Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “leakage current”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Atomic-scale oxygen-vacancy engineering in Sub-2 nm thin Al 2 O 3 /MgO memristors

Ultrathin (sub-2 nm) Al 2 O 3 /MgO memristors were recently developed using an in vacuo atomic layer deposition (ALD) process that minimizes unintended defects and prevents undesirable leakage current. These memristors provide a unique platform that allows oxygen vacancies (V O ) to be inserted into the memristor with atomic precision and study how this affects the formation and rupture of conductive filaments (CFs) during memristive switching. Herein, we present a systematic study on three sets of ultrathin Al 2 O 3 /MgO memristors with V O -doping via modular MgO atomic layer insertion into an otherwise pristine insulating Al 2 O 3 atomic layer stack (ALS) using an in vacuo ALD. At a fixed memristor thickness of 17 Al 2 O 3 /MgO atomic layers (~1.9 nm), the properties of the memristors were found to be affected by the number and stacking pattern of the MgO atomic layers in the Al 2 O 3 /MgO ALS. Importantly, the trend of reduced low-state resistance and the increasing appearance of multi-step switches with an increasing number of MgO atomic layers suggests a direct correlation between the dimension and dynamic evolution of the conducting filaments and the V O concentration and distribution. Understanding such a correlation is critical to an atomic-scale control of the switching behavior of ultrathin memristors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Room-temperature large magnetoelectricity in a transition metal doped ferroelectric perovskite

There is increasing interest in novel magnetoelectric (ME) materials that exhibit robust ME coupling at room-temperature (RT) for advanced memory, energy, spintronics, and other multifunctional device applications, by making use of the ability to control polarization with a magnetic field and/or magnetization via an electric field. Obtaining ME materials with strong ME coupling, understanding the origin, and manipulating its processing along with composition to realize large ME coefficients at RT constitute an important step in multiferroic research. To address this, we have investigated the multiferroic and ME properties of Ni-doped Pb(Zr 0.20 Ti 0.80 )O 3 (PZT). We find that the ferroelectric (T C ~ 700 K) and weak ferromagnetic (~ 602 K) phase transitions of Ni-doped PZT are well above RT, leading to a strong ME coupling coefficient (α E,31 ) of 11.7 mVcm -1 Oe -1 (H ac = 1 Oe and f = 1 kHz). While X-ray diffraction suggests a single-phase material, high resolution transmission electron microscopy reveals regions with and without Ni present; thus magnetoelectric coupling between two phases is possible. First-principle calculations suggest the (Ni Pb ) × defect is likely to be responsible for the experimental observed magnetism and ME coupling in Ni-doped PZT. Furthermore, we demonstrate that Ni-doped PZT exhibits low loss tangent, low leakage current, large saturation polarization and weak ferromagnetism. Ultimately, our work demonstrates that Ni-doped PZT is a cost-effective RT multiferroic with strong ME coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Measuring the impact ionization and charge trapping probabilities in SuperCDMS HVeV phonon sensing detectors

A 0.93 g 1×1×0.4 cm 3 SuperCDMS silicon HVeV detector operated at 30 mK was illuminated by 1.91 eV photons using a room temperature pulsed laser coupled to the cryostat via fiber optic. In this work, the detector’s response under a variety of specific operating conditions was used to study the detector leakage current, charge trapping, and impact ionization in the high-purity Si substrate. The measured probabilities for a charge carrier in the detector to undergo charge trapping (0.713±0.093%) or cause impact ionization (1.576±0.110%) were found to be nearly independent of bias polarity and charge-carrier type (electron or hole) for substrate biases of ±140 V.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Charge trapping at Al/Al 2 ⁢O 3 interface facilitates hydrogen-induced superabundant metal vacancy formation

Hydrogen is a ubiquitous impurity that deteriorates the metal/oxide interface, causing challenges such as current leakage and blistering. Here, in this work, we uncover the mechanisms behind hydrogen-induced damage at the prototypical Al/A⁢l 2 ⁢O 3 interface. The precursor that we identify is charge trapping at the interface, which facilitates hydrogen segregation to the interface plane as H – . Presence of hydrogen increases aluminum vacancy concentration at the interfacial metal and oxide planes. Each Al vacancy can trap multiple hydrogen atoms. As a result, the interfacial aluminum vacancy and hydrogen concentrations increase by orders of magnitude. Additionally, hydrogen behaves as an n-type dopant and increases electronic conductivity at the oxide layer adjacent to the interface by forming H + , and the [V Al –H] complex is the predominant defect at this layer. These findings provide the precursor mechanisms of hydrogen-induced damage at the metal-oxide interfaces and have implications for advancing Al/A⁢l 2 ⁢O 3 –based coatings and electronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Vertical GaN Superjunction Diode on Sapphire with Kilovolt Dynamic Breakdown Voltage

