Tuning Voltage Research Articles

Mechanisms of instability retention for ferroelectric field effect transistors with HfZrO2 gate stack scaling down

Instability threshold voltage (VT) with retention loss of read-after-write is a critical issue with fundamental physics for ferroelectric field effect transistors (FeFETs) scaling down under high-speed operation. The mechanisms including charge trapping and depolarization field (Edep) are discovered and related to surface potential and coercive field (EC). The trapped charge can be effectively detrapped by opposite polarity stimulation and validated by technology computer-aided design modeling. In addition, the Edep is revealed to be serious with ferroelectric HfZrO2 (FE-HZO) thin-down due to the unstable low-VT state at a gate voltage (VG) of 0 V. The tunable base voltage (Vbase) compensates the Edep-based polarization degradation. A stable low-VT read-after-write for a 5-nm-thick HZO FeFET is experimentally demonstrated by the opposite polarity detrapping scheme hybrid with a Vbase optimization simultaneously for a wide range of delay times from 10−7 to 102 s. This result provides the feasibility for scaling down FeFETs for nonvolatile memory applications in the future.

Experimental investigation of rotating nodal line of MEMS-based nonlinear multi-mode resonators.

Nonlinear phenomenon is presently attracting considerable attention in the field of microelectromechanical systems (MEMS). By adjusting a controllable tuning voltage, the nonlinearity of microdevices, especially on microactuators, can be precisely manipulated. To trap and separate small particles, generating a large and stable rotation force is critical in micromanipulations. Here, we report a simple and potential angular momentum cell comprising a piezoelectric MEMS-based nonlinear multi-mode resonator with integrated electrodes. A nonlinear rotating nodal line has been observed in specific frequency bands by applying a controllable low voltage of sub 5V on a 4-port resonator made of lead zirconate titanate (PZT) thin films. The magnitude of the actuated voltage is Complementary-Metal-Oxide-Semiconductor (CMOS)-compatible and easy to integrate with the circuit. Furthermore, the real-time rotation motion of the MEMS-based nonlinear multi-mode resonator is also verified by a laser doppler vibrometer (LDV) at both chirp and single input frequencies, respectively. Therefore, this angular momentum cell shows great potential in the application of micromanipulation.

Nonlinear effects and applications for piezoelectric materials

The requirements of high quality factor, low power consumption, easy design techniques and compatibility with the main standard fabrication processes of integrated circuits (IC) make the tunable piezoelectric resonators a suitable option for the new technologies of fifth generation of telecommunication (5G) and Internet of Things (IoT). In this work the nonlinear state equations for piezoelectric effect are presented. From these equations we may deduce which materials can be used in applications where a hysteresis behavior or resonance frequency tunability are required, additionally, it is shown which crystals have the nonlinear tensor’s symmetry compatible with each application field. A novel model for the tunable piezoelectric devices is shown taking into account the consequences of voltage tuning. Finally, three different ways to design and implement the nonlinear behavior of piezoelectric materials to tune devices are introduced.

Polyaniline-based Schottky-triboelectric hybrid DC generators with tunable electrical outputs

Schottky direct-current (DC) generators can convert ambient mechanical energy into DC power, showing potential in portable electronics, wireless networks, and the Internet of Things. However, most Schottky DC generators generate a voltage output below 1 volt. Increasing the voltage output would considerably broaden their applications but remains challenging to achieve. In this study, we developed a novel DC generator that shows increased and tunable voltage outputs by combing the Schottky DC generator with triboelectric components. Using polyaniline-coated fabric and metal aluminum to prepare Schottky DC devices, we showed that the device voltage outputs were increased largely when a scatting layer of polyvinylidene fluoride (PVDF) powder covered the surface of either the metal Al or the polyaniline-coated fabric between them. Under compression impact, the PVDF-involved device (areal coverage 46.26 ± 0.60% on the Al surface) generated a peak open-circuit voltage of 3.2 ± 0.10 V and a short-circuit current of 15.06 ± 0.3 μA (current density 3.77 ± 0.08 μA cm−2), with a power of 12.32 ± 0.45 μW (measured by an external resistor method). The open-circuit voltage and power were 3.7 times and 1.5 times higher when compared with the same DC generator without PVDF. By changing the PVDF powder coverage area, the DC output voltage can be tuned linearly in the range of 0.86–3.20 V. However, when the coverage was above 50%, the outputs turned from DC to AC. We also simulated the electrical outputs using a circuit simulation program (LTspice XVII). The simulation results agreed well with the experimental findings, suggesting the improvement of the electrical output follows the classic electrical principle. Such Schottky diode-triboelectric hybrid may form a novel approach for developing DC energy harvesters and self-powered sensors with adjustable voltage output for various applications.

