High On-off Ratio Research Articles

Fabrication and Characterization of p-Type Thin-Film Transistors Using Sete Active Layer Deposited by Pulsed Laser Ablation

We fabricated p-type thin-film transistors(TFTs) using SeTe films deposited by pulsed laser ablation at room temperature. The TFTs were thermally annealed at different temperatures (150°C, 200°C, 250°C) under oxygen ambient. It was found that the thermal annealing can improve the crystallinity and induce the surface oxidation of the SeTe films. This gave rise to enhancement the performance of the TFTs. As the annealing temperature increases, the field-effect mobility and the on/off current ratio was increased and the off-state current was decreased. The 250°C-annealed TFT shows the best performance with a high filed effect mobility of 3.5cm2/Vs and a high on-off current ratio of 1X105. We also successfully demonstrated a CMOS inverter with the p-SeTe and a n-ITZO TFT. The CMOS inverter exhibits a gain of ~12 at a transition voltage of ~0.8V under a supply voltage of 5V.

Vertical Barrier Heterostructures for Reliable, Robust, and High-Performance Ultraviolet Detection.

Photodetectors based on low-dimensional materials usually suffer from serious optical power-dependent photoresponse and low reliability, particularly in the ultraviolet regime. The barrier photodetector is an effective and reliable strategy where the barrier layer can block the low-energy charge carriers while allowing for a flow of the high-energy photocarriers. Here, vertical barrier heterostructure photodetectors (VBHPs), consisting of a graphene bottom electrode, a MoS2 light absorber, and an h-BN energy barrier, for reliable, robust, and high-performance ultraviolet detection are reported. The asymmetric barrier distribution in the conduction/valence band at the MoS2 /h-BN interface results in an ultralow noise current of 1.69 × 10-15 A Hz-1/2 at room temperature, stable photo on/off states exceeding 104 cycles at 300 K and 400 K, a light power-independent high responsivity of 416.2 mA W-1 at 360 nm, a high photo on-off ratio of 1.2 × 105 at 360 nm, high measured detectivities (3.2 × 1010 Jones at 266 nm and 9.9 × 1010 Jones at 360nm), and wide linear dynamic ranges. The VBHPs show a high potential for new-type reliable ultraviolet detection.

A novel normally-off GaN vertical Schottky source tunnel-junction field-effect transistor

In this work, a novel normally-off GaN vertical tunnel-junction field-effect transistor (VTJFET) was proposed and investigated by the Silvaco ATLAS simulator. The topology structure and operation mechanism of the VTJFET are completely different from those of previous GaN vertical power devices. The VTJFET exhibited normally-off operation with a threshold voltage VTH of +2.5 V. The specific on-resistance Ron,sp and the breakdown voltage BV were 1.78 mΩ cm2 and 2940 V, respectively. A high on-off current ratio of 1011 and high power figure of merit (FOM) of 4.9 GW/cm2 were achieved. The Ron,sp and BV of the VTJFET are affected by the doping concentration Ndrift and thickness Tdrift of the drift layer, and a record high optimized FOM of 7.4 GW/cm2 was obtained by varying Ndrift and Tdrift. The VTJFET is intrinsically normally-off and exhibited excellent performance, providing a new direction for the development of GaN vertical devices.

Ovonic threshold switching device and its application to logic gate function and steep slope in field effect transistors

We report the poly(p-vinylphenol) (PVP)-based ovonic threshold switching devices. By optimizing the effective device area of the PVP-based device, low threshold voltage and low threshold voltage variation were achieved. By changing the compliance current to affect the strength of the conductive filaments, the threshold switching characteristics of the devices were tested at four different compliance currents of 1 × 10−4 A, 5 × 10−5 A, 1 × 10−5 A, 5 × 10−6, the results show that the lower the limiting current, the lower the on state current. The PVP-based device is used in the design of logic gates to realize the function of “AND” and “OR”. Furthermore, a steep slope FET was realized by connecting the PVP based device in series to the gate electrode of the graphene oxide-field effect transistor. The proposed device achieves an extremely low subthreshold swing of 23.7 mV/decade and a high on-off ratio of∼105 due to the steep switching of the threshold switching device at the gate region.

