Junction Devices Research Articles

Perpendicular magnetic anisotropy and its electrical control in FeNiB ultrathin films

We study the perpendicular magnetic anisotropy in (Fe100−xNix)80B20 (FeNiB) films with various Ni contents. Perpendicularly magnetized films are achieved when the Ni content is in the range of 30 at. %–70 at. %. An effective perpendicular magnetic anisotropy (PMA) constant of 1.1× 105 J/m3 is achieved for the (Fe50Ni50)80B20 film. We also fabricate magnetic tunnel junction devices containing FeNiB films, and electrical measurements show that a tunneling magnetoresistance ratio of more than 20% can be achieved for devices having an orthogonal magnetization configuration. The PMA of the FeNiB film clearly changes by varying the bias voltage applied along the FeNiB/MgO junction, and a voltage-controlled magnetic anisotropy (VCMA) efficiency of over 30 fJ/Vm is demonstrated. From systematic investigations, there is no clear correlation between PMA and VCMA efficiency in the FeNiB/MgO junction. These experimental results should facilitate the development of energy-efficient magnetic random-access memory.

A Task-Schedulable Nonvolatile Spintronic Field-Programmable Gate Array

Despite the vast hardware resources available in field-programmable gate arrays (FPGAs), the implementation of very large and complex designs on these platforms is a challenging problem. One effective solution is to use task scheduling. In this method, the FPGA configuration is changed according to the required task. This requires access to external nonvolatile memory, which significantly reduces system performance. In this letter, the development of a nonvolatile spintronic FPGA structure with task-scheduling capability is described. By using the nonvolatile feature of the magnetic tunnel junction device, the structure can store two different configurations in a nonvolatile way, which eliminates the need for external memory access and significantly enhances system performance.

FS-MPC Based Thermal Stress Balancing and Reliability Analysis for NPC Converters

Active thermal control has been introduced to regulate the steady state and reduce the transient thermal-mechanical stress in power electronic modules. Specifically, it can equally distribute the temperature among the devices, thereby better distributing the stress among a set of devices and reducing the failure probability in the most thermally-stressed devices. This is of great importance for multilevel topologies and in particular for the Neutral Point Clamped (NPC) topologies, which have an inherent thermal unbalance among devices of the same phase. In hybrid structures, whereby Si and SiC devices are mixed to achieve a better trade-off between efficiency and cost, this problem is even worse due to technology differences. This paper investigates the advantages introduced by using Finite-Set Model Predictive Control (FS-MPC) algorithms designed for achieving a balanced device junction temperature in hybrid NPC and Active-NPC converters. Moreover, a novel setup composed by a hybrid ANPC based power modules is used to experimentally validate the presented FS-MPC algorithm. A lifetime estimation is performed for the two topologies to highlight the long-term benefits of FS-MPC algorithm in these hybrid topologies for UPS applications.

Influence of morphological tuned nanostructure hybrid layers on efficient bulk heterojunction organic solar cell and X-ray detector performances

This work involves the investigation of effects of nanostructures composed PCDTBT and PCBM active layers in glass/ITO/HTL/active-layer/LiF/Al structured bulk heterojunction (BHJ) organic solar cells and photodetectors. Solution-treated MoO3, MoS2, and MoO3-MoS2 hybrids were used to fabricate the BHJ solar cells and photodetectors. The results show that the MoO3-MoS2 incorporated active layers possessed high charge carrier capacities and exciton dissociation properties compared with the pure MoS2 and MoO3 blended matrices. Microscopic studies revealed the formation of palm-bark-cell structured MoO3-MoS2 hybrid which efficiently influenced for better charge carrier transport behavior. Further, different weight ratios of MoO3-MoS2 dispersed polymer junctions were fabricated to evaluate the impact of conjunction formation on developing charge transport characteristics. The power conversion efficiency (PCE) of ~6.18% for MoO3-MoS2 dispersed polymer junction device realized the 38% improvement with respect to pure PCDTBT:PCBM active layer (PCE = 4.47%). Moreover, a maximum sensitivity of 1.89 mA/Gy·cm2 was realized under X-ray airing for the photodetector with the MoO3-MoS2 blended PCDTBT and PCBM active layer. Owing to the ease of fabrication and morphologically tuned 2D atomic layer infusion into fullerene derivative/polymer junctions, it would be feasible for improving the interfacial behaviors to achieve better organic electronic devices.