Threshold Voltage Control in Dual‐Gate Organic Electrochemical Transistors

AbstractOrganic electrochemical transistors (OECTs) based on Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) are a benchmark system in organic bioelectronics. In particular, the superior mechanical properties and the ionic‐electronic transduction yield excellent potential for the field of implantable or wearable sensing technology. However, depletion‐mode operation PEDOT:PSS‐based OECTs cause high static power dissipation in electronic circuits, limiting their application in electronic systems. Hence, having control over the threshold voltage is of utmost technological importance. Here, PEDOT:PSS‐based dual‐gate OECTs with solid‐state electrolyte where the threshold voltage is seamlessly adjustable during operation are demonstrated. It is shown that the degree of threshold voltage tuning linearly depends on the gate capacitance, which is a straightforward approach for circuit designers to adjust the threshold voltage only by the device dimensions. The PEDOT:PSS‐based dual‐gate OECTs show excellent device performance and can be pushed to accumulation‐mode operation, resulting in a simplified and relaxed design of complementary inverters.

A Vertical Single Transistor Neuron with Core-Shell Dual-Gate for Excitatory-Inhibitory Function and Tunable Firing Threshold Voltage.

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core–shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve an excitatory–inhibitory transition and a firing threshold voltage adjustment, respectively. By utilizing the shell gate, the firing of specific neuron can be inhibited for winner-takes-all learning. It was confirmed that the independently accessed core gate can be used for adjustment of the firing threshold voltage to compensate random conductance variation before the learning and to fix inference error caused by unwanted synapse conductance change after the learning. This threshold voltage tuning can also be utilized for homeostatic function during the learning process. Furthermore, a myelination function which controls the transmission rate was obtained based on the inherent asymmetry between the source and drain in vertical NW structure. Finally, using the CSDG NW neuron device, a letter recognition test was conducted by SPICE simulation for a system-level validation. This multi-functional neuron device can contribute to construct a high-density monolithic SNN hardware combining with the previously developed vertical synapse MOSFET devices.

Rapid joule heating improves vitrification based cryopreservation

Cryopreservation by vitrification has far-reaching implications. However, rewarming techniques that are rapid and scalable (both in throughput and biosystem size) for low concentrations of cryoprotective agent (CPA) for reduced toxicity are lacking, limiting the potential for translation. Here, we introduce a joule heating–based platform technology, whereby biosystems are rapidly rewarmed by contact with an electrical conductor that is fed a voltage pulse. We demonstrate successful cryopreservation of three model biosystems with thicknesses across three orders of magnitude, including adherent cells (~4 µm), Drosophila melanogaster embryos (~50 µm) and rat kidney slices (~1.2 mm) using low CPA concentrations (2–4 M). Using tunable voltage pulse widths from 10 µs to 100 ms, numerical simulation predicts that warming rates from 5 × 104 to 6 × 108 °C/min can be achieved. Altogether, our results present a general solution to the cryopreservation of a broad spectrum of cellular, organismal and tissue-based biosystems.

