Operation of 4H-SiC high voltage normally-OFF V-JFET in radiation hard conditions: Simulations and experiment

Operation of high-voltage 4H-SiC vertical-JFET in radiation hard environment was investigated by simulation and experiment. Commercial 1700 V normally-OFF SiC JFETs in TO-247 package were irradiated with fast neutrons to fluences of 4.0 × 10¹⁴ cm^− 2 (1 MeV Si equivalent) and the effect of radiation on their characteristics was then thoroughly analyzed. Four degradation mechanisms were identified, of which the most important is the increase of JFETs ON-state resistance due to the mobility degradation and removal of carriers from transistor's light doped channel and drift regions. As a result, the JFET ON-state losses grow and, at fluences higher than 4 × 10¹⁴ cm^− 2, the low doped n-regions are fully compensated and transistor loses its functionality. On the contrary, irradiation slightly improves JFET's switching characteristics. The effect of neutron irradiation on operation of SiC V-JFET in a real application was then investigated on the step-UP 15 V/60 V DC-DC converter where the SiC JFET was used as an active switch. Converter characteristics were analyzed by means of the mixed-mode simulation using the developed 2D model of the neutron irradiated transistor. Results showed that the duty cycle of the PWM regulator is growing due to the increase in the voltage drop on the switching JFET. This effect, which is caused by the abovementioned increase the JFET's ON-state resistance, increases power dissipation and deteriorates converter efficiency. Finally, the effect of neutron irradiation on operation SiC V-JFET in the 850 V/24 V auxiliary flyback switching mode power supply was analyzed. We showed that the growth of the ON-state resistance increases transistor's conduction losses and decreases converter efficiency. Exceeding the fluence of 3.3 × 10¹⁴ cm^− 2 neutrons then causes JFET overheating and subsequent destruction.     

Reliability investigations of 850 nm silicon photodiodes under proton irradiation for space applications

This paper deals with the robustness of silicon photodiodes under proton irradiation for space applications. Our interest is focused on the impact on darkness current and noise equivalent power (NEP), which corresponds to the smaller optical signal detectable by photodiodes. The photodiodes studied were selected for their very small NEP (2 × 10^?14 W/Hz^1/2) and darkness current (50 pA at ?10 mV). Proton irradiations at 60, 100 and 150 MeV energies with fluences ranging from 10¹⁰ to 10¹¹ protons/cm² have been conducted. After irradiation, the darkness current and the NEP at 870 nm of photodiodes dramatically, respectively, increase of about 10,000% and 1000% requiring to estimate the critical dose which can be tolerated by the photodiode before reaching failure criteria and to accurately calculate the minimal shield thickness embedded around the system. Lifetime distributions are also computed in operating conditions using an electrical model based on the decrease of carriers lifetimes caused by formation of defects during irradiation.     

Soft error rate comparison of 6T and 8T SRAM ICs using mono-energetic proton and neutron irradiation sources

We present experimental results of soft errors produced by proton and neutron irradiation of minimum-size six-transistors (6T) and eight-transistors (8T) bit-cells SRAM memories produced with 65 nm CMOS technology using an 18 MeV proton beam and a neutron beam of 4.3–8.5 MeV. All experiments have been carried out at the National Center of Accelerators (CNA) in Seville, Spain. Similar soft error rate levels have been observed for both cell designs despite the larger area occupied by the 8T cells, although the trend for multiple events has been higher in 6T.     

Investigation of deep level defects in copper irradiated bipolar junction transistor

Commercial bipolar junction transistor (2N 2219A, npn) irradiated with 150 MeV Cu¹¹⁺-ions with fluence of the order 10¹² ions cm^?2, is studied for radiation induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. The properties such as activation energy, trap concentration and capture cross-section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap levels with energies ranging from E_C ? 0.164 eV to E_C ? 0.695 eV are observed in the base–collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from E_V + 0.203 eV to E_V + 0.526 eV. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 350 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.     

Radiation effects in silicon detectors processed on carbon and oxygen-rich substrates

Radiation hardness results of silicon detectors fabricated on bulk float-zone (FZ) material enriched either by carbon or by oxygen are reported. The detectors were irradiated by nuclear reactor neutrons, by 24 GeV/c protons and by 192 MeV pions. It has been shown that the leakage current increases with fluence equally in all silicon detectors under study, regardless of the oxygen or carbon concentrations. The variations in the space-charge density were found to be very different in the oxygen and carbon-enriched materials in the case of irradiation by charged particles, yet rather similar in case of neutrons.     

