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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.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Plasma-assisted deposition and characterization of Al 2 O 3 dielectric layers on (001) β -Ga 2 O 3

In this work, we have investigated plasma-assisted deposition of Al 2 O 3 on HVPE (001) β-Ga 2 O 3 and evaluated the dielectric quality from electrical measurements on fabricated metal-oxide-semiconductor (MOS) capacitors. The interface structure and crystallinity of the films were investigated as a function of the growth temperature. The dielectric/semiconductor interfaces were found to have reverse breakdown electric fields up to 5.3 MV/cm in the β-Ga 2 O 3 , with relatively low hysteresis in capacitance–voltage and low leakage current. We determined a negative fixed interface charge density at the interface from analysis of thickness-dependent capacitance voltage data. In conclusion, this study shows the advantage of using plasma-assisted deposition to achieve high breakdown strength Al 2 O 3 /β-Ga 2 O 3 MOS structures for device application purposes.

42 ENGINEERING↗
DOE OSTI2024

Voltage waveform tailoring for high aspect ratio plasma etching of SiO 2 using Ar/CF 4 /O 2 mixtures: Consequences of low fundamental frequency biases

The use of non-sinusoidal waveforms in low pressure capacitively coupled plasmas intended for microelectronics fabrication has the goal of customizing ion and electron energy and angular distributions to the wafer. One such non-sinusoidal waveform uses the sum of consecutive harmonics of a fundamental sinusoidal frequency, f 0 , having a variable phase offset between the fundamental and even harmonics. In this paper, we discuss results from a computational investigation of the relation between ion energy and DC self-bias when varying the fundamental frequency f 0 for capacitively coupled plasmas sustained in Ar/CF 4 /O 2 and how those trends translate to a high aspect ratio etching of trenches in SiO 2 . The fundamental frequency, f 0 , was varied from 1 to 10 MHz and the relative phase from 0° to 180°. Two distinct regimes were identified. Average ion energy onto the wafer is strongly correlated with the DC self-bias at high f 0 , with there being a maximum at φ = 0° and minimum at φ = 180°. In the low frequency regime, this correlation is weak. Average ion energy onto the wafer is instead dominated by dynamic transients in the applied voltage waveforms, with a maximum at φ = 180° and minimum at φ = 0°. The trends in ion energy translate to etch properties. In both, the high and low frequency regimes, higher ion energies translate to higher etch rates and generally preferable final features, though behaving differently with phase angle.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optimizing protic ionic liquid electrolyte for pre-intercalated Ti 3 C 2 T x MXene supercapacitor electrodes

Electrical double-layer capacitors (EDLCs) are of increasing importance in energy storage from renewable sources. The properties of the electrode and electrolyte materials influence the energy and power densities of EDLCs. We examined the specific capacitance and ion dynamics of a protic ionic liquid confined in pre-intercalated Ti 3 C 2 T x MXene. Our electrochemical measurements demonstrated that the creation of a protic ionic liquid, 1-butyl-3-H-imidazolium bis(trifluoromethanesulfonyl)imide (BuIMH-NTf2), using a mixture of ionic liquid, 1-butyl imidazole (BuIM), and salt, bis(trifluoromethanesulfonyl)imide (HNTf2), in a ratio of 0.8:0.2 led to the optimal capacitance. Remarkably, quasi-elastic neutron scattering measurements revealed increased particle mobility at this composition, attributed to the more efficient accumulation of BuIMH + on the electrode surface. This deposit of additional ions results in fewer BuIM molecules away from the surface, enhancing their mobility due to reduced crowding. This composition-dependent electrochemical behavior will guide the formulation of more efficient protic ionic liquid systems, enabling faster ion transport in energy storage devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Origin of proton irradiation-induced deep acceptors in Al 0.70 Ga 0.30 N

