Low-noise Charge-sensitive Preamplifier Research Articles

Charge sensitive preamplifier design optimization for low-pressure Micro-Megas gaseous detector operations

Using a bulk Micro-Megas (MM) detector an energy measurement can be obtained collecting the total charge reaching the mesh electrode connected to a low noise charge sensitive preamplifier. When operating such a device in a low-pressure gas regime, it is necessary to modify the amplification gap geometry to reach the optimal detector gain. This implies changes in the input capacitance of the preamplifier influencing its signal to noise ratio and thus the detector energy resolution. An ad-hoc high-gain and low-noise charge preamplifier has been developed to cope with the requirements of our application field. In this short report, we present the development activities focused to the study of a configurable charge amplifier to be connected to a MM detector having different mesh capacitances.

Mo/4H-SiC Schottky diodes for room temperature X-ray and [formula omitted]-ray spectroscopy

Mo/4H-SiC Schottky diodes were investigated as detectors for their suitability in photon counting X-ray and γ-ray spectroscopy. The Schottky diodes, with a 35μm thick n− epitaxial layer, were treated with a phosphorus pentoxide surface passivation, which had been previously shown to improve the homogeneity of the metal–semiconductor interface and suppress leakage current. One device was coupled to a low-noise charge sensitive preamplifier and standard onwards readout electronics; the resultant spectrometer was used to accumulated X-ray and γ-ray spectra. The spectrometer had an energy resolution of 1.67 keV ± 0.08 keV (97 e− rms ± 5 e− rms) at 5.9 keV and 1.6 keV ± 0.1 keV (93 e− rms ± 6 e− rms) at 59.54 keV. Despite the moderate energy resolution achieved, the results suggested that the leakage current of the Mo/4H-SiC Schottky diode detector was not the dominant source of noise limiting the energy resolution of the spectrometer at the optimum operating conditions at room temperature; lossy dielectrics in close proximity to the input of the preamplifier (including stray dielectrics) and the relatively large average electron–hole pair creation energy of 4H-SiC (an inherent property) were the main contributors to the achieved energy resolution in energy terms.

A prototype AlInP electron spectrometer

The development and characterization of a prototype temperature tolerant (capable of operation up to at least 100 ​°C) particle counting electron spectrometer with an AlInP detector is reported. This is the first time that the response of an AlInP detector to electrons (β− particles) has been reported. The detector was a custom made circular mesa (200 ​μm diameter) Al0.52In0.48P p+-i-n+ (2 ​μm i layer) photodiode; this was coupled to a custom made low-noise charge-sensitive preamplifier and otherwise standard readout electronics. The detector was electrically characterized and the spectrometer was investigated for its response to illumination from a63Ni radioisotope β− particle source over the temperature range 100 ​°C–20 ​°C. The absorbed electron energy within the active region (i layer) of the AlInP detector and the expected to be detected spectra were calculated using Monte Carlo simulations. Comparisons between the simulated and measured spectra indicated that the response of the spectrometer was in agreement with the Monte Carlo model. Future generations of electron spectrometers of this type are expected to be useful for space science missions where the instrumentation would be subject to high temperatures and intense radiation (e.g. to study the radiolytic processes in comets close to perihelion). In order to inform development of future generations of AlInP electron detectors for such applications, the response of the prototype instrument to illumination with solar wind electrons was modelled within the experimentally verified energy range of the detector; avenues of future development to improve AlInP detector performance, identified from the presently reported results, was investigated and discussed.