Output Power Regulation of a Series-Series Inductive Power Transfer System Based on Hybrid Voltage and Frequency Tuning Method for Electric Vehicle Charging

In the inductive charging scenario of an electric vehicle (EV), the charger should have the capability to flexibly regulate the output power regardless of the misalignment and EV battery voltage. This article proposes a hybrid voltage and frequency tuning strategy for a series-series (SS) inductive power transfer (IPT) system to regulate power through 0 to 3.3 kW at any battery voltages and misalignment conditions without using additional converters. A voltage tuning is used to achieve full-power of 3.3 kW and partly contribute to reducing the power. When the input voltage achieves the lower limit, a frequency tuning is used to further decrease the power to 0 W, achieving the regulation through 0 to full power. The practical charging region is specified by 110 mm airgap, 100 mm misalignment in both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> directions, and 180–240 V battery voltage range. Experiments are carried out at various conditions, and it shows that with an input voltage range of 180–380 V and a frequency of 82.5–87.9 kHz, the charging power can be regulated between 100 W and 3.3 kW at any case in the specified working region. In addition, a peak dc-dc efficiency of 95.7% is achieved at 3.29 kW.

Optically Transparent Frequency-Tunable Microwave Absorber Based on Patterned Graphene-ITO Structure

In this work, the authors report the design, fabrication, and measurement of an optically transparent microwave absorber with tunable absorption frequency based on a patterned graphene-indium tin oxide (ITO) hybrid structure. This transparent tunable absorber consists of periodically patterned graphene sandwich structure (GSS), patterned ITO layer, polyvinyl chloride (PVC) substrate, and ITO ground plane from top to bottom. The frequency of absorption peak can be dynamically controlled from 13.1 to 10.9 GHz by regulating the bias voltage between the graphene sheets from 0 to 30 V, in which the peak absorption rates remain above 99.7%. An inhomogeneous doping model for graphene patterns is introduced to interpret the usage of relatively large tuning voltage. The engineered absorber also exhibits polarization-insensitive characteristics attributed to the symmetrical design of the hybrid structure. This tunable device with optical transparency achieved by integrating different transparent materials has broad prospects in the application of multispectral and smart stealth technology.

Organic Vapor Sensing Mechanisms by Large-Area Graphene Back-Gated Field-Effect Transistors under UV Irradiation.

The gas sensing properties of graphene back-gated field-effect transistor (GFET) sensors toward acetonitrile, tetrahydrofuran, and chloroform vapors were investigated with the focus on unfolding possible gas detection mechanisms. The FET configuration of the sensor device enabled gate voltage tuning for enhanced measurements of changes in DC electrical characteristics. Electrical measurements were combined with a fluctuation-enhanced sensing methodology and intermittent UV irradiation. Distinctly different features in 1/f noise spectra for the organic gases measured under UV irradiation and in the dark were observed. The most intense response observed for tetrahydrofuran prompted the decomposition of the DC characteristic, revealing the photoconductive and photogating effect occurring in the graphene channel with the dominance of the latter. Our observations shed light on understanding surface processes at the interface between graphene and volatile organic compounds for graphene-based sensors in ambient conditions that yield enhanced sensitivity and selectivity.

Nonlinear deformation and instability of a dielectric elastomer tube actuator

The mechanical response and electromechanical instability (EMI) of a dielectric elastomer tube actuator (DETA) under the coupling loadings of voltage, internal pressure and axial force are studied in this paper. Based on the Gent model and considering the nonlinear relationship between dielectric permittivity and stretches, two different loading conditions are discussed: force tuning and voltage tuning. For the force tuning, it is found that the radius of the DETA first decreases, then increases and finally decreases due to the competition between the axial force and voltage as well as the strain-stiffening property of the Gent model under the large deformation. For the voltage tuning, the effects of axial force, internal pressure and electrostrictive coefficient on the electromechanical response are explored. The electrical breakdown (EB) during the nonlinear deformation of DETA is also analyzed. The stress distribution along the thickness of the DETA is given by the analytical solution, and the two failure modes including EMI and loss of tension for the DETA are studied with axial constraints. It is found that the EMI can be eliminated by changing the stretch in the z-direction and internal pressure, which may also lead to the failure of loss of tension. The competitive relations of the two failure modes are discussed in detail. This work can contribute to the design of DETAs with a large actuation.