Interface and surface engineering of black phosphorus: a review for optoelectronic and photonic applications

Abstract Since being rediscovered as an emerging 2D material, black phosphorus (BP), with an extraordinary energy structure and unusually strong interlayer interactions, offers new opportunities for optoelectronics and photonics. However, due to the thin atomic body and the ease of degradation with water and oxides, BP is highly sensitive to the surrounding environment. Therefore, high-quality engineering of interfaces and surfaces plays an essential role in BP-based applications. In this review, begun with a review of properties of BP, different strategies of interface and surfaces engineering for high ON-OFF ratio, enhanced optical absorption, and fast optical response are reviewed and highlighted, and recent state-of-the-art advances on optoelectronic and photonic devices are demonstrated. Finally, the opportunities and challenges for future BP-related research are considered.

Collective cloaking of a cluster of electrostatically defined core–shell quantum dots in graphene

We study cloaking of a cluster of electrostatically defined core–shell quantum dots in graphene. Guided by the generalized multiparticle Mie theory, the Dirac electron scattering from a cluster of quantum dots is addressed. Indeed distant quantum dots may experience a sort of individual cloaking. But despite the multiple scattering of an incident electron from a set of adjacent quantum dots, collective cloaking may happen. Via a proper choice of the radii and bias voltages of shells, two most important scattering coefficients and hence the scattering efficiency of the cluster dramatically decrease. Energy-selective electron cloaks are realizable. More importantly, clusters simultaneously transparent to electrons of different energies, are achievable. Being quite sensitive to applied bias voltages, clusters of core–shell quantum dots may be used to develop switches with high on-off ratios.

Coupled Nanoring Resonators Based Reconfigurable and Multifunctional Platform for Photonic Integrated Circuits

A novel coupled nanoring resonators-based reconfigurable and multifunctional platform is designed with high-speed, low input power and ultra-compact size for scalable and high performance Photonic Integrated Circuits. This single nanostructure platform is used to realize five different optical components such as wavelength multiplexer, D-flip flop, power splitter, reconfigurable switch, and bandpass filter. The performance of these optical components is analyzed by Finite-Difference Time Domain (FDTD) method. The coupled resonator platform plays a very significant role in wavelength filtering, light signal routing, multiplexing, power dividing and logical operations. The multipurpose structure is numerically investigated and optimized to achieve a high data rate of 5.4 Tbps, high ON-OFF ratio of 36.98 dB, ultra-compact size of 186.48 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and low insertion loss of 0.0043 dB. Hence, this nanoscale structure is highly suitable for optical computing, wavelength division-based photonic communication systems and optical interconnects.

Conductive Domain-Wall Temperature Sensors of LiNbO3 Ferroelectric Single-Crystal Thin Films

Domain wall current (DWC) plays a key role in storage devices, logic devices and sensors due to its high on-off ratio and nano structure size in the era of nanoelectronics technology. In this work, the DWC of single crystal LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin film was studied by piezoresponse force microscope (PFM) and conducting atomic force microscope (c-AFM). We mainly focus on voltage and temperature dependence of DWC which increases with the voltage and temperatures. Based on this research, the packaged DWC temperature sensor is fabricated and applied in wide temperature range. The existence of domain walls makes the current on-off ratio as high as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> at the voltage of 15 V. Our study shows that DWC has a negative temperature coefficient (NTC) from 140 K to 500 K. The current increases from 3 pA to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$57 ~\mu \text{A}$ </tex-math></inline-formula> , which is attributed to the conductivity of switched domain. This work proposes a new type temperature sensor with wide temperature range and high compatibility and sensitivity. In addition, it provides support for harsh environment applications of ferroelectric domain engineering devices.

Complementary Two-Dimensional (2-D) FET Technology With MoS2/hBN/Graphene Stack

This paper demonstrates a complementary 2-D field-effect transistor (FET) technology with molybdenum disulfide (MoS2) as the active film, hexagonal boron nitride (hBN) as the gate dielectric, and graphene as the gate electrode. The active region of the n-channel (n-FET) and p-channel (p-FET) devices are formed by undoped and Nb-doped MoS2, respectively. The complementary FETs have the desirable threshold voltage polarity, similar current drive, and high on-off current ratios of more than 106. A complementary metal-oxidesemiconductor (CMOS) inverter has been fabricated and the measured gain is about 14 with 90% noise margin at a 2 V power supply.

