Improvement Performance of p-GaN Gate High-Electron-Mobility Transistors with GaN/AlN/AlGaN Barrier Structure

This study demonstrates a particular composited barrier structure of high-electron-mobility transistors (HEMTs) with an enhancement mode composed of p-GaN/GaN/AlN/AlGaN/GaN. The purpose of the composite barrier structure device is to increase the maximum drain current, reduce gate leakage, and achieve lower on-resistance (Ron) performance. A comparison was made between the conventional device without the composited barrier and the device with the composited barrier structure. The maximum drain current is significantly increased by 37%, and Ron is significantly reduced by 23%, highlighting the synergistic impact of the composite barrier structure on device performance improvement. This reason can be attributed to the undoped GaN (u-GaN) barrier layer beneath p-GaN, which was introduced to mitigate Mg diffusion in the capping layer, thus addressing its negative effects. Furthermore, the AlN barrier layer exhibits enhanced electrical properties, which can be attributed to the critical role of high-energy-gap properties that increase the 2DEG carrier density and block leakage pathways. These traps impact the device behavior mechanism, and the simulation for a more in-depth analysis of how the composited barrier structure brings improvement is introduced using Synopsys Sentaurus TCAD.

Reversible Charge Transfer Doping in Atomically Thin In2O3 by Viologens

Atomically thin oxide semiconductors are emerging as potential materials for their potentiality in monolithic 3D integration and sensor applications. In this study, a charge transfer method employing viologen, an organic compound with exceptional reduction potential among n-type organics, is presented to modulate the carrier concentration in atomically thin In2O3 without the need of annealing. This study highlights the critical role of channel thickness on doping efficiency, revealing that viologen charge transfer doping is increasingly pronounced in thinner channels owing to their increased surface-to-volume ratio. Upon viologen doping, an electron sheet density of 6.8 × 1012 cm-2 is achieved in 2 nm In2O3 back gate device while preserving carrier mobility. Moreover, by the modification of the functional groups, viologens can be conveniently removed with acetone and an ultrasonic cleaner, making the viologen treatment a reversible process. Based on this doping scheme, we demonstrate an n-type metal oxide semiconductor inverter with viologen-doped In2O3, exhibiting a voltage gain of 26 at VD = 5 V. This complementary pairing of viologen and In2O3 offers ease of control over the carrier concentration, making it suitable for the next-generation electronic applications.

Review on Main Gate Characteristics of P-Type GaN Gate High-Electron-Mobility Transistors

As wide bandgap semiconductors, gallium nitride (GaN) lateral high-electron-mobility transistors (HEMTs) possess high breakdown voltage, low resistance and high frequency performance. PGaN gate HEMTs are promising candidates for high-voltage, high-power applications due to the normally off operation and robust gate reliability. However, the threshold and gate-breakdown voltages are relatively low compared with Si-based and SiC-based power MOSFETs. The epitaxial layers and device structures were optimized to enhance the main characteristics of pGaN HEMTs. In this work, various methods to improve threshold and gate-breakdown voltages are presented, such as the top-layer optimization of the pGaN cap, hole-concentration enhancement, the low-work-function gate electrode, and the MIS-type pGaN gate. The discussion of the main gate characteristic enhancement of p-type GaN gate HEMTs would accelerate the development of GaN power electronics to some extent.

Design and Analysis of a Low-Voltage VCO: Reliability and Variability Performance

This paper investigates an adaptive body biasing (ABB) circuit to improve the reliability and variability of a low-voltage inductor-capacitor (LC) voltage-controlled oscillator (VCO). The ABB circuit provides VCO resilience to process variability and reliability variation through the threshold voltage adjustment of VCO's transistors. Analytical equations considering the body bias effect are derived for the most important relations of the VCO and then the performance is verified using the post-layout simulation results. Under a 0.16% threshold voltage shift, the sensitivity of the normalized phase noise and transconductance of the VCO with the ABB circuit compared to the constant body bias (CBB) decreases by around 8.4 times and 3.1 times, respectively. Also, the sensitivity of the normalized phase noise and transconductance of the proposed VCO under 0.16% mobility variations decreases by around 1.5 times and 1.7 times compared to the CBB, respectively. The robustness of the VCO is also examined using process variation analysis through Monte Carlo and corner case simulations. The post-layout results in the 180 nm CMOS process indicate that the proposed VCO draws a power consumption of only 398 µW from a 0.6 V supply when the VCO frequency is 2.4 GHz. It achieves a phase noise of -123.19 dBc/Hz at a 1 MHz offset and provides a figure of merit (FoM) of -194.82 dBc/Hz.

Improving Performance of Al2O3/AlN/GaN MIS HEMTs via In Situ N2 Plasma Annealing

A novel monocrystalline AlN interfacial layer formation method is proposed to improve the device performance of the fully recessed-gate Al₂O₃/AlN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs), which is achieved by plasma-enhanced atomic layer deposition (PEALD) and in situ N₂ plasma annealing (NPA). Compared with the traditional RTA method, the NPA process not only avoids the device damage caused by high temperatures but also obtains a high-quality AlN monocrystalline film that avoids natural oxidation by in situ growth. As a contrast with the conventional PELAD amorphous AlN, C-V results indicated a significantly lower interface density of states (D_it) in a MIS C-V characterization, which could be attributed to the polarization effect induced by the AlN crystal from the X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) characterizations. The proposed method could reduce the subthreshold swing, and the Al₂O₃/AlN/GaN MIS-HEMTs were significantly enhanced with ~38% lower on-resistance at V_g = 10 V. What is more, in situ NPA provides a more stable threshold voltage (V_th) after a long gate stress time, and ΔV_th is inhibited by about 40 mV under V_g,stress = 10 V for 1000 s, showing great potential for improving Al₂O₃/AlN/GaN MIS-HEMT gate reliability.

