Showing papers on "Biasing published in 2020"

Doping-free complementary WSe2 circuit via van der Waals metal integration.

Abstract: Two-dimensional (2D) semiconductors have attracted considerable attention for the development of ultra-thin body transistors. However, the polarity control of 2D transistors and the achievement of complementary logic functions remain critical challenges. Here, we report a doping-free strategy to modulate the polarity of WSe2 transistors using same contact metal but different integration methods. By applying low-energy van der Waals integration of Au electrodes, we observed robust and optimized p-type transistor behavior, which is in great contrast to the transistors fabricated on the same WSe2 flake using conventional deposited Au contacts with pronounced n-type characteristics. With the ability to switch majority carrier type and to achieve optimized contact for both electrons and holes, a doping-free logic inverter is demonstrated with higher voltage gain of 340, at the bias voltage of 5.5 V. Furthermore, the simple polarity control strategy is extended for realizing more complex logic functions such as NAND and NOR.

An Electrically Modulated Single-Color/Dual-Color Imaging Photodetector.

Abstract: An electrically modulated single-/dual-color imaging photodetector with fast response speed is developed based on a small molecule (COi 8DFIC)/perovskite (CH3 NH3 PbBr3 ) hybrid film. Owing to the type-I heterojunction, the device can facilely transform dual-color images to single-color images by applying a small bias voltage. The photodetector exhibits two distinct cut-off wavelengths at ≈544 nm (visible region) and ≈920 nm (near-infrared region), respectively, without any power supply. Its two peak responsivities are 0.16 A W-1 at ≈525 nm and 0.041 A W-1 at ≈860 nm with a fast response speed (≈102 ns). Under 0.6 V bias, the photodetector can operate in a single-color mode with a peak responsivity of 0.09 A W-1 at ≈475 nm, showing a fast response speed (≈102 ns). A physical model based on band energy theory is developed to illustrate the origin of the tunable single-/dual-color photodetection. This work will stimulate new approaches for developing solution-processed multifunctional photodetectors for imaging photodetection in complex circumstances.

Instability of p–i–n perovskite solar cells under reverse bias

Abstract: Partial shading can trigger permanent damage in photovoltaic modules because the illuminated solar cells drive the shaded cells into reverse bias. Under reverse bias conditions, perovskite solar cells have been shown to degrade quickly due to processes that have so far remained elusive. Here, we combine optical, microstructural, and electrical characterization to address the mechanisms governing perovskite solar cell degradation under reverse bias. Three main processes are shown to occur in cesium/formamidinium lead iodide/bromide cells depending on the reverse voltage applied, the duration of the reverse bias treatment and the cell structure. The first and most severe involves the formation of highly conductive shunts, preferentially in regions covered by the metal electrode (with apparently equal propensity for various metals) and, at higher reverse voltages, within the perovskite active area. Second, we find that iodide is reversibly driven into the organic electron transport layer, causing an S-shape in the current–voltage curve and lowering power conversion efficiency. Finally, under heavy reverse biasing the perovskite absorber is shown to degrade into iodide- and bromide-rich sub-layers, an irreversible process associated with a shift in the effective band gap and changes to the perovskite microstructure. Criteria that must be met to pass partial shading tests defined by the International Electrotechnical Commission are also discussed in relation to these issues, indicating the urgent need for device structures far more robust than those usually reported.

Tunable Electronic, Optical, and Thermal Properties of two- dimensional Germanene via an external electric field.

Abstract: In this paper, we present a tight-binding model based on DFT calculations for investigation the electronic and optical properties of monolayer Germanene. The thermal properties are investigated using Green function method. The required tight binding parameters including the onsite energies and third nearest neighbors hopping and overlap integrals are obtained based on our DFT calculations. Germanene is a semiconductor with zero band gap and linear band dispersion around the K point. The band gap opening occurs in the presence of bias voltage. The band gap is increased linearly with increase of the bias voltage strength. The tight binding results for position of the two first peaks in the optical Infrared region is same with the DFT results. By applying and increasing bias voltage, the dielectric function shows the blue shift by reduction the peak intensity in the energy range E < 1 eV. The thermal conductivity and heat capacity increase with increasing the temperature due to the increasing of thermal energy of charge carriers and excitation them to the conduction bands. The thermal properties of Germanene in the absence of bias U = 0 is larger than that U ≠ 0 and they decrease by further bias strength increasing, due to the increasing band gap with bias.

