Transistor Characteristics Research Articles

Mechanically Adaptive Mixed Ionic-Electronic Conductors Based on a Polar Polythiophene Reinforced with Cellulose Nanofibrils.

Conjugated polymers with oligoether side chains are promising mixed ionic-electronic conductors, but they tend to feature a low glass transition temperature and hence a low elastic modulus, which prevents their use if mechanical robust materials are required. Carboxymethylated cellulose nanofibrils (CNF) are found to be a suitable reinforcing agent for a soft polythiophene with tetraethylene glycol side chains. Dry nanocomposites feature a Young's modulus of more than 400 MPa, which reversibly decreases to 10 MPa or less upon passive swelling through water uptake. The presence of CNF results in a slight decrease in electronic mobility but enhances the ionic mobility and volumetric capacitance, with the latter increasing from 164 to 197 F cm-3 upon the addition of 20 vol % CNF. Overall, organic electrochemical transistors (OECTs) feature a higher switching speed and a transconductance that is independent of the CNF content up to at least 20 vol % CNF. Hence, CNF-reinforced conjugated polymers with oligoether side chains facilitate the design of mechanically adaptive mixed ionic-electronic conductors for wearable electronics and bioelectronics.

Electronic and Charge Transport Properties in Bridged versus Unbridged Nanohoops: Role of the Nanohoop Size.

In the field of π-conjugated nanohoops, the size of the macrocycle has a strong impact on its structural characteristics, which in turn affect its electronic properties. In this work, we report the first experimental investigations linking the size of a nanohoop to its charge transport properties, a key property in organic electronics. We describe the synthesis and study of the first example of a cyclocarbazole possessing five constituting building units, namely [5]-cyclo-N-butyl-2,7-carbazole, [5]C-Bu-Cbz. By comparison with a shorter analogue, [4]-cyclo-N-butyl-2,7-carbazole, [4]C-Bu-Cbz, we detail the photophysical, electrochemical, morphological and charge transport properties, highlighting the key role played by the hoop size. In particular, we show that the saturated field effect mobility of [5]C-Bu-Cbz is four times higher than that of its smaller analogue [4]C-Bu-Cbz (4.22×10-5 vs 1.04×10-5 cm2 V-1 s-1 ). However, the study of the other organic field-effect transistor characteristics (threshold voltage VTH and subthreshold slope SS) suggest that a small nanohoop is beneficial for good organization of the molecules in thin films, whereas a large one increases the density of structural defects, and hence of traps for the charge carriers. The present findings are of interest for the further development of nanohoops in electronics.

Temperature Dependence of Electrical Characteristics of ZnO Nanowire Field-Effect Transistors with AZO and Aluminium Source/Drain Contact

In this study, ZnO nanowire field-effect transistor (FET) with an aluminium-doped ZnO (AZO) and an aluminium (Al) dual layer source and drain contact are fabricated and temperature dependent characteristics in the range of 200 – 300 K are analyzed through experimental measurements. The effect of temperature on threshold voltage, subthreshold slope, transconductance, and field effect mobility are analysed. The transfer curve exhibits a parallel shift toward a negative gate voltage direction with a negative shift of the threshold voltage, an increase in the subthreshold slope, and a field-effect mobility as the temperature rises. The electrical properties of the transistors demonstrate typical behaviour at various temperatures.

AlN/AlGaN/AlN quantum well channel HEMTs

We present a compositional dependence study of electrical characteristics of AlxGa1−xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs) with x=0.25,0.44, and 0.58. This ultra-wide bandgap heterostructure is a candidate for next-generation radio frequency and power electronics. The use of selectively regrown n-type GaN Ohmic contacts results in contact resistance that increases as the Al content of the channel increases. The DC HEMT device characteristics reveal that the maximum drain current densities progressively reduce from 280 to 30 to 1.7 mA/mm for x=0.25,0.44, and 0.58, respectively. This is accompanied by a simultaneous decrease (in magnitude) in threshold voltage from −5.2 to −4.9 to −2.4 V for the three HEMTs. This systematic experimental study of the effects of Al composition x on the transistor characteristics provides valuable insights for engineering AlGaN channel HEMTs on AlN for extreme electronics at high voltages and high temperatures.

Equivalent small-signal model of InP-based HEMTs with accurate radiation effects characterization

In this paper, an effective equivalent modeling technique has been proposed to describe small-signal characteristics of InP-based high electron mobility transistors (HEMTs) after proton radiation, which is composed of an artificial neural network and equivalent-circuit models. Small-signal intrinsic parameters of InP-based HEMTs are extracted from S-parameters before and after 2 MeV proton radiation as modeling objects. The deep learning model of a generative adversarial network has been explored to expand the measured finite data samples. Four feedforward neural networks are incorporated to equivalent-circuit topology to form the equivalent model, which are trained to accurately predict the radiation-induced variations of Cgs, Cgd, Rds, and gm, respectively. The prediction accuracy of the developed equivalent model has been well verified in terms of the broad-band S-parameters under radiation fluence of 1 × 1014 and 5 × 1013 H+/cm2. This equivalent modeling method with characterization of radiation damage effects could provide significant guidance for the aerospace monolithic millimeter-wave integrated circuit design.

