction due to the presence of sufficient functional groups, which can facilitate the redox reactions. The effect of various concentrations of rGO on the electrochemical performance is investigated. The current collector (carbon cloth (CC) electrode) was further characterized using different physico-chemical techniques to underpin the stability of rGO nanofluids. The results suggested that the electrochemical performance of vanadium electrolyte increases with the concentration of rGO. Improvements of approx. 15% to 20% were achieved in peak potential separation and current density rates, respectively. In addition, the incorporation of rGO in nanofluidic electrolyte significantly decreases the electrolyte and charge transfer resistance by ∼10% and ∼99%, respectively, and improves the vanadium ion diffusion process by ∼50%.

A Vacuum Transistor Based on Field-Assisted Thermionic Emission from a Multiwalled Carbon Nanotube

Vacuum triodes have been scaled down to the microscale on a chip by microfabrication technologies to be vacuum transistors. Most of the reported devices are based on field electron emission, which suffer from the problems of unstable electron emission, poor uniformity, and high requirement for operating vacuum. Here, to overcome these problems, a vacuum transistor based on Field-Assisted thermionic emission from individual carbon nanotubes is proposed and fabricated using microfabrication technologies. The carbon nanotube vacuum transistor exhibits an ON/OFF current ratio as high as 104 and a subthreshold slope of ~4 V·dec−1. The gate controllability is found to be strongly dependent on the distance between the collector electrodes and electron emitter, and a device with the distance of 1.5 μm shows a better gate controllability than that with the distance of 0.5 μm. Benefiting from Field-Assisted thermionic emission mechanism, electric field required in our devices is about one order of magnitude smaller than that in the devices based on field electron emission, and the surface of the emitters shows much less gas molecule absorption than cold field emitters. These are expected to be helpful for improving the stability and uniformity of the devices.

Field-induced self-assembly formation of carbon nanotube filaments triggered via gas discharge breakdown

Self-assembly formation of dense carbon nanotube (CNT) filaments is demonstrated with gas discharge breakdown. CNT filament formation is triggered by irradiation of ions generated by gas discharge breakdown on a CNT mat placed on a cathode. The ion irradiation causes detachment of CNTs from the CNT mat on the cathode. Those CNTs are collected on a counter electrode and reassembled into filaments from the effect of an electric field. We examined the CNT filament formation characteristics using the combination of a plate-shaped cathode covered with a CNT mat and a wire-shaped anode as the discharge electrodes. CNT filament formation strongly depended on the discharge gas (Ar) pressure. Low Ar gas pressure of 4–6 kPa resulted in dense tree-like CNT filament formation on the anode. Addition of a collection electrode to the anode and cathode resulted in drastic enhancement of CNT filament formation. Dense and long filaments, approximately 10 mm in length, formed on the collection electrode. These results indicate that CNT filament formation by discharge breakdown can be used as a versatile dry spinning method for various kinds of CNTs that are unspinnable by conventional methods.