Threshold-Voltage Extraction Methods for Atomically Deposited Disordered ZnO Thin-Film Transistors

In this paper, we present a threshold-voltage extraction method for zinc oxide (ZnO) thin-film transistors (TFTs). Bottom-gate atomic-layer-deposited ZnO TFTs exhibit typical n-type enhancement-mode transfer characteristics but a gate-voltage-dependent, unreliable threshold voltage. We posit that this obscure threshold voltage is attributed to the localized trap states of ZnO TFTs, of which the field-effect mobility can be expressed as a gate-bias-dependent power law. Hence, we derived the current-voltage relationship by dividing the drain current with the transconductance to rule out the gate-bias-dependent factors and successfully extract the reliable threshold voltage. Furthermore, we investigated the temperature-dependent characteristics of the ZnO TFTs to validate that the observed threshold voltage was genuine. Notably, the required activation energies from the low-temperature measurements displayed an abrupt decrease at the threshold voltage, which was attributed to the conduction route change from diffusion to drift. Thus, we conclude that the reliable threshold voltage of accumulation-mode ZnO TFTs can be determined using a gate-bias-dependent factor-removed current-voltage relationship with a low-temperature analysis.

A Novel Dielectric Modulated Gate-Stack Double-Gate Metal-Oxide-Semiconductor Field-Effect Transistor-Based Sensor for Detecting Biomolecules

In this article, the performance of n-type junctionless (JL) double-gate (DG) MOSFET-based biosensors with and without gate stack (GS) has been studied. Here, the dielectric modulation (DM) method is applied to detect biomolecules in the cavity. The sensitivity of n-type JL-DM-DG-MOSFET and n-type JL-DM-GSDG-MOSFET-based biosensors have also been evaluated. The sensitivity (ΔV_th) improved in JL-DM-GSDG MOSFET/JL-DM-DG-MOSFET-based biosensors for neutral/charged biomolecules is 116.66%/66.66% and 1165.78%/978.94%, respectively, compared with the previously reported results. The electrical detection of biomolecules is validated using the ATLAS device simulator. The noise and analog/RF parameters are compared between both biosensors. A lower threshold voltage is observed in the GSDG-MOSFET-based biosensor. The I_on/I_off ratio is higher for DG-MOSFET-based biosensors. The proposed GSDG-MOSFET-based biosensor demonstrates higher sensitivity than the DG-MOSFET-based biosensor. The GSDG-MOSFET-based biosensor is suitable for low-power, high-speed, and high sensitivity applications.

Improving Stability of Roll-to-Roll (R2R) Gravure-Printed Carbon Nanotube-Based Thin Film Transistors via R2R Plasma-Enhanced Chemical Vapor-Deposited Silicon Nitride

Single-walled carbon nanotubes (SWCNTs) have an advantage in printing thin film transistors (TFTs) due to their high carrier mobility, excellent chemical stability, mechanical flexibility, and compatibility with solution-based processing. Thus, the printed SWCNT-based TFTs (pSWCNT-TFTs) showed significant technological potential such as integrated circuits, conformable sensors, and display backplanes. However, the long-term environmental stability of the pSWCNT-TFTs hinders their commercialization. Thus, to extend the stability of the pSWCNT-TFTs, such devices should be passivated with low water and oxygen permeability. Herein, we introduced the silicon nitride (SiNx) passivation method on the pSWCNT-TFTs via a combination of roll-to-roll (R2R) gravure and the roll-to-roll plasma-enhanced vapor deposition (R2R-PECVD) process at low temperature (45 °C). We found that SiNx-passivated pSWCNT-TFTs showed ± 0.50 V of threshold voltage change at room temperature for 3 days and ±1.2 V of threshold voltage change for 3 h through a Temperature Humidity Test (85/85 test: Humidity 85%/Temperature 85 °C) for both p-type and n-type pSWCNT-TFTs. In addition, we found that the SiNx-passivated p-type and n-type pSWCNT-TFT-based CMOS-like ring oscillator, or 1-bit code generator, operated well after the 85/85 test for 24 h.

Electrical Performance of 28 nm-Node Varying Channel-Width nMOSFETs under DPN Process Treatments

The decoupled-plasma nitridation treatment process is an effective recipe for repairing the trap issues when depositing high-k gate dielectric. Because of this effect, electrical performance is not only increased with the relative dielectric constant, but there is also a reduction in gate leakage. In the past, the effect of nitridation treatment on channel-length was revealed, but a channel-width effect with that treatment was not found. Sensing the different nano-node channel-width n-channel MOSFETs, the electrical characteristics of these test devices with nitridation treatments were studied and the relationship among them was analyzed. Based on measurement of the V_T, SS, G_m, I_ON, and I_OFF values of the tested devices, the electrical performance of them related to process treatment is improved, including the roll-off effect of channel-width devices. On the whole, the lower thermal budget in nitridation treatment shows better electrical performance for the tested channel-width devices.

Investigation of the Combined Effect of Total Ionizing Dose and Time-Dependent Dielectric Breakdown on PDSOI Devices

The combined effect of total ionization dose (TID) and time-dependent dielectric breakdown (TDDB) of partially depleted silicon-on-insulator (PDSOI) NMOSFET is investigated. First, the effect of TDDB on the parameter degradation of the devices was investigated by accelerated stress tests. It is found that TDDB stress leads to a decrease in off-state current, a positive drift in threshold voltage, and a reduction of maximum transconductance. Next, the degradation patterns of TID effect on the devices are obtained. The results show that the parameter degradation due to gamma radiation is opposite to the TDDB stress. Finally, the combined effect of TID and TDDB is investigated. It is found that the drift of the devices' sensitive parameters due to TDDB stress decreases in a total dose of gamma radiation environment. The TDDB lifetime is shortened, but the pattern of gate current change remains unchanged. The failure mechanism of the gate oxide layer under TDDB stress is not changed after irradiation.

Tuning Organic Electrochemical Transistor Threshold Voltage using Chemically Doped Polymer Gates

Organic electrochemical transistors (OECTs) have shown promise as transducers and amplifiers of minute electronic potentials due to their large transconductances. Tuning the OECT threshold voltage is important to achieve low-powered devices with amplification properties within the desired operational voltage range. However, traditional design approaches have struggled to decouple channel and materials properties from threshold voltage, thereby compromising on several other OECT performance metrics, such as electrochemical stability, transconductance, and dynamic range. In this work, simple solution-processing methods are utilized to chemically dope polymer gate electrodes, thereby controlling their work function, which in turn tunes the operation voltage range of the OECTs without perturbing their channel properties. Chemical doping of initially air-sensitive polymer electrodes further improves their electrochemical stability in ambient conditions. Thus, OECTs that are simultaneously low-powered and electrochemically resistant to oxidative side reactions under ambient conditions are demonstrated. This approach shows that threshold voltage, which is once interwoven with other OECT properties, can in fact be an independent design parameter, expanding the design space of OECTs.