A Gd@C82 single-molecule electret

Abstract: Electrets are dielectric materials that have a quasi-permanent dipole polarization. A single-molecule electret is a long-sought-after nanoscale component because it can lead to miniaturized non-volatile memory storage devices. The signature of a single-molecule electret is the switching between two electric dipole states by an external electric field. The existence of these electrets has remained controversial because of the poor electric dipole stability in single molecules. Here we report the observation of a gate-controlled switching between two electronic states in Gd@C82. The encapsulated Gd atom forms a charged centre that sets up two single-electron transport channels. A gate voltage of ±11 V (corresponding to a coercive field of ~50 mV A–1) switches the system between the two transport channels with a ferroelectricity-like hysteresis loop. Using density functional theory, we assign the two states to two different permanent electrical dipole orientations generated from the Gd atom being trapped at two different sites inside the C82 cage. The two dipole states are separated by a transition energy barrier of 11 meV. The conductance switching is then attributed to the electric-field-driven reorientation of the individual dipole, as the coercive field provides the necessary energy to overcome the transition barrier. A Gd@C82 molecule shows electric polarization switching behaviour under a gate bias voltage, thus demonstrating a single-molecule electret device.

Micro-Transfer-Printed III-V-on-Silicon C-Band Semiconductor Optical Amplifiers

Abstract: The micro-transfer-printing of prefabricated C-band semiconductor optical amplifiers (SOAs) on a silicon waveguide circuit is reported. The SOAs are 1.35 mm in length and 40 mu m in width. Dense arrays of III-V SOAs are fabricated on the source InP wafer. These can then be micro-transfer-printed on the target SOI photonic circuits in a massively parallel fashion. Additionally, this approach allows for greater flexibility in terms of integrating different epitaxial layer structures on the same SOI waveguide circuit. The technique allows integrating SOAs on a complex silicon photonic circuit platform without changing the foundry process-flow. Two different SOA designs with different optical confinement factor in the quantum wells of the III-V waveguide are discussed. This allows tuning the small-signal gain and output saturation power of the SOA. The design with higher optical confinement in the quantum wells has a small-signal gain of up to 23 dB and an on-chip saturation power of 9.2 mW at 140 mA bias current and the lower optical confinement factor design has a small-signal gain of 17 dB and power saturation of 15 mW at 160 mA of bias current.

Broadband and Tunable Radar Absorber Based on Graphene Capacitor Integrated With Resistive Frequency-Selective Surface

Abstract: In this communication, a broadband and tunable radar absorber is proposed by integrating graphene capacitor with resistive frequency-selective surfaces (RFSS). The microwave reflectivity can be dynamically controlled by changing the effective sheet resistance of graphene through an electrostatic field bias. The simulated results indicate that this structure can tune its reflectivity over a wide frequency band ranging from 2.9 to 15.9 GHz under the normal incidence, when the graphene resistance is varied from 120 to $700~\Omega $ /sq. The tuning range of the average reflectivity is from −4.6 to −15.3 dB. The physical mechanism of this tunable absorber is discussed by studying the electric field distribution and power loss density. We fabricated this absorber and measured its tunable reflectivity by applying different biasing voltages. The experimental results are in a good agreement with those of the simulation results. In addition, this absorber is also verified to have a good angular stability and polarization insensitivity, which will have broad prospects in the application of stealth technology.

Tribo-mechanical properties of CrNbTiMoZr high-entropy alloy film synthesized by direct current magnetron sputtering

Abstract: The deposition parameters of high-entropy alloy films significantly influence their performance due to effective control of their microstructure. Thus, these parameters have become a research hotspot. In this study, CrNbTiMoZr high-entropy alloy films of amorphous or nanocrystalline solid solution were synthesized by direct current magnetron sputtering on silicon wafers and 304 stainless steel under different substrate bias voltages. The films' microstructure and tribo-mechanical properties were studied in detail. Results showed that the microstructure of films transformed from columnar structure to featureless with increased substrate bias voltage. In the nanoindentation test, the film deposited at −150 V exhibited the highest hardness of 9.7 GPa. Nevertheless, the CrNbTiMoZr films displayed excellent tribological properties under low bias voltage. Overall, our findings can guide the design of other novel high-entropy alloy films.

