Nonlinear Junction Research Articles

Computing the dynamic response of a periodic structure coupled with a nonlinear junction using the harmonic balance method and Floquet-Bloch modelling

Structures constituted of assembled sub-components are often subject to nonlinear effects due to the presence of joints or contacts, which can induce higher-order harmonics of the source excitation. In the context of periodic structures, these nonlinearities cannot be tackled using the Floquet-Bloch theory in its usual harmonic formulation. This study hence presents an adaptation of the classical Floquet-Bloch theory to address multi-harmonic systems arising from a finite number of localized nonlinearities in periodic waveguides. We adopt the Harmonic Balance Method to recast the governing equations into a nonlinear algebraic system, which can then be solved using numerical continuation algorithms. To demonstrate the validity and benefit of this approach, the predictions derived from the proposed methodology are compared to results obtained through conventional Finite Element analysis. Excellent agreement and a notable reduction in computational cost are observed. This efficient procedure for analysing the nonlinear dynamic response of periodic waveguides opens up new possibilities in the study of damaged composite structures.

Effects of Nonlinear Junction Capacitance of Rectifiers on Performance of High Voltage Power Supplies

Effects of Nonlinear Junction Capacitance of Rectifiers on Performance of High Voltage Power Supplies

Spray pyrolyzed lead oxide films for Schottky junction solar cells

In this paper, we report the fabrication of Schottky solar cell based on spray pyrolysed lead oxide semiconductor thin films. The non-linear junction were created by using high work function metal alloy of Au–Pd with hydrogen treated undoped and Indium doped lead oxide films. The output of Schottky device with different thickness of absorber layer is presented. The electrical parameters of the device are ascertained from the I–V measurements. The device with 2 μm thickness of absorber layer gives a Voc value of 148 mV and Jsc value of 0.21 mA/cm2. The high ideality factor obtained for all varying thickness is attributed to both the surface states generated under illumination and non-homogeneous interface due to the rough surfaces of spray pyrolysed films. In case of Indium doped lead oxide films, an enhanced Voc value of 570 mV and Jsc of 0.11 mA/cm2 is observed. The pristine films and doped films have been characterized by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy.

A Multitime-Scale Analytical Model of ZVS Buck Converter

This paper presents a modeling method to build the complete and accurate multi-time-scale analytical model for low-voltage eGaN HEMTs based zero voltage switching (ZVS) Buck converter with consideration of parasitic inductors, nonlinear junction capacitors and nonlinear transconductance, etc. The switching steady-state modes and switching transient modes are discussed in detail based on their corresponding equivalent circuits. The state equations of each mode are solved by MATLAB software to obtain the key operating waveforms throughout one switching cycle. Moreover, the established switching steady-state model and switching transient model are numerically merged together through continuous state variables, and then the multi-time-scale model for stable operation is formed based on the iterative method. The waveforms and switching energy losses predicted by the model within one switching cycle are compared with the experimental results, respectively, to verify the accuracy of the model. In the end, the dead time is optimized based on the proposed model, and the optimization result is verified to be effective in reducing the switching energy loss through experiment.

A High-Precision Current-Mode Bandgap Reference with Nonlinear Temperature Compensation.

A high-precision current-mode bandgap reference (BGR) circuit with a high-order temperature compensation is presented in this paper. In order to achieve a high-precision BGR circuit, the equation of the nonlinear current has been modified and the high-order term of the current flowing into the nonlinear compensation bipolar junction transistor (NLCBJT) is compensated further. According to the modified equation, two solutions are designed to improve the output accuracy of BGR circuits. The first solution is to divide the NLCBJT branch into two branches to reduce the coefficient of the nonlinear temperature compensation current. The second solution is to inject the nonlinear current into the two branches based on the first one to further eliminate the temperature coefficient (TC) of the current flowing into the NLCBJT. The proposed BGR circuit has been designed using the Semiconductor Manufacturing International Corporation (SMIC) 55 nm CMOS process. The simulation results show that the variations in currents flowing into NLCBJTs improved from 148.41 nA to 69.35 nA and 7.4 nA, respectively, the TC of the output reference current of the proposed circuit is approximately 3.78 ppm/°C at a temperature range of -50 °C to 120 °C with a supply voltage of 3.3 V, the quiescent current consumption of the entire BGR circuit is 42.13 μA, and the size of the BGR layout is 0.044 mm2, leading to the development of a high-precision BGR circuit.

