Non-irradiated Devices Research Articles

Gamma-Irradiation-Induced Electrical Characteristic Variations in MoS2 Field-Effect Transistors with Buried Local Back-Gate Structure.

The impact of radiation on MoS2-based devices is an important factor in the utilization of two-dimensional semiconductor-based technology in radiation-sensitive environments. In this study, the effects of gamma irradiation on the electrical variations in MoS2 field-effect transistors with buried local back-gate structures were investigated, and their related effects on Al2O3 gate dielectrics and MoS2/Al2O3 interfaces were also analyzed. The transfer and output characteristics were analyzed before and after irradiation. The current levels decreased by 15.7% under an exposure of 3 kGy. Additionally, positive shifts in the threshold voltages of 0.50, 0.99, and 1.15 V were observed under irradiations of 1, 2, and 3 kGy, respectively, compared to the non-irradiated devices. This behavior is attributable to the comprehensive effects of hole accumulation in the Al2O3 dielectric interface near the MoS2 side and the formation of electron trapping sites at the interface, which increased the electron tunneling at the MoS2 channel/dielectric interface.

Swift heavy ion irradiation-driven energy band engineering and its profound influence on the photoresponse of β-Ga2O3 ultraviolet photodetectors

Swift heavy Ta ions with an ultra-high energy of 2896 MeV are utilized for irradiation of β-Ga2O3 photodetectors. Noteworthy variations in device performance under different wavelengths are observed. Under 254 nm light illumination, the photocurrent of the devices exhibit degradation at low ion fluences but gradually recover and even surpass the performance of non-irradiated devices at the irradiation fluence of 1 × 1010 cm−2. Conversely, under 365 nm light illumination, photocurrent increases at low fluence but slightly decreases at the same high fluence of 1 × 1010 cm−2. Cathodoluminescence spectra and first-principles calculations elucidate the mechanism underlying the evolution of device performance with irradiation fluence. At low irradiation fluence, the introduction of point defects such as oxygen vacancies and gallium vacancies leads to an expansion of the bandgap, resulting in a decline in photocurrent under 254 nm light illumination. Additionally, deep defect levels are generated by these point defects, promoting an enhancement of photocurrent under 365 nm light illumination. Higher fluences transform these point defects into complex defects such as Ga–O pair vacancies, resulting in a reduction in the bandgap. Consequently, an increase in photocurrent is observed for devices illuminated with 254 nm light. However, at high irradiation fluences, charge recombination induced by the presence of deep defect levels becomes more significant, leading to a decrease in photocurrent when exposed to 365 nm light. No matter what, at 1 × 1010 cm−2 fluence, β-Ga2O3 photodetectors still maintain excellent performance, implying their strong radiation resistance and immense potential for application in space environments.

Controlling magnetic skyrmion nucleation with Ga+ ion irradiation

In this paper, we show that magnetic skyrmion nucleation can be controlled using ${\mathrm{Ga}}^{+}$ ion irradiation, which manipulates the magnetic interface effects (in particular, the magnetic anisotropy and Dzyaloshinskii-Moriya interaction) that govern the stability and energy cost of skyrmions in thin-film systems. We systematically and quantitatively investigate what effect these changes have on the nucleation of magnetic skyrmions. Our results indicate that the energy cost of skyrmion nucleation can be reduced up to $26%$ in the studied dose range and that it scales approximately linearly with the square root of the domain wall energy density. Moreover, the total number of nucleated skyrmions in irradiated devices after nucleation was found to depend linearly on the ion dose and could be doubled compared to nonirradiated devices. These results show that ion irradiation cannot only be used to enable local nucleation of skyrmions but also allows for fine control of the threshold and efficiency of the nucleation process.

Understanding High-Energy 75-MeV Sulfur-Ion Irradiation-Induced Degradation in GaN-Based Heterostructures: The Role of the GaN Channel Layer

AlInN/GaN on Si high-electron mobility transistors (HEMTs) are irradiated with various fluences of 75-MeV sulfur ions to study the radiation-induced degradation mechanisms. Heavy-ion irradiation has been found to reduce saturation ON- and OFF-state current and, at higher fluence, to induce a large positive threshold voltage shift. Irradiated structures reveal a consistent carrier density and mobility reduction as a function of fluence. To demonstrate the buffer-induced threshold shift, a series of samples with various GaN channel layer thicknesses defined by carbon-doped GaN buffer layers are characterized. By comparison of the threshold voltage of nonirradiated devices with reduced channel layer thickness, we assign the observed effects mainly to carrier depletion. Thus, formation of acceptor-like traps upon irradiation is concluded as primary degradation mechanism in GaN-based HEMTs. AlInN/GaN HEMT structures are, therefore, more tolerant to heavy-ion irradiation than AlGaN/GaN transistors as their intrinsic channel conductivity is higher.