InGaP 2 [formula omitted] 2 pixel array for X-ray and [formula omitted]-ray spectroscopy

A 2 × 2 square pixel In0.5Ga0.5P p+-i-n+ mesa photodiode array was fabricated and investigated for its suitability in photon counting X-ray and γ-ray spectroscopy. Each pixel, which had an area of 200μm×200μm and a 5μm thick i layer, was coupled to a low-noise charge-sensitive preamplifier and standard onwards readout electronics to form an X-ray and γ-ray photon counting spectrometer. The pixels were illuminated in turn with an 55Fe radioisotope X-ray source, an 241Am radioisotope X-ray and γ-ray source, and a 109Cd radioisotope X-ray and γ-ray source. The mean value (across all pixels) of the best energy resolution (Full Width at Half Maximum, FWHM) at 20 °C was 770 eV ± 30 eV at 5.9 keV, 840 eV ± 20 eV at 22.16 keV, and 870 eV ± 30 eV at 59.54 keV. The spectroscopic response of one of the pixels was then investigated at temperatures up to 100 °C; noise analysis was performed and the different noise contributions were identified. The FWHM at 100 °C was 1.29 keV ± 0.04 keV at 5.9 keV, 1.32 keV ± 0.06 keV at 22.16 keV, 1.34 keV ± 0.06 keV at 59.54 keV, and 1.43 keV ± 0.08 keV at 88.03 keV. The results indicate that the detector did not suffer from incomplete charge collection, and that the spectrometer had better energy resolution at 100 °C than any other multi-pixel radiation spectrometer so far reported.

InGaAs x-ray photodiode for spectroscopy

A prototype In0.53Ga0.47As p+-i-n+ x-ray photodiode, fabricated from material grown by metalorganic vapour phase epitaxy, was investigated as a novel detector of x-rays. The detector was connected to a custom low-noise charge sensitive preamplifier and standard readout electronics to produce an x-ray spectrometer. The detector and preamplifier were operated at a temperature of 233 K (−40 °C). An energy resolution of 1.18 keV ± 0.06 keV Full Width at Half Maximum at 5.9 keV was achieved. This is the first time InGaAs (GaInAs) has been shown to be capable of spectroscopic photon counting x-ray detection.

Hard X-ray and [formula omitted]-ray spectroscopy at high temperatures using a COTS SiC photodiode

A commercial-off-the-shelf (COTS) silicon carbide (4H-SiC) UV photodiode was electrically characterized and investigated as a low-cost spectroscopic photon counting detector of X-rays and γ-rays. The detector was coupled to a custom-built low-noise charge-sensitive preamplifier, and illuminated by 55Fe and 109Cd radioisotope X-ray sources and an 241Am radioisotope γ-ray source, thus providing photon energies from 5.9 keV to 59.5 keV. The detector and preamplifier were operated uncooled at temperatures between 20 °C and 100 °C. The energy resolution (full width at half maximum, FWHM) of the spectrometer was found to be 1.66 keV ± 0.15 keV at 5.9 keV and 22.16 keV, and 1.83 keV ± 0.15 keV at 59.5 keV when operated at 20 °C. At a temperature of 100 °C, the FWHM were 2.69 ± 0.25 keV, 2.65 keV± 0.25 keV, and 3.30 keV ± 0.30 keV, at the same energies. Shaping time noise analysis found dielectric noise to be the dominant noise source, except when long amplifier shaping times were used at high temperatures when white parallel noise dominated. Noise associated with incomplete charge collection was found to be negligible at energies up to 22.16 keV and at temperatures ≤60 °C; but incomplete charge collection noise could not be discounted when the spectrometer was operated at higher temperature (80 °C) and at higher energy (59.5 keV). Although the detector was thin (and thus inefficient at high photon energies) the low cost and commercial availability of the SiC device make it an attractive prospect for use in cost-sensitive applications such as university-led CubeSat missions.