Recent Progress and Challenges toward Highly Stable Nonfullerene Acceptor‐Based Organic Solar Cells

AbstractOrganic solar cells (OSCs) based on nonfullerene acceptors (NFAs) have made significant breakthrough in their device performance, now achieving a power conversion efficiency of ≈18% for single junction devices, driven by the rapid development in their molecular design and device engineering in recent years. However, achieving long‐term stability remains a major challenge to overcome for their commercialization, due in large part to the current lack of understanding of their degradation mechanisms as well as the design rules for enhancing their stability. In this review, the recent progress in understanding the degradation mechanisms and enhancing the stability of high performance NFA‐based OSCs is a specific focus. First, an overview of the recent advances in the molecular design and device engineering of several classes of high performance NFA‐based OSCs for various targeted applications is provided, before presenting a critical review of the different degradation mechanisms identified through photochemical‐, photo‐, and morphological degradation pathways. Potential strategies to address these degradation mechanisms for further stability enhancement, from molecular design, interfacial engineering, and morphology control perspectives, are also discussed. Finally, an outlook is given highlighting the remaining key challenges toward achieving the long‐term stability of NFA‐OSCs.

MANA: A Monolithic Adiabatic iNtegration Architecture Microprocessor Using 1.4-zJ/op Unshunted Superconductor Josephson Junction Devices

We conducted the first successful demonstration of an adiabatic microprocessor based on unshunted Josephson junction (JJ) devices manufactured using a Nb/AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb superconductor IC fabrication process. It is a hybrid of RISC and dataflow architectures operating on 4-b data words. We demonstrate register file R/W access, ALU execution, hardware stalling, and program branching performed at 100 kHz under the cryogenic temperature of 4.2 K. We also successfully demonstrated a high-speed breakout chip of the microprocessor execution units up to 2.5 GHz. We use a logic primitive called the adiabatic quantum-flux-parametron (AQFP), which has a switching energy of 1.4 zJ per JJ when driven by a four-phase 5-GHz sinusoidal ac-clock at 4.2 K. These demonstrations show that AQFP logic is capable of both processing and memory operations and that we have a path toward practical adiabatic computing operating at high-clock rates while dissipating very little energy.

Calibration and Parameter Extraction of STT-MTJ Device at High Frequency by Using De-Embedding Approach Based on TRL Calibration

Spin-Torque-Transfer Magnetic Tunnel Junction (STT-MTJ) device shows wide applications in many important scenarios, including magnetic random access memory (MRAM), logic design, and high-frequency application. Its characterizations at the high frequency are studied intensively recently. In this article, the high-frequency properties of the STT-MTJ device are investigated thoroughly, including a de-embedding approach followed by an extraction procedure for removing the influences from the environment and the package. The de-embedding approach is performed on the STT-MTJ device operated at a high frequency, which can be used to calibrate its electrical characteristics by eliminating the environmental influence. After the calibration, the equivalent circuit for the MTJ device at high frequency can be set up, followed by the extraction procedure of the parasitic parameters of the high-frequency-equivalent-circuit. Combined with the extracted parameters, the equivalent circuit can be used for the simulation work with the MTJ device involved in the high-frequency operation.

Pt/AlGaN Nanoarchitecture: Toward High Responsivity, Self-Powered Ultraviolet-Sensitive Photodetection.