The development of superjunction structures for use in vertical wide bandgap power devices promise to break the 1-D material limits. Additionally, the possibility of utilizing heteroepitaxial GaN-on-Sapphire wafer for vertical devices can significantly trim the material and device cost. This work introduces a quasi-vertical GaN-on-Sapphire superjunction PN diode design utilizing sputtered p-NiO on the etched GaN fins for superjunction formation. DC breakdown voltage is shown to vary with superjunction charge imbalance and significantly exceed the expected 1-D planar limit of 350V given the epilayer design used. A maximum breakdown voltage of 840 V is extracted for near charge balance conditions limited by leakage current. Dynamic breakdown of the device is characterized as a function of reverse voltage slew rate. A maximum dynamic breakdown voltage of 1160 V under a reverse voltage slew rate of 2000 V/μs is found.

Porter, Matthew↗
DOE OSTI2021

Cadmium Magnesium Telluride for Next Generation X-Ray Free Electron Laser, Synchrotron and Many Other Applications

We developed a picosecond photodetector based on our Bridgman grown and specially engineered Cadmium Magnesium Telluride (Cd 1-x Mg x Te) single crystal that is sensitive to both optical and x-ray pulses for coarse timing in Free Electron Laser applications. Cd 1-x Mg x Te is a wide bandgap semiconductor material with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma ray radiation, thermal neutrons, and medical imaging. However, for femtosecond optical and x-ray cross correlation, the material has to have very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have very low bulk leakage current, in the 0.10 pA range. Hence the ability to tailor or engineer the material is very crucial. In this paper, picosecond response and the crystal growth of this specially engineered cadmium magnesium telluride material will be presented. Other material characterization and transient measurements will also be discussed along with room temperature semiconductor detector performance for other nuclear radiation detection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Aluminum-Based Superconducting Tunnel Junction Sensors for Nuclear Recoil Spectroscopy

The BeEST experiment is searching for sub-MeV sterile neutrinos by measuring nuclear recoil energies from the decay of 7 Be implanted into superconducting tunnel junction (STJ) sensors. The recoil spectra are affected by interactions between the radioactive implants and the sensor materials. We are therefore developing aluminum-based STJs (Al-STJs) as an alternative to existing tantalum devices (Ta-STJs) to investigate how to separate material effects in the recoil spectrum from potential signatures of physics beyond the Standard Model. Three iterations of Al-STJs were fabricated. The first had electrode thicknesses similar to existing Ta-STJs. They had low responsivity and reduced resolution, but were used successfully to measure 7 Be nuclear recoil spectra. The second iteration had STJs suspended on thin SiN membranes by backside etching. These devices had low leakage current, but also low yield. The final iteration was not backside etched, and the Al-STJs had thinner electrodes and thinner tunnel barriers to increase signal amplitudes. These devices achieved 2.96 eV FWHM energy resolution at 50 eV using a pulsed 355 nm (~3.5 eV) laser. These results establish Al-STJs as viable detectors for systematic material studies in the BeEST experiment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Response of Integrated Silicon Microwave pin Diodes to X-ray and Fast-Neutron Irradiation

Here, integrated silicon microwave pin diodes are exposed to 10-keV X-rays up to a dose of 2 Mrad(SiO 2 ) and 14-MeV fast neutrons up to a fluence of 2.2×10 13 cm -2 . Changes in both DC leakage current and small-signal circuit components are examined. Degradation in performance due to total-ionizing dose is shown to be suppressed by non-quasi-static effects during RF operation. Tolerance to displacement damage from fast neutrons is also observed, which is explained using TCAD simulations. Overall, the characterized pin diodes are tolerant to cumulative radiation at levels consistent with space applications such as geosynchronous weather satellites.

42 ENGINEERING↗
DOE OSTI2023

Cadmium Magnesium Telluride for Next-Generation X-Ray Free Electron Laser, Synchrotron, and Many Other Applications

We developed a picosecond photodetector based on our Bridgman-grown and specially engineered cadmium magnesium telluride (Cd 1–x MgxTe) single crystal that is sensitive to both optical and X-ray pulses for coarse timing in free-electron laser applications. Cd 1–x MgxTe is a widebandgap semiconductor with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma-ray radiation, thermal neutrons, and medical imaging. For femtosecond optical and X-ray crosscorrelation, the material must have a very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have a very low bulk leakage current, in the 10–90 nA range for voltages to even 1000 V. Hence, the ability to tailor or engineer the material is very crucial. Picosecond response and the crystal growth of this specially engineered Cd 1–x MgxTe material are presented. Furthermore, other characterization and transient measurements are discussed along with room-temperature semiconductor detector performance for other nuclear radiation detection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Temperature-induced degradation of GaN HEMT: An in situ heating study