Deep level defect introduction and carrier removal were characterized using steady-state photocapacitance (SSPC), deep level transient spectroscopy (DLTS) and lighted capacitance–voltage for proton irradiated n-type Al 0.70 Ga 0.30 N Schottky diodes grown by metal-organic vapor phase epitaxy on AlN-on-sapphire templates. SSPC observed deep levels in the as-grown diode with zero-phonon transition energies of 2.20, 2.65, 3.10, 3.40, and 4.65 eV relative to the conduction band minimum (E c ), and an additional deep level emerged at 1.20 eV with irradiation. Lighted capacitance–voltage measurements quantified the deep level concentration (N t ) of states detected by SSPC, and it was observed that N t increased with proton fluence only for the 1.2 and 4.65 eV levels. Carrier removal was much larger than the increase in N t of the 1.2 and 4.65 eV deep levels, suggesting that radiation-induced deep level compensators existed beyond what was detected with SSPC. DLTS detected additional, proton-induced deep acceptors at E c —0.55, 0.82, and 1.16 eV, the latter of which is likely the same 1.20 eV deep state observed by SSPC. The concentration of the E c —0.82 eV defect state was large enough to reconcile carrier removal with total deep level introduction. Comparing the E c —0.82 and 1.16 eV deep acceptor levels to previous experimental and theoretical reports suggests that their atomistic origins could be the nitrogen vacancy (V N ) and oxygen substituting on the nitrogen sub-lattice (O N ), respectively. This defect behavior contrasts starkly with GaN, where V N and O N are shallow donors, and demonstrates that the electronic properties of defects can evolve drastically within the AlGaN alloy system ranging from wide bandgap GaN to ultra-wide bandgap AlN.

Armstrong, Andrew Michael [Sandia National Laborat↗
DOE OSTI2025

A sensing material-free and simple readout MEMS sensor for detecting Helium

Abstract In this work, we report a method that enables a standard electrostatic MEMS device to perform complex sensing functionalities, such as detecting the presence of helium without a sensing material or a conditioning circuit. Helium is a noble, odorless, non-reactive gas that is very challenging to detect. It is used in critical applications such as storing nuclear fuel waste inside a dry cask. In these applications, its leakage from the dry cask may indicate the cask's safe operation's degradation. A departure from the common practice of exciting the MEMS around its mechanical resonance, the method is based on exciting the MEMS around its electrical resonance circuit. This method shows that the tiny difference between the air dielectric constant (1.00059) and helium (1.000067) corresponding to only a few Femtofarad level capacitances produces a 25 mV difference without a conditioning circuit. Simulation results confirmed those findings and explored the sensor response at different operation conditions. This method eliminates the need for a heated microstructure and the need for absorption material. This method is not limited to gas sensing. It can be applied to other sensing mechanisms, such as acceleration and pressure measurements, and eliminate the complex circuit to read small capacitance in these applications.

Mohaidat, Sulaiman↗
DOE OSTI2022

Trivalent ion overcharging on electrified graphene

We report the structure of the electrical double layer (EDL) formed near graphene in aqueous environments strongly impacts its performance for a plethora of applications, including capacitive deionization. In particular, adsorption and organization of multivalent counterions near the graphene interface can promote nonclassical behaviors of EDL including overcharging followed by co-ion adsorption. In this paper, we characterize the EDL formed near an electrified graphene interface in dilute aqueous YCl 3 solution using in situ high resolution x-ray reflectivity (also known as crystal truncation rod) and resonant anomalous x-ray reflectivity (RAXR). These interface-specific techniques reveal the electron density profiles with molecular-scale resolution. We find that yttrium ions (Y 3+ ) readily adsorb to the negatively charged graphene surface to form an extended ion profile. This ion distribution resembles a classical diffuse layer but with a significantly high ion coverage, i.e., 1 Y 3+ per 11.4 ± 1.6 Å 2 , compared to the value calculated from the capacitance measured by cyclic voltammetry (1 Y 3+ per ~240 Å 2 ). Such overcharging can be explained by co-adsorption of chloride that effectively screens the excess positive charge. The adsorbed Y 3+ profile also shows a molecular-scale gap (≥ 5 Å) from the top graphene surfaces, which is attributed to the presence of intervening water molecules between the adsorbents and adsorbates as well as the lack of inner-sphere surface complexation on chemically inert graphene. We also demonstrate controlled adsorption by varying the applied potential and reveal consistent Y 3+ ion position with respect to the surface and increasing cation coverage with increasing the magnitude of the negative potential. This is the first experimental description of a model graphene-aqueous system with controlled potential and provides important insights into the application of graphene-based systems for enhanced and selective ion separations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Optical characterization of deep-level defects in n-type Al x In y Ga 1- x - y P for the development of solid-state photomultiplier analogs

