Lateral Voltage Research Articles

Low contact resistance and high breakdown voltage of AlGaN/GaN HEMT grown on silicon using both AlN/GaN superlattice and Al0.07Ga0.93N back barrier layer

In this study, the growth of a high-quality AlGaN/GaN high electron mobility transistor (HEMT) heterostructure on silicon (Si) by metal–organic chemical vapor deposition was investigated by utilizing both the AlN/GaN superlattice (SL) and Al0.07Ga0.93N back barrier (BB) techniques. An atomic force microscope and high-resolution x-ray diffractometer confirm a low surface roughness of 0.26–0.34 nm and the formation of a high-quality AlN/GaN SL and GaN channel. The AlGaN/GaN heterostructures exhibit a high electron mobility of up to 1700 cm2 V−1∙s and a high carrier concentration density of (1.02–1.06 × 1013 cm−2) for both heterostructures. The AlGaN/GaN HEMT devices demonstrate a low specific contact resistivity (ρ c) of 2.7 × 10−6 Ω·cm2 and a low contact resistance (RC ) of 0.3 Ω·mm for the heterostructure with a BB layer. Furthermore, the DC characteristics demonstrate that incorporating Al0.07Ga0.93N BB in the heterostructure results in a 19.2% increase in lateral breakdown voltage (with a 10 µm spacing) and a 27.5% increase in vertical breakdown voltage (at 1 mA cm−2) compared to heterostructures without Al0.07Ga0.93N BB within the AlN/GaN SL structure. Moreover, an improvement of 10.6% in the maximum saturation current (I DS) and 15.2% in on-resistance (R ON) has been achieved for the device fabricated on an Al0.07Ga0.93N BB structure. The insertion loss of the buffer layer improves to −1.40 dB mm−1 at 40 GHz. Consequently, the proposed heterostructure investigated in this study demonstrates suitability for electronic device applications.

GaAs Cone-Shell Quantum Dots in a Lateral Electric Field: Exciton Stark-Shift, Lifetime, and Fine-Structure Splitting.

Strain-free GaAs cone-shell quantum dots have a unique shape, which allows a wide tunability of the charge-carrier probability densities by external electric and magnetic fields. Here, the influence of a lateral electric field on the optical emission is studied experimentally using simulations. The simulations predict that the electron and hole form a lateral dipole when subjected to a lateral electric field. To evaluate this prediction experimentally, we integrate the dots in a lateral gate geometry and measure the Stark-shift of the exciton energy, the exciton intensity, the radiative lifetime, and the fine-structure splitting (FSS) using single-dot photoluminescence spectroscopy. The respective gate voltage dependencies show nontrivial trends with three pronounced regimes. We assume that the respective dominant processes are charge-carrier deformation at a low gate voltage U, a vertical charge-carrier shift at medium U, and a lateral charge-carrier polarization at high U. The lateral polarization forms a dipole, which can either enhance or compensate the intrinsic FSS induced by the QD shape anisotropy, dependent on the in-plane orientation of the electric field. Furthermore, the data show that the biexciton peak can be suppressed by a lateral gate voltage, and we assume the presence of an additional vertical electric field induced by surface charges.

Impact of eliminating ungated access regions on DC and thermal performance of GaN-based MIS-HEMT

The impacts of eliminating access regions (AR) on DC and thermal performance of GaN-based MIS-HEMT have been studied using a device of 4 µm gate length. Nominal absence of ARs was achieved by a metal-organic chemical vapor deposition-regrown heavily n-doped GaN contact region extended to the two-dimensional electron gas (2DEG) channel (with sheet resistance as low as 14 Ω/ ◻ and ohmic contact resistance of 0.20 Ω⋅ mm) and 22-nm-thick AlN/Al2O3/HfO2 insulator layers acting as both gate dielectrics and sidewall spacers. As a result, a low knee voltage (2.5 V @ VGS = +2 V) comparable to deeply-scaled devices was attained, revealing the dominant role of ARs in knee voltages. High linearity at lower supply voltages (gate voltage swing of 7.3 V @ VDS = 5 V) and a faster GVS saturation trend with V DS increasing were observed, benefiting from the improved utility of applied lateral voltage. Moreover, a much lower thermal resistance compared to that of the conventional MIS-HEMT structure (146 vs. 202 K W−1) was extracted by a static-pulsed I-V measurement method. Simplified TCAD simulations were conducted to explain the underlying mechanisms, demonstrating that the enhanced surface heat flow covered by the gate metal as well as the more uniform electric field along the 2DEG channel accounts for the better capability of heat management in the device free of ARs. Our results indicate the size of DC and thermal performance enhancements obtained by eliminating ARs in a GaN-based MIS-HEMT structure.

