10-keV X-ray Research Articles

Ultra-thin oxide growth on silicon during 10keV x-ray irradiation

Abstract Surface effects on silicon wafers irradiated by 10 keV x-rays at room temperature were characterized using x-ray photoelectron spectroscopy and spectroscopic ellipsometry. The samples were exposed to total ionizing doses ranging from 1.0 to 12 Mrad(SiO2) at x-ray dose rates ranging from 5.8 krad(SiO2)/min to 67 krad(SiO2)/min. Accelerated thin oxide growth on irradiated samples compared to natural native oxide growth under room temperature conditions was demonstrated, and the composition of the irradiation-accelerated oxide was investigated. The presence of suboxides along with silicon dioxide was confirmed on the irradiated silicon sample. Two thin oxide growth models were applied to characterize the enhanced oxidation rate observed for irradiated wafers.

Impact of Total Ionizing Dose on a 4th Generation, 90 nm SiGe HBT Gaussian Pulse Generator

We investigate the effects of total ionizing dose (TID) on a Gaussian pulse generator implemented in IBM's new 9HP SiGe BiCMOS platform, which combines 300 GHz fT SiGe HBTs and 90 nm CMOS. Total dose effects were examined using a 10-keV X-ray source. The effects of TID on the performance of the pulse generator were investigated with the pulse generator exhibiting a tpw variation of less than 7% for total dose of up to 3.0 Mrad. This circuit is intended for low-power autonomous high-altitude and space-based imaging radars.

Total Ionizing Dose Effects on hBN Encapsulated Graphene Devices

The constant-voltage electrical stress and 10-keV X-ray irradiation responses of encapsulated graphene-hBN devices are evaluated. Both constant-voltage stress and X-ray exposure induce only modest shifts in the current and the Dirac point of the graphene. Charge trapping at or near the graphene/BN interface is observed after X-ray irradiation. The experimental results suggest that net hole trapping occurs in the BN at low doses and that net electron trapping occurs at higher doses. First-principles calculations also demonstrate that hydrogenated substitutional carbon impurities at B/N sites at or near the graphene/BN interface can play an additional role in the radiation response of these structures.

Electrical Stress and Total Ionizing Dose Effects on <formula formulatype="inline"><tex Notation="TeX">${\hbox {MoS}}_{2}$</tex> </formula> Transistors

Electrical stress and 10-keV x-ray irradiation and annealing responses are evaluated for back-gate MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> transistors. Relative stability of device characteristics is observed for constant-voltage stress. The drain current decreases significantly after both positive and negative bias irradiation. Density functional theory calculations and ozone exposure experiments suggest that O atoms adsorbed on the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surface during 10-keV x-ray irradiation function as electron traps, causing mobility degradation and voltage shifts.

Total Ionizing Dose Effects in Si-Based Tunnel FETs

Total ionizing dose (TID) effects in Si-based tunnel finite element transfers (FETs) were investigated for the first time. Under 10-keV X-ray irradiation environment, along with the increase in total dose, a shift of the transfer characteristics and an increase in the interface trap density could be observed. After irradiation at 1 Mrad (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) (and higher dose), the threshold voltage and the band-to-band tunneling conduction were only modestly affected, despite the thick buried oxide (140 nm). In contrast, under the same bias and irradiation environment, a FDSOI nMOSFET fabricated with a similar process presented a more severe degradation, suggesting the robustness of TFETs against TID effects. The underlying mechanism was explored through device simulation and ascribed to be due to the peculiarity of the doping structures of TFETs.

DLSR design and plans: an international overview.

It has been known for decades that the emittance of multi-GeV storage rings can be reduced to very small values using multi-bend achromat (MBA) lattices. However, a practical design of a ring having emittance approaching the diffraction limit for multi-keV photons, i.e. a diffraction-limited storage ring (DLSR), with a circumference of order 1 km or less was not possible before the development of small-aperture vacuum systems and other accelerator technology, together with an evolution in the understanding and accurate simulation of non-linear beam dynamics, had taken place. The 3-GeV MAX IV project in Sweden has initiated a new era of MBA storage ring light source design, i.e. a fourth generation, with the Sirius project in Brazil now following suit, each having an order of magnitude smaller horizontal emittance than third-generation machines. The ESRF, APS and SPring-8 are all exploring 6-GeV MBA lattice conversions in the imminent future while China is considering a similar-energy green-field machine. Other lower-energy facilities, including the ALS, SLS, Soleil, Diamond and others, are studying the possibility of such conversions. Future larger-circumference rings, possibly housed in >2-km tunnels made available by decommissioned high-energy physics accelerators, could have sub-10-pm-rad emittances, providing very high coherence for >10-keV X-rays. A review of fourth-generation ring design concepts and plans in the world is presented.