Characterizing intrinsic defects is an essential step in evaluating materials for novel optoelectronic device applications. For photomultipliers, suppressing dark currents is critical, but a tradeoff is present between maximizing the band gap while remaining sensitive to the wavelength of interest and minimizing the incorporation of fresh defects by growing not-yet-optimized alloys. We present a series of capacitance-based measurements, including deep-level optical spectroscopy, steady-state photocapacitance, and illuminated capacitance-voltage, on photodiodes with lightly n-type Al x In y Ga 1−x−y P absorber regions. Several deep levels are identified, including one near the midgap. Although the inclusion of aluminum increases each trap density by approximately 10×, the hole capture cross-section also appears to decrease, suggesting that Shockley–Read–Hall dark currents may be suppressed. These materials may be good candidates for the development into silicon photomultiplier analogs with a wider bandgap for scintillator applications.

III–V↗
DOE OSTI2024

Magnetization dynamics driven by displacement currents across a magnetic tunnel junction

Understanding the high-frequency transport characteristics of magnetic tunnel junctions (MTJs) is crucial for the development of fast-operating spintronics memories and radio frequency devices. Here, we present the study of a frequency-dependent capacitive current effect in Co Fe B / Mg O -based MTJs and its influence on magnetization dynamics using a time-resolved magneto-optical Kerr effect technique. In our device, operating at gigahertz frequencies, we find a large displacement current of the order of mA, which does not break the tunnel barrier of the MTJ. Importantly, this current generates an Oersted field and spin-orbit torque, inducing magnetization dynamics. Our discovery holds promise for building robust MTJ devices operating under high current conditions, also highlighting the significance of capacitive impedance in high-frequency magnetotransport techniques. Published by the American Physical Society 2024

Safeer, C. K. (ORCID:0000000323969730)↗
DOE OSTI2021

Correlated Double-Electron Additions at the Edge of a Two-Dimensional Electronic System

We create laterally large and low-disorder GaAs quantum-well-based quantum dots that act as small two-dimensional electron systems. We monitor tunneling of single electrons to the dots by means of capacitance measurements and identify single-electron capacitance peaks in the addition spectrum from occupancies of one up to thousands of electrons. The data show two remarkable phenomena in the Landau level filling factor range ν = 2 to ν = 5 in selective probing of the edge states of the dot: (i) Coulomb blockade peaks arise from the entrance of two electrons rather than one; (ii) at and near ν = 5/2 and at fixed gate voltage, these double-height peaks appear uniformly in a magnetic field with a flux periodicity of h/2e, but they group into pairs at other filling factors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Loop Antennas for Use On/Off Ground Planes

Many applications benefit from the ability of an RFID tag to operate both on and off a conducting ground plane. This paper presents an electrically small loop antenna at 433 MHz that passively maintains its free-space tune and match when located a certain distance away from a large conducting ground plane. The design achieves this using a single radiation mechanism (that of a loop) in both environments without the use of a ground plane or EBG/AMC structure. An equivalent circuit model is developed that explains the dual-environment behavior and shows that the geometry balances inductive and capacitive parasitics introduced by the ground plane such that the free-space loop reactance, and thus resonant frequency, does not change. A design equation for balancing the inductive and capacitive parasitic effects is derived. Finally, experimental data showing the design eliminates ground plane detuning in practice is presented. The design is suitable for active, “hard” RFID tag applications.

42 ENGINEERING↗
DOE OSTI2019

A Simple Control to Reduce Device Over-Voltage Caused by Non-Active Switch Loop in Three-Level ANPC Converters

With the development of wide band-gap (WBG) technology, the switching speed of power semiconductor devices increases, which makes circuits more sensitive to parasitics. For three-level active neutral point clamped (3L-ANPC) converters, the over-voltage caused by additional non-active switch loop can be an issue. This paper analyzes the multiple commutation loops in 3L-ANPC converter and summarizes the impact factors of the device over-voltage. The nonlinearity of the output capacitance of the device can significantly influence the over-voltage. A simple control without introducing additional hardware circuit or complex software algorithm is proposed to attenuate the effect of the nonlinear output capacitance. Multi-pulse test is conducted for a 3L-ANPC converter built with silicon carbide (SiC) MOSFETs. With the proposed control, the testing results show that the peak drain-source voltage of both active and non-active switches is reduced by more than 20% compared to the conventional control.