Driving Principle and Stability Analysis of Vertical Comb-Drive Actuator for Scanning Micromirrors.

We have developed a manufacturing process for micromirrors based on microelectromechanical systems (MEMS) technology. The process involves designing an electrostatic vertically comb-driven actuator and utilizing a self-alignment process to produce a height difference between the movable comb structure and the fixed comb structure of the micromirror. To improve the stability of the micromirror, we propose four instability models in micromirror operation with the quasi-static driving principle and structure of the micromirror considered, which can provide a basic guarantee for the performance of vertical comb actuators. This analysis pinpoints factors leading to instability, including the left and right gap of the movable comb, the torsion beams of the micromirror, and the comb-to-beams distance. Ultimately, the voltages at which device failure occurs can be determined. We successfully fabricated a one-dimensional micromirror featuring a 0.8 mm mirror diameter and a 30 μm device layer thickness. The height difference between the movable and fixed comb structures was 10 μm. The micromirror was able to achieve a static mechanical angle of 2.25° with 60 V@DC. Stable operation was observed at voltages below 60 V, in close agreement with the theoretical calculations and simulations. At the driving voltage of 80 V, we observed the longitudinal displacement movement of the comb fingers. Furthermore, at a voltage of 129 V, comb adhesion occurred, resulting in device failure. This failure voltage corresponds to the lateral torsional failure voltage.

Numerical Investigation of Transient Breakdown Voltage Enhancement in SOI LDMOS by Using a Step P-Type Doping Buried Layer

In this paper, the transient breakdown voltage (TrBV) of a silicon-on-insulator (SOI) laterally diffused metal-oxide-semiconductor (LDMOS) device was increased by introducing a step P-type doping buried layer (SPBL) below the buried oxide (BOX). Device simulation software MEDICI 0.13.2 was used to investigate the electrical characteristics of the new devices. When the device was turned off, the SPBL could enhance the reduced surface field (RESURF) effect and modulate the lateral electric field in the drift region to ensure that the surface electric field was evenly distributed, thus increasing the lateral breakdown voltage (BVlat). The enhancement of the RESURF effect while maintaining a high doping concentration in the drift region (Nd) in the SPBL SOI LDMOS resulted in a reduction in the substrate doping concentration (Psub) and an expansion of the substrate depletion layer. Therefore, the SPBL both improved the vertical breakdown voltage (BVver) and suppressed an increase in the specific on-resistance (Ron,sp). The results of simulations showed a 14.46% higher TrBV and a 46.25% lower Ron,sp for the SPBL SOI LDMOS compared to those of the SOI LDMOS. As the SPBL optimized the vertical electric field at the drain, the turn-off non-breakdown time (Tnonbv) of the SPBL SOI LDMOS was 65.64% longer than that of the SOI LDMOS. The SPBL SOI LDMOS also demonstrated that TrBV was 10% higher, Ron,sp was 37.74% lower, and Tnonbv was 10% longer than those of the double RESURF SOI LDMOS.