Total-ionizing-dose effects and reliability of carbon nanotube FET devices

Electrical stress and 10-keV X-ray irradiation and annealing responses are evaluated for carbon nanotube field effect transistors for nonvolatile memory applications. Less than 3% change in the drain current is observed during constant-voltage stress. Irradiation and annealing under positive gate bias induces more degradation in both drain current and memory window than under negative bias. Cycling of the on/off state leads to significant degradation in the memory window.

The Impact of X-Ray and Proton Irradiation on ${\rm HfO}_2/{\rm Hf}$-Based Bipolar Resistive Memories

This paper investigates total-ionizing dose effects on the electrical characteristics of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Hf-based bipolar resistive-random-access-memory (RRAM) devices. 10-keV x-ray irradiation does not cause significant changes in resistance at levels up to 7 Mrad( SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). Excess carriers generated by x-ray irradiation in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer recombine or are trapped at defect sites in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer or at interfaces between layers. They have no effect, however, on the conductive path of the RRAM devices. 1.8 MeV proton irradiation causes resistance degradation through simultaneous introduction of oxygen vacancies and displacement damage. TRIM simulations are used to explain the physical mechanisms of the radiation-induced damage. The devices are promising for radiation-hardened memory applications.

An Investigation of Total Ionizing Dose Damage on a Pulse Generator Intended for Space-Based Impulse Radio UWB Transceivers

We investigate, for the first time, the effects of total ionizing dose (TID) on a CMOS pulse generator implemented in a SiGe BiCMOS platform, and which is intended for use in space-based impulse radio ultra-wideband transceivers. The pulse generator was fabricated in Jazz Semiconductor's SBC18-H3 SiGe BiCMOS process technology, which combines 250 GHz SiGe HBTs and 180 nm CMOS. Total dose effects were examined using a 10-keV X-ray source. The effects of the TID on the performance of the pulse generator were investigated and a compensation scheme for mitigating these radiation effects is proposed.

ZnO nanowires in polycarbonate membrane as a high resolution X-ray detector (a Geant4 simulation)

The capability of polycarbonate cladded ZnO nanowires as scintillating optical fibers, in the presence of the 10keV X-ray is simulated using the Geant4 Monte Carlo simulation code. The simulated results show that using millions of scintillating fibers in a 1mm2 area, which are packed together in a polycarbonate membrane, have additional light guiding role that reduces the scattering of the X-ray generated optical photons inside the detector. This new low-cost technique can provide a higher spatial resolution X-ray imager with sharper edges at the object boundaries in comparison to a single crystal scintillating macro detectors.

Micro-focusing of hard x-ray free electron laser radiation using Kirkpatrick-Baez mirror system

We developed micro-focusing Kirkpatrick-Baez (K-B) mirror optics for the X-ray free electron laser (XFEL) at the SPring-8 Angstrom Compact free electron Laser (SACLA) facility in Japan. The K-B focusing mirrors have a spatial acceptance of 600 × 600 μm2 and ultra-precision surfaces. A manipulator for precise alignment of the mirrors was also developed. The focusing properties for 10-keV X-rays were evaluated with a wire-scanning method. The focal beam size was determined to be 0.95 μm × 1.20 μm at the full width at half maximum. An increased power density of 1018 W/cm2 was achieved at the focal point. These properties were confirmed to be in good agreement with the designed value.

Proposal for a Pulse-Compression Scheme in X-Ray Free-Electron Lasers to Generate a Multiterawatt, Attosecond X-Ray Pulse

A novel scheme to compress the radiation pulse in x-ray free electron lasers is proposed not only to shorten the pulse length but also to enhance the peak power of the radiation, by inducing a periodic current enhancement with an optical laser and applying a temporal shift between the optical and electron beams. Calculations show that a 10-keV x-ray pulse with a peak power of 5 TW and a pulse length of 50 asec can be generated by applying this scheme to an existing x-ray free electron laser facility.