High Displacement Damage Dose Effects in Radiation Hardened CMOS Image Sensors

CMOS image sensors (CISs) hardened by design against total ionizing dose (TID) are exposed to neutron fluences beyond 1014 n(1 MeV)/cm2. Neutron-irradiated devices show a huge increase in the dark current affecting uniformly the pixel array which leads to Gaussian shape dark current distributions. Moreover, random telegraph signal behavior is hardly detectable at these very high neutron fluences since the fluctuation amplitudes are hidden by the dark current shot noise. It is observed that neutrons induce a change in the depleted volume in impacted photodiodes because of doping profile modifications which are responsible for the decrease in the charge-to-voltage conversion factor and quantum efficiency. Even if neutron-induced degradations affect all the image sensor performances, results show that this technology is still functional after having absorbed $8.1\times 10^{14}$ n(1 MeV)/cm2. Image sensors are still able to capture an image without significant degradation compared to nonirradiated devices. Such TID radiation-hardened CISs are thus highly promising for applications where both high TID and high neutron fluence radiation tolerance are required.

Ionizing Radiation Effect on Memory Characteristics for HfO2-Based Ferroelectric Field-Effect Transistors

HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based ferroelectric field-effect transistors (FeFET) on Si were employed as the platform to investigate the impact of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co γ-rays radiation on memory characteristics. For pristine state, the memory window by ±4 V sweeping for non-irradiated devices is 1.48 V which does not degrade with 300-krad and 10-Mrad radiation dose even though the remnant polarization (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) decreases due to radiation-induced oxygen vacancies (Vo) and lattice distortion in the ferroelectric material HfZrOx (HZO). With the radiation dose level, the devices still hold the current ratio between “1” and “0” state of 2.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> by extrapolating to 10 years at 25 °C, which is comparable to that of non-irradiated devices. The most adverse effect of radiation is the deteriorated endurance caused by the increased number of Vo during cycling test (+5.5 V, -5 V/10 μs) as evidenced by memory window of 0.52 V at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cycles for devices with 300-krad radiation dose. Furthermore, robust HZO and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> interacial layer against radiation is required to suppress the bond break so that the reliability can be improved.

Impact of Electron Injection and Temperature on Minority Carrier Transport in Alpha-Irradiated ß-Ga2O3 Schottky Rectifiers

The effect of electron injection on minority carrier transport in Si-doped β-Ga2O3 Schottky rectifiers with 18 MeV alpha particle exposure (fluences of 1012–1013 cm−2) was studied from room temperature to 120°C. Electron Beam-Induced Current technique in-situ in Scanning Electron Microscope was used to find the diffusion length of holes as a function of duration of electron injection and temperature for alpha-particle irradiated rectifiers and compared with non-irradiated reference devices. The activation energy for electron injection-induced effect on diffusion length for the alpha-particle irradiated sample was determined to be ∼ 49 meV as compared to ∼74 meV for the reference sample. The decrease in activation energy of the electron injection effect on diffusion length for irradiated sample is attributed to radiation-induced generation of additional shallow recombination centers closer to the conduction band edge.

Impact of X-Ray Radiation on SOI Mosfet: Insulator Film Degradation and Hot-Carrier Reliability