Investigating spatial macroscopic metastability of perovskite solar cells with voltage dependent photoluminescence imaging

Metastability is a characteristic feature of perovskite solar cell (PSC) devices that affects power rating measurements and general electrical behaviour. In this work the metastability of different types of PSC devices is investigated through current–voltage (I–V) testing and voltage dependent photoluminescence (PL-V) imaging. We show that advanced I–V parameter acquisition methods need to be applied for accurate PSC performance evaluation, and that misleading results can be obtained when using simple fast I–V curves, which can lead to incorrect estimation of cell efficiency. The method, as applied in this work, can also distinguish between metastability and degradation, which is a crucial step towards reporting stabilised efficiencies of PSC devices. PL-V is then used to investigate temporal and spatial PL response at different voltage steps. In addition to the impact on current response, metastability effects are clearly observed in the spatial PL response of different types of PSCs. The results imply that a high density of local defects and non-uniformities leads to increased lateral metastability visible in PL-V measurements, which is directly linked to electrical metastability. This work indicates that existing quantitative PL imaging methods and point-based PL measurements of PSC devices may need to be revisited, as assumptions such as the absence of lateral currents or uniform voltage bias across a cell area may not be valid.

Passive Directivity Detection Using Individual Biaxial Ultrasound Transducers.

Biaxial transducers are an emerging technology that can steer generated ultrasound waves using a single piezoceramic component. Simulations have also shown that biaxial transducers can passively estimate the direction of arrival (DOA) of sound waves when operating in the receive mode. This research seeks to experimentally verify biaxial directivity estimates and establish directivity as an independent parameter detected by biaxial transducers. Three cuboid ( 3.84×3.84×5.92 mm) biaxial piezoceramics with two pairs of orthogonal electrodes (one pair applied laterally and one pair applied in the polling direction) were manufactured and characterized. Each transducer was placed in a water tank where an independent hemispherical source was attached to a moveable arm and operated at 250 kHz. Terminal voltages were recorded for 81 source positions in a plane parallel to the transducer's front face and at a depth of approximately 9 cm. Collection was repeated three times per transducer to ensure reproducibility. In silico results were compared with the experimental results. Two derived metrics were then calculated using both the forward and lateral terminal voltages: the phase difference and amplitude ratio. Biaxial transducers demonstrate an ability to estimate the DOA of incident sound waves, independently of any time-of-flight (TOF) information. The phase difference and amplitude ratio complement each other to provide statistically significant and repeatable estimates over a range of 48° (from -24° to +24°). These results can be used to augment a variety of medical, geophysical, and industrial passive ultrasound imaging techniques.

Study of TID radiation effects on the breakdown voltage of buried P-pillar SOI LDMOSFETs with P-top region

This article presents the numerical investigation on the total ionizing dose (TID) radiation induced breakdown voltage shifting behavior of the silicon-on-insulator (SOI) buried P-pillar (BP) lateral double-diffused metal-oxide semiconductor (LDMOS) with a P-top region (TP). We validate the employed simulation models and structure parameters by the experiments of the 200 V rated SOI BP-LDMOS devices. We also discuss the breakdown voltage (BV) analysis of the SOI BPTP-LDMOS under different doping concentrations in the drift region. Because the lateral breakdown voltage can be effectively enhanced by the P-top region under STI layer, the SOI BPTP-LDMOS behaves a wider Nd window for rated 200 V compared with the SOI BP-LDMOS. Finally, we perform the numerical investigation of the TID radiation effect on the BV shift. Using the TID hardening design with the electric field modulation method, the hardened BPTP-LDMOS can achieve a significant improvement in the TID tolerance compared with the hardened SOI BP-LDMOS, from 575 to 775 krad(Si).