Prediction of Static Characteristic Parameters of an Insulated Gate Bipolar Transistor Using Artificial Neural Network

Breakdown voltage (BV), on-state voltage (V_on), static latch-up voltage (V_lu), static latch-up current density (J_lu), and threshold voltage (V_th), etc., are critical static characteristic parameters of an IGBT for researchers. V_on and V_th can characterize the conduction capability of the device, while BV, V_lu, and J_lu can help designers analyze the safe operating area (SOA) of the device and its reliability. In this paper, we propose a multi-layer artificial neural network (ANN) framework to predict these characteristic parameters. The proposed scheme can accurately fit the relationship between structural parameters and static characteristic parameters. Given the structural parameters of the device, characteristic parameters can be generated accurately and efficiently. Compared with technology computer-aided design (TCAD) simulation, the average errors of our scheme for each characteristic parameter are within 8%, especially for BV and V_th, while the errors are controlled within 1%, and the evaluation speed is improved more than 10⁷ times. In addition, since the prediction process is mathematically a matrix operation process, there is no convergence problem, which there is in a TCAD simulation.

Fluoride-Induced Negative Differential Resistance in Nanopores: Experimental and Theoretical Characterization

We describe experimentally and theoretically the fluoride-induced negative differential resistance (NDR) phenomena observed in conical nanopores operating in aqueous electrolyte solutions. The threshold voltage switching occurs around 1 V and leads to sharp current drops in the nA range with a peak-to-valley ratio close to 10. The experimental characterization of the NDR effect with single pore and multipore samples concern different pore radii, charge concentrations, scan rates, salt concentrations, solvents, and cations. The experimental fact that the effective radius of the pore tip zone is of the same order of magnitude as the Debye length for the low salt concentrations used here is suggestive of a mixed pore surface and bulk conduction regime. Thus, we propose a two-region conductance model where the mobile cations in the vicinity of the negative pore charges are responsible for the surface conductance, while the bulk solution conductance is assumed for the pore center region.

Experimental study of threshold voltage shift for Si:HfO2based ferroelectric field effect transistor

For a given three different Si doping concentrations at room and high temperatures, the threshold voltage shift (ΔV_th) on silicon-doped hafnium-oxide-based ferroelectric field effect transistor (FeFET) is experimentally investigated. It turned out that charge trapping in the gate stack of FeFET (versus polarization switching in the gate stack of FeFET) adversely affects ΔV_th. Charge trapping causes the positive ΔV_th, while polarization switching causes the negative ΔV_th. The dominance of polarization switching is predominantly determined by the total remnant polarization (2P_r), which can be controlled by adjusting Si doping concentration in the hafnium-oxide layer. As the Si doping concentration increases from 2.5% to 3.6%, and 5.0%, 2P_rdecreases 19.8μC cm^-2to 15.25μC cm^-2, and 12.5μC cm^-2, which leads to ΔV_thof -0.8 V, -0.09 V, and +0.1 V, respectively, at room temperature. At high temperature, the effect of polarization switching is degraded due to the decreasedP_r, while the effect of charge trapping is very independent of temperature. For those three different Si doping concentrations (i.e. 2.5%, 3.6%, and 5.0%), at the high temperature, ΔV_thof FeFET is -0.675 V, -0.075 V, and +0.15 V, respectively. This experimental work should provide an insight for designing FeFET for memory and logic applications.

Challenges and Perspectives for Vertical GaN-on-Si Trench MOS Reliability: From Leakage Current Analysis to Gate Stack Optimization

The vertical Gallium Nitride-on-Silicon (GaN-on-Si) trench metal-oxide-semiconductor field effect transistor (MOSFET) is a promising architecture for the development of efficient GaN-based power transistors on foreign substrates for power conversion applications. This work presents an overview of recent case studies, to discuss the most relevant challenges related to the development of reliable vertical GaN-on-Si trench MOSFETs. The focus lies on strategies to identify and tackle the most relevant reliability issues. First, we describe leakage and doping considerations, which must be considered to design vertical GaN-on-Si stacks with high breakdown voltage. Next, we describe gate design techniques to improve breakdown performance, through variation of dielectric composition coupled with optimization of the trench structure. Finally, we describe how to identify and compare trapping effects with the help of pulsed techniques, combined with light-assisted de-trapping analyses, in order to assess the dynamic performance of the devices.

Near-Infrared Organic Phototransistors with Polymeric Channel/Dielectric/Sensing Triple Layers

A new type of near-infrared (NIR)-sensing organic phototransistor (OPTR) was designed and fabricated by employing a channel/dielectric/sensing (CDS) triple layer structure. The CDS structures were prepared by inserting poly(methyl methacrylate) (PMMA) dielectric layers (DLs) between poly(3-hexylthiophene) (P3HT) channel layers and poly[{2,5-bis-(2-octyldodecyl)-3,6-bis-(thien-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-diyl}-co-{2,2′-(2,1,3-benzothiadiazole)-5,5′-diyl}] (PODTPPD-BT) top sensing layers. Two different thicknesses of PMMA DLs (20 nm and 50 nm) were applied to understand the effect of DL thickness on the sensing performance of devices. Results showed that the NIR-OPTRs with the CDS structures were operated in a typical n-channel mode with a hole mobility of ca. 0.7~3.2 × 10⁻⁴ cm²/Vs in the dark and delivered gradually increased photocurrents upon illumination with an NIR light (905 nm). As the NIR light intensity increased, the threshold voltage was noticeably shifted, and the resulting transfer curves showed a saturation tendency in terms of curve shape. The operation of the NIR-OPTRs with the CDS structures was explained by the sensing mechanism that the excitons generated in the PODTPPD-BT top sensing layers could induce charges (holes) in the P3HT channel layers via the PMMA DLs. The optically modulated and reflected NIR light could be successfully detected by the present NIR-OPTRs with the CDS structures.