Energy-saving photodetectors are the key components in future photonic systems. Particularly, self-powered photoelectrochemical-type photodetectors (PEC-PDs), which depart completely from the classical solid-state junction device, have lately intrigued intensive interest to meet next-generation power-independent and environment-sensitive photodetection. Herein, we construct, for the first time, solar-blind PEC PDs based on self-assembled AlGaN nanostructures on silicon. Importantly, with the proper surface platinum (Pt) decoration, a significant boost of photon responsivity by more than an order of magnitude was achieved in the newly built Pt/AlGaN nanoarchitectures, demonstrating strikingly high responsivity of 45 mA/W and record fast response/recovery time of 47/20 ms without external power source. Such high solar-blind photodetection originates from the unparalleled material quality, fast interfacial kinetics, as well as high carrier separation efficiency which suggests that embracement of defect-free wide-bandgap semiconductor nanostructures with appropriate surface decoration offers an unprecedented opportunity for designing future energy-efficient and large-scale optoelectronic systems on a silicon platform.

High Efficiency Inverted GaAs and GaInP/GaAs Solar Cells With Strain‐Balanced GaInAs/GaAsP Quantum Wells

AbstractHigh‐efficiency solar cells are essential for high‐density terrestrial applications, as well as space and potentially vehicle applications. The optimum bandgap for the terrestrial spectrum lies beyond the absorption range of a traditional dual junction GaInP/GaAs cell, with the bottom GaAs cell having higher bandgap energy than necessary. Lower energy bandgaps can be achieved with multiple quantum wells (QWs), but such a pathway requires advanced management of the epitaxial growth conditions in order to be useful. Strain‐balanced GaAsP/GaInAs QWs are incorporated into a single junction GaAs solar cell and a dual junction GaInP/GaAs solar cell, leading to 27.2% efficiency in the single junction device and a one‐sun record 32.9% efficiency in the tandem device. Good carrier collection and low non‐radiative recombination are observed in the cells with up to 80 QWs. The GaAs cells employ a rear‐heterojunction architecture to boost the open‐circuit voltage to over 1.04 V in the quantum well device, despite the large number of QWs.

A computed tomography study of coronary access and coronary obstruction after redo transcatheter aortic valve implantation.

The aim of this study was to investigate the risk of impaired coronary access and coronary obstruction after redo TAVI. Post-procedure multidetector computed tomography (MDCT) scans of 221 TAVI recipients were analysed. Increased risk of impaired coronary access was defined as a coronary ostium below the TAVI commissures with a valve-to-aorta distance <2 mm at this level. Increased risk was found in 123 (55.6%) cases: the left main was involved in 109 (49.3%), the right coronary in 79 (35.7%), and both were involved in 65 (29.4%) patients. A small sinotubular junction (STJ width OR 0.68, CI: 0.56-0.81, p<0.001; STJ height OR 0.81, CI: 0.69-0.95, p<0.011) and supra-annular devices (OR 19.8, CI: 6.6-58.8, p<0.001) predicted increased risk. Increased risk of coronary obstruction, defined as a coronary ostium below the TAVI commissures with a valve-to-coronary distance <2 mm, was observed in 14.9% of patients; in 17.2% of cases complete sealing of the STJ would occur. Post-TAVI MDCT suggested an increased potential risk of impaired coronary access in more than half of the patients should redo TAVI be required, predicted by a small STJ and supra-annular device design. Furthermore, 10-20% of patients presented an increased risk of coronary obstruction. While this theoretical study is hypothesis-generating, it raises concerns that need to be further investigated and addressed before TAVI is extended to patients with longer life expectancy.