Development of Low-Noise Charge-Sensitive Preamplifier Based on PIPS Detector

In this paper, a low-noise charge-sensitive preamplifier (CSA) is designed based on passivation ion implanted planar silicon (PIPS: The Passivated Implanted Planar Silicon) detectors. This charge-sensitive preamplifier uses Junction Field-Effect Transistor (JFET) as the first stage of the amplifier. In order to maximize the signal-to-noise ratio and consider the resistance-capacitance matching problem, according to different PIPS detector junction capacitances, different numbers of junction field effect transistors are matched in parallel in the first stage. Slotting technology is used at the feedback end to reduce the influence of the parasitic capacitance of the PCB board on the feedback, and the feedback capacitor resistance is adjusted to achieve the best signal-to-noise ratio. Experimental test results show that the charge-sensitive preamplifier can achieve a signal-to-noise ratio greater than 100 at room temperature, the output signal rise time is less than 60 ns, and the electronic equivalent capacitance noise is 19 eV/pF. The charge-sensitive preamplifier is connected to the Canberra PD450-17-100AM PIPS detector, and the standard α source 238Pu is measured in a vacuum environment. The energy resolution can reach 17keV@5499keV.

High temperature AlInP X-ray spectrometers

Two custom-made Al0.52In0.48P p+-i-n+ mesa photodiodes with different diameters (217 µm ± 15 µm and 409 µm ± 28 µm) and i layer thicknesses of 6 µm have been electrically characterised over the temperature range 0 °C to 100 °C. Each photodiode was then investigated as a high-temperature-tolerant photon counting X-ray detector by connecting it to a custom-made low-noise charge-sensitive preamplifier and illuminating it with an 55Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV). At 100 °C, the best energy resolutions (full width at half maximum at 5.9 keV) achieved using the 217 µm ± 15 µm diameter photodiode and the 409 µm ± 28 µm diameter photodiode were 1.31 keV ± 0.04 keV and 1.64 keV ± 0.08 keV, respectively. Noise analysis of the system is presented. The dielectric dissipation factor of Al0.52In0.48P was estimated as a function of temperature, up to 100 °C. The results show the performance of the thickest Al0.52In0.48P X-ray detectors so far reported at high temperature. The work has relevance for the development of novel space science instrumentation for use in hot space environments and extreme terrestrial applications.

InGaP electron spectrometer for high temperature environments

In this work, a 200 μm diameter InGaP (GaInP) p+-i-n+ mesa photodiode was studied across the temperature range 100 °C to 20 °C for the development of a temperature-tolerant electron spectrometer. The depletion layer thickness of the InGaP device was 5 μm. The performance of the InGaP detector was analysed under dark conditions and then under the illumination of a 183 MBq 63Ni radioisotope beta particle source. The InGaP photodiode was connected to a custom-made low-noise charge-sensitive preamplifier to realise a particle counting electron spectrometer. Beta spectra were collected at temperatures up to 100 °C with the InGaP device reverse biased at 5 V. The spectrum accumulated at 20 °C was compared with the spectrum predicted using Monte Carlo simulations; good agreement was found between the predicted and experimental spectra. The work is of importance for the development of electron spectrometers that can be used for planetary and space science missions to environments of high temperature or extreme radiation (e.g. Mercury, Jupiter’s moon Europa, near-Sun comets), as well as terrestrial applications.

AlInP photodiode x-ray detectors

Four Al0.52In0.48P p+-i-n+ mesa photodiodes with 6 μm thick i layers and two different diameters (217 μm ± 15 μm and 409 μm ± 28 μm) were studied at room temperature (24 °C). Electrical characterisation measurements are reported along with measurements showing the performance of the devices as x-ray detectors. The devices exhibited leakage currents <3 pA (corresponding to leakage current densities <2 nA cm−2) at 100 V reverse bias (electric field strength of 167 kV cm−1). The photodiodes were coupled to a custom-made low-noise charge-sensitive preamplifier, the noise characteristics of the resultant spectrometers were investigated as functions of shaping times. The best energy resolutions (full width at half maximum of the 5.9 keV photopeak from an 55Fe radioisotope x-ray source) achieved with the 217 μm ± 15 μm and 409 μm ± 28 μm diameter photodiodes were 0.89 keV and 1.05 keV, respectively. The dielectric dissipation factor of Al0.52In0.48P was estimated to be (2.2 ± 1.1) × 10−3 at room temperature.