Analytic Device Model of Organic Field-Effect Transistors with Doped Channels

Doping has been shown to not only provide additional degrees of freedom in the design of organic field-effect transistors (OFETs) but to increase their performance and stability as well. An analytical model based on the assumption of a square doping profile inside the channel is presented here that describes the effect of doping on the transfer characteristic of OFETs. The model is validated experimentally by a series of OFETs with varying doping conditions. The precise doping profile in the transistor channel is determined by fitting the capacitance/voltage response of doped metal-insulator-semiconductor (MIS) junctions using an AC small-signal drift-diffusion simulation. It is shown that the real doping profile deviates from the simplifying assumptions of the analytical model, i.e., it is found that the effective doping concentration at the dielectric/semiconductor interface is reduced. However, it is shown that the analytical model is not sensitive to this deviation as only the total density charges per unit area determine the changes in the transistor behavior. Overall, the presented theory provides new design rules that can be used to guide the development of doped OFETs with high performance.

Enhanced Functionality of Dual-Gate Organic Transistors Based on Semiconducting/Insulating Polyblend-Induced Asymmetric Charge Modulation Layers

Dual-gate organic thin-film transistors (DG-OTFTs) with enhanced functionality, including large current enhancement behavior, highly efficient threshold voltage controllability, and self-contained dual-mode logic gate features, are reported. These DG-OTFTs are based on a semiconducting/insulating polyblend-based active layer with asymmetric top and bottom charge modulation layers (atb-CMLs). The atb-CMLs are automatically generated through the preparation of multilayer stacks of phase-separated semiconducting poly(3-hexylthiophene) (P3HT):insulating poly(methylmethacrylate) (PMMA) polyblend layer, poly(vinylidene fluoride) (PVDF) layer, and cross-linked-poly(4-vinylphenol) (cPVP) layer. They consist of a thin PMMA bottom layer and an uneven-shaped PMMA:PVDF miscible mixture-based top layer. The presence of the polarizable insulating PMMA, PVDF, and PMMA:PVDF mixture regions causes the bottom and top CMLs to experience electrical polarization, which induces the dipole field to achieve efficient charge modulation functions in DG-OTFTs. Owing to the presence of atb-CMLs, the DG-OTFTs exhibit unprecedented electrical characteristics, such as the easy depletion of the bottom channel by the top gate potential. However, the top channel can work properly only when given a bottom gate potential (either positive or negative). Given these unusual electrical features, the design of the fundamental dual-mode logic gates (e.g., AND and OR gates) can be achieved with just one DG transistor. This finding opens an interesting direction for the preparation of DG-OTFTs with diverse operating modes and increasing functionality, thereby widening the application potential of such transistors.

A 0.026 mm2 Time Domain CMOS Temperature Sensor with Simple Current Source

This paper presents a time domain CMOS temperature sensor with a simple current source. This sensor chip only occupies a small active die area of 0.026 mm² because it adopts a simple current source consisting of an n-type poly resistor and a PMOS transistor and a simple current controlled oscillator consisting of three current starved inverter delay cells. Although this current source is based on a simple architecture, it has better temperature linearity than the conventional approach that generates a temperature-dependent current through a poly resistor using a feedback loop. This temperature sensor is designed in a 0.18 μm 1P6M CMOS process. In the post-layout simulations, the temperature error was measured within a range from −1.0 to +0.7 °C over the temperature range of 0 to 100 °C after two point calibration was carried out at 20 and 80 °C, respectively. The temperature resolution was set as 0.32 °C and the temperature to digital conversion rate was 50 kHz. The energy efficiency is 1.4 nJ/sample and the supply voltage sensitivity is 0.077 °C/mV at 27 °C while the supply voltage varies from 1.65 to 1.95 V.

Capping Layers to Improve the Electrical Stress Stability of MoS2 Transistors

Two-dimensional (2D) materials offer exciting possibilities for numerous applications, including next-generation sensors and field-effect transistors (FETs). With their atomically thin form factor, it is evident that molecular activity at the interfaces of 2D materials can shape their electronic properties. Although much attention has focused on engineering the contact and dielectric interfaces in 2D material-based transistors to boost their drive current, less is understood about how to tune these interfaces to improve the long-term stability of devices. In this work, we evaluated molybdenum disulfide (MoS₂) transistors under continuous electrical stress for periods lasting up to several days. During stress in ambient air, we observed temporary threshold voltage shifts that increased at higher gate voltages or longer stress durations, correlating to changes in interface trap states (ΔN_it) of up to 10¹² cm^-2. By modifying the device to include either SU-8 or Al₂O₃ as an additional dielectric capping layer on top of the MoS₂ channel, we were able to effectively reduce or even eliminate this unstable behavior. However, we found this encapsulating material must be selected carefully, as certain choices actually amplified instability or compromised device yield, as was the case for Al₂O₃, which reduced yield by 20% versus all other capping layers. Further refining these strategies to preserve stability in 2D devices will be crucial for their continued integration into future technologies.

Homeostatic Recovery of Embryonic Spinal Activity Initiated by Compensatory Changes in Resting Membrane Potential

When baseline activity in a neuronal network is modified by external challenges, a set of mechanisms is prompted to homeostatically restore activity levels. These homeostatic mechanisms are thought to be profoundly important in the maturation of the network. It has been shown that blockade of either excitatory GABAergic or glutamatergic transmission in the living chick embryo transiently blocks the movements generated by spontaneous network activity (SNA) in the spinal cord. However, the embryonic movements then begin to recover by 2 h and are completely restored by 12 h of persistent receptor blockade. It remains unclear what mechanisms mediate this early recovery (first hours) after neurotransmitter blockade, or even if the same mechanisms are triggered following GABAergic and glutamatergic antagonists. Here we find two distinct mechanisms that could underlie this homeostatic recovery. First, we see a highly robust compensatory mechanism observed shortly after neurotransmitter receptor blockade. In the first 2 h of GABAergic or glutamatergic blockade in vitro, there was a clear depolarization of resting membrane potential (RMP) in both motoneurons and interneurons. These changes reduced threshold current and were observed in the continued presence of the antagonist. Therefore, it appears that fast changes in RMP represent a key fast homeostatic mechanism for the maintenance of network activity. Second, we see a less consistent compensatory change in the absolute threshold voltage in the first several hours of in vitro and in vivo neurotransmitter blockade. These mechanisms likely contribute to the homeostatic recovery of embryonic movements following neurotransmitter blockade.