Bipolar thermoelectricity in S/I/NS and S/I/SN superconducting tunnel junctions

Recent studies have shown the potential for bipolar thermoelectricity in superconducting tunnel junctions with asymmetric energy gaps. The thermoelectric performance of these systems is significantly impacted by the inverse proximity effects present in the normal-superconducting bilayer, which is utilized to adjust the gap asymmetry in the junction. Here, we identify the most effective bilayer configurations, and we find that directly tunnel-coupling the normal metal side of the cold bilayer with the hot superconductor is more advantageous compared to the scheme used in experiments. By utilizing quasiclassical equations, we examined the nonlinear thermoelectric junction performance as a function of the normal metal film thickness and the quality of the normal-superconducting interface within the bilayer, thereby determining the optimal design to observe and maximize this nonequilibrium effect. Our results offer a roadmap to achieve improved thermoelectric performance in superconducting tunnel junctions, with promising implications for a number of applications.

A physics-based modeling method of THz Schottky diode for circuit simulation

A modeling method for terahertz Schottky diode is proposed based on the special physical effects of Schottky diode in the terahertz frequency band. In this method, the device is split into a nonlinear Schottky junction part and a linear parasitic part, which are modeled separately. The nonlinear part uses the physical based modeling method by analyzing the special nonlinear effects generated by the device in the terahertz band, focusing on the modeling of the current saturation effect, and then extracting the intrinsic parameters according to the established model; for the linear part of the diode, its 3D electromagnetic (EM) model is built in the EM field simulation software to extract the parasitic parameters of the diode. Finally, the model is implemented using the circuit simulator HSpice. The model is verified by comparing the parameters extracted from the model with the actual device electrical parameters. This method ensures accuracy and convenience at the same time.

A Temperature-Dependent Analytical Model of SiC MOSFET Short-Circuit Behavior Considering Parasitic Parameters

The superior electrical and thermal characteristics of silicon carbide (SiC) MOSFETs bring major challenges to its short-circuit reliability. To fully understand its short-circuit mechanism, estimate its safe operating area, and provide guidance for circuit design, it is crucial to establish a theoretical model to quantize the relationship between circuit parameters and short-circuit behavior of SiC MOSFETs. A temperature-dependent analytical model considering the parasitic inductances, nonlinear junction capacitances, and temperature dependence of the channel current is proposed in this article, which uses only the parameters in the datasheet or provided by manufacturers. The proposed model is established based on the analysis for each short-circuit stage in both single-device configuration and half-bridge configuration, and the quantitatively analytical results of the transient short-circuit waveforms, energy loss, and junction temperature rise can be calculated by solving the model. The accuracy of the analytical model is verified by comparing the analytical results with the experimental results. Furthermore, the effects of varied parameters on the short-circuit behavior are evaluated by the proposed analytical model. And the corresponding circuit design guidance for higher short-circuit reliability is given.

An Accurate Switching Transient Analytical Model for GaN HEMT under the Influence of Nonlinear Parameters

The Gallium Nitride high electron mobility transistor (GaN HEMT) has been considered as a potential power semiconductor device for high switching speed and high power density application since its commercialization. Compared with the traditional Si transistors, GaN HEMT has faster switching speed and lower on-off loss. As a result, it is more sensitive to the nonlinear parameters due to the fast switching speed. The subsequent voltage and current overshooting will affect the efficiency and safety of the GaN HEMT and power electronic systems. In this paper, an accurate switching transient analytical model for GaN HEMT is proposed, which considers the effects of parasitic inductances, nonlinear junction capacitances and nonlinear transconductance. The model characteristic of turn-ON process and turn-OFF process is illustrated in detail, and the equivalent circuits are derived for each switching transition. The accuracy of the proposed model can be verified by comparing the predicted switching waveform and switching loss with that of the experimental results based on the double pulse test (DPT) circuit. Compared with the conventional model, the proposed model is more accurate and matches better with the experimental results than the conventional model. Finally, this model can be used for analyzing the influences of gate resistance, nonlinear junction capacitances, and parasitic inductances on switching transient waveform and refining calculation switching loss.