2 MeV ion irradiation effects on AlGaN/GaN HFET devices

AlGaN/GaN heterostructure field effect transistors (HFETs) were irradiated with 2 MeV protons, carbon, oxygen, iron and krypton ions with fluences ranging from 1 × 10⁹ cm^?2 to 1 × 10¹³ cm^?2. DC, pulsed I–V characteristics, loadpull and S-parameters of the AlGaN HFET devices were measured before and after irradiation. In parallel, a thick GaN reference layer was also irradiated with the same ions and was characterized by X-ray diffraction, photoluminescence, Hall measurements before and after irradiation. Small changes in the device performance were observed after irradiation with carbon and oxygen at a fluence of 5 × 10¹⁰ cm^?2. Remarkable changes in device characteristics were seen at a fluence of 1 × 10¹² cm^?2 for carbon, oxygen, iron and krypton irradiation. Similarly, remarkable changes were also observed in the GaN layer for irradiations with fluence of 1 × 10¹² cm^?2. The results found on devices and on the GaN layer were compared and correlated.     

High linearity,low power RF mixer design in 65 nm CMOS technology

A design of RF down-conversion Gilbert-Cell, with 65 nm CMOS technology, at a supply voltage of 1.8 V, with a new degenerating structure to improve linearity. This architecture opens the way to more integrated CMOS RF circuits and to achieve a good characteristics in terms of evaluating parameters of RF mixers with a very low power consumption (2.17 mW). At 1.9 GHz RF frequency; obtained results show a third order input intercept point (IIP3) equal to 11.6 dBm, Noise Figure (NF) is 4.12 dB, when conversion gain is 8.75 dB.     

Single event effects sensitivity of low energy proton in Xilinx Zynq-7010 system-on chip

In this paper, experimental methods are emphatically described for measuring the proton single event effects (SEE) in Xilinx Zynq-7010 system-on chip. Experimental data are presented showing that low energy (3 MeV ≤ Energy ≤ 10 MeV) proton irradiation can cause single event effects in different hardware blocks of Xilinx Zynq-7010 SoC, including D-Cache, programmable logic (PL), arithmetic logical unit (ALU), float point unit (FPU) and direct memory access (DMA). Moreover, the sensitivities of different hardware blocks to single event effects are different. Finally, the Stopping and Range of Ions in Matter (SRIM) software calculations show the possible reasons for this difference.     

The correlation of γ-irradiation,particle size and their effects on physical properties of AgInSe2 nanostructure thin films

In this work the effect of γ-irradiation on the optical and electrical properties of near stoichiometric AgInSe₂ nanostructure thin films have been characterized. The XRD pattern of ingot AgInSe₂ powder prepared by solid state reaction showed tetragonal polycrystalline single-phase structure. The thin films of thickness 75 nm were prepared by inert gas condensation (IGC) technique at using constant Ar flow and substrate temperature of 300 K.Thin films were exposed to annealing process at 473 K for 2 h in vacuum of 10⁻² Torr. The amorphous and tetragonal nanocrystalline structures were detected for as-deposited and annealed films respectively by grazing incident in-plane X-ray diffraction (GIIXD) technique. The structure and average particle size of annealed irradiated films by different γ-doses from 0 to 4 Mrad were determined using high resolution transmission electron microscope (HRTEM). Optical transmission, reflection and absorption spectra were studied for both annealed unirradiated and irradiated films. Two optical transitions for each annealed unirradiated and film exposed to γ-irradiation doses from 0 to 4 Mrad were observed. The evaluated E_g1 due to 1^st transition have decreased from 1.52 to 1.44 eV and E_g2 due to 2^nd transition have decreased from 2.83 to 2.30 eV as the particle size increased from 7.3 to 9.5 nm by raising the irradiation dose up to 1 Mrad. The behavior of d.c. electrical conductivity with temperature that measured under vacuum was examined for all films under investigation. The evaluated activation energies due to irradiation doses are ranging from 0.58 to 0.68 eV.     

Selective activation of failure mechanisms in packaged double-heterostructure light emitting diodes using controlled neutron energy irradiation

This paper demonstrates the feasibility of creating specific defects in double-heterostructure AlGaAsGaAs commercial light emitting diode by neutron irradiation. Using controlled neutron energy, only one failure mechanism can be activated. Defects are located in the side of the chip and increase the leakage current driven by the well-known Pool–Frenkel effect with E_c ? E_T = 130 meV electron trap energy level. The maximal amplitude of optical spectrum also reveals a drop about 20% associated to the rise of leakage current.     