Atomic Layer Deposition of GexSe1-x Thin Films for Endurable Ovonic Threshold Selectors with a Low Threshold Voltage

An ovonic threshold switch (OTS) based on amorphous chalcogenide materials possesses several desirable characteristics, including high selectivity and fast switching speed, enabling the fabrication of one selector-one resistor (1S-1R) crossbar array (CBA) for random access memory. Among the several chalcogenide materials, GeSe offers high selectivity and a strong glass-forming ability with environment-friendly, simple binary composition. In this report, the GeSe thin films were deposited via atomic layer deposition (ALD) using Ge(N(Si(CH₃)₃)₂)₂ and ((CH₃)₃Si)₂Se for its envisioned application in fabricating three-dimensional vertical-type phase-change memory. Highly conformal Ge_xSe_1-x films were obtained at a substrate temperature ranging from 70 to 160 °C. The unique deposition mechanism that involves Ge intermediates provided a way to modulate the composition of the Ge-Se films from 5:5 to 7:3. Low threshold voltages ranging from 1.2 to 1.4 V were observed depending on the composition. A cycling endurance of more than 10⁶ was achieved with the Ge_0.6Se_0.4 composition with 10⁴ half-bias nonlinearity. This work presents the foundations for the future development of vertical-type 1S-1R arrays when combined with the ALD technique for Ge₂Sb₂Te₅ phase-change materials.

Impact of Organic Molecule-Induced Charge Transfer on Operating Voltage Control of Both n-MoS2 and p-MoTe2 Transistors

Since transition metal dichalcogenide (TMD) semiconductors are found as two-dimensional van der Waals materials with a discrete energy bandgap, many TMD based field effect transistors (FETs) are reported as prototype devices. However, overall reports indicate that threshold voltage ( V_th) of those FETs are located far away from 0 V whether the channel is p- or n-type. This definitely causes high switching voltage and unintended OFF-state leakage current. Here, a facile way to simultaneously modulate the V_th of both p- and n-channel FETs with TMDs is reported. The deposition of various organic small molecules on the channel results in charge transfer between the organic molecule and TMD channels. Especially, HAT-CN molecule is found to ideally work for both p- and n-channels, shifting their V_th toward 0 V concurrently. As a proof of concept, a complementary metal oxide semiconductor (CMOS) inverter with p-MoTe₂ and n-MoS₂ channels shows superior voltage gain and minimal power consumption after HAT-CN deposition, compared to its initial performance. When the same TMD FETs of the CMOS structure are integrated into an OLED pixel circuit for ambipolar switching, the circuit with HAT-CN film demonstrates complete ON/OFF switching of OLED pixel, which was not switched off without HAT-CN.

Grain Boundaries as Electrical Conduction Channels in Polycrystalline Monolayer WS2

We show that grain boundaries (GBs) in polycrystalline monolayer WS₂ can act as conduction channels with a lower gate onset potential for field-effect transistors made parallel, compared to devices made in pristine areas and perpendicular to GBs. Localized doping at the GB causes photoluminescence quenching and a reduced Schottky barrier with the metal electrodes, resulting in higher conductivity at lower applied bias values. Samples are grown by chemical vapor deposition with large domains of ∼100 μm, enabling numerous devices to be made within single domains, across GBs and at many similar sites across the substrate to reveal similar behaviors. We corroborate our electrical measurements with Kelvin probe microscopy, highlighting the nature of the doping-type in the material to change at the grain boundaries. Molecular dynamics simulations of the GB are used to predict the atomic structure of the dislocations and meandering tilt GB behavior on the nanoscale. These results show that GBs can be used to provide conduction pathways that are different to transport across GBs and in pristine area for potential electronic applications.

Threshold voltage decrease in a thermotropic nematic liquid crystal doped with graphene oxide flakes

We report a threshold voltage decrease in a nematic liquid crystal compound, 4-cyano-4'-pentylbiphenyl (5CB), doped with graphene oxide (GO) flakes at a concentration of 0.05-0.3 wt %. The threshold voltage decrease was observed at the same concentration in electro-optic and dielectric spectroscopy measurements. The effect is related to the disrupted planar alignment due to the strong π-π stacking between the 5CB's benzene rings and the graphene oxide's structure. Additionally, we present the GO concentration dependence on the isotropic-nematic phase transition temperature, electric anisotropy, splay elastic constant, switch-on time, and switch-off time. The shape and dimensions of the GO flakes were studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The influence of the GO concentration on the physical properties and switching process in the presence of the electric field was discussed.

Dynamic and Tunable Threshold Voltage in Organic Electrochemical Transistors

In recent years, organic electrochemical transistors (OECTs) have found applications in chemical and biological sensing and interfacing, neuromorphic computing, digital logic, and printed electronics. However, the incorporation of OECTs in practical electronic circuits is limited by the relative lack of control over their threshold voltage, which is important for controlling the power consumption and noise margin in complementary and unipolar circuits. Here, the threshold voltage of OECTs is precisely tuned over a range of more than 1 V by chemically controlling the electrochemical potential at the gate electrode. This threshold voltage tunability is exploited to prepare inverters and amplifiers with improved noise margin and gain, respectively. By coupling the gate electrode with an electrochemical oscillator, single-transistor oscillators based on OECTs with dynamic time-varying threshold voltages are prepared. This work highlights the importance of electrochemistry at the gate electrode in determining the electrical properties of OECTs, and opens a path toward the system-level design of low-power OECT-based electronics.

Electrostatic Selectivity of Volatile Organic Compounds Using Electrostatically Formed Nanowire Sensor

For the past several decades, there is growing demand for the development of low-power gas sensing technology for the selective detection of volatile organic compounds (VOCs), important for monitoring safety, pollution, and healthcare. Here we report the selective detection of homologous alcohols and different functional groups containing VOCs using the electrostatically formed nanowire (EFN) sensor without any surface modification of the device. Selectivity toward specific VOC is achieved by training machine-learning based classifiers using the calculated changes in the threshold voltage and the drain-source on current, obtained from systematically controlled biasing of the surrounding gates (junction and back gates) of the field-effect transistors (FET). This work paves the way for a Si complementary metal-oxide-semiconductor (CMOS)-based FET device as an electrostatically selective sensor suitable for mass production and low-power sensing technology.