High-sensitivity position-sensitive detectors to low-power light spots

This work reported on detecting properties of a p + -i-n + position-sensitive detector (PSD) which has a thin heavily-doped p + -GaAs layer and a thick lightly-doped i-GaAs layer as a resistive layer and an optical absorption layer, respectively. Two lateral electrodes on the p + -GaAs layer were separated by a distance of 12 mm to provide lateral photovoltaic voltages. The p + -GaAs layer with a small resistivity produces a long diffusion length for excess holes. Thus, a high linearity of > 99.8 % and a detection error of < 3.2 % are achieved when a visible light spot with a low power of < 3 mW is used. Measured sensitivities as a function of light-spot power are also indicative of a small power constant of 1.4 mW for a 638 nm light spot. A power efficiency of 9.66 mV·mm −1 mW −1 at 0.5 mW is obtained. Together with mature optoelectronic and microelectronic technologies, the proposed structure is very promising for a high-sensitivity PSD to low-power light-spot detection. On the other hand, response times of the PSD reflecting light on and off were also studied for further understanding insight the positioning mechanism. Measured results reveal that transverse depth where electron-hole pairs generated is one of key factors influencing the response time. Visible-light position-sensitive detector is proposed to be possibly combined with mature optoelectronic and microelectronic devices. The p-i-n like PSD with a thin heavily-doped resistive layer and a thick lightly-doped absorption layer shows high-sensitive, high-linearity, and low-detection error performances. Besides, high power efficiencies at a low power is very promising for low-power applications. • High-sensitive position-sensitive detector to low-power light spots was studied. • A power efficiency of 9.66 mV·mm −1 mW −1 at 0.5 mW was obtained. • Response times of the PSD reflecting light on and off were studied. • Detection errors < 3.2 % by using light-spot power < 3 mW were obtained.

New Aspects of Bilayer Lipid Membranes for the Analysis of Ion Channel Functions.

The bilayer lipid membrane (BLM) is the main structural component of cell membranes, in which various membrane proteins are embedded. Artificially formed BLMs have been used as a platform in studies of the functions of membrane proteins, including various ion channels. In this review, we summarize recent advances that have been made on artificial BLM systems for the analysis of ion channel functions. We focus on two BLM-based systems, cell-membrane mimicry and four-terminal BLM systems. As a cell-membrane-mimicking system, an efficient screening platform for the evaluation of drug side effects that act on a cell-free synthesized channel has been developed, and its prospects for use in personalized medicine will be discussed. In the four-terminal BLMs, we introduce “lateral voltage” to BLM systems as a novel input to regulate channel activities, in addition to the traditional transmembrane voltages. Such state-of-the-art technologies and new system setups are predicted to pave the way for a variety of applications, in both fundamental physiology and in drug discovery.

Room-temperature electrical control of polarization and emission angle in a cavity-integrated 2D pulsed LED

Devices based on two-dimensional (2D) semiconductors hold promise for the realization of compact and versatile on-chip interconnects between electrical and optical signals. Although light emitting diodes (LEDs) are fundamental building blocks for integrated photonics, the fabrication of light sources made of bulk materials on complementary metal-oxide-semiconductor (CMOS) circuits is challenging. While LEDs based on van der Waals heterostructures have been realized, the control of the emission properties necessary for information processing remains limited. Here, we show room-temperature electrical control of the location, directionality and polarization of light emitted from a 2D LED operating at MHz frequencies. We integrate the LED in a planar cavity to couple the polariton emission angle and polarization to the in-plane exciton momentum, controlled by a lateral voltage. These findings demonstrate the potential of TMDCs as fast, compact and tunable light sources, promising for the realization of electrically driven polariton lasers.

Channel-Length-Modulated Avalanche Multiplication in Ambipolar WSe2 Field-Effect Transistors.

Recently there has been growing interest in avalanche multiplication in two-dimensional (2D) materials and device applications such as avalanche photodetectors and transistors. Previous studies have mainly utilized unipolar semiconductors as the active material and focused on developing high-performance devices. However, fundamental analysis of the multiplication process, particularly in ambipolar materials, is required to establish high-performance electronic devices and emerging architectures. Although ambipolar 2D materials have the advantage of facile carrier-type tuning through electrostatic gating, simultaneously allowing both carrier types in a single channel poses an inherent difficulty in analyzing their individual contributions to avalanche multiplication. In ambipolar field-effect transistors (FETs), two phenomena of ambipolar transport and avalanche multiplication can occur, and both exhibit secondary rise of output current at high lateral voltage. We distinguished these two competing phenomena using the method of channel length modulation and successfully analyzed the properties of electron- and hole-initiated multiplication in ambipolar WSe2 FETs. Our study provides a simple and robust method to examine carrier multiplication in ambipolar materials and will foster the development of high-performance atomically thin electronic devices utilizing avalanche multiplication.