Detecting the Presence of Electronic Devices in Smart Homes Using Harmonic Radar Technology

Data about users is collected constantly by phones, cameras, Internet websites, and others. The advent of so-called ‘Smart Things’ now enable ever-more sensitive data to be collected inside that most private of spaces: the home. The first step in helping users regain control of their information (inside their home) is to alert them to the presence of potentially unwanted electronics. In this paper, we present a system that could help homeowners (or home dwellers) find electronic devices in their living space. Specifically, we demonstrate the use of harmonic radars (sometimes called nonlinear junction detectors), which have also been used in applications ranging from explosives detection to insect tracking. We adapt this radar technology to detect consumer electronics in a home setting and show that we can indeed accurately detect the presence of even ‘simple’ electronic devices like a smart lightbulb. We evaluate the performance of our radar in both wired and over-the-air transmission scenarios.

Nonlinearity and parameterization of Schottky diodes-based battery-free harmonic transponder for millimeter-wave 5G applications

Deployment of 5G network infrastructure is a timely opportunity for millimeter-sized battery-free sensors. However, millimeter-wave (mmW) devices often suffer from high conversion loss and path loss that are heavily limiting their communication/detection distance, especially for the case of harmonic transponders based on Schottky diodes. A deep and comprehensive parametric understanding of the second-harmonic generation mechanism of Schottky diodes in the mmW 5G bands can help us to identify suitable diodes or guide diode fabrication to reduce transponder conversion loss. This work reveals that both diode nonlinear junction resistance and capacitance contribute to the second-harmonic generation across the mid-band (sub-7 GHz) and high-band (mmW) 5G frequency bands. However, the nonlinear junction capacitance dominates the second-harmonic generation in the mmW bands. Without Joule heating during the conversion process, the capacitive nonlinearity is more efficient than the resistive nonlinearity, which means that a Schottky diode with a lower junction capacitance will efficiently reduce its associated conversion loss. The VDI GaAs zero bias diode with a low zero bias nonlinear junction capacitance (19.19 fF) shows superior conversion loss performance, which indicates that it can be employed to enhance the detection distance of battery-free harmonic transponders in the mmW 5G bands.

Validation of Circular RNAs Using RT-qPCR After Effective Removal of Linear RNAs by Ribonuclease R.

Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs that have been shown to play a role in normal development, homeostasis, and disease, including cancer. CircRNAs are formed through a process called back-splicing, which results in a covalently closed loop with a nonlinear back-spliced junction (BSJ). In general, circRNA BSJs are predicted in RNA sequencing data using one of numerous circRNA detection algorithms. Selected circRNAs are then typically validated using an orthogonal method such as reverse transcription quantitative PCR (RT-qPCR) with circRNA-specific primers. However, linear transcripts originating from endogenous trans-splicing can lead to false-positive signals both in RNA sequencing and in RT-qPCR experiments. Therefore, it is essential to perform the RT-qPCR validation step only after linear RNAs have been degraded using an exonuclease such as ribonuclease R (RNase R). Several RNase R protocols are available for circRNA detection using RNA sequencing or RT-qPCR. These protocols-which vary in enzyme concentration, RNA input amount, incubation times, and cleanup steps-typically lack a detailed validated standard protocol and fail to provide a range of conditions that deliver accurate results. As such, some protocols use RNase R concentrations that are too high, resulting in partial degradation of the target circRNAs. Here, we describe an optimized workflow for circRNA validation, combining RNase R treatment and RT-qPCR. First, we outline the steps for circRNA primer design and qPCR assay validation. Then, we describe RNase R treatment of total RNA and, importantly, a subsequent essential buffer cleanup step. Lastly, we outline the steps to perform the RT-qPCR and discuss the downstream data analyses. © 2021 Wiley Periodicals LLC. Basic Protocol 1: CircRNA primer design and qPCR assay validation Basic Protocol 2: RNase R treatment, cleanup, and RT-qPCR.