Gui, Handong↗
DOE OSTI2020

DC Link Capacitor Reduction with Feedforward Control in Series-Series Compensated Wireless Power Transfer Systems

This paper presents the use of feedforward control to reduce the input side DC link capacitance of series-series compensated wireless power transfer (WPT) systems. Compared to conventional control schemes for WPT systems, the proposed feedforward-based approach achieves significant reduction in the DC link capacitor without any complicated voltage or current sensing requirements from the secondary side. This results in more compact hardware architecture. The proposed method shows minimal increase in the turn-on switching loss of the inverter. The switching loss is analyzed, and detailed results are presented relating the switching loss to the DC link capacitance and voltage ripple for proper tradeoff between losses and capacitor size. Simulation and experimental results presented validate the proposed scheme.

Mukherjee, Subho↗
DOE OSTI2023

A Multi-Harmonic System Identification Method for Internal Circuit Element Monitoring

Many critical infrastructures depend on the reliability of electronic circuits, whose health depends on the values of internal circuit elements that degrade over time. It is therefore important to estimate the values of internal circuit elements from external measurements and monitor them for changes. The challenge to doing so is that, typically, the internal voltages and currents are not accessible for measurement. Prior work on internal circuit element monitoring uses data obtained from sensors placed inside the circuit or requires additional circuitry to be added to the given system, both of which are undesirable. We propose a new multi-harmonic frequency-domain based system identification method that is non-intrusive. It exploits the latent non-idealities already present in the system, specifically harmonics in the measured input and output signals. We show how sensitivity analysis can be used to both assess the accuracy of the method as well as to optimize the choice of harmonics to use. We use as a motivation and illustrative example the problem of determining the equivalent series resistance and capacitance in a class of dc-link capacitance circuits in Adjustable Speed Drives. We assess the performance of this method using simulations, and establish its validity by experimental results.

Deshpande, Ankit Vivek↗
DOE OSTI2024

First Demonstration of Vertical 2T-nC FeRAM Hybrid Cell and its Scalability for High-Density 3D Ferroelectric Capacitor Memory

In this article, we perform a comprehensive experimental and modeling study into the scaling of vertical 2T-nC ferroelectric random-access memory (FeRAM) hybrid cell to demonstrate a high performance and high-density 3D capacitor memory. We demonstrate: i) first time successful integration of the vertical 2T-3C FeRAM cell by stacking the vertical metal-ferroelectricmetal (MFM) stack on top of Si CMOS transistors; ii) successful experimental operation of the memory cell, including the quasi-nondestructive read out (QNRO) of the polarization without write back after 106 read cycles; iii) the write bit line (WBL) heavily screens the coupling between neighboring strings, making it a minor concern; V ) aggressive stacking of the WBLs, i.e., number of MFMs in a string, could facilitate the self-boosting during write operation due to ferroelectric linear capacitance (CFE), which allows self-boosted inhibition for Vw/2 scheme and worsens the Vw/3 scheme as disturb increases to intolerable 2Vw/3; v) aggressive horizontal scaling significantly increases the read disturb to cells on neighboring planes due to capacitance between two WBLs (Cz).

42 ENGINEERING↗
DOE OSTI2024

Power Layout Design of a GaN HEMTs-Based High-Power High-Efficiency Three-Level ANPC Inverter for 800 V DC Bus System