Comparison of JFET/MOS/HEMT Based Low Noise Charge Sensitive Preamplifiers for HPGe Detectors in Cryogenic Temperature

The paper presents development of three different types of low noise charge sensitive preamplifiers (CSA) for HPGe detectors for basic physics experiments such as CDEX (China dark matter search experiment) and spectroscopy applications, based on JFET, MOS and HEMT transistors respectively. For the JFET and HEMT based CSAs, only the input transistor of the corresponding type was used and their secondary amplifiers were designed with commercial opamps and worked at room temperature. For the MOS based CSA, a monolithic ASIC of CMOS CSA was developed using a 350 nm CMOS process. The noise performances of these CSAs were optimized for a point-contact HPGe detector with ∼2 pF input capacitance and were tested at liquid nitrogen temperature. JFET suffered from the ‘freeze-out’ effect and the noise performance of the JFET CSA degraded from 64 electrons to 134 electrons when the temperature went from 120 K to 77 K. For comparison, the noises of the MOS and HEMT based CSAs kept getting better down to 77 K. The serial noises of the MOS and HEMT CSAs were similar and the HEMT CSA showed significant parallel noise contribution. The CMOS CSA has also been tested with a 0.5 kg point-contact HPGe detector. The energy spectrum was measured and the electronics noise was monitored to be 186 eV, corresponding to 26 electrons ENC (equivalent noise charge) in rms.

A segmented neutron detector based on Silicon-PIN photodiodes using neutron-proton converters

A segmented neutron detection system based on windowless silicon-PIN photodiodes has been designed and tested with various hydrogen rich converter materials. Each channel from the segmented structure uses an independent custom-made low noise charge sensitive preamplifier and an OPAMP based shaping amplifier. Signals from each channel were digitized using a fast, single bit digitizer and the pulses from each channel were simultaneously recorded with an FPGA board. An AmBe neutron source was used for the test measurements and relative neutron detection efficiencies were determined. This low-cost detector can be used for monitoring fast neutrons in reactors, accelerator facilities or medical centers using neutron therapy.

Experimental performance of a highly-innovative low-noise charge-sensitive preamplifier with integrated range-booster

Integrated charge-sensitive preamplifiers suffer from a reduced available dynamic range respect to discrete-type equivalents. This is due to the limits on maximum supply voltages that modern scaled technologies can tolerate. In this work we present a low-noise low-power integrated charge-sensitive preamplifier (CSP) for solid-state detectors. This device is equipped with an integrated range-booster that can enhance the spectroscopic range of the preamplifier by more than one order of magnitude, enabling high-resolution spectroscopy even if the preamplifier is in deep saturation condition. If the input signals from the detector are under the natural saturation threshold (40 MeV), the preamplifier works in an usual linear way, producing at the output the typical exponential signals. With proper filtering a resolution of approximately 1 keV is achievable. When a large signal from the detector saturates the preamplifier, a sensing circuit detects the saturation and switches the operation mode of the CSP to the “fast-reset mode”. In this mode a constant and controlled current generator discharges the input node of the preamplifier until the normal operating point is reached. Meanwhile an auxiliary circuit similar to a TAC (Time-to-Amplitude converter) retrieves the energy of the signal that caused saturation. Although the natural dynamic range of the CSP is 40 MeV, the fast-reset mode enables for high-resolution spectroscopy (under 0.2% FWHM) up to several hundreds of MeV (700 MeV typically). One issue in this kind of circuits is the dependence of the energy measured with the TAC circuit on the baseline value of the CSP before the “fast-reset event” [1]. As a solution to this problem we propose a correction algorithm implemented inside the TAC block in the form of an analog circuit. On a test-bench a series of large 3 pC charge signals is injected in the input node of the preamplifier through a test capacitor. Before these events, residual charges ranging from 0 to 0.56 pC produce non-zero baseline voltages at the output of the CSP. The TAC with correction not only retrieves correctly the energy of the main event, but also rejects the baseline voltages, leaving the energy measurement unaffected. The fluctuations of the flat-top voltage in the signals produced by the auxiliary TAC circuit due to the different baseline voltages are under the 0.6% of the total signal amplitude.