A 10-mA LDO With 16-nA IQ and Operating From 800-mV Supply

Abstract: A low-dropout (LDO) regulator with a quiescent current in the tens of nanoampere range and operating from 800-mV supply is proposed. A rail-to-rail buffer with zero input–output (I/O) voltage shift and based on the differential flipped voltage follower is used for combined gate and bulk driving of the output device. Therefore, bulk modulation with forward body bias is implemented without any additional amplifier. The proposed buffer is a crucial block for the sub-1-V supply and for limiting the contribution of the output device to the quiescent current. The error amplifier (EA) is adaptively biased with a bias shaper block, which implements a current limiting at high loads and a linear dependence on the output current at moderate loads. The feedback signal for the bias control is the output of the amplifier instead of the gate voltage of the pass device, thus combining a nanoampere bias at light load with the ability to follow a fast output current transient. Finally, a corner-tracking load is used to set the bias current of the output device to the minimum value at the target stability margin over the temperature and process parameters’ space. The LDO was implemented in a 55-nm CMOS technology. The measured quiescent current is 16 nA with a minimum power supply rejection of 42.7 dB up to 50 kHz and a maximum load current of 10 mA. In order to compare the transient behavior of the state-of-the-art designs, a modified figure of merit is proposed, taking into account the penalty caused by the low supply.

Broadband Polarization-Insensitive Tunable Absorber Using Active Frequency Selective Surface

Abstract: In this letter, a broadband polarization-independent tunable absorber is proposed based on active frequency selective surface (AFSS). The AFSS consists of periodic patterns of four-patch array with four p-i-n diodes loaded among them, and a simple bias network is designed behind the ground plane through metalized via holes, which can effectively reduce the influence on the absorbing performance. By changing the bias voltage applied on the p-i-n diodes, the reflectivity of our absorber can be dynamically adjusted from near-unity reflection to less than −10 dB absorptivity under normal incidence over a wide frequency band ranging from 8.5 to 18.2 GHz. Due to the symmetrical structure of the AFSS, our absorber still has polarization insensitivity. We fabricated this AFSS absorber sample, and its measured results agree well with the simulated ones.

Epitaxial synthesis of ultrathin β-In2Se3/MoS2 heterostructures with high visible/near-infrared photoresponse.

Abstract: van der Waals (vdWs) heterostructures, combining different two-dimensional (2D) layered materials with diverse properties, have been demonstrated to be a very promising platform to explore a new physical phenomenon and realize various potential applications in atomically thin electronic and optoelectronic devices. Here, we report the controlled growth of vertically stacked β-In2Se3/MoS2 vdWs heterostructures (despite the existence of large lattice mismatching ∼29%) through a typical two-step chemical vapor deposition (CVD) method. The crystal structure of the achieved heterostructures is characterized by transmission electron microscopy, where evident Moire patterns are observed, indicating well-aligned lattice orientation. Strong photoluminescence quenching is obeserved in the heterostructure, revealing effective interlayer charge transfer at the interface. Electrical devices are further constructed based on the achieved heterostructures, which have a high on/off ratio and a typical rectifying behavior. Upon laser irradiation, the devices show excellent photosensing properties. A high responsivity of 4.47 A W-1 and a detectivity of 1.07 × 109 Jones are obtained under 450 nm laser illumination with a bias voltage of 1 V, which are much better than those of heterostructures grown via CVD. Most significantly, the detection range can be extended to near-infrared due to the relatively small bandgap nature of β-In2Se3. With 830 nm laser illumination, the devices also show distinct photoresponses with fast response speed even when operating at room temperature. The high-quality β-In2Se3/MoS2 heterostructures broaden the family of the 2D layered heterostructure system and should have significant potential applications in high-performance broadband photodetectors.