This paper discusses the impact of X-ray radiation in the SOI MOSFET in terms of hot-carrier reliability. We examine sub-micron complimentary SOI MOSFETs in order to investigate the various factors influencing device characteristics [1]. All devices were fabricated using conventional photolithography in the 1990s, and after fabrication were subjected to continuous X-ray radiation in the range of 1J/cm2 to 10J/cm2. N-channel MOSFETs are inversion-channel devices, and p-channel MOSFETs are buried-channel devices. They have 0.36-μm or 1-μm channel length and 4.5-μm or 20.6-μm channel width. Some devices were annealed at 400 C with the ambient being the forming gas. D. C. characteristics of as-irradiated devices and post-annealed devices and hot-carrier reliability of post-annealed devices were fully investigated. Figure 1 shows front ID-VG transfer characteristics of X-ray irradiated nMOS devices and post-annealed nMOS devices. It is seen that X-ray irradiation increases the gate SiO2/SOI interface state density (Dit) and that annealing under the forming gas reduced the Dit value to almost the same value as the non-irradiated device. Figure 2 shows back ID-VB transfer characteristics of X-ray irradiated nMOS devices and post-annealed nMOS devices, where VB is the substrate voltage. It is seen that positive ionized charges are generated inside the buried oxide with 10-J/cm2 X-ray radiation, and that SOI/buried oxide interface state density increased with 1-J/cm2 and 5-J/cm2 X-ray radiation. The Dit values are not reduced to those of non-irradiated devices and non-negligible band-to-band tunneling current around the drain junction is present. It is anticipated that electron trap sites are generated inside the buried oxide but near the SOI/buried oxide [2]. Figure 3 shows front ID-VG transfer characteristics of X-ray irradiated pMOS devices and post-annealed pMOS devices. It is seen that X-ray irradiation alters the threshold voltage (VTH); the annealing under the forming gas reduced the VTH value to almost the same value as the non-irradiated device. In addition, it is seen that X-ray irradiation increases the SOI/buried oxide interface states density (Dit); the annealing under the forming gas reduced the Dit value to almost reduced the same value as the non-irradiated device. This suggests that holes near the SOI/buried oxide are not sensitive to the behavior of trap sites generated inside the buried oxide. Figure 4 shows back ID-VB transfer characteristics of X-ray irradiated pMOS devices and post-annealed pMOS devices. It is seen that the positive ionized charges are generated inside the gate SiO2, regardless of integrated X-ray radiation energy, and that the gate SiO2/SOI interface state density increases regardless of the integrated X-ray radiation energy. The Dit values and VTH values are recovered by annealing in the forming gas. The above experimental results are summarized as X-ray radiation generates gate SiO2/SOI interface states around the midgap of Si.X-ray radiation generates positive ionized traps inside the buried oxide and the SOI/buried oxide interface states.Electron trap sites are generated inside the buried oxide but near the SOI/buried oxide; these sites are not readily eliminated by annealing in the forming gas.Holes are not sensitive to the behavior of trap sited generated inside the buried oxide. Finally, we investigated the hot-carrier immunity of X-ray irradiated 0.36-μm gate devices. The results of pMOS devices suggest that their lifetime is strongly influenced by the SOI/buried oxide interface property, while the lifetime behavior of nMOS devices is insensitive to the SOI/buried oxide interface property. In summary, our analysis of device characteristics strongly suggests that SOI MOSFETs have high immunity to X-ray irradiation. The devices examined here worked over 20 years after their fabrication. It can be considered that chemical structures of the thermal SiO2 film and the buried oxide film played important roles in achieving such robustness [3-5].

Planar n-in-n quad module prototypes for the ATLAS ITk upgrade at HL-LHC

In order to meet the requirements of the High Luminosity LHC (HL-LHC), it will be necessary to replace the current tracker of the ATLAS experiment. Therefore, a new all-silicon tracking detector is being developed, the so-called Inner Tracker (ITk). The use of quad chip modules is intended in its pixel region. These modules consist of a silicon sensor that forms a unit along with four read-out chips. The current ATLAS pixel detector consists of planar n-in-n silicon pixel sensors. Similar sensors and four FE-I4 read-out chips were assembled to first prototypes of planar n-in-n quad modules. The main focus of the investigation of these modules was the region between the read-out chips, especially the central area between all four read-out chips. There are special pixel cells placed on the sensor which cover the gap between the read-out chips. This contribution focuses on the characterization of a non-irradiated device, including important sensor characteristics, charge collection determined with radioactive sources as well as hit efficiency measurements, performed in the laboratory and at testbeams. In addition, first laboratory results of an irradiated device are presented.

10 μ m-thick four-quadrant transmissive silicon photodiodes for beam position monitor application: electrical characterization and gamma irradiation effects

Silicon photodiodes are very useful devices as X-ray beam monitors in synchrotron radiation beamlines. Owing to Si absorption, devices thinner than 10 μ m are needed to achieve transmission over 90% for energies above 10 keV . In this work, new segmented four-quadrant diodes for beam alignment purposes are fabricated on both ultrathin (10 μ m-thick) and bulk silicon substrates. Four-quadrant diodes implementing different design parameters as well as auxiliary test structures (single diodes and MOS capacitors) are studied. An extensive electrical characterization, including current-voltage (I-V) and capacitance-voltage (C-V) techniques, is carried out on non-irradiated and gamma-irradiated devices up to 100 Mrad doses. Special attention is devoted to the study of radiation-induced charge build-up in diode interquadrant isolation dielectric, as well as its impact on device interquadrant resistance. Finally, the devices have been characterized with an 8 keV laboratory X-ray source at 108 ph/s and in BL13-XALOC ALBA Synchroton beamline with 1011 ph/s and energies from 6 to 16 keV . Sensitivity, spatial resolution and uniformity of the devices have been evaluated.