Proton-induced SEU in SiGe digital logic at cryogenic temperatures

We present the first experimental results confirming the increased SEE sensitivity of SiGe digital bipolar logic circuits operating in a 63 MeV proton environment at cryogenic temperatures. A 3× increase in both the error-event and bit-error cross sections is observed as the circuits are cooled from 300 K to 77 K, with error signature analyses indicating corresponding increases in the average number of bits-in-error and error length over data rates ranging from 50 Mbit/s to 4 Gbit/s. Single-bit-errors dominate the proton-induced SEU response at both 300 K and 77 K, as opposed to the multiple-bit-errors seen in the heavy-ion SEU response. Temperature dependent substrate carrier lifetime measurements, when combined with calibrated 2 D DESSIS simulations, suggest that the increased transistor charge collection at low temperature is a mobility driven phenomenon. Circuit-level RHBD techniques are shown to be very efficient in mitigating the proton- induced SEU at both 300 K and 77 K over the data rates tested. These results suggest that the circuit operating temperature must be carefully considered during component qualification for SEE tolerance and indicate the need for broad-beam heavy-ion testing at low temperatures.     

A low power MEMS gas sensor based on nanocrystalline ZnO thin films for sensing methane

Nanocrystalline ZnO based sensor using micromachined silicon substrate has been reported for efficient detection of methane as opposed to conventional SnO₂ based micromachined sensors for its higher compatibility to silicon IC technology and greater response. A suitably designed nickel microheater has been fabricated on to the micromachined Si platform. The optimum temperature for highest response magnitude and lowest response time were found to be 250 °C although relatively high (76.6%) response is obtained even at as low as 150 °C. Our study showed quite high response magnitude (87.3%), appreciably fast response time (8.3 s) and recovery time (17.8 s) to 1.0% methane at 250 °C. The sensor showed appreciably fast response (14.3 s) and recovery time (28.7 s) at 150 °C. The power consumption at an operating temperature of 250 °C was 120 mW and at 150 °C is only ～70 mW. Moreover, this type of sensor was found to give fairly appreciable response for lower methane concentrations (0.01%) also. For higher methane concentrations (>0.5%) response is detectable even at 100 °C where the power consumption is only ～40 mW.     

The role of electronic energy loss in SHI irradiated Ni/oxide/n-GaP Schottky diode

The impact of energy loss mechanism by 100 MeV Au^8 + ion on the dielectric parameters of Ni/oxide/n-GaP Schottky diode was studied under different fluences. The Schottky barrier height, donor ion concentration and interface states density of the diode were varied considerably under different ion fluence. The various dielectric parameters were altered significantly by the ion fluence. The reduction in dielectric constant after irradiation was ascribed to screening of space charge polarization due to reduction in interface states density. The relaxation peak of imaginary electric modulus indicates hopping type conduction mechanisms in the intermediate voltage range. The sensitive behavior of dielectric parameters with fluence dose was attributed to the alteration of interface state density due to high electronic energy loss of 100 MeV Au^8 + ions at the interface.     

Blue/green luminescence based on Zn(S)Se/GaAs heterostructures

Substantial advances have been realized in the aim to achieve blue–green light emitting devices based on Zn(S)Se wide band gap II–VI semi-conductor materials. Two light emitting diodes p on n and n on p heterostructures were grown on GaAs substrate by molecular beam epitaxy. The active layer was a single ZnCdSe quantum well, with ZnSSe guiding layers and ZnSe cladding layers. p-GaInP, p-AlGaAs and p-CdZnSe buffer layers were deposited at the p-ZnSe/GaAs interface to reduce the valence band offset in the case of n on p heterostructures. Electrical and optical properties were investigated using current voltage, capacitance voltage, electroluminescence, photoluminescence and photocurrent measurements at room temperature. Blue–green luminescence centered at 516.7 nm is observed. The highest luminescence intensity is observed under 7 V forward bias. Photoluminescence spectrum shows two wide peaks at 2.2 and 1.9 eV energies. These energies are attributed to the transitions between ZnSe and GaAs conduction bands and the deep level at E_v−0.6 eV. Absorption process from ZnSe and ZnSSe conduction bands to the shallow nitrogen acceptor level (2.6 and 2.8 eV, respectively) have been observed using photocurrent measurements. From these results we present a band alignment diagram which confirms the presence of the two levels at 0.1 and 0.6 eV from the valence band of ZnSe.     