GaN HEMTs on low resistivity Si substrates with thick buffer layers for RF signal amplification and power conversion

We report GaN high-electron-mobility transistors (HEMTs) with a thick (7.7 µm) GaN buffer on a Czochralski low resistivity Si (LRS) substrate. The GaN HEMTs exhibit high performance for both radio-frequency (RF) amplification and power conversion. The thick GaN buffer was grown by means of vacancy engineering, delivering a low dislocation density of ∼1.6 × 108 cm−2, contributing to suppressed RF signal coupling to the lossy Si substrate and a high vertical voltage blocking capability. For RF performance, GaN HEMTs with a 650 nm gate exhibit an fT/fMAX value of 25.1/32.3 GHz and a maximum output power POUT of 2.2 W/mm at 4 GHz with a drain voltage VDS of 20 V, which is comparable with the performance of RF GaN HEMTs on a high-resistivity silicon substrate without the existence of the field plate. For power performance, the vertical breakdown voltage of the wafer is 1160 V, and the three-terminal lateral breakdown voltage is 885 V in a GaN HEMT with a gate-to-drain distance of 8 µm. The thick GaN layer on the LRS substrate scheme thus provides a compelling platform for monolithic integration of high-performance RF devices and high-voltage power devices.

Effect of Adjacent Lateral Inhibition on Light and Electric-Stimulated Synaptic Transistors

Lateral inhibition is one of the basic principles of information processing in nervous system, which exists in various sensory systems from touch to vision. Here, synaptic transistors with lateral gates were fabricated on plastic substrate. Negative lateral gate voltage which can depress the channel current was used to emulate lateral inhibition. Influences of lateral inhibition on light-induced and electric-induced synaptic characteristics of synaptic transistors were investigated. Experiments demonstrated that in our devices, lateral inhibition can enhance electric-induced paired pulse facilitation (PPF) gain ratio, amplify current variation ratio in light-induced channel excitability and also modulate light-induced memory duration from long term memory to short term memory.

Transport properties of a thin GaN channel formed in an Al0.9Ga0.1N/GaN heterostructure grown on AlN/sapphire template

Despite a high lateral breakdown voltage above 10 kV for large contact distances and a breakdown field of 5 MV cm−1 for short contact distances, an Al0.9Ga0.1N/GaN heterostructure with an 8 nm strained GaN channel grown on an AlN/sapphire template suffers from a low and anisotropic mobility. This work deals with a material study to elucidate this issue. Threading dislocations were observed along the growth direction in transmission electron microscopy pictures and are more in number in the (11−20) plane. Steps were also detected in this plane at the GaN channel interfaces. With the help of device simulations and static characterizations, the deep level transient spectroscopy technique allowed five traps located in the GaN channel to be identified. Most of them are associated with nitrogen- or gallium-vacancy-related defects and are expected to be localized at the interfaces of GaN with the buffer and the barrier. It is likely that these electrically active defects contribute to reduce the mobility in the two-dimensional electron gas. In addition, a link was established between the mobility and the dependence of the quality of the channel interfaces on the crystallographic orientation.

Lateral voltage as a new input for artificial lipid bilayer systems.

In this work, we propose lateral voltage as a new input for use in artificial lipid bilayer systems in addition to the commonly used transmembrane voltage. To apply a lateral voltage to bilayer lipid membranes, we fabricated electrode-equipped silicon and Teflon chips. The Si chips could be used for photodetector devices based on fullerene-doped lipid bilayers, and the Teflon chips were used in a study of the ion channel functions in the lipid bilayer. The findings indicate that the lateral voltage effectively regulates the transmembrane current, in both ion-channel-incorporated and fullerene-incorporated lipid bilayer systems, suggesting that the lateral voltage is a practicable and useful additional input for use in lipid bilayer systems.