Quantitative evaluation of extrinsic factors influencing electrical excitability in neuronal networks: Voltage Threshold Measurement Method (VTMM)

The electrical excitability of neural networks is influenced by different environmental factors. Effective and simple methods are required to objectively and quantitatively evaluate the influence of such factors, including variations in temperature and pharmaceutical dosage. The aim of this paper was to introduce ‘the voltage threshold measurement method’, which is a new method using microelectrode arrays that can quantitatively evaluate the influence of different factors on the electrical excitability of neural networks. We sought to verify the feasibility and efficacy of the method by studying the effects of acetylcholine, ethanol, and temperature on hippocampal neuronal networks and hippocampal brain slices. First, we determined the voltage of the stimulation pulse signal that elicited action potentials in the two types of neural networks under normal conditions. Second, we obtained the voltage thresholds for the two types of neural networks under different concentrations of acetylcholine, ethanol, and different temperatures. Finally, we obtained the relationship between voltage threshold and the three influential factors. Our results indicated that the normal voltage thresholds of the hippocampal neuronal network and hippocampal slice preparation were 56 and 31 mV, respectively. The voltage thresholds of the two types of neural networks were inversely proportional to acetylcholine concentration, and had an exponential dependency on ethanol concentration. The curves of the voltage threshold and the temperature of the medium for the two types of neural networks were U-shaped. The hippocampal neuronal network and hippocampal slice preparations lost their excitability when the temperature of the medium decreased below 34 and 33°C or increased above 42 and 43°C, respectively. These results demonstrate that the voltage threshold measurement method is effective and simple for examining the performance/excitability of neuronal networks.

Effect of ferroelectric BaTiO3 particles on the threshold voltage of a smectic A liquid crystal

The influence of small ferroelectric BaTiO₃ particles on the planar-homeotropic transition threshold voltage in smectic A liquid crystals consisting of p-nitrophenyl p-decyloxybenzoate and 4-cyano-4'-pentylbiphenyl were studied by using capacitance-voltage (C-V) measurements. It was shown that the BaTiO₃ particles significantly reduce the threshold voltage. The obtained result is explained by two factors: an increase of dielectric anisotropy of the liquid crystals and the formation of a strong electric field near polarized particles of BaTiO₃. It was shown that the role of the second factor is dominant. The explanations of some features observed in the C-V characteristics are given.

Improvement of Image Sticking in Liquid Crystal Display Doped with γ-Fe₂O₃ Nanoparticles

Image sticking in thin film transistor-liquid crystal displays (TFT-LCD) is related to the dielectric property of liquid crystal (LC) material. Low threshold value TFT LC materials have a weak stability and the free ions in them will be increased because of their own decomposition. In this study, the property of TFT LC material MAT-09-1284 doped with γ-Fe₂O₃ nanoparticles was investigated. The capacitances of parallel-aligned nematic LC cells and vertically aligned nematic LC cells with different doping concentrations were measured at different temperatures and frequencies. The dielectric constants perpendicular and parallel to long axis of the LC molecules ε_⊥ and ε_//, as well as the dielectric anisotropy Δε, were obtained. The dynamic responses and the direct current threshold voltages in parallel-aligned nematic LC cells for different doping concentrations were also measured. Although the dielectric anisotropy Δε decreased gradually with increasing temperature and frequency at the certain frequency and temperature in LC state for each concentration, the doping concentration of γ-Fe₂O₃ nanoparticles less than or equal to 0.145 wt % should be selected for maintaining dynamic response and decreasing free ions. This study has some guiding significance for improving the image sticking in TFT-LCD.

Low Variability in Synthetic Monolayer MoS2 Devices

Despite much interest in applications of two-dimensional (2D) fabrics such as MoS₂, to date most studies have focused on single or few devices. Here we examine the variability of hundreds of transistors from monolayer MoS₂ synthesized by chemical vapor deposition. Ultraclean fabrication yields low surface roughness of ∼3 Å and surprisingly low variability of key device parameters, considering the atomically thin nature of the material. Threshold voltage variation and very low hysteresis suggest variations in charge density and traps as low as ∼10¹¹ cm^-2. Three extraction methods (field-effect, Y-function, and effective mobility) independently reveal mobility from 30 to 45 cm²/V/s (10th to 90th percentile; highest value ∼48 cm²/V/s) across areas >1 cm². Electrical properties are remarkably immune to the presence of bilayer regions, which cause only small conduction band offsets (∼55 meV) measured by scanning Kelvin probe microscopy, an order of magnitude lower than energy variations in Si films of comparable thickness. Data are also used as inputs to Monte Carlo circuit simulations to understand the effects of material variability on circuit variation. These advances address key missing steps required to scale 2D semiconductors into functional systems.

Carbon Nanotube Reinforced Polymer-Stabilized Liquid Crystal Device: Lowered and Thermally Invariant Threshold with Accelerated Dynamics

Polymer-stabilized liquid crystal (PSLC) devices comprise a polymer matrix in an otherwise continuous phase of liquid crystal. The fibrils of the polymer provide, even in the bulk, virtual surfaces with finite anchoring energy resulting in attractive electro-optic properties. Here, we describe a novel variation of the PSLC device fabricated by reinforcing the polymer matrix with polymer-capped single-walled carbon nanotubes (CNTs). The most important outcome of this strengthening of the polymer strands is that the threshold voltage associated with the electro-optic switching becomes essentially temperature independent in marked contrast to the significant thermal variation seen in the absence of the nanotubes. The reinforcement reduces the magnitude of the threshold voltage, and notably accelerates the switching dynamics and the effective splay elasticity. Each of these attributes is quite attractive from the device operation point of view, especially the circuit design of the required drivers. The amelioration is caused by the polymer decorating CNTs being structurally identical to that of the matrix. The resulting good compatibility between CNTs and the matrix prevents the CNTs from drifting away from the matrix polymer, a lacuna in previous attempts to have CNTs in PSLC systems. The difference in the morphology, perhaps the primary cause for the effects seen, is noted in the electron microscopy images of the films.