Influence of Nitrogen Content and Bias Voltage on Residual Stress and the Tribological and Mechanical Properties of CrAlN Films

Abstract: This study deposited CrAlN coatings from Al50Cr50 targets using high-power impulse magnetron sputtering, with a focus on the effects of nitrogen content and substrate bias voltage on the deposition rate, microstructure, crystal orientation, residual stress, and mechanical properties of the coating. The nitrogen content was adjusted by varying the N2/Ar flow ratio between 20% and 140%. Increasing the nitrogen flow rate during deposition led to corresponding decreases in the deposition rate and film thickness. X-ray diffractometer (XRD) analysis revealed that a low N2/Ar flow ratio ( 40%) resulted in an face-centered cubic (FCC) phase. Bias voltage also had considerable influence on the residual stress and grain size. A refined grain structure and high internal stress resulted in hard CrAlN coatings. Among the various parameter combinations evaluated in this study, the highest hardness (35.4 GPa) and highest elastic modulus (426 GPa) were obtained using an N2/Ar flow ratio of 100% and a bias voltage of −120 V.

An Electret-Augmented Low-Voltage MEMS Electrostatic Out-of-Plane Actuator for Acoustic Transducer Applications.

Abstract: Despite the development of energy-efficient devices in various applications, microelectromechanical system (MEMS) electrostatic actuators yet require high voltages to generate large displacements. In this respect, electrets exhibiting quasi-permanent electrical charges allow large fixed voltages to be integrated directly within electrode structures to reduce or eliminate the need of DC bias electronics. For verification, a − 40 V biased electret layer was fabricated at the inner surface of a silicon on insulator (SOI) structure facing a 2 μm gap owing to the high compatibility of silicon micromachining and the potassium-ion-electret fabrication method. A − 10 V electret-augmented actuator with an out-of-plane motion membrane reached a sound pressure level (SPL) of 50 dB maximum with AC input voltage of V i n = 5 V pp alone, indicating a potential for acoustic transducer usage such as microspeakers. Such devices with electret biasing require only the input signal voltage, thus contributing to reducing the overall power consumption of the device system.

Modeling and Characterization of a Pull-in Free MEMS Microphone

Abstract: In this study, we examine the feasibility of designing a MEMS microphone employing a levitation based electrode configuration. This electrode scheme enables capacitive MEMS sensors that could work for large bias voltages without pull-in failure. Our experiments and simulations indicate that it is possible to create robust sensors properly working at high DC voltages, which is not feasible for most of the conventional parallel plate electrode-based-microscale devices. In addition, the use of larger bias voltages will improve signal-to-noise ratios in MEMS sensors because it increases the signal relative to the noise in read-out circuits. This study presents the design, fabrication, and testing of a capacitive microphone, which is made of approximately 2 μm thick highly-doped polysilicon as a diaphragm. It has approximately 1 mm 2 surface area and incorporates interdigitated sensing electrodes on three of its sides. Right underneath these moving electrodes, there are fixed fingers being held at the same voltage potential as the moving electrodes and separated from them with a 2 μm thick air gap. The electronic output is obtained using a charge amplifier. Measured results obtained on three different microphone chips using bias voltages up to 200 volts indicate that pull-in failure is completely avoided. The sensitivity of this initial design was measured to be 16.1 mV/Pa at 200 V bias voltage, and the bandwidth was from 100 Hz to 4.9 kHz.

Precise ion energy control with tailored waveform biasing for atomic scale processing

Abstract: Anisotropic plasma-enhanced atomic layer etching (ALE) requires directional ions with a well-defined ion energy to remove materials in a highly selective and self-limiting fashion. In many plasma etching systems, the ion energy is controlled using radio-frequency (13.56 MHz) sinusoidal waveform biasing. However, this yields ions with a broad energy distribution, while also inducing electron heating mechanisms that can affect the ion flux. In this work, we report on precise ion energy control—independent of the ion flux—using low-frequency (LF: 100 kHz) tailored bias voltage waveforms in a commercial remote plasma reactor. A prototype LF bias generator has been used to apply tailored waveforms consisting of a positive voltage pulse and a negative linear voltage ramp. These waveforms yielded ions having narrow energy distributions (7 ± 1 eV full-width-at-half-maximum) measured on dielectric SiO2 substrates for ion energies up to 200 eV in collisionless Ar plasmas. The mono-energetic ions were used to etch SiO2 thin films by physical sputtering. In these sputter etch experiments, the ability to accurately control the ion energy in the <100 eV range is demonstrated to allow for a more precise determination of sputter thresholds, which serve as valuable input for the design of novel ALE chemistries. The feasibility of performing anisotropic plasma etching using LF tailored waveform biasing was established by etching a SiO2 layer on a 3D trench nanostructure. The potential merits of this technique for the field of atomic scale processing are discussed.