Theoretical explanation of rotational flow in the liquid-film motor

A liquid film that is under the action of two electric forces, an external electric field parallel to the film and a lateral voltage difference applied to both edges of the film, exhibits a universal rotational flow. In this article, we revisit this phenomena by considering an idealized so-called liquid-film motor and provide a theoretical description of the underlying physical mechanism that is responsible for the rotation. Based on this theory, the external electric field induces a non-uniform distribution of freely moving charges on the film. Then the internal field that is mainly resulted from the lateral voltage difference, will exert forces on induced charges and subsequently will result the rotational flow. We show, how the fields contribute in developing a universal flow pattern.

A Global Shutter Wide Dynamic Range Soft X-Ray CMOS Image Sensor With Backside- Illuminated Pinned Photodiode, Two-Stage Lateral Overflow Integration Capacitor, and Voltage Domain Memory Bank

This article presents a prototype $22.4~\mu \text{m}$ pixel pitch global shutter (GS) wide dynamic range (WDR) soft X-ray CMOS image sensor (sxCMOS). Backside-illuminated (BSI) pinned photodiodes with a 45- $\mu \text{m}$ thick Si substrate were introduced for low noise and high radiation hardness to high energy photons. Two-stage lateral overflow integration capacitor (LOFIC) and voltage domain memory bank with high-density Si trench capacitors were introduced for WDR and for GS. The developed sxCMOS achieved maximum 21.9 Me− full well capacity with a single exposure 129 dB dynamic range by GS operation. Over 70% quantum efficiency (QE) toward soft X-ray was successfully achieved. The developed prototype sxCMOS is a step forward toward a 4 M pixel detector system to be utilized in next-generation synchrotron radiation facilities and X-ray free-electron lasers.

Laser sintering of copper conductive traces on primer pre-treated additive manufactured 3D surfaces

This paper introduces a novel process for creating conductive copper traces on 3D surfaces from different additive manufacturing technologies by employing printed electronics techniques. An essential step in this process was the dip-coating pre-treatment with a primer to reduce the surface roughness below 100 nm, seal pores if present, and increase the thermal stability. This was followed by a dip-coating with copper nanoparticle ink, drying using a heat gun and thermal curing by laser sintering. The experiments determined the optimal laser peak intensity for achieving conductors with the lowest electrical resistance possible. The laser parameters’ processing window provided conductive traces on 3D surfaces with properties comparable to photonic sintering on planar substrates. Thereby, the conductive traces reached electrical specific resistances lower than 18 µΩ cm (elemental copper: ρ = 1.8 µΩ cm) and a copper material percentage higher than 90 atom %. Shear tests validated the assembly with surfacemount device (SMD) resistors. Electrical tests resulted in maximum current densities higher than 100 A mm−2 and lateral breakdown voltages higher than 2kV mm−1. Thus, this paper presents essential prerequisites for a future application of the technology.

Coulomb drag transistor using a graphene and MoS2 heterostructure

Two-dimensional (2D) heterostructures often provide extraordinary carrier transport as exemplified by superconductivity or excitonic superfluidity. Recently, a double-layer graphene (Gr) separated by few-layered boron nitride demonstrated the Coulomb drag phenomenon: carriers in the active layer drag carriers in the passive layer. Here, we propose high-performance Gr/MoS2 heterostructure transistors operating via Coulomb drag, exhibiting a high carrier mobility (∼3700 cm2 V−1 s−1) and on/off-current ratio (∼108) at room temperature. The van der Waals gap at the Gr/MoS2 interface induces strong interactions between the interlayer carriers, whose recombination is suppressed by the Schottky barrier between p-Gr and n-MoS2, clearly distinct from the presence of insulating layers. The sign reversal of lateral voltage clearly demonstrates the Coulomb drag in carrier transport. Hole-like behavior of electrons in the n-MoS2 is observed in magnetic field, indicating strong Coulomb drag at low temperature. Our Coulomb drag transistor thus provides a shortcut for the practical application of 2D heterostructures.