Impact of contact resistance on the electrical properties of MoS2 transistors at practical operating temperatures

Molybdenum disulphide (MoS₂) is currently regarded as a promising material for the next generation of electronic and optoelectronic devices. However, several issues need to be addressed to fully exploit its potential for field effect transistor (FET) applications. In this context, the contact resistance, R_C, associated with the Schottky barrier between source/drain metals and MoS₂ currently represents one of the main limiting factors for suitable device performance. Furthermore, to gain a deeper understanding of MoS₂ FETs under practical operating conditions, it is necessary to investigate the temperature dependence of the main electrical parameters, such as the field effect mobility (μ) and the threshold voltage (V_th). This paper reports a detailed electrical characterization of back-gated multilayer MoS₂ transistors with Ni source/drain contacts at temperatures from T = 298 to 373 K, i.e., the expected range for transistor operation in circuits/systems, considering heating effects due to inefficient power dissipation. From the analysis of the transfer characteristics (I_D-V_G) in the subthreshold regime, the Schottky barrier height (Φ_B ≈ 0.18 eV) associated with the Ni/MoS₂ contact was evaluated. The resulting contact resistance in the on-state (electron accumulation in the channel) was also determined and it was found to increase with T as R_C proportional to T^3.1. The contribution of R_C to the extraction of μ and V_th was evaluated, showing a more than 10% underestimation of μ when the effect of R_C is neglected, whereas the effect on V_th is less significant. The temperature dependence of μ and V_th was also investigated. A decrease of μ proportional to 1/T^α with α = 1.4 ± 0.3 was found, indicating scattering by optical phonons as the main limiting mechanism for mobility above room temperature. The value of V_th showed a large negative shift (about 6 V) increasing the temperature from 298 to 373 K, which was explained in terms of electron trapping at MoS₂/SiO₂ interface states.

Electrodeposited, Transverse Nanowire Electroluminescent Junctions

The preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described, and the electroluminescence (EL) properties of these devices are characterized. The lithographically patterned nanowire electrodeposition process is first used to prepare long (millimeters), linear, nanocrystalline CdSe nanowires on glass. The thickness of these nanowires along the emission axis is 60 nm, and the width, wCdSe, along the electrical axis is adjustable from 100 to 450 nm. Ten pairs of nickel-gold electrical contacts are then positioned along the axis of this nanowire using lithographically directed electrodeposition. The resulting linear array of nickel-CdSe-gold junctions produces EL with an external quantum efficiency, EQE, and threshold voltage, Vth, that depend sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe and, therefore, the electrical resistance of the tn-ELJs. Vth down to 1.8(±0.2) V (for wCdSe ≈ 100 nm) and EQE of 5.5(±0.5) × 10(-5) (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 to 960 nm.

Synthesis of WS2xSe2-2x Alloy Nanosheets with Composition-Tunable Electronic Properties

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe2 and intrinsically n-type WS2 with variable alloy compositions. We show that a series of WS2xSe2-2x alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS2xSe2-2x nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics.

Doping-Induced Carrier Density Modulation in Polymer Field-Effect Transistors

Controlled device parameters of high-mobility polymer field-effect transistors (FETs) are demonstrated by modest doping and charge compensation. Through fleeting chemical vapor treatments of aligned poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine] (PCDTPT) thin films as the charge transport layer in the FET channel, the FET properties are tailored by controlling doping concentration of the PCDTPT adjacent to metal electrodes.

Effects of Ambient Air and Temperature on Ionic Gel Gated Single-Walled Carbon Nanotube Thin-Film Transistor and Circuits

Single-walled carbon nanotube thin-film transistor (SWCNT TFT) and circuits were fabricated by fully inkjet printing gold nanoparticles as source/drain electrodes, semiconducting SWCNT thin films as channel materials, PS-PMMA-PS/EMIM TFSI composite gel as gate dielectrics, and PEDOT/PSS as gate electrodes. The ionic gel gated SWCNT TFT shows reversible conversion from p-type transistor behavior in air to ambipolar features under vacuum due to reversible oxygen doping in semiconducting SWCNT thin films. The threshold voltages of ionic gel gated SWCNT TFT and inverters are largely shifted to the low value (0.5 V for p-region and 1.0 V for n-region) by vacuum annealing at 140 °C to exhausively remove water that is incorporated in the ionic gel as floating gates. The vacuum annealed ionic gel gated SWCNT TFT shows linear temperature dependent transconductances and threshold voltages for both p- and n-regions. The strong temperature dependent transconductances (0.08 μS/K for p-region, 0.4 μS/K for n-region) indicate their potential application in thermal sensors. In the other hand, the weak temperature dependent threshold voltages (-1.5 mV/K for p-region, -1.1 mV/K for n-region) reflect their excellent thermal stability.

Highly Stable, Dual-Gated MoS2 Transistors Encapsulated by Hexagonal Boron Nitride with Gate-Controllable Contact, Resistance, and Threshold Voltage

Emerging two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS2) have been intensively studied because of their novel properties for advanced electronics and optoelectronics. However, 2D materials are by nature sensitive to environmental influences, such as temperature, humidity, adsorbates, and trapped charges in neighboring dielectrics. Therefore, it is crucial to develop device architectures that provide both high performance and long-term stability. Here we report high performance of dual-gated van der Waals (vdW) heterostructure devices in which MoS2 layers are fully encapsulated by hexagonal boron nitride (hBN) and contacts are formed using graphene. The hBN-encapsulation provides excellent protection from environmental factors, resulting in highly stable device performance, even at elevated temperatures. Our measurements also reveal high-quality electrical contacts and reduced hysteresis, leading to high two-terminal carrier mobility (33-151 cm(2) V(-1) s(-1)) and low subthreshold swing (80 mV/dec) at room temperature. Furthermore, adjustment of graphene Fermi level and use of dual gates enable us to separately control contact resistance and threshold voltage. This novel vdW heterostructure device opens up a new way toward fabrication of stable, high-performance devices based on 2D materials.