Hybrid ZnO Flowers-Rods Nanostructure for Improved Photodetection Compared to Standalone Flowers and Rods

Different Zinc Oxide (ZnO) morphologies have been used to improve photodetector efficiencies for optoelectronic applications. Herein, we present the very novel hybrid ZnO flower-rod (HZFR) morphology, to improve photodetector response and efficiency when compared to the prevalently used ZnO nanorods (NRs) and ZnO nanoflowers (NFs). The HZFR was fabricated via sol-gel microwave-assisted hydrothermal methods. HZFR achieves the benefits of both NFs, by trapping a greater amount of UV light for the generation of e-h pairs, and NRs, by effectively transporting the generated e-h pairs to the channel. The fabricated photosensors were characterized with scanning electron microscopy, X-ray diffraction, photoluminescence, and a Keithley 4200A-SCS parameter analyzer for their morphology, structural characteristics, optical performance, and electrical characteristics, respectively. The transient current response, current-voltage characteristics, and responsivity measurements were set as a benchmark of success to compare the sensor response of the three different morphologies. It was found that the novel HZFR showed the best UV sensor performance with the fastest response time (~7 s), the highest on-off ratio (52), and the best responsivity (126 A/W) when compared to the NRs and NFs. Hence, it was inferred that the HZFR morphology would be a great addition to the ZnO family for photodetector applications.

Mechanically Induced Switching between Two Discrete Conductance States: A Potential Single-Molecule Variable Resistor.

The fabrication of solid-state single-molecule switches with high on-off conductance ratios has been proposed to advance conventional technology in areas such as molecular electronics. Herein, we employed the scanning tunneling microscope break junction (STM-BJ) technique to modulate conductance in single-molecule junctions using mechanically induced stretching. Compound 1a possesses two dihydrobenzothiophene (DHBT) anchoring groups at the opposite ends linked with rigid alkyne side arms to form a gold-molecule-gold junction, while 1b contains 4-pyridine-anchoring groups. The incorporation of ferrocene into the backbone of each compound allows rotational freedom to the cyclopentadienyl (Cp) rings to give two distinct conductance states (high and low) for each. Various control experiments and suspended junction compression/retraction measurements indicate that these high- and low-conductance plateaus are the results of conformational changes within the junctions (extended and folded states) brought about by mechanically induced stretching. A high-low switching factor of 42 was achieved for 1a, whereas an exceptional conductance ratio in excess of 2 orders of magnitude (205) was observed for 1b. To the best of our knowledge, this is the highest experimental on-off conductance switching ratio for a single-molecule junction exploiting the mechanically induced STM-BJ method. Computational studies indicated that the two disparate conductance states observed for 1a and 1b result from mechanically induced conformational changes due to an interplay between conductance and the dihedral angles associated with the electrode-molecule interfaces. Our study reveals the structure-function relationship that determines conductance in such flexible and dynamic systems and promotes the development of a single-molecule variable resistor with high on-off switching factors.

Toward High-Performance Self-Driven Photodetectors via Multistacking Van der Waals Heterostructures.

The unique optoelectronic properties of layered van der Waals (vdW) heterostructures open up exciting opportunities for high-performance photodetectors. Self-driven photodetectors are desirable for reducing power consumption and minimizing the device size. Here, a semiconductor-insulator-semiconductor-type multistacking WSe2/graphene/h-BN/MoS2 vdW heterostructure is demonstrated to realize an enhanced self-powered photodetector with a high on-off current ratio of about 1.2 × 105 and a high photoresponsivity of 3.6 A/W without applying bias, which is the highest photoresponsivity ever reported for self-powered photodetectors. Because of the difference in the Fermi level, a built-in electrical field is formed at the WSe2/graphene junction, where the photoexcited electrons and holes can be efficiently separated and the carriers can easily tunnel through the MoS2/h-BN junction driven by the enhanced potential. Therefore, the enhanced self-powered photodetection is attributable to highly efficient carrier tunneling through large h-BN electron barriers. By comparison, when the stacking sequence is changed to make WSe2/MoS2 p-n heterojunctions lay on graphene/h-BN, the self-powered photocurrent is still generated because of the type-II band alignment, which exhibits lower but still relevant values with a light on/off ratio of ∼8 × 103 and a photoresponsivity of ∼2.39 A/W. The efficient enhancement demonstrates that multistacking heterostructures significantly elevate the performance of self-powered photodetectors, providing a feasible route to develop high-performance self-powered optoelectronic devices and extend their applications in integrated optoelectronic systems.