Investigation of deep level defects in electron irradiated indium arsenide quantum dots embedded in a gallium arsenide matrix

Gallium arsenide diodes with and without indium arsenide quantum dots were electron irradiated to investigate radiation induced defects. Baseline and quantum dot gallium arsenide pn-junction diodes were characterized by capacitance–voltage measurements, and deep level transient spectroscopy. Carrier accumulation was observed in the gallium arsenide quantum dot sample at the designed depth for the quantum dots via capacitance–voltage measurements. Prior to irradiation, a defect 0.84 eV below the conduction band (E_C – 0.84 eV) was observed in the baseline sample which is consistent with the native EL2 defect seen in gallium arsenide. After 1 MeV electron irradiation three new defects were observed in the baseline sample, labeled as E3 (E_C – 0.25 eV), E4 (E_C – 0.55 eV), and E5 (E_C – 0.76 eV), consistent with literature reports of electron irradiated gallium arsenide. Prior to irradiation, the addition of quantum dots appeared to have introduced defect levels at E_C – 0.21, E_C – 0.38, and E_C – 0.75 eV denoted as QD–DX1, QD–DX2, and QD–EL2 respectively. In the quantum dot sample after 1 MeV electron irradiation, QD–E3 (E_C – 0.28 eV), QD–E4 (E_C – 0.49 eV), and QD–EL2 (E_C – 0.72 eV) defects, similar to the baseline sample, were observed, although the trap density was dissimilar to that of the baseline sample. The quantum dot sample showed a higher density of the QD–E4 defect and a lower density of QD–E3, while the QD–EL2 defect seemed to be unaffected by electron irradiation. These findings suggest that the quantum dot sample may be more radiation tolerant to the E3 defect as compared to the baseline sample.     

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×10¹⁵ cm⁻³ has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×10¹⁴ electrons-cm⁻². For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×10¹⁵ to 6.8×10¹⁵ cm⁻³ after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm⁻² K⁻² for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.     

A cross-linked poly(methyl methacrylate) gate dielectric by ion-beam irradiation for organic thin-film transistors

The electrical characteristics of pentacene organic thin-film transistors (OTFTs) using cross-linked poly(methyl methacrylate) (PMMA) as the gate dielectric are reported. Ultra-thin films of cross-linked PMMA could be obtained by spin-coating and subsequent irradiation using a 1.515 MeV ⁴He⁺ ion beam. The resulting film, with a thickness of 33 nm, possessed a low leakage current density of about 10^?6 A cm^?2 for fields up to 2 MV cm^?1. OTFTs incorporating the cross-linked dielectric operated at relatively low voltages, <10 V, and exhibited a mobility of 1.1 cm² V^?1 s^?1, a threshold voltage of ?1 V, a sub-threshold slope of 220 mV per decade and an on/off current ratio of 1.0 × 10⁶.     

High fluence 1.8 MeV proton irradiation effects on n-type MOS capacitors

MOS capacitors with 7 nm SiO₂ dielectrics and n-doped Si substrate were irradiated by 1.8 MeV protons with fluences ranging from 10¹² to 5 × 10¹³ cm^?2 which correspond to the typical LHC fluence range. No significant increase in gate oxide leakage current was detected. A decrease of the capacitance was observed in the accumulation regime. This effect is explained by an increase of the substrate resistivity caused by displacement damage.     

All-fiber chalcogenide-based mid-infrared supercontinuum source

An all-fiber based supercontinuum source with emission covering the wavelength range of 1.9–4.8 μm is demonstrated. The laser source is based on a combination of silica commercial off-the shelf components and a chalcogenide-based nonlinear optical fiber. The system provides 10 dB spectral flatness from 2.0 to 4.6 μm, and ?20 dBm points from 1.9 to 4.8 μm. The output power is 565 mW but scalable by scaling the repetition rate. The limit on the long wavelength edge of the system is identified as an extrinsic absorption feature in the fiber used; confirming the system could be scaled to generated a broadband source even further in the infrared.     

8 MeV electron beam induced modifications in the structural,optical and electrical properties of Al doped ZnO thin film

The influence of high energy (8 MeV) electron irradiation, with different dose rates (0 kGy, 1 kGy, 5 kGy, 10 kGy), on the structural, optical and electrical properties of sol-gel spin coated Al-doped ZnO (AZO) thin films have been studied. The X-ray diffraction curve displays the coating of c-axis oriented films under the state of compressive stress. A further analysis reveals that the interstitial sites were occupied by the Al in AZO upon electron irradiation. With the increase in irradiation dose, the energy gap of the film shows a redshift due to the enhanced localized states in the band structure. An increment in the values of refractive index of the films after irradiation is attributed to their enhanced optical density. Steady state luminescence spectra reveal the presence of zinc interstitial and oxygen interstitial defects in the irradiated film. Time-resolved photoluminescence (PL) measurement shows that the dominant defect related recombination mechanism in the irradiated films is arising due to the increased dangling bonds and defect related transitions. The increase in sheet resistance upon electron irradiation is attributed to decreasing carrier concentration in the film. The irradiated AZO film may be useful for space applications and in the radiation environment.