Abnormal behavior of threshold voltage shift in bias-stressed a-Si:H thin film transistor under extremely high intensity illumination

We report on the unusual behavior of threshold voltage turnaround in a hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) when biased under extremely high intensity illumination. The threshold voltage shift changes from negative to positive gate bias direction after ∼30 min of bias stress even when the negative gate bias stress is applied under high intensity illumination (>400 000 Cd/cm(2)), which has not been observed in low intensity (∼6000 Cd/cm(2)). This behavior is more pronounced in a low work function gate metal structure (Al: 4.1-4.3 eV), compared to the high work function of Cu (4.5-5.1 eV). Also this is mainly observed in shorter wavelength of high photon energy illumination. However, this behavior is effectively prohibited by embedding the high energy band gap (∼8.6 eV) of SiOx in the gate insulator layer. These imply that this behavior could be originated from the injection of electrons from gate electrode, transported and trapped in the electron trap sites of the SiNx/a-Si:H interface, which causes the shift of threshold voltage toward positive gate bias direction. The results reported here can be applicable to the large-sized outdoor displays which are usually exposed to the extremely high intensity illumination.

Voltage-Controlled Ring Oscillators Based on Inkjet Printed Carbon Nanotubes and Zinc Tin Oxide

A voltage-controlled ring oscillator is implemented with double-gate complementary transistors where both the n- and p-channel semiconductors are deposited by inkjet printing. Top gates added to transistors in conventional ring oscillator circuits control not only threshold voltages of the constituent transistors but also the oscillation frequencies of the ring oscillators. The oscillation frequency increases or decreases linearly with applied top gate potential. The field-effect transistor materials system that yields such linear behavior has not been previously reported. In this work, we demonstrate details of a material system (gate insulator, p- and n-channel semiconductors) that results in very linear frequency changes with control gate potential. Our use of a double layer top dielectric consisting of a combination of solution processed P(VDF-TrFE) and Al2O3 deposited by atomic layer deposition leads to low operating voltages and near-optimal device characteristics from a circuit standpoint. Such functional blocks will enable the realization of printed voltage-controlled oscillator-based analog-to-digital converters.

Enhanced mobility and effective control of threshold voltage in P3HT-based field-effect transistors via inclusion of oligothiophenes

Improved organic field-effect transistor (OFET) performance through a polymer-oligomer semiconductor blend approach is demonstrated. Incorporation of 2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene (BTTT) into poly(3-hexylthiophene) (P3HT) thin films leads to approximately a 5-fold increase in charge carrier mobility, a 10-fold increase in current on-off ratio, and concomitantly, a decreased threshold voltage to as low as 1.7 V in comparison to single component thin films. The blend approach required no pre- and/or post treatments, and processing was conducted under ambient conditions. The correlation of crystallinity, surface morphology and photophysical properties of the blend thin films was systematically investigated via X-ray diffraction, atomic force microscopy and optical absorption measurements respectively, as a function of blend composition. The dependence of thin-film morphology on the blend composition is illustrated for the P3HT:BTTT system. The blend approach provides an alternative avenue to combine the advantageous properties of conjugated polymers and oligomers for optimized semiconductor performance.

Origins and characteristics of the threshold voltage variability of quasiballistic single-walled carbon nanotube field-effect transistors

Ultrascaled transistors based on single-walled carbon nanotubes are identified as one of the top candidates for future microprocessor chips as they provide significantly better device performance and scaling properties than conventional silicon technologies. From the perspective of the chip performance, the device variability is as important as the device performance for practical applications. This paper presents a systematic investigation on the origins and characteristics of the threshold voltage (VT) variability of scaled quasiballistic nanotube transistors. Analysis of experimental results from variable-temperature measurement as well as gate oxide thickness scaling studies shows that the random variation from fixed charges present on the oxide surface close to nanotubes dominates the VT variability of nanotube transistors. The VT variability of single-tube transistors has a figure of merit that is quantitatively comparable with that of current silicon devices; and it could be reduced with the adoption of improved device passivation schemes, which might be necessary for practical devices incorporating multiple nanotubes, whose area normalized VT variability becomes worse due to the synergic effects from the limited surface coverage of nanotubes and the nonlinearity of the device off-state leakage current, as predicted by the Monte Carlo simulation.

Characteristics of mobile MOSFET dosimetry system for megavoltage photon beams

The characteristics of a mobile metal oxide semiconductor field effect transistor (mobile MOSFET) detector for standard bias were investigated for megavoltage photon beams. This study was performed with a brass alloy build-up cap for three energies namely Co-60, 6 and 15 MV photon beams. The MOSFETs were calibrated and the performance characteristics were analyzed with respect to dose rate dependence, energy dependence, field size dependence, linearity, build-up factor, and angular dependence for all the three energies. A linear dose-response curve was noted for Co-60, 6 MV, and 15 MV photons. The calibration factors were found to be 1.03, 1, and 0.79 cGy/mV for Co-60, 6 MV, and 15 MV photon energies, respectively. The calibration graph has been obtained to the dose up to 600 cGy, and the dose-response curve was found to be linear. The MOSFETs were found to be energy independent both for measurements performed at depth as well as on the surface with build-up. However, field size dependence was also analyzed for variable field sizes and found to be field size independent. Angular dependence was analyzed by keeping the MOSFET dosimeter in parallel and perpendicular orientation to the angle of incidence of the radiation with and without build-up on the surface of the phantom. The maximum variation for the three energies was found to be within ± 2% for the gantry angles 90° and 270°, the deviations without the build-up for the same gantry angles were found to be 6%, 25%, and 60%, respectively. The MOSFET response was found to be independent of dose rate for all three energies. The dosimetric characteristics of the MOSFET detector make it a suitable in vivo dosimeter for megavoltage photon beams.

Highly stable carbon nanotube top-gate transistors with tunable threshold voltage

Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time.

Charge trapping by self-assembled monolayers as the origin of the threshold voltage shift in organic field-effect transistors

The threshold voltage is an important property of organic field-effect transistors. By applying a self-assembled monolayer (SAM) on the gate dielectric, the value can be tuned. After electrical characterization, the semiconductor is delaminated. The surface potentials of the revealed SAM perfectly agree with the threshold voltages, which demonstrate that the shift is not due to the dipolar contribution, but due to charge trapping by the SAM.