High-power electronics, such as GaN high electron mobility transistors (HEMTs), are expected to perform reliably in high-temperature conditions. This study aims to gain an understanding of the microscopic origin of both material and device vulnerabilities to high temperatures by real-time monitoring of the onset of structural degradation under varying temperature conditions. This is achieved by operating GaN HEMT devices in situ inside a transmission electron microscope (TEM). Electron-transparent specimens are prepared from a bulk device and heated up to 800 °C. High-resolution TEM (HRTEM), scanning TEM (STEM), energy-dispersive x-ray spectroscopy (EDS), and geometric phase analysis (GPA) are performed to evaluate crystal quality, material diffusion, and strain propagation in the sample before and after heating. Gate contact area reduction is visible from 470 °C accompanied by Ni/Au intermixing near the gate/AlGaN interface. Elevated temperatures induce significant out-of-plane lattice expansion at the SiNx/GaN/AlGaN interface, as revealed by geometry-phase GPA strain maps, while in-plane strains remain relatively consistent. Exposure to temperatures exceeding 500 °C leads to almost two orders of magnitude increase in leakage current in bulk devices in this study, which complements the results from our TEM experiment. The findings of this study offer real-time visual insights into identifying the initial location of degradation and highlight the impact of temperature on the bulk device’s structure, electrical properties, and material degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterization of high-purity germanium detectors with amorphous germanium contacts in cryogenic liquids

For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the Max-Planck-Institut für Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and cons of using thin amorphous semiconductor materials as an alternative contact technology in large-scale germanium experiments searching for physics beyond the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Development of planar P-type point contact germanium detectors for low-mass dark matter searches

The detection of low-energy deposition in the range of sub-eV through ionization using germanium (Ge) with a bandgap of ~ 0.7 eV requires internal amplification of the charge signal. This can be achieved through high electric field that accelerates charge carriers, which can then generate more charge carriers. The minimum electric field required to generate internal charge amplification is derived for different temperatures. We report the development of a planar point contact Ge detector in terms of its fabrication and the measurements of its leakage current and capacitance as a function of applied bias voltage. With the determination of the measured depletion voltage, the field distribution is calculated using GeFiCa, which predicts that the required electric field for internal charge amplification can be achieved in proximity to the point contact. The energy response to an Am-241 source is characterized and discussed. We conclude that such a detector with internal charge amplification can be used to search for low-mass dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Physics-Based Model to Represent Membrane-Electrode Assemblies of Solid-Oxide Fuel Cells Based on Gadolinium-Doped Ceria

This paper reports a physics-based model that predicts membrane-electrode assembly (MEA) performance of solid-oxide fuel cells (SOFCs) with Ce 0.9 Gd 0.1 O 2− δ (GDC10) electrolyte membranes. The paper derives self-consistent thermodynamic and transport properties for GDC1o mobile charged defects (oxide vacancies and reduced-ceria small polarons) by fitting published measurements of oxygen non-stoichiometry and conductivity over ranges of temperature and O 2 partial pressures. The button-cell model is applied to evaluate how mixed ionic-electronic conductivity influences the performance of an SOFC MEA with a GDC10 electrolyte sandwiched between a porous, composite Ni-GDC10 anode and a porous, composite cathode of Sm 0.5 Sr 0.5 CoO 3− δ (i.e., SSC) and GDC10. SSC properties are also derived by fitting published conductivity and oxygen non-stoichiometry measurements. Mixed conductivity of GDC10 and competing charge transfer reactions at both electrodes reduce open circuit voltages due to leakage current and buildup of defect concentrations at electrode-electrolyte interfaces. To fit polarization data, the button-cell model includes heterogeneous reaction rates for defect incorporation on the GDC10 surface along with Butler–Volmer expressions derived for competing charge transfer reaction rates from rigorous analyses assuming rate-limiting, elementary charge transfer reactions for each electrode. The calibrated MEA model can support rigorous SOFC modeling with GDC10 electrolytes over the range of conditions within a fully operating cell.