Ab Initio Study of Magnetic Tunnel Junctions Based on Half-Metallic and Spin-Gapless Semiconducting Heusler Compounds: Reconfigurable Diode and Inverse Tunnel-Magnetoresistance Effect

Magnetic tunnel junctions (MTJs) have attracted strong research interest within the last decades due to their potential use as nonvolatile memory such as magnetoresistive random access memory as well as for magnetic logic applications. Half-metallic magnets (HMMs) have been suggested as ideal electrode materials for MTJs to achieve an extremely large tunnel-magnetoresistance (TMR) effect. Despite their high TMR ratios, MTJs based on HMMs do not exhibit current rectification, i.e., a diode effect, which was achieved in a magnetic tunnel junction concept [E. \ifmmode \mbox{\c{S}}\else \c{S}\fi{}a\ifmmode \mbox{\c{s}}\else \c{s}\fi{}\ifmmode \imath \else \i \fi{}o\ifmmode \breve{g}\else \u{g}\fi{}lu et al., ACS Appl. Electron. Mater. 1, 1552--9 (2019)] based on HMMs and type-II spin-gapless semiconductors (SGSs). The proposed concept has recently been experimentally demonstrated using Heusler compounds. In the present work, we investigate from first-principles MTJs based on type-II SGS and HMM quaternary Heusler compounds $\mathrm{Fe}\mathrm{V}\mathrm{Ta}\mathrm{Al}$, $\mathrm{Fe}\mathrm{V}\mathrm{Ti}\mathrm{Si}$, $\mathrm{Mn}\mathrm{V}\mathrm{Ti}\mathrm{Al}$, and $\mathrm{Co}\mathrm{V}\mathrm{Ti}\mathrm{Sb}$. Our ab initio quantum transport calculations based on a nonequilibrium Green's function method have demonstrated that the MTJs under consideration exhibit current rectification with relatively high on:off ratios. We show that, in contrast to conventional semiconductor diodes, the rectification bias voltage window (or breakdown voltage) of the MTJs is limited by the spin gap of the HMM and SGS Heusler compounds. A unique feature of the present MTJs is that the diode effect can be configured dynamically, i.e., depending on the relative orientation of the magnetization of the electrodes, the MTJ allows the electrical current to pass either in one or the other direction, which leads to an inverse TMR effect. The combination of nonvolatility, reconfigurable diode functionality, tunable rectification voltage window, and high Curie temperature of the electrode materials makes the proposed MTJs very promising for room-temperature spintronic applications and opens ways to magnetic memory and logic concepts as well as logic-in-memory computing.

Determining dielectric properties of nematic liquid crystals at microwave frequencies using inverted microstrip lines

ABSTRACT In this paper, we have investigated the dielectric properties of nematic liquid crystals (NLCs) by measuring the resonant frequencies of inverted microstrip lines (IMSLs) of NLC being the substrate material at the microwave frequency band. The designed IMSL devices consist of a cavity for NLC mixture between the inverted microstrip line and the ground plane. The anisotropy values of the NLCs were determined by observing the change of the resonant frequency when the strength of external electric fields applied on the NLCs varied. The experiments demonstrated that the effective dielectric constant of the NLC can be manipulated by the proposed devices via external bias voltage for tuning. The accuracy of the method for determining the dielectric constants of JC-M-LC-E7 (JC-E7) and QYPD-036 LCs was analysed with several prototypes based on two separate designs. The high accuracy of 91% in permittivity determination was demonstrated, and the design and fabrication techniques are beneficial for making microwave components of high tunability.

Research on coupled cavity mechanical tuning extended interaction oscillator with broad tuning range.

This paper proposes a new way to improve the tuning range of the extended interaction oscillator (EIO). Compared with the conventional EIO structure, the fundamental wave changes from the forward wave to the backward wave when the circuit structure changes from the strong-coupling characteristic of the grating to the weak-coupling characteristic. Simultaneously, the tuning range of the EIO can be greatly enhanced by mechanically tuning the coupling cavity. The results show that, compared with the strong-coupling structure of the grating, the extended interaction oscillation circuit has stronger dispersion sensitivity and greater frequency tuning characteristics under the weak-coupling characteristics of the grating. By mechanically tuning the width of the coupling cavity by 0.8mm, its center frequency can be varied by 9.5GHz. This paper also studies and compares the electronic displacement jump phenomenon that occurs in the mechanical tuning process. Similar to the electronic voltage tuning, the output dips suddenly at the operating point of the coupling mismatch. The effective output can be obtained by changing the operating mode in conjunction with electronic tuning. This article provides a new reference method for expanding the tuning range of the extended interaction oscillator.