A graphene-silicon Schottky photodetector with graphene oxide interlayer

Abstract: A photodetector based on graphene-silicon Schottky diode with graphene oxide (GO) interlayer was prepared in this research. The GO interlayer suppressed the dark current, and increased the photocurrent 2.73 times. With the reverse bias of 2 V, the responsivity of Gr/GO/n-Si Schottky photodiode was 0.65 A/W under 633 nm illumination, meanwhile the ON/OFF ratio reaches 2.73 × 105 due to the insertion of GO interlayer. The characterization of photoelectric properties showed stable photo sensing performance with the increase of bias voltage and incident light power. The response time and recovery time were 1 ms, which indicated that the response speed of graphene-silicon Schottky photodiode was well preserved after inserting GO interlayer.

Optimized Substrate for Improved Performance of Stacked Nanosheet Field-Effect Transistor

Abstract: The recently proposed stacked nanosheet-field-effect transistor (SNSH-FET) is considered as a promising candidate for continued scaling with silicon. While using punchthrough-stopper-doped (or) ground-plane-doped silicon substrate (PTS-Si substrate) in which the top part of the substrate is doped heavily with the p-type (for nMOS) impurity to avoid punchthrough leakage between the source and the drain. The heavily doped p–n junction formed at the drain–substrate junction acts as a reverse-biased tunnel diode during ${V}_{{\text {DS}}}$ biasing, which leads to large substrate leakage current. We presented SuperSteep-Retrograde silicon substrate (SSR-Si substrate) configuration which reduces the tunneling current by increasing the tunnel barrier width and diminishing the peak electric field at the drain–substrate junction. The SSR-Si substrate is achieved by growing a lightly doped or undoped layer of silicon (SSR-buffer layer) on the PTS-doped substrate. The impact of SSR-buffer layer thickness is studied and the optimal thickness (12 nm) is presented. The vertically stacked channels’ configuration leads to position-dependent current densities in different channels due to position-dependent series resistance. Herein, we present nanosheet width optimization as a solution to achieve homogeneous current ratio between all the channels thereby resulting in better linearity performance. The self-heating and RF performance of the presented SSR-Si substrate is compared with the silicon-on-insulator (SOI) substrate. The results show that SSR-Si substrate can be a better substrate for SNSH-FET because of better self-heating performance.

An Electrically Controlled Wavelength-Tunable Nanoribbon Laser.

Abstract: Nanoscale laser sources with downscaled device footprint, high energy efficiency, and high operation speed are pivotal for a wide array of optoelectronic and nanophotonic applications ranging from on-chip interconnects, nanospectroscopy, and sensing to optical communication. The capability of on-demand lasing output with reversible and continuous wavelength tunability over a broad spectral range enables key functionalities in wavelength-division multiplexing and finely controlled light-matter interaction, which remains an important subject under intense research. In this study, we demonstrate an electrically controlled wavelength-tunable laser based on a CdS nanoribbon (NR) structure. Typical "S"-shaped characteristics of pump power dependence were observed for dominant lasing lines, with concomitant line width narrowing. By applying an increased bias voltage across the NR device, the lasing resonance exhibits a continuous tuning from 510 to 520 nm for a bias field in the range 0-15.4 kV/cm. Systematic bias-dependent absorption and time-resolved photoluminescence (PL) measurements were performed, revealing a red-shifted band edge of gain medium and prolonged PL lifetime with increased electric field over the device. Both current-induced thermal reduction of the band gap and the Franz-Keldysh effect were identified to account for the modification of the lasing profile, with the former factor playing the leading role. Furthermore, dynamical switching of NR lasing was successfully demonstrated, yielding a modulation ratio up to ∼21 dB. The electrically tuned wavelength-reversible CdS NR laser in this work, therefore, presents an important step toward color-selective coherent emitters for future chip-based nanophotonic and optoelectronic circuitry.