High Speed Terahertz Devices via Emerging Hybrid GNRFET/Josephson Junction Technologies

An approach to merge superconducting Josephson junction (JJ) devices with nanoscale Graphene devices in order to achieve high gain-bandwidth-product on the order of THz is proposed. While JJ-based devices have existed since nearly 1962, interfacing or interacting with them with standard electrical systems has been a challenge for several reasons, including operating temperature, switching speed, and low-signal sensitivity. In this article, we investigated the possibility of utilizing JJ's so-called ac effect in order to generate high frequency signals that can be accommodated by high speed nanoscale devices. Graphene nanoribbon field effect transistors (GNRFET) have been emphasized for their very high frequency operation that is appropriate to accommodate the very high switching speed of the JJ devices. The article is based on the ac JJ effect with generating a sinusoidal current whose frequency directly scales with voltage. For a single-stage GNRFET CS amplifier, a gain of 35.7 dB with a bandwidth of 217 GHz was achieved, while 10.8 dB with a unitary gain of 2.5 THz was also accomplished. This article details the design and interface of the JJ with GNRFET devices, targeting high frequency signal generation on the order of hundreds of GHz to THz, with the purpose of providing a foundation on top of which further developments can be made, especially in the areas of communications, medical devices, instrumentation and measurement devices, high-speed imaging, subinfrared antenna arrays, and computer architecture and hardware, by providing a system, which can respond to speeds on the order of fifty to one hundred times faster than current commercial computer equipment or signal generation/processing.

Key Roles of Trace Oxygen Treatment for High‐Performance Zn‐Doped CuI p‐Channel Transistors

AbstractThe development of transparent and high‐performance p‐type semiconductors as a counterpart of n‐type metal oxide semiconductors has attracted significant interest for the integration of complementary circuits and p–n junction devices. This study investigates the effect of trace O2 for high‐performance and solution‐processed inorganic p‐channel Zn‐doped copper iodide (CuI) thin‐film transistors (TFTs) via a combined computation–experiment approach. The absorbed O2 molecules in the CuI film can occupy iodine vacancies, acting as trap passivator. Meanwhile, the strong electronegativity of O2 enables electron capture from the CuI matrix, leading to p‐doping. Trace O2‐treated Zn‐doped CuI TFTs exhibit significantly improved electrical performance compared to untreated devices. Optimized TFTs exhibit a high field‐effect hole mobility of 4.4 cm2 V−1 s−1, high on/off current ratio of ≈107, and small hysteresis. These findings provide a clear basis for realizing reproducible and high‐performance metal‐halide (e.g., CuI and perovskite) optoelectronic devices using low‐cost solution process.

About 335 nm Ultraviolet Emissions Obtained from Simple Metal–Insulator–Semiconductor Light‐Emitting Tunnel Diodes

To overcome the low external quantum efficiency of ultraviolet light‐emitting diodes (UV LEDs) in the technologically significant wavelength range of 300–350 nm, a change of approach to device design may be required. Herein, room‐temperature electroluminescence (EL) at 335 nm is achieved from simple aluminum gallium nitride (AlGaN)‐based metal–insulator–semiconductor (MIS) light‐emitting diodes (LEDs), which do not contain any p‐doped material. Current–voltage and capacitance–voltage measurements indicate that electrons in the valence band of the n‐Al0.14Ga0.86 N layer efficiently tunnel via localized states in the thin, sputter‐deposited aluminum nitride (AlN) barrier of the MIS device to provide the source of holes needed for near‐band‐edge luminescence. The full width at half maximum (FWHM) in the UV emission peak is only around 18 nm and it is very close to the photoluminescence (PL) peak of the active n‐Al0.14Ga0.86N layer, confirming that the EL is derived from band‐to‐band radiative transitions in the simple non‐p‐doped MIS diode. This design is a potential option to overcome the problem of the poor thermal excitation of holes in the AlGaN‐based pn junction devices.