A Learning-Rate Modulable and Reliable TiOx Memristor Array for Robust, Fast, and Accurate Neuromorphic Computing.

Realization of memristor‐based neuromorphic hardware system is important to achieve energy efficient bigdata processing and artificial intelligence in integrated device system‐level. In this sense, uniform and reliable titanium oxide (TiO x ) memristor array devices are fabricated to be utilized as constituent device element in hardware neural network, representing passive matrix array structure enabling vector‐matrix multiplication process between multisignal and trained synaptic weight. In particular, in situ convolutional neural network hardware system is designed and implemented using a multiple 25 × 25 TiO x memristor arrays and the memristor device parameters are developed to bring global constant voltage programming scheme for entire cells in crossbar array without any voltage tuning peripheral circuit such as transistor. Moreover, the learning rate modulation during in situ hardware training process is successfully achieved due to superior TiO x memristor performance such as threshold uniformity (≈2.7%), device yield (> 99%), repetitive stability (≈3000 spikes), low asymmetry value of ≈1.43, ambient stability (6 months), and nonlinear pulse response. The learning rate modulable fast‐converging in situ training based on direct memristor operation shows five times less training iterations and reduces training energy compared to the conventional hardware in situ training at ≈95.2% of classification accuracy.

A Millimeter-Wave Broadband Reflectionless ESD Protection Device

In this letter, a broadband millimeter-wave (mm-wave) electrostatic discharge (ESD) protection structure is proposed and verified in a 40-nm CMOS process. The main ESD protection device is a diode-triggered silicon-controlled rectifier (DTSCR) with a tunable trigger voltage. Two weakly-coupled inductors are embedded to increase the operating bandwidth. Both theoretical analysis and simulation results show that a low coupling factor is necessary to obtain the wideband characteristic. The proposed design exhibits good ESD protection performance (HBM robustness >1.875kV), fast turn-on speed, wideband reflectionless characteristic (S11<–15dB within 33.6-50GHz), tunable trigger voltage and low leakage current. Therefore, this new device is suitable for ESD protection of input/output (I/O) pads in mm-wave-communication applications.

A Scalable High-Current High-Accuracy Dual-Loop Four-Phase Switching LDO for Microprocessors

High-performance microprocessors need high current (ampere-level), high accuracy, and fast-response power supplies. Comparing to analog and digital low-dropout (LDO) regulators, the switching LDO can be a better candidate for such requirements, as it can drive large power transistor(s) fast and accurately. However, conventional switching LDOs need large load capacitance to reduce the output ripple, which restricts their applications. This article presents a 1.5-A fully-integrated switching LDO for microprocessors, with an easily scalable load capability. Here, we introduce three techniques together to relief the output capacitance requirement: 1) four-phase 500-MHz pulsewidth modulation (PWM) with inherent current balancing; 2) current-limited power cells resisting processor voltage and temperature (PVT) variations; and 3) hybrid fast-slow power transistors. Therefore, we reduce significantly the load capacitance to maximum load current ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\mathrm {L}} / I_{\mathrm {MAX}}$ </tex-math></inline-formula> when compared with the prior switching LDOs. Also, the proposed dual-loop architecture not only achieves a fast transient response, but also provides high-accuracy regulation. In addition, we design the tunable active voltage positioning (AVP). Fabricated in 28-nm CMOS, the proposed switching LDO measures a maximum 70-mV undershoot with a 1-A load current step with 10-ns edge time. The measured load regulation is 1 mV/A and the line regulation is 1.5 mV/V. Also, we obtain a good power supply rejection (PSR) of −63 dB at 10 kHz and −20 dB at 1 MHz. The PWM automatically moves to a pulse-skipping mode at light load, reducing the quiescent current to 1.8 mA, while the peak current efficiency is 99.27%.