A configurable two-layer four-bias graphene-based THz absorber

Abstract: A novel structure for a THz absorber covering the THz band (0.1–10 THz) is presented. Exploiting nanographene disks and ribbons beside the dual-bias method, three modes of operation are introduced with the graphene gate biasing as the control parameter. The structure includes two layers consisting of graphene patterns on TOPAS dielectric and a thick gold plate at the bottom. The superior performance of the structure mainly relies on the use of feasible geometric patterns and the characteristics of graphene, while an evolutionary genetic algorithm is used to optimize a cost function defined based on four chemical potential values. In comparison with conventional structures, the device proposed herein offers an increased number of gate biases and thereby more degrees of freedom to achieve greater tunability. To model the proposed device, a recently developed circuit model approach is modified to include the dual-bias scheme introduced herein, enabling a very simple calculation of the referred input impedance of the device that lies at the heart of the design procedure. The input impedance required for impedance matching theory is matched with the free space incident medium (120π Ω) to maximize the absorption. Finally, the results from the MATLAB algorithm are verified against finite element method simulations using the CST simulator, confirming the validity and accuracy of the proposed design. According to both the circuit model representation and the full-wave numerical modeling, the presented device absorbs THz waves with an absorption ratio of more than 90% in three operational modes, viz. mode A (0.7–2.2 THz), mode B (5.3–6.6 THz), and mode C (7.4–8.4 THz). This increases its potential for use in numerous applications in the THz band such as sensors, detectors, modulators, and even optical processors.

Dual-functional ultraviolet photodetector with graphene electrodes on AlGaN/GaN heterostructure.

Abstract: A dual-functional ultraviolet (UV) photodetector with a large UV-to-visible rejection ratio is presented, in which interdigitated finger-type two-dimensional graphene electrodes are introduced to an AlGaN/GaN heterostructure. Two photocurrent generation mechanisms of photovoltaic and photoconductive dominances coexist in the device. The dominance of the mechanisms changes with the induced bias voltage. Below a threshold voltage, the device showed fairly low responsivities but fast response times, as well as a constant photocurrent against the induced bias. However, the opposite characteristics appeared with high bias voltage. Specifically, above the threshold voltage, the device showed high responsivities with additional gain, but slow rise and recovery times. For instance, the responsivity of 10.9 A/W was observed with the gain of 760 at the induced bias voltage of 5 V. This unique multifunctionality enabled by the combination of an AlGaN/GaN heterostructure with graphene electrodes facilitates the development of a single device that can achieve multiple purposes of photodetection.

A 48 pW, 0.34 V, 0.019%/V Line Sensitivity Self-Biased Subthreshold Voltage Reference With DIBL Effect Compensation

Abstract: This paper presents a self-biased subthreshold CMOS voltage reference for low-power and low-voltage applications. To achieve near-zero line sensitivity and high PSRR, a compensation structure utilizing the drain-induced-barrier-lowering (DIBL) effect is proposed to sink a supply dependent current from the output branch of a self-biased CMOS reference, which cancels the bias current’s dependence on the supply voltage due to the DIBL effect. Fabricated in a 0.18- $\mu \text{m}$ CMOS technology, the measurement results demonstrate that the proposed circuit could operate under a minimum supply voltage of 0.34 V and generate a reference voltage of 147 mV, while consuming only 48 pW power. The PSRRs measured at 1 Hz and 10 kHz are −70.6 dB and −50.2 dB, respectively. For 39 measured samples, the mean line sensitivity is 0.019%/V in a supply voltage range from 0.34 to 1.8 V, and the average temperature coefficients before and after trimming are 64.81 and 10.06 ppm/°C in 0 ~ 100 °C temperature range, respectively. The total area of the voltage reference circuit is 0.0332mm2.