Fiber based organic electrochemical transistor integrated with molecularly imprinted membrane for uric acid detection

In this study, poly(3, 4-ethylenedioxythiophene) (PEDOT) nanocluster structure was synthesized on the reduced graphene oxide (rGO) modified cotton fibers. The organic electrochemical transistors based on the modified fiber have been assembled and their performance of different gate electrode transistors has been investigated. The transistor exhibits an excellent transconductance of up to 15.5 mS and a high on-off ratio close to 2*102. The bending angle and bending times have little effect on the device performance. The uric acid (UA) sensor based transistor has been fabricated for the first time. Flexible sensors based on molecularly imprinted polymer (MIP) membrane with different fiber gate electrodes have been investigated. The UA sensor with MIP/PEDOT/carbon fiber as the gate electrode has a sensitivity of 100 μA per decade from 1 nM to 500 μM, a linear coefficient of 0.97143, excellent selectivity, and good reproducibility. In addition, fiber based organic electrochemical transistors (FECTs) can be sewn into the fabric for monitoring and have successfully evaluated the detection of UA in artificial urine sample, with data consistent well with the UA concentration obtained from single fiber. Therefore, the sensor based FECTs can be used for low cost, accurate, non-enzymatic detection of UA in clinical diagnostics and bioanalytical applications.

Gradual Edge Contact between Mo and MoS2 Formed by Graphene-Masked Sulfurization for High-Performance Field-Effect Transistors.

Two-dimensional materials have attracted great attention for their outstanding electronic properties. In particular, molybdenum disulfide (MoS2) shows great potential as a next-generation semiconductor due to its tunable direct bandgap with a high on-off ratio and extraordinary stability. However, the performance of MoS2 synthesized by physical vapor deposition has been limited by contact resistance between an electrode and MoS2, which determines overall device characteristics. Here, in order to reduce the contact resistance, we use in situ sulfurization of Mo by H2S gas treatment masked by a patterned graphene gas barrier, so that the Mo channel area can be selectively formed, resulting in a gradual edge contact between Mo and MoS2. Compared with field-effect transistors with a top contact between the Au/Ti electrode and the MoS2 channel, a gradual edge contact between the Mo electrode and the MoS2 channel provides a considerably enhanced electrical performance.

Surface Passivation Treatment to Improve Performance and Stability of Solution-Processed Metal Oxide Transistors for Hybrid Complementary Circuits on Polymer Substrates.

Hybrid integration of n‐type oxide with p‐type polymer transistors is an attractive approach for realizing high performance complementary circuits on flexible substrates. However, the stability of solution‐processed oxide transistors is limiting the lifetime and reliability of such circuits. Oxygen vacancies are the main defect degrading metal oxide transistor performance when ambient oxygen adsorbs onto metal oxide films. Here, an effective surface passivation treatment based on negative oxygen ion exposure combined with UV light is demonstrated, that is able to significantly reduce surface oxygen vacancy concentration and improve the field effect mobility to values up to 41 cm2 V−1 s−1 with high on–off current ratio of 108. The treatment also reduces the threshold voltage shift after 2 days in air from 5 to 0.07 V. The improved stability of the oxide transistors also improves the lifetime of hybrid complementary circuits and stable operation of complementary, analog amplifiers is confirmed for 60 days in air. The suggested approach is facile and can be widely applicable for flexible electronics using low‐temperature solution‐processed metal oxide semiconductors.

Analysis of Interface Phenomena for High-Performance Dual-Stacked Oxide Thin-Film Transistors via Equivalent Circuit Modeling.

Oxide thin-film transistors (TFTs) have attracted much attention because they can be applied to flexible and large-scaled switching devices. Especially, oxide semiconductors (OSs) have been developed as active layers of TFTs. Among them, indium-gallium-zinc oxide (IGZO) is actively used in the organic light-emitting diode display field. However, despite their superior off-state properties, IGZO TFTs are limited by low field-effect mobility, which critically affects display resolution and power consumption. Herein, we determine new working mechanisms in dual-stacked OS, and based on this, we develop a dual-stacked OS-based TFT with improved performance: high field-effect mobility (∼80 cm2/V·s), ideal threshold voltage near 0 V, high on-off current ratio (>109), and good stability at bias stress. Induced areas are formed at the interface by the band offset: band offset-induced area (BOIA) and BOIA-induced area (BIA). They connect the gate bias-induced area (GBIA) and electrode bias-induced area (EBIA), resulting in high current flow. Equivalent circuit modeling and the transmission line method are also introduced for more precise verification. By verifying current change with gate voltage in the single OS layer, the current flowing direction in the dual-stacked OS is calculated and estimated. This is powerful evidence to understand the conduction mechanism in a dual-stacked OS-based TFT, and it will provide new design rules for high-performance OS-based TFTs.