Multiple commutation paths exist for switching devices in a three-level active neutral point clamped (3L-ANPC) inverter operation based on the selected switching state and current direction. In addition, the capacitive coupling path of the nonswitching device is a key design aspect for enabling high voltage and high current operation of gallium nitride (GaN) switches in 3L-ANPC topology. A comprehensive study of the switching transient events of inner, outer, and clamping devices of 3L-ANPC is presented in this article. The commutation mechanisms for worst-case transient voltage overshoots (TVOs) are identified. A simplified equivalent circuit model is presented to determine the design criteria for the power layout structure's parasitic inductances. A power layout strategy satisfying the design criteria is then proposed using an insulated metal substrate power printed circuit board (PCB) to enable efficient high-power operation. The proposed design minimizes the commutation and capacitive coupling path inductances to 6 nH and 11.5 nH, respectively. This enables the fast switching operation of GaN HEMTs at 800 V dc, 36 A with a low TVO of 31% verified through experimental three-level double pulse test results. Experimental evaluation of a three-phase 3L-ANPC hardware prototype based on the proposed power layout shows 99% efficiency at 800 V, 9.5 kVA and 50 kHz switching frequency. The proposed design achieves a low case-to-ambient thermal resistance of 2.3 °C/W.

42 ENGINEERING↗
DOE OSTI2025

Pyrolyzer Assisted Vapor Transport Deposition of Antimony-Doped Cadmium Telluride

In this study, we developed a new method for in situ Sb doping of CdTe thin films combining vapor transport deposition with a Group V pyrolyzer to address Sb doping concentration and doping efficiency. The Sb doped CdSeTe (CdSeTe:Sb) films were deposited in solar cell structures under variations of Sb dopant source heater, vapor pyrolyzer temperature, and Cd vapor excess. Results indicate that although these parameters do not affect the CdTe morphology or crystal structure, they critically influence doping efficiency and trap concentration. Capacitance-voltage measurements show that a higher dopant heater (TD) or pyrolyzer (TP) temperature leads to higher net carrier concentration, achieving a net carrier concentration of 1016 cm-3 and 20% doping efficiency with a TD/TP combination of 600 degrees C/1100 degrees C. By tuning the Cd/Sb flux ratio during CdSeTe:Sb deposition, the lowest defect concentration is achieved at Cd/Sb of 1.4:1, which produced the best VOC CdSeTe:Sb cell. This demonstrates a path to produce high net carrier concentration polycrystalline CdTe thin film with a low concentration of dopant-induced defects.

14 SOLAR ENERGY↗
DOE OSTI2021

Flexible Fabric-Based IDC Sensors for Conformal Curved Surface Applications

Interdigital capacitor (IDC) sensors are attractive in-situ sensors that can be used to measure permittivity variations in materials. Such sensors could be powerful enablers for cable insulation aging detection. Since insulation aging is correlated with a change in its material permittivity an IDC can measure that change via its measured capacitance. A new thin, flexible fabric-based IDC sensor is introduced for application on conformal curved surfaces such as an electrical cable surface. A multielectrode IDC and its backplane were fabricated using conductive copper polyester taffeta fabrics that were adhesively bonded to nonconductive polyester fabric. The sensor because of its soft flexible structure eliminates the problem of sensor conductor damage which is common for printed circuit board (PCB) type sensors when conformed to the surface of a cable. It also significantly reduces the airgap between the electrodes and the surface that they must contact in order to measure the capacitance. Airgap reduction and consistency are important in order to accurately predict permittivity variations in cable insulation material due to aging. Both PCB-based sensors and the new fabric-based sensors were built and tested on unaged cables and cables that underwent accelerated aging. Results demonstrate the proposed advantages of the novel fabric-based IDC sensor.

interdigital capacitor sensor, IDC, NDE, PCB senso↗
DOE OSTI2018

Electrically Driven Insulator–Metal Transition-Based Devices—Part II: Transient Characteristics

Part II of this paper discusses the transient characteristics of the electrically driven insulator–metal transition (E-IMT) material-based device. To model the full transient characteristics, we modify the electrothermal model developed in Part I to capture extrinsic capacitance and 2-D heat transport effects. In order to test the model against the experiment, we fabricated and tested scaled E-IMT devices with a necked-down design to minimize nonhomogeneity. We show excellent agreement of the predictions of the model with the experimental data, and we find that the IMT device goes through three stages before a steady state is established.These three stages are identified as the times required for the incubation of the IMT transition, positive feedback, and width expansion of the IMT zone within the device. The impact of capacitance and 2-D heat transport is discussed. Furthermore, we show an inverse relation arises between the incubation time and the applied voltage. This paper satisfactorily explains the turn-on transient in a nanoscale E-IMT device within the framework of our electrothermal (Joule heating) model.

Insulator–to-metal transition (IMT)↗