Electron spectroscopy with a commercial 4H-SiC photodiode

A Commercial-Off-The-Shelf (COTS) 4H-SiC p-n photodiode (sold as a UV detector) was investigated as detector of electrons (β− particles) over the temperature range 100 °C to 20 °C. The photodiode had an active area of 0.06 mm2. The currents of the photodiode were measured in dark condition and under the illumination of a 63Ni radioisotope β− particle source (endpoint energy = 66 keV). The photodiode was then coupled to a custom-made low-noise charge-sensitive preamplifier to make a direct detection particle counting electron spectrometer. 63Ni β− particle spectra were accumulated with the spectrometer operating at temperatures up to 100 °C. The quantum efficiency of the photodiode as well as the spectrum expected to be detected were calculated via Monte Carlo simulations produced using the CASINO computer program. Comparisons between the simulated and detected 63Ni β− particle spectra are presented. The work was motivated by efforts to apply COTS technologies to develop low-cost space science instrumentation; a low-cost electron spectrometer of this type could be included on a university-led CubeSat mission for space plasma physics and magnetosphere experiments.

Characterization of a novel pixelated Silicon Drift Detector (PixDD) for high-throughput X-ray astrophysics

Multi-pixel fast silicon detectors represent the enabling technology for the next generation of space-borne experiments devoted to high-resolution spectral-timing studies of low-flux compact cosmic sources. Several imaging detectors based on frame-integration have been developed as focal plane devices for X-ray space-borne missions but, when coupled to large-area concentrator X-ray optics, these detectors are affected by strong pile-up and dead-time effects, thus limiting the time and energy resolution as well as the overall system sensitivity. The current technological gap in the capability to realize pixelated silicon detectors for soft X-rays with fast, photon-by-photon response and nearly Fano-limited energy resolution therefore translates into the unavailability of sparse read-out sensors suitable for high throughput X-ray astronomy applications. In the framework of the ReDSoX Italian collaboration, we developed a new, sparse read-out, pixelated silicon drift detector which operates in the energy range 0.5–15 keV with nearly Fano-limited energy resolution (⩽150 eV FWHM @ 6 keV) at room temperature or with moderate cooling (∼0°C to +20°C). In this paper, we present the design and the laboratory characterization of the first 16-pixel (4 × 4) drift detector prototype (PixDD), read-out by individual ultra low-noise charge sensitive preamplifiers (SIRIO) and we discuss the future PixDD prototype developments.

HYTAR: A HYbrid Telescope ARray detection system for heavy ion nuclear reactions around Coulomb barrier

Characteristics and performance of a HYbrid Telescope ARray (HYTAR) detector system for heavy ions are presented. The system has been developed for the study of reaction mechanisms in nuclear physics experiments around the Coulomb barrier. HYTAR apparatus is an array of hybrid telescopes, each unit comprising of a gas ionization chamber followed by a silicon detector. Gas ionization chamber, operated in axial field mode, measures the differential energy loss (ΔE), while the residual energies are measured by silicon detector. Particle identification is realized by implementing ΔE-E technique. Use of gas ionization chamber as ΔE detector allows identification of reaction channels down to low energy thresholds ∼ 0.1 MeV/A in A∼ 100 region. The detector system has been developed to investigate the fusion and fusion–fission dynamics by performing quasi-elastic scattering and fission angular distribution experiments. Processing of the detector signals is realized with compact and simple high density front-end electronics, which consists of custom developed low noise charge sensitive preamplifiers (operated inside vacuum) and differential driver NIM modules, followed by commercially available spectroscopy amplifiers, logic modules, analog to digital converters etc. Design features of the HYTAR and measurements performed with it are described in this article.

Dual-polarity pulse processing and analysis for charge-loss correction in cadmium-zinc-telluride pixel detectors.