Dual source negative capacitance GaSb/InGaAsSb/InAs heterostructure based vertical TFET with steep subthreshold swing and high on-off current ratio

Continuous downscaling of CMOS technology at the nanometer scale with conventional MOSFETs leads to short channel effects (SCE), increased subthreshold slope (SS), and leakage current, degrading the performance of ICs. We proposed a dual-source vertical tunnel field-effect transistor (TFET) with a steeper subthreshold swing (SS) and superior electrostatic control thanks to quantum mechanical band-to-band tunneling. We show that the use of GaSb/InGaAsSb/InAs heterostructure boosts the band-to-band tunneling rate in TFETs, resulting in higher on-state current. Incorporating the negative capacitance effect using ferroelectric materials further enhances the performance of the proposed device greatly. The lowest SS of 21.94 mV/dec and an on–off current ratio of 4.3267 × 1011 were obtained for dual source GaSb/InGaAsSb/InAs heterostructure based vertical TFET. The lowest subthreshold swing was found as 17.37 mV/dec after integrating Hf1–xZrxO2 ferroelectric material into the gate stack. The negative capacitance effect also increases the on-state current tenfold, resulting in an incredible ION/IOFF ratio of 1012. The suggested device focuses on low power consumption applications by assuring a very low leakage current and a reduced subthreshold swing.

Ultrawide-bandgap (6.14 eV) (AlGa)2O3/Ga2O3 heterostructure designed by lattice matching strategy for highly sensitive vacuum ultraviolet photodetection

One judiciously designed strategy of utilizing an ultrathin but conductive Ga2O3:Si nanolayer to prepare (AlGa)2O3 crystalline film is demonstrated. Benefiting from the existence of Ga2O3:Si nanolayer, a high-quality (Al0.68Ga0.32)2O3 sesquioxide film with 68 at.% aluminum was epitaxially grown on sapphire substrates, which was characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Its bandgap was broadened to 6.14 eV, and a vacuum ultraviolet (VUV) (AlGa)2O3/Ga2O3:Si photodetector was subsequently fabricated. The detector exhibits a pretty high on-off ratio of about 103, an open-circuit voltage of 1.0 V and a responsivity of 8.1 mA W−1 at 0 V bias voltage. The performances imply that the proposed strategy is valuable for improving the quality and also adjusting the bandgap of (AlGa)2O3 sesquioxides, which is expected to facilitate their application in VUV photodetection.

Write-once-read-many-times resistive switching behavior of amorphous barium titanate based device with very high on-off ratio and stability

Write once read many times (WORM) memory devices based on the resistive switching mechanism of a sputtered amorphous BaTiO3 (am-BTO) thin film in a metal–insulator–metal structure is fabricated on a FTO coated glass substrate with a silver top contact. Fabricated devices show the switching from a low-conductance state to a high-conductance state with the formation of conductive filament(s) in the am-BTO layer. The memory characteristics are investigated as a function of thickness of am-BTO layer, which is determined by varying the deposition time. Devices with all deposited thicknesses show data retention for more than 4000 s and 300 reading cycle. Devices with 180 nm thickness show a high on-off ratio on the order of 106. The fabricated WORM devices exhibit good reading-endurance and data-retention characteristics.

Energy-efficient three-terminal SiO memristor crossbar array enabled by vertical Si/graphene heterojunction barristor

A three-terminal memristor is an electronic memory architecture that is particularly suitable for next-generation devices owing to its customizable intrinsic switching characteristics. However, its slow switching speed and lack of high-density array structure has hindered its applicability thus far. In this study, we have designed and fabricated a novel architecture by vertically integrating a silicon oxide (SiOx) memristor and a graphene barristor, which can be readily extended to a 16 × 16 crossbar array. Notably, the unipolar resistive switching of the SiOx memristor can be actively modulated by controlling a silicon (Si) phase filament via the barristor’s electrostatic gating. Such gate-tunable SiOx memristor in the array was observed to exhibit excellent electrical performance, e.g., increased switching speed (up to ~35 ns), increased switching probability, enhanced uniformity, and decreased operating voltage. The energy consumption is also significantly improved 4 nJ to 2 pJ via the gating, which exhibits lower than other three-terminal memristors. Moreover, it was able to sustain a high ON–OFF ratio (>106), multi-bit capability (~9 states), and stable endurance and retention properties regardless of gating. As an additional potential application, nonvolatile universal logic gates, including NOT, NOR, and NAND gates, were successfully implemented in this study based on simple circuits containing gate-tunable SiOx memristors. We believe that the proposed gate-tunable SiOx memristor represents a distinctive and novel development toward a fast, low energy, and extendable three-terminal memristor platform for electronic devices, thus undertaking a major step in unleashing the potential of memristors to support the growing demands of cutting-edge technologies.