GaN-Based Megahertz Single-Phase Inverter With a Hybrid TCM Control Method for High Efficiency and High-Power Density

Compared with traditional frequency limitation method DCM and QCFTCM for TCM-based inverter, this article proposes a hybrid TCM method, which can achieve both full range ZVS and frequency variation limitation. An accurate resonant transition model is established and the switching frequency variation range can be obtained for TCM. The hybrid control can be implemented according to the variation ratio γ. In order to determine the optimal γ, an offline optimization algorithm based on loss estimation is proposed. Therefore, an accurate analytical loss model for GaN HEMTs considering the nonlinear junction capacitance is given for TCM and hybrid TCM. The loss model shows that the total losses of hybrid TCM inverter are reduced compared with TCM. Moreover, an interleaved GaN-based megahertz single-phase inverter with digital control is demonstrated with 120 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density. The aforementioned benefits are experimentally verified in the optimal hybrid TCM. With this hybrid control, the measured peak efficiency is 98%. Compared with pure TCM mode, there is a 70% reduction in the switching frequency and the related efficiency is 0.8% higher at light loads. Higher power density (135 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) can be achieved in hybrid TCM through further increasing the switching frequency compared with pure TCM.

The effects of nonlinear thermal fluctuation and series junction array on high-T c superconducting terahertz mixer performance

Sensitive high-T c superconducting (HTS) heterodyne receivers are envisioned as promising technologies for terahertz (THz) communication and sensing applications due to the lack of power efficient sources in the band. HTS device properties, particularly the noise temperature, are dependent on complicated factors that include multiple noise sources as well as the interaction between Josephson junction and radio-frequency (RF) networks. We report investigations on the device properties of an HTS THz mixer in the presence of nonlinear thermal fluctuation and series junction array. By using the three-port analysis method, it is observed that the Planck and quantum noises representing nonlinear thermal fluctuation plays a significant role in the cases of smaller fluctuation parameters and higher signal frequencies. The influence of series junction array on mixer performance is also studied, which shows that there is an optimum junction number dependent on the normalized RF source impedance. The measured results of a broadband antenna-coupled HTS single-junction mixer agree well with that obtained by numerical simulation. The results predict that noise performance, conversion gain and operating bandwidth would be considerably improved if a series junction array with a suitable junction number is used for heterodyne mixing.

Modeling and Analysis of Bridge-Leg Crosstalk of GaN HEMT Considering Nonlinear Junction Capacitances

Gallium nitride high electron mobility transistor (GaN HEMT) has fast switching speed and low threshold voltage, which could result in a severe false triggering voltage pulse at the synchronous freewheeling transistor in bridge-leg circuit when the control transistor turns on. To suppress the crosstalk phenomenon, this article proposes an analytical model about the crosstalk voltage, with consideration of nonlinearities in capacitance-voltage (C-V) of GaN HEMT. By utilizing the equivalent circuit of control transistor and synchronous freewheeling transistor, the number of analytical model parameters to be extracted can be reduced significantly. Besides, the nonlinear characteristic of junction capacitances is taken into account in the model, and the accuracy is verified by the current-voltage (I-V) curve of capacitances. Based on the model, an exhaustive investigation into the impact of device and circuit parameters on the crosstalk phenomenon is conducted. Further, for the purpose of evaluating the oscillation of crosstalk voltage, the damping ratio and oscillation frequency are acquired. The proposed model can be applied to guiding GaN device selection and printed circuit board (PCB) circuit design. The effectiveness and superiority of the proposed model are verified with simulations and experiments on a double pulse test platform.