Impact of Varied Buffer Layer Designs on Single-Event Response of 1.2-kV SiC Power MOSFETs

Abstract: In this article, the single-event response of the 1.2-kV silicon-carbide (SiC) power MOSFETs with varied buffer layer designs is investigated by the 2-D numerical simulations. The structural parameters of the buffer layers are compared and analyzed to understand the transient response after the heavy ion strike and the related physical mechanisms comprehensively. Simulation results reveal that an optimized single buffer structure can be acquired by using a relatively thicker buffer layer (T $\mu \text{m}$ ) and a moderate doping concentration (D cm−3). It demonstrates that the single-event-burnout (SEB) performance can be improved significantly under the worst case bias conditions [a drain bias voltage of 1.2 kV and a linear energy transfer (LET) of 1 pC/ $\mu \text{m}$ ]. In addition, the optimized structural combinations adopted in the dual or triple buffer layers can strengthen the SEB performance further. The simulation results show that a step electric field distribution is established inside the optimized dual or triple buffers, where the electric field peak is mitigated from 3 to 2.2 MV/cm. Moreover, the excess carrier generation is suppressed and the local temperature rise is weakened during the transient electrothermal process. Consequently, the structure with the optimal buffer layer designs can enlarge the SEB safe operating area (SOA) from 30%–50% to 100% rated breakdown voltage at high LET bias, which makes the SiC power MOSFETs used in aerospace and aviation power electronic systems become possible.

Ridge Gap Waveguide Based Liquid Crystal Phase Shifter

Abstract: In this paper, the gap waveguide technology is examined for packaging liquid crystal (LC) in tunable microwave devices. For this purpose, a line based passive phase shifter is designed and implemented in a ridge gap waveguide (RGW) topology and filled with LC serving as functional material. The inherent direct current (DC) decoupling property of gap waveguides is used to utilize the waveguide surroundings as biasing electrodes for tuning the LC. The bed of nails structure of the RGW exhibits an E-field suppression of 76 dB in simulation, forming a completely shielded device. The phase shifter shows a maximum figure of merit (FoM) of 70 °/dB from 20 GHz to 30 GHz with a differential phase shift of 387° at 25 GHz. The insertion loss ranges from 3.5 dB to 5.5 dB depending on the applied biasing voltage of 0 V to 60 V.

Single digit parts-per-billion NOx detection using MoS2/hBN transistors

Abstract: 2D materials offer excellent possibilities for high performance gas detection due to their high surface-to-volume ratio, high surface activities, tunable electronic properties and dramatic change in resistivity upon molecular adsorption. This paper demonstrates a simple field effect transistor (FET) of molybdenum disulphide (MoS2) fabricated on a hexagonal boron nitride (hBN) substrate that can detect NOx down to concentrations of 6 ppb and possibly far below at room temperature (RT) with a systematic optimization of the device design and fabrication parameters as well as the device operating conditions. The effects of the substrate, number of MoS2 layers, channel layout and biasing conditions on the response of MoS2 FETs to NOx were investigated, providing directions for maximizing the sensitivity. This work also sheds light the issues of recovery and stability and present a methodology for calibration of the sensors which is critical for repeatable and reliable measurements.

Low voltage charge-plasma based dopingless Tunnel Field Effect Transistor: analysis and optimization

Abstract: In this reported work, we have analyzed the different figure of merits for dopingless TFET. The charge-plasma based Planar-TFET does have a dual-gate with a half structure made from Silicon–Germanium (Si–Ge) compound. The Si–Ge is used with a composition factor of 0.45. The Si0.55Ge0.45 helped in the current enhancement of the Silicon-based TFET device. Several linearity parameters are calculated for low and high drain bias to acknowledge the device behavior at different biasing conditions. The heteromaterial planar-TFET is optimized according to the physical conditions where the source contact is considered as Schottky contact with barrier lowering. The work function of the source electrode is varied to check the effects of the Schottky barrier on the device characteristics. The optimized dopingless TFET is scaled down to lower dimensions for the possibility of nano-TFET devices without compromising the device performance. The nanoscaled dopingless nanowire TFET performs better as compared to dopingless planar TFET with similar dimensions. The obtained cutoff frequency is greater than 10 GHz and intermodulation distortion is less than − 650 dBm. The optimized structure showed low noise and harmonic distortions to be used for better sensing applications.