Commercial-off-the-shelf algan/gan hemt device reliability study after exposure to heavy ion radiation

The reliability of commercial-off-the-shelf (COTS) GaN HEMTs was studied after irradiation using heavy ions of Neon (Ne), Silicon (Si), and Argon (Ar). Devices were exposed to heavy ions at a flux of ~1.8e4 ions/cm2-sec to a fluence of 1.5e5 ions/cm2 and DC characterization measurements taken immediately after exposure exhibited no change. Additionally, no change in device performance was observed in DC or RF characterization taken prior to RF stress testing. Infrared (IR) and electroluminescence (EL) characterization was conducted before irradiation, post irradiation, and following stress testing to assess changes in emissions. After heavy ion exposure, irradiated devices and non-irradiated devices were subjected to an RF stress test at an elevated baseplate temperature. Results imply the irradiated devices degraded at a different rate than the non-irradiated device which suggests potential for confounding effects on long term reliability from heavy ion exposure. Future studies should be conducted using larger sample sizes and different radiation sources to determine if additional stress testing is required for GaN HEMT space qualification.

TCAD simulation of Low Gain Avalanche Detectors

In the present work, detailed simulation using Technology Computer Aided Design (TCAD) tool, Silvaco for non-irradiated and irradiated LGAD (Low Gain Avalanche Detector) devices has been carried out. The effects of different design parameters and proton irradiation on LGAD operation are discussed in detail. An already published effective two trap bulk damage model is used to simulate the radiation damage without implementing any acceptor removal term. The TCAD simulation for irradiated LGAD devices produce decreasing gain with increasing fluence, similar to the measurement results. The space charge density and electric field distribution are used to illustrate the possible reasons for the degradation of gain of the irradiated LGAD devices.

3D silicon sensors with variable electrode depth for radiation hard high resolution particle tracking

3D sensors, with electrodes micro-processed inside the silicon bulk using Micro-Electro-Mechanical System (MEMS) technology, were industrialized in 2012 and were installed in the first detector upgrade at the LHC, the ATLAS IBL in 2014. They are the radiation hardest sensors ever made. A new idea is now being explored to enhance the three-dimensional nature of 3D sensors by processing collecting electrodes at different depths inside the silicon bulk. This technique uses the electric field strength to suppress the charge collection effectiveness of the regions outside the p-n electrodes' overlap. Evidence of this property is supported by test beam data of irradiated and non-irradiated devices bump-bonded with pixel readout electronics and simulations. Applications include High-Luminosity Tracking in the high multiplicity LHC forward regions. This paper will describe the technical advantages of this idea and the tracking application rationale.

Manganite based memristors: Influence of the electroforming polarity on the electrical behavior and radiation hardness

We report on the fabrication and characterization of La2/3Ca1/3MnO3 manganite-based memristive devices. Polycrystalline manganite thin films were grown by Pulsed Laser Deposition, while metallic electrodes were deposited by sputtering. We show that, depending on the polarity of the initial electroforming, both clockwise and anti-clockwise current–voltage curves can be obtained. We attribute this behavior to the coexistence of different resistive switching mechanisms. We finally evaluate the electrical behavior of our devices after irradiation with high energy oxygen ions. We find no significant difference in the dielectric breakdown voltages between irradiated and non-irradiated devices, indicating that they may present radiation hardness and could be therefore appropriate for space or nuclear applications.

Technology developments and first measurements of Low Gain Avalanche Detectors (LGAD) for high energy physics applications

This paper introduces a new concept of silicon radiation detector with intrinsic multiplication of the charge, called Low Gain Avalanche Detector (LGAD). These new devices are based on the standard Avalanche Photo Diodes (APD) normally used for optical and X-ray detection applications. The main differences to standard APD detectors are the low gain requested to detect high energy charged particles, and the possibility to have fine segmentation pitches: this allows fabrication of microstrip or pixel devices which do not suffer from the limitations normally found [1] in avalanche detectors. In addition, a moderate multiplication value will allow the fabrication of thinner devices with the same output signal of standard thick substrates.The investigation of these detectors provides important indications on the ability of such modified electrode geometry to control and optimize the charge multiplication effect, in order to fully recover the collection efficiency of heavily irradiated silicon detectors, at reasonable bias voltage, compatible with the voltage feed limitation of the CERN High Luminosity Large Hadron Collider (HL-LHC) experiments [2]. For instance, the inner most pixel detector layers of the ATLAS tracker will be exposed to fluences up to 2×10161MeVneq/cm2, while for the inner strip detector region fluences of 1×1015neq/cm2 are expected.The gain implemented in the non-irradiated devices must retain some effect also after irradiation, with a higher multiplication factor with respect to standard structures, in order to be used in harsh environments such those expected at collider experiments.