Influence of Parametric Nonlinearities on Closed-Loop Operated MEMS Gyroscopes

The influence of parametric nonlinearities on the mode matching of closed-loop operated MEMS gyroscopes is investigated. Accurate resonance tuning of mechanical detection modes is essential for optimal noise suppression in closed-loop resonators. Large deflections of the drive mode lead to a geometric nonlinearity, which induces a phase-dependency in the mode-matching procedure. Those effects are known to amplify signal-to-noise ratio in open-loop vibratory MEMS gyroscopes. Predicted and measured tuning voltages and folded response of a sense mode in a prototype gyroscope are compared. Using simulations, it is shown that the pilottone with a 90° phase can confine the crosstalk of the Coriolis and quadrature channel to the quadrature channel exclusively. When applying a quadrature compensation in the simplified model, nonlinear amplification is prohibited in the output channel even for low gain of the force-to-rebalance loop. Furthermore, it is shown that in a simulation with idealized drive motion and demodulation signals the cross-coupling nonlinearity by itself does not have a major impact on standard noise suppression capabilities. [2021-0232]

Characterization and compensation of thermal bias drift of a stiffness-tunable MEMS accelerometer

This paper presents characterization and compensation of the thermal bias drift of a MEMS accelerometer whose effective stiffness is electrostatically tuned to a low value with the help of the single-sided parallel plates (SSPPs) capacitors. A temperature drift model for the proposed accelerometer is built and the temperature effect on the mechanical stiffness and the circuit gains is characterized. The characterization reveals that the variations of the feedforward coefficient including the mechanical stiffness and the readout gain due to the temperature change play a significant role in the bias drift of output of the proposed closed-loop accelerometer. On the other hand, the variations of both feedback gain and tuning gain as a function of temperature are one-order-of-magnitude less than that of the feedforward coefficient. To calibrate the feedforward coefficient, an excitation signal as a form of AC reference displacement is introduced to drive the proof mass and the readout response is demodulated to calibrate the variance of the feedforward coefficient correspondingly. An open-loop compensation scheme for the temperature-induced bias drift using the variance of the calibrated response is proposed accordingly. Alternatively, the calibrated response can be controlled to a preset value by a new proportion integral derivative (PID) controller by the adjustment of the SSPP tuning voltage. The output of the PID controller is used for the calibration of the introduced bias from the electrostatic tuning force. Therefore, a closed-loop compensation of the thermal bias drift is achieved by remaining the feedforward coefficient while eliminating the calibrated bias. Experiments under a temperature cooling process and different tuning voltages are carried out to verify two proposed compensation schemes. The temperature drift coefficients (TDCs) of both compensated outputs exhibit at least one-order-of-magnitude reduction in response to the temperature change. When the effective stiffness of the accelerometer is tuned to about 4.19 N m−1, the TDC of the compensated output using the proposed open-loop or closed-loop compensation schemes is reduced to about 0.1136 or 0.0391 mg °C−1, respectively and meanwhile, the Allan bias instability is slightly increased to 48.63 or 56.14 μg, respectively.

A Monolithic CMOS-MEMS Reconfigurable/Tunable Capacitive Accelerometer with Integrated Sensing Circuits

MEMS accelerometers have been widely used in various applications with a wide range of signal levels and bandwidth. Therefore it is desired to have a sensor whose characteristics such as sensitivity and bandwidth can be reconfigured/tuned depending on specific applications. This paper presents a reconfigurable/tunable z-axis accelerometer whose mechanical resonant frequency, sensitivity and sensing bandwidth can be tuned by the electrostatic spring softening effect. The proposed accelerometer was designed using a commercial 0.35 μm CMOS foundry service. The tuning electrodes were implemented in the metal and polysilicon layers in the standard CMOS process. An on-chip chopper stabilized readout circuit was designed to convert the capacitance signal to a voltage readout. The sensing structure was released by post-CMOS wet metal etching. Measurement results showed the proposed accelerometer had a sensitivity of 12 mV/g in the range of 0–5 g. The sensitivity and bandwidth tuning ranges are 50% and 18%, respectively, for an applied tuning voltage of 25 V. The demonstrated device is the first reconfigurable/tunable CMOS-MEMS accelerometer in the literature to our best knowledge.