X-RAY PROPERTIES OF THE NORTHERN GALACTIC CAP SOURCES IN THE 58 MONTHSWIFT/BAT CATALOG

We present a detailed X-ray spectral analysis of a complete sample of hard X-ray selected AGN in the Northern Galactic Cap of the 58-month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGN with b>50deg. This region has excellent potential for further study due to the availability of a wide range of archival multi-wavelength data, and we propose it as a low-redshift analog to the `deep fields' work on AGN at higher redshifts. We present distributions of luminosity, absorption, and other key quantities, from fitting new and archival X-ray data gathered from XMM-Newton, Swift/XRT, ASCA and Swift/BAT. We probe to deeper redshifts than the 9-month BAT catalog (<z>=0.043), and uncover a broader absorbing column density distribution. The fraction of obscured (log N_H >= 22) objects in the sample is ~60%, and 43--56% of the sample exhibits `complex' 0.4--10keV spectra. The soft excess is either well-detected in AGN or undetected, suggesting that the process responsible for producing the soft excess is not ubiquitous. The fraction of Compton-thick sources in our sample is ~9%, and `hidden/buried AGN' constitute ~14% of our sample. Compton reflection is found to be important in a large fraction of our sample using joint XMM-Newton+BAT fits (reflection amplitude <R> = 2.7 +/- 0.75), indicating light bending or extremely complex absorption. The average 1--10keV spectrum for the sample reproduces the 1--10keV X-ray background slope as found for the 9-month BAT AGN sample. The completeness limit for the sample is ~4 times fainter than that for the 9-month catalog (abridged).

Electrical Stress and Total Ionizing Dose Effects on Graphene-Based Non-Volatile Memory Devices

Electrical stress and 10-keV x-ray and 1.8-MeV proton irradiation and annealing responses are evaluated for graphene-based non-volatile memory devices. The memory characteristics of these structures derive primarily from hysteretic charge exchange between the graphene and interface and border traps, similar to the operation of metal-nitride-oxide-semiconductor memory devices. Excellent stability and memory retention are observed for ionizing radiation exposure or constant-voltage stress. Cycling of the memory state leads to a significant reduction in memory window.

Surface Reactions and Defect Formation in Irradiated Graphene Devices

Quantum mechanical-based kinetic Monte-Carlo calculations (KMC) are used to investigate mechanisms of degradation of graphene devices subjected to 10-keV x-ray irradiation, ozone exposure, and subsequent high-temperature annealing. Using KMC, we monitor the time evolution of defect concentrations on a graphene surface. The degradation mechanism for oxygen exposure and subsequent anneal of graphene surface greatly depends on the temperature and initial concentrations of H and O atoms on the graphene surface. At oxygen surface coverage of ~0.05 and higher, the damage is caused by formation of vacancies due to desorption of CO and CO2. Hydrogen facilitates the removal of O without introducing vacancies.

Particle induced X-ray emission and ion dose distribution in a biological micro-beam: Geant4 Monte Carlo simulations

The goal of a microbeam is to deliver a highly localized and small dose to the biological medium. This can be achieved by using a set of collimators that confine the charged particle beam to a very small spatial area of the order of microns in diameter. By using a system that combines an appropriate beam detection method that signals to a beam shut-down mechanism, a predetermined and counted number of energetic particles can be delivered to targeted biological cells. Since the shutter and the collimators block a significant proportion of the beam, there is a probability of the production of low energy X-rays and secondary electrons through interactions with the beam. There is little information in the biological microbeam literature on potential X-ray production. We therefore used Monte Carlo simulations to investigate the potential production of particle-induced X-rays and secondary electrons in the collimation system (which is predominantly made of tungsten) and the subsequent possible effects on the total absorbed dose delivered to the biological medium.We found, through the simulation, no evidence of the escape of X-rays or secondary electrons from the collimation system for proton energies up to 3MeV as we found that the thickness of the collimators is sufficient to reabsorb all of the generated low energy X-rays and secondary electrons. However, if the proton energy exceeds 3MeV our simulations suggest that 10keV X-rays can escape the collimator and expose the overlying layer of cells and medium. If the proton energy is further increased to 4.5MeV or beyond, the collimator can become a significant source of 10keV and 59keV X-rays. These additional radiation fields could have effects on cells and these results should be verified through experimental measurement. We suggest that researchers using biological microbeams at higher energies need to be aware that cells may be exposed to a mixed LET radiation field and be careful in their interpretation of data.Two other factors can affect the pattern of dose deposition in the biological medium: the phase space distribution of the beam particles and the production of secondary electrons (known as δ-rays). We investigated this by projecting simulated particles oriented at small angles with the beam axis. For lower fluence (2.6×104 protons mm−2), we determined that despite only the target cell being assumed to be hit by the particle beam, some significant level of radiation dose was, in fact, delivered to the adjacent cells. This was most probably due to secondary electrons. The simulation showed that two of the cells adjacent to the target cell received 42% and 5% of the dose delivered to the target cell per proton. When the incident fluence on the collimator was increased to 1.3×106 protons mm−2, it was observed that a significant number of protons deflected from the collimator spread into an area of 4340μm2. This is a significant spread when compared to the target area of 25μm2. The maximum number of particles that were delivered off-target was 25% of the particles delivered to the target cell. This equates to a probability of delivering 1 particle anywhere in an area of 4340μm2 for every 4 particles delivered to the target cell. This result has significant implications. Results of this work warrant a further investigation because if these results can be re validated, perhaps experimentally or through another simulation code, then they may have significant implications on the interpretation of published data from biological microbeam experiments.