Parametric oscillations in a dissipative bosonic Josephson junction

We study the dynamics of a nonlinear dissipative bosonic Josephson junction with a time-dependent sinusoidal perturbation in the interaction term. We demonstrate parametric resonance, where the system undergoes sustained periodic oscillations even in the presence of dissipation. This happens when the frequency of the perturbation is close to twice the frequency of the unperturbed Josephson oscillations and the strength of perturbation exceeds a critical threshold. We have formulated the threshold conditions for parametric oscillations. To explore the nature of the oscillations, we carry out a multiple time scale analysis of the stability boundaries in terms of the V-shaped Arnold tongue in the parameter space. Full numerical simulations have been performed for the zero-, running-, and π-phase modes of the nonlinear Josephson effect. Our results demonstrate that in the π-phase mode the system is capable of making a transition from regular parametric to chaotic parametric oscillations as one crosses the stability boundary. Also, the phase difference undergoes phase slip before executing sustained parametric oscillations.

Low-power linear computation using nonlinear ferroelectric tunnel junction memristors

Analogue in-memory computing using memristors could alleviate the performance constraints imposed by digital von Neumann systems in data-intensive tasks. Conventional linear memristors typically operate at high currents, potentially limiting power efficiency and scalability in practical applications. Here, we show that nonlinear ferroelectric tunnel junction memristors can perform linear computation at ultralow currents. Using logarithmic line drivers, we demonstrate that analogue-voltage-amplitude vector–matrix multiplication (VMM) can be performed in selectorless ferroelectric tunnel junction crossbars by exploiting a device nonlinearity factor that remains constant for multiple conductive states. We also show that our ferroelectric tunnel junction crossbars have the attributes required to scale analogue VMM-intensive applications, such as neural inference engines, towards energy efficiencies above 100 tera-operations per second per watt. Nonlinear ferroelectric tunnel junction memristors can be used to perform linear vector–matrix multiplication operations at ultralow currents.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality.

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

A High Efficiency Model-Based Adaptive Dead-Time Control Method for GaN HEMTs Considering Nonlinear Junction Capacitors in Triangular Current Mode Operation

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) has the advantages of high switching speed and low ON-resistance, which make it widely used in high-frequency applications to realize high power density. Triangular current mode (TCM) modulation has been used in GaN-based converters to simultaneously achieve high power density and high efficiency through full-range zero voltage switching (ZVS). However, as switching frequency increases, the effect of dead time becomes more significant. Meanwhile, because of the junction capacitors of GaN HEMTs, the optimum dead time changes greatly with the turn-off current. Inappropriate dead time will induce extra loss that goes against the further improvement of power density. In order to minimize the dead-time loss in GaN HEMT-based TCM converter, this article proposes a strategy of adaptive dead-time control. An accurate turn-off transient model is proposed to calculate optimal dead time with consideration of the nonlinear capacitors. Based on this model, a loss model is established to evaluate the effect of dead time involving the short circuit in dead time. A new method of drive signal generation in TCM is proposed to increase the accuracy of dead-time control and reduce the current ripple. By reusing the detection signal in TCM, the adaptive dead-time control is realized without extra sensors. The proposed model is verified by a dual-pulse test, which shows the maximum error between the calculated and the experimental turn-off time is below 3 ns. The proposed adaptive dead-time control is implemented in a GaN HEMT-based boost converter. The experimental results show that the adaptive dead-time control can improve the efficiency over all operation conditions compared with using the fixed dead time, and the total loss is reduced by 26.7% at 800-W load and 70.8% at 50-W load.

Simplified analytical model for estimation of switching loss of cascode GaN HEMTs in totem-pole PFC converters

A practical analytical model to calculate the switching loss of cascode gallium nitride high electron mobility transistors (GaN HEMTs) is proposed. To facilitate analysis and application, the transmission delays introduced by Si MOSFET and interconnection inductances are ignored in modeling. Meanwhile, the nonlinear junction capacitances of the device and circuit stray inductances are also incorporated to increase the accuracy of the model. The turn-on and turn-off switching processes are described in detail and the simplified equations can be easily solved by using mathematical tools. Based on the analytical model, loss evaluation of totem-pole PFC converter is introduced briefly. Finally, the accuracy of the model is validated by comparing the calculated loss and converter's efficiency with experiment results. Peak efficiency of 99.26% is achieved for a 3.6 kW single phase CCM Totem-Pole PFC AC/DC converter switching at 50 kHz based on 650 V cascode GaN HEMTs.