Charge losses at the inter-pixel gap are typical drawbacks in cadmium-zinc-telluride (CZT) pixel detectors. In this work, an original technique able to correct charge losses occurring after the application of charge-sharing addition (CSA) is presented. The method, exploiting the strong relation between the energy after CSA and the beam position at the inter-pixel gap, allows the recovery of charge losses and improvements in energy resolution. Sub-millimetre CZT pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X-rays, at energies below and above the K-shell absorption energy of the CZT material. The detectors are DC coupled to fast and low-noise charge-sensitive preamplifiers (PIXIE ASIC) and followed by a 16-channel digital readout electronics, performing multi-parameter analysis (event arrival time, pulse shape, pulse height). Induced-charge pulses with negative polarity were also observed in the waveforms from the charge-sensitive preamplifiers (CSPs) at energies >60 keV. The shape and the height of these pulses were analysed, and their role in the mitigation of charge losses in CZT pixel detectors. These activities are in the framework of an international collaboration on the development of energy-resolved photon-counting systems for spectroscopic X-ray imaging (5-140 keV).

X-ray spectrometer with a low-cost SiC photodiode

A low-cost Commercial-Off-The-Shelf (COTS) 4H-SiC 0.06 mm2 UV p-n photodiode was coupled to a low-noise charge-sensitive preamplifier and used as photon counting X-ray spectrometer. The photodiode/spectrometer was investigated at X-ray energies from 4.95 keV to 21.17 keV: a Mo cathode X-ray tube was used to fluoresce eight high-purity metal foils to produce characteristic X-ray emission lines which were used to characterise the instrument. The energy resolution (full width at half maximum, FWHM) of the spectrometer was found to be 1.6 keV to 1.8 keV, across the energy range. The energy linearity of the detector/spectrometer (i.e. the detector’s charge output per photon as a function of incident photon energy across the 4.95 keV to 21.17 keV energy range), as well as the count rate linearity of the detector/spectrometer (i.e. number of detected photons as a function of photon fluence at a specific energy) were investigated. The energy linearity of the detector/spectrometer was linear with an error <± 0.7 %; the count rate linearity of the detector/spectrometer was linear with an error <± 2 %. The use of COTS SiC photodiodes as detectors for X-ray spectrometers is attractive for nanosatellite/CubeSat applications (including solar flare monitoring), and for cost sensitive industrial uses.

Measurement of the electron–hole pair creation energy in [formula omitted]P using X-ray radiation

The average energy consumed in the generation of an electron–hole pair (εAlInP) in Al0.52In0.48P was experimentally measured across the temperature range −20 °C to 100∘C, using a custom AlInP X-ray-photodiode, an 55Fe radioisotope X-ray source, and custom low-noise charge-sensitive preamplifier electronics. εAlInP was found to linearly decrease with increasing temperature according to the equation εAlInP = (-0.0033 eV/K ± 0.0003 eV/K)T + (6.31 eV ± 0.10 eV). At room temperature (20 °C), εAlInP= 5.34 eV ± 0.07 eV.

InGaP (GaInP) mesa p-i-n photodiodes for X-ray photon counting spectroscopy

In this paper, for the first time an InGaP (GaInP) photon counting X-ray photodiode has been developed and shown to be suitable for photon counting X-ray spectroscopy when coupled to a low-noise charge-sensitive preamplifier. The characterisation of two randomly selected 200 μm diameter and two randomly selected 400 μm diameter In0.5Ga0.5P p+-i-n+ mesa photodiodes is reported; the i-layer of the p+-i-n+ structure was 5 μm thick. At room temperature, and under illumination from an 55Fe radioisotope X-ray source, X-ray spectra were accumulated; the best spectrometer energy resolution (FWHM) achieved at 5.9 keV was 900 eV for the 200 μm In0.5Ga0.5P diameter devices at reverse biases above 5 V. System noise analysis was also carried out and the different noise contributions were computed.