Design and Fabrication of a MEMS-Based Break Junction Device for Mechanical Strain-Correlated Optical Characterization of a Single-Molecule

Here, we propose a robust lab-on-a-chip system for multi-dimensional (electrical, optical, and mechanical) characterization of a single-molecule utilizing a Si micromachined micro-electromechanical-system (MEMS) chip. Our MEMS-based break junction (MEMS-BJ) utilizes conventional MEMS chip fabrication techniques to create an electrostatic comb actuator capable of trapping a single-molecule between two nanoscale metal electrodes with sub-nanometer displacement resolution. In order to achieve this functionality, components of the chip (e.g flexural spring, comb drive fingers) are delicately designed based on an analytical model and basic performance parameters are verified using a finite element analysis simulation and capacitive sensor measurements. Using this system, we are able to perform combined single-molecule Raman spectroscopy and molecular conductance measurements in real-time. Finally, we present a representative case study of the multi-dimensional characterization of a single-molecule junction by analyzing correlated electrical, optical, and mechanical information while mechanically modulating the strain on the junction which allows for direct observation of the interplay between molecular structure and electron transport. We believe that our MEMS-BJ system will enable a deeper multi-dimensional study at a single-molecule level promoting the development of new methods for chemical and biological sensor applications.

Microwave Photon Detection Using a Topological Josephson Junction

Single photon detection (SPD) has found increasingly important applications in many forefront areas of fundamental science and advanced engineering applications, ranging from studying the galaxy formation though cosmic infrared background to entanglement of superconducting qubits, single molecular spectroscopy, and remote sensing. In recent years, the rapid developments in superconducting quantum computation, high fidelity quantum measurement, quantum key distribution, and quantum network call for SPD in the microwave frequency range.In this talk, I will first present our recent experimental work on topological Josephson junctions in Dirac semimetal Cd3As2. In high quality aluminum-Cd3As2-aluminum Josephson junctions, we observe both π and 4π periodic supercurrents. The π period is manifested by both the magnetic-field dependence of the critical supercurrent and the appearance of half-integer Shapiro steps in the ac Josephson effect. Our simulation by a resistively shunted junction model suggests that the π period arises from interference between the induced bulk superconductivity and the induced Fermi-arc surface superconductivity. In the second part of the talk, I will discuss microwave photon detection using these topological Josephson junctions. The temperature dependence and microwave power dependence of the junction resistance are studied. It is observed the effective temperature of the junction device under microwave radiation increases with microwave power, suggesting a promising potential for photon number-resolving capability.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under Contract No. DE-NA-0003525.

Use of carrier injection engineering to increase the light intensity of a polycrystalline silicon avalanche mode light-emitting device

This paper demonstrates a polycrystalline silicon avalanche mode light-emitting device. The unique N+PN+PN+ cascade structure is designed to enhance light intensity via carrier injection engineering, in which the minority carriers are injected from the forward-biased junction to the light emission junction. Visible light can be observed at the reverse-biased PN junctions when the device operating voltage exceeds 20 V. In particular, the phonon-assisted indirect interband recombination of carriers with excess energy may be the main mechanism of photon emission. A specific junction model is proposed to explain that the light intensity peaks are generated primarily via carrier injection. Comparing the spectral measurements of a single polysilicon N+P junction device and the proposed cascade device shows that the strategy of improving the luminous intensity via carrier injection engineering is feasible and effective.

Terephthalic acid‐directed supramolecular Cu(II)‐metallogel for photosensitive semiconducting Schottky diode with promising electronic charge transportation

SummaryTerephthalic acid‐based supramolecular metallogel of Cu(II) (ie, Cu‐TA) is developed by sonicating the mixture of copper(II) acetate monohydrate and terephthalic acid in N,N‐dimethyl formamide solvent. The rheological study is performed to expose the mechanical property of metallogel. The flake‐like morphological patterns are found through FESEM microstructural investigations. The formation strategy, crystalline nature, and thermal behavior of the Cu‐TA metallogel are also studied. The optical and electrical properties of Cu‐TA metallogel are exhaustively scrutinized, and the measured data show that Cu‐TA metallogel is semiconducting in nature. The electrical analysis indicates that the conductivity of Cu‐TA metallogel increased up to ~four times under illumination (7.49 × 10−5 S m−1) rather than the nonirradiation condition (1.83 × 10−5 S m−1). The measured I‐V characteristics of Cu‐TA metallogel‐based thin‐film metal‐semiconductor (MS) junction devices under irradiation and nonirradiation conditions show a nonlinear rectifying behavior, typical of a Schottky diode (SD).