Evaluating the influence of MCM-D post-processing on silicon microstrip sensors

Silicon micro-strip modules are traditionally built as a composite object of sensors, front-end ASICs, electronics hybrid, pitch adapters and passive components. This paper reports on a novel approach to use Multi-chip Module-Deposited (MCM-D) technology to build the electronics hybrid and pitch adapter directly on the silicon sensor, by post-processing the sensor wafers. A first prototype was made to evaluate the influence of the post-processing on the sensors in terms of the electrical performance, mechanical stability and the radiation hardness. The processing was done on a wafer with miniature strip sensors and featured one dielectric layer, one metal layer and one passivation layer. This paper summarises the results from this prototype run. It reports on the sensor leakage current, strip capacitance, inter-strip resistance and charge collection efficiency. These measurements are done on non-irradiated devices and devices subjected to proton irradiation. Furthermore it reports on the mechanical integrity of the post-processed assembly.

Irradiation tests on InP based Mach Zehnder modulator

Particle detectors in High Energy Physics experimentscontain various types of mixed-signal integrated circuits and demand datarates of multiple Gigabits per second per chip and several Terabits persecond for the whole detector. Optical transmission by external modulationof a continuous wave laser is a possible solution to solve the problem ofhigh data rates. The detectors have to operate in a high radiationenvironment and particles passing through the circuits alter the propertiesof the circuits giving rise to performance issues. In this paper, weinvestigate the radiation hardness performance of Indium Phosphide (InP)based Mach-Zehnder modulators (MZM). The modulator circuit has beenirradiated with a 24 GeV/c proton beam at CERN up to various fluences. Theirradiated samples have been characterized and compared against measurementsof non-irradiated devices. Also, a design of an optical integrated circuitusing the Generic Integration philosophy is presented.

1.6 MeV Electron Irradiation on the Characteristics of CdTe Thin Film Solar Cells

The CdTe thin film solar cells with the structure of ITO/ZnO/CdS/CdTe/Au were irradiated by 1.6MeV high-energy electrons with the fluences from 5×1013/cm2 to 1×1016/cm2. The characteristics of devices before and after irradiation were studied using dark current-voltage (I-V), capacitance-voltage (C-V) and admittance spectroscopy (AS) measurements in the temperature range from 303K to 353K. The results are shown that the diode ideal factor and dark saturation current for irradiated devices first decrease and then increase significantly with fluences from 5×1013/cm2 to 1×1016/cm2, meantime the effective carrier concentration at room temperature of CdTe absorbing layer increases first and then decreases. The carrier transport mechanisms in CdTe solar cells are analyzed before and after irradiation. The non-irradiated devices and irradiated devices with fluences less than 5×1014/cm2 are dominated by the recombination current of electron-hole pairs in the depletion layer. However, it is dominated by the recombination current of tunneling at the interface after the irradiation of higher fluences. The changes of types and amount of defects caused by electron irradiation are the major reasons for the above mentioned variations.

Design and performance of the silicon sensors for the CMS barrel pixel detector

The CMS experiment at the (LHC) includes a hybrid silicon pixel detector for the reconstruction of charged tracks and of the interaction vertices. The barrel region consists of n-in-n sensors with 100 × 150 μ m 2 cell size processed on diffusion oxygenated float zone silicon. A biasing grid is implemented and pixel isolation is achieved with the moderated p-spray technique. An extensive test program was carried out on the H 2 beam line of the CERN-SPS. In this paper we describe the sensor layout, the beam test setup and the results obtained with both irradiated and non-irradiated prototype devices. Measurements of charge collection, hit detection efficiency, Lorentz angle and spatial resolution are presented.

Electrical stress on irradiated thin gate oxide partially depleted SOI nMOSFETs

The effect of hot-carrier stress on 60 MeV proton irradiated thin gate oxide partially depleted SOI nMOSFETs has been studied. The results are compared with those from the electrical stress of non-irradiated devices. Whereas no significant differences are observed for the front channel degradation, hot-electron trapping in the buried oxide is found to be enhanced in the irradiated devices. This hot-electron trapping leads to a compensation or neutralization of the effects caused by the radiation-induced positive trapped charges. It is shown that a similar hot-electron trapping enhancement can be achieved in non-irradiated devices stressed under certain back gate bias conditions.