Accelerated Oxidation of Silicon Due to X-ray Irradiation

Enhanced rates of oxide growth have been observed on silicon upon exposure to 10-keV X-ray irradiation. Oxide thicknesses were determined using spectroscopic ellipsometry on irradiated and control samples, and confirmed via X-ray photoelectron spectroscopy. The oxidation rate varied with the radiation total dose and dose rate. The increased oxidation rate is attributed to the generation of ozone, which decomposes into molecular oxygen and highly reactive atomic oxygen at the surface of the Si wafer. The generation of ozone by 10-keV X-rays was found to increase linearly with increasing dose rate. UV irradiation led to similarly enhanced oxidation rates. The potential application of this phenomenon to dosimetry is explored.

Effects of Metal Gates and Back-End-of-Line Materials on X-Ray Dose in ${\rm HfO}_{2}$ Gate Oxide

The effects of 10-keV and 400-keV endpoint-energy bremsstrahlung x-rays have been studied using the Monte Carlo simulator, MRED, for MOS capacitors with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics and TiN and TaN metal gates. We compute the reduction in dose that occurs for 10-keV x-ray irradiation of thin HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics sandwiched between the metal gate and the Si substrate. We quantify the effects of back-end-of-line metallization layers, including copper interconnects, W vias, and borophosphosilicate glass (BPSG) and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> passivation layers for low and medium energy x-rays. For thick metallization stacks irradiated by 10-keV x-rays, dose enhancement or attenuation can occur, depending on material type and overlayer thicknesses. For similar stacks irradiated with 400-keV endpoint-energy bremsstrahlung x-rays, significant dose enhancement is observed.

Low-Energy X-ray and Ozone-Exposure Induced Defect Formation in Graphene Materials and Devices

We have evaluated the responses of graphene materials and devices to 10-keV X-ray irradiation and ozone exposure. Large positive shifts are observed in the current-voltage characteristics of graphene-on- SiO2 transistors irradiated under negative gate bias. Moreover, significant radiation-induced increases are found in the resistance of suspended graphene layers; the charge neutral point (CNP) of the graphene layer also shifts positively with increasing total dose. Raman spectroscopy shows that similar defects are generated in graphene-on-SiO2 sheets by 10-keV X-ray irradiation and ozone exposure. First principles calculations of the relevant binding energies, and reaction and diffusion barriers for oxygen on graphene, strongly suggest that oxygen adsorption and reactions, along with the resulting p -type doping, can lead to the observed degradation of irradiated or ozone-exposed graphene materials and devices.

Dose Enhancement and Reduction in SiO$_{2}$ and High-$\kappa$ MOS Insulators

The effects of 10-keV X-rays and 400-keV endpoint-energy bremsstrahlung X-rays on MOS capacitors with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics and Al and TaSi gate metallization have been studied using the Monte Carlo simulator, MRED. We compare these calculations with previous results in the literature obtained with other Monte Carlo and discrete ordinates codes, and with experiments on devices with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectrics, and find generally good agreement. There is a significant dose reduction in thin HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers exposed to 10-keV X-rays, when the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is surrounded by lower-Z materials (e.g., Si, Al). This dose reduction does not occur in a medium-energy bremsstrahlung X-ray environment; in that case, the dose in a HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate dielectric can be ~10 times higher than the dose in a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric, for the same incident X-ray fluence. These results demonstrate the capability of MRED to assist in the evaluation of dose enhancement and reduction in regions including or nearby high-Z materials in microelectronic materials and devices.