Mesoscopic quantum superposition states of weakly-coupled matter-wave solitons

The Josephson junctions (JJs) are at the heart of modern quantum technologies and metrology. In this work we establish quantum features of an atomic soliton Josephson junction (SJJ) device, which consists of two weakly-coupled condensates with negative scattering length. The condensates are trapped in a double-well potential and elongated in one dimension. Starting with classical field theory we map for the first time a two-soliton problem onto the effective two-mode Hamiltonian and perform a second quantization procedure. Compared to the conventional bosonic Josephson junction condensate system, we show that the SJJ-model in quantum domain exhibits unusual features due to its effective nonlinear strength proportional to the square of total particle number, N2. A novel self-tuning effect for the effective tunneling parameter is also demonstrated in the SJJ-model, which depends on the particle number and rapidly vanishes as the JJ population imbalance increases. The formation of entangled Fock state superposition is predicted for the quantum SJJ-model, revealing dominant N00N-state components at the ‘edges’ for n = 0, N particle number. We have shown that the obtained quantum state is more resistant to few particle losses from the condensates if tiny components of entangled Fock states are present in the vicinity of the major N00N-state component. This peculiarity of the quantum SJJ-model establishes an important difference from its semiclassical analogue obtained in the framework of Hartree approach. Our results are confirmed by studying the first and N-order Hillery–Zubairy criteria applied for studying multiparticle entanglement and planar spin squeezing. The Einstein–Podolsky–Rosen quantum steering represents an important prerequisite for the crossover to the mesoscopic superposition Schrödinger-cat and/or N00N-states. The feasibility in observation for these predicted states of the SJJ-model in the experiments is also discussed by taking into account one- and three-body losses for lithium condensates.

SQUID pattern disruption in transition metal dichalcogenide Josephson junctions due to nonparabolic dispersion of the edge states

We theoretically study Josephson junctions with a transition metal dichalcogenide zigzag ribbon as a weak link. We demonstrate that the spatial profile of the supercurrent carried by the edge modes determines the critical current dependence on the perpendicular magnetic field. We explore this finding and analyze the impact of Zeeman interaction and the orbital effects of the magnetic field on the Andreev bound states energies. We show that the unequal Fermi velocities of the spin-opposite edge modes lead to an anomalous shift of the Andreev bound states in the presence of the magnetic field. This is manifested in a pronounced modification of the SQUID critical current oscillations when two opposite edges of the ribbon are conducting and can be exploited in order to reveal the anomalous phase shift of the Andreev bound states in a single Josephson junction device.

Optimization of process parameters of anodic aluminium oxide using an orthogonal array technique for thermal management applications

The semiconductor packaging field is evolving rapidly due to strong competition in customer demands for increased functionality and performance, further miniaturization, heightened reliability and lower costs. The lifetime reliability and sequential performance of solid-state products are mainly based on the device junction temperature (Tj). The main concerns of efficient thermal management in heat source-based electronic packages are controlling and reducing the device junction temperature and total thermal resistance (Rth). The optimization of process parameters to develop an anodic aluminium oxide nanopore (AAO-np) structure on an Al5052 alloy substrate using an electrochemical process (two-step anodization) is proposed based on the Taguchi orthogonal array (L9). The four major parameters are the electrolyte, anodization time, bath temperature, and applied voltage, which are varied at three different levels. This experiments aim to finalize suitable process parameters and their levels towards optimum Rth and Tj. The morphology of the step-wise preparation of AAO-np structure is discussed for the optimized conditions of 0.3 M oxalic acid, a 3 h anodization time, a 30 V applied voltage, and a bath at room temperature. The resulting AAO-np structure has a pore diameter of 40 to 55 nm and a height of 6 to 7 μm. This formation significantly reduces Rth by 24.58% and Tj by 24.66% for the electronic package compared to a bare Al substrate.