Electrochemistry↗
DOE OSTI2025

Modeling a High-Temperature Electrochemically Driven Water-Gas-Shift Process Using a Mixed-Conducting Membrane without External Electrical Power

This paper develops a model to predict and interpret the performance of an elevated-temperature, electrochemical, membrane-assisted, water-gas-shift process. The process uses separated feed streams of H 2 O and CO to produce separated streams of H 2 and CO 2 , without an external electrical power source. The dense ceramic membrane is mixed ionic-electronic-conducting (MIEC) gadolinium-doped ceria (GDC) and the porous composite electrodes are Ni-YSZ. At elevated temperature, GDC conducts both oxygen ions and small polarons. The present process uses chemical potential to drive the process. Electrochemical oxidation of CO proceeds within the composite anode and H 2 O reduction proceeds within the composite cathode. At high temperature (e.g., T > 700 °C), GDC has significant electronic leakage in the form of a reduced-cerium small polaron, which supports the charge-transfer reactions. In a typical electrolyzer or fuel cell, this leakage is significantly problematic. However, the present process depends on the leakage current to complete the electrochemical circuit. Model development and validation is based on measured material properties and reactor performance. Potential applications include using CO-rich blast-furnace off gases in steel processing, producing separated streams of H 2 and CO 2 .

Zhu, Huayang↗
DOE OSTI2023

Enhancement in electro-optic performance of InAlGaAs/GaAs quantum dot lasers by ex situ thermal annealing

Here, this Letter reports the growth, fabrication, and characterization of molecular beam epitaxy (MBE)-grown quaternary InAlGaAs/GaAs quantum dot (QD) lasers emitting at sub-900 nm. The presence of Al in QD-based active regions acts as the origin of defects and non-radiative recombination centers. Applying optimized thermal annealing annihilates the defects in p-i-n diodes, thus lowering the reverse leakage current by six orders of magnitude compared to as-grown devices. A systematic improvement in the optical properties of the devices is also observed in the laser devices with increasing annealing time. At an annealing temperature of 700°C for 180 s, Fabry–Pérot lasers exhibit a lower pulsed threshold current density at infinite length of 570 A/cm 2 .

42 ENGINEERING↗
DOE OSTI2022

Ultra-power-efficient heterogeneous III–V/Si MOSCAP (de-)interleavers for DWDM optical links

We discuss the design and demonstration of various III–V/Si asymmetric Mach–Zehnder interferometer (AMZI) and ring-assisted AMZI (de-)interleavers operating at O-band wavelengths with 65 GHz channel spacing. The wafer-bonded III–V/Si metal-oxide-semiconductor capacitor (MOSCAP) structure facilitates ultra-low-power phase tuning on a heterogeneous platform that allows for complete monolithic transceiver photonic integration. The second- and third-order MOSCAP AMZI (de-)interleavers exhibit cross-talk (XT) levels down to − 22 dB and − 32 dB with tuning powers of 83.0 nW and 53.0 nW, respectively. The one-, two-, and three-ring-assisted MOSCAP AMZI (de-)interleavers have XT levels down to − 27 dB, − 22 dB, and − 20 dB for tuning powers of 10.0 nW, 7220.0 nW, and 33.6 nW, respectively. The leakage current density is measured to be in the range of 1.6 – 27 μA / cm 2 . To the best of our knowledge, we have demonstrated for the first time, athermal III–V/Si MOSCAP (de-)interleavers with the lowest XT and reconfiguration power consumption on a silicon platform.

Cheung, Stanley (ORCID:0000000248860013)↗
DOE OSTI2025

A high-temperature Rutherford Backscattering Spectrometry apparatus for in situ material characterization

A new methodology for high-temperature Rutherford Backscattering Spectrometry (HT-RBS) has been developed to enable in situ material characterization at elevated temperatures. A 3.5 MeV proton beam penetrates a 10-µm-thick 316L stainless steel foil mounted on a graphite substrate, with backscattered signals detected using an HT-RBS system. Conventional semiconductor detectors, primarily based on silicon, suffer significant performance degradation at temperatures higher than ~ 60 °C due to increased leakage current and noise, leading to signal distortion and failure. Here, to preserve spectral quality, a 5 µm aluminum foil shields the detector from thermal radiation, allowing reliable operation up to 900 °C at the target. A rotatable shutter provides additional thermal isolation during data collection pauses. In situ measurements of areal density changes of 316L stainless steel were conducted to validate the technique, revealing consistency with the known thermal expansion coefficient. The method facilitates seamless switching between irradiation and analysis, enabling continuous studies. This approach supports in situ investigations of diffusion, void swelling, creep, and corrosion, offering a versatile tool for advanced materials research.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Collider Physics (Final Technical Report)

The UNM members of the ATLAS Collaboration published a comprehensive study of ATLAS Pixel leakage current recorded from the beginning of Run 1 through the end of Run 2. This study depended upon a hardware system that was designed and built by UNM and installed by us in the ATLAS cavern. The study compared ATLAS data to predictions by the Hamburg Model, thereby leveraging ATLAS data to improve a widely used simulation that has application to other LHC experiments as well as silicon systems in radiation environments outside HEP applications. Having validated the model in this way, we then used it to make predictions for ATLAS tracker design and operational conditions in Run 3 and beyond.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