Characteristics of Offset Corbino Thin Film Transistor: A Physical Model

Offset Corbino thin film transistor is a good candidate for high voltage thin film transistor (HVTFT) due to the uniform drain electric field distribution benefiting from the circular structure. The physical model of offset Corbino thin film transistor characteristics has yet to be clarified. In this study, Equations are derived to describe the current–voltage relations of Corbino TFT with offset at the drain or source sides. The influence of offset position and parameters on the saturation voltage and the saturation current was described quantitatively. Three-dimensional Computer-Aided Design simulation and experiment results verify the theoretical physical model. Our physical model provides design rules for high voltage offset Corbino TFT when considering the voltage tolerance and saturation current balance.

A Competitive n‐Type OECT Material via Copolymerization of Electron Deficient Building Blocks

AbstractThe classical acceptor motifs diketopyrrolopyrrole (DPP) and thienopyrrolodione (TPD) are copolymerized to yield the acceptor–acceptor polymer “Poly(DPP‐TPD).” The fundamental design idea is to maximize the electron affinity (EA), thus increasing the ambient stability of the reduced state against oxygen and water while ensuring high ion compatibility through the incorporation of hydrophilic oligoethylene glycol N‐substituents. Additionally, a highly planarized polymer structure is anticipated, due to the extended noncovalent interactions (conformational locking) between the carbonyl oxygen and the thiophene protons. Cyclic voltammetry, spectroelectrochemistry, ultraviolet photoelectron spectroscopy, ultraviolet‐visible absorption spectroscopy, and organic field effect transistor (OFET) characterization demonstrate the suitability for n‐type organic electrochemical transistor (OECT) devices. High EA, ionization potential, and good electron mobility (µe(OFET)) are shown, in addition to the electrochemical reduction of polymer films in aqueous electrolyte. In n‐type OECTs, poly(DPP‐TPD) demonstrates a moderate threshold voltage of Vth = 0.58 V and an outstanding µC* value of 7.62 F cm−1 V−1 s−1. Cycling studies consisting of pulsed on‐ and off‐switching of the device at gate voltages between Vg = 0.6–0.8 V in the saturation regime reveal high stability for more than 2700 cycles with rapid switching kinetics.

GaN-Based Double-Heterojunction Bipolar Transistors With a Composition Graded p-InGaN Base

The influence of energy band structure on the electrical characteristics of GaN-based double-heterojunction bipolar transistors (DHBTs) has been studied through both simulation and fabrication. According to the simulation result, a novel DHBT structure with a composition graded base was grown and fabricated. A long minority carrier lifetime of 4.08 ns has been achieved for the composition graded p-InGaN base with a greatly improved material quality. The indium composition grading of the p-InGaN base layer combined with Si doping profile tuning for the collector layer was proposed to eliminate the energy barrier usually formed at the conventional GaN/InGaN/GaN base–collector (B–C) junction interface due to the band discontinuity and polarization effect. As a result, the as-fabricated DHBT presents a high intercept voltage of 225 V extracted from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{I}_{\textit{C}}$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{V}_{\text{CE}}$</tex-math> </inline-formula> curves and a high current gain of 49.

Study of IGZO thin film transistors with Al2O3 gate insulator

In this study focuses on the dielectric layer materials of thin film transistors (TFTs). Gate oxide was deposited using a RF Magnetron Sputtering control system. The first studied the aluminium oxide (Al2O3) dielectric layer material deposited with different oxygen flow and annealed by the furnace tube. The study found that the properties of aluminium oxide (Al2O3) thin film transistors (TFTs) after furnace tube annealing reduced the interface trap density and the roughness of the thin film after annealing. The above dielectric layer is used to make thin film transistors (TFTs) with a bottom gate structure. The characteristics of thin film transistors (TFTs) are significantly improved by higher oxygen flow and additional thermal anneal. By analyzing the structure and electrical measurement of the thin film, the influence of the dielectric layer material on the thin film transistors (TFTs) is analyzed.

Кремниевый с полностью охватывающим затвором полевой нанотранзистор с нелинейной геометрией рабочей области

A silicon CMOS nanotransistor with a cylindrical geometry with a fully enclosing gate with a non-linear geometry of the working area is discussed. Numerical studies of prototypes with a parabolic working area were performed using mathematical modeling using the software environment for instrumental technological modeling TCAD, based on the models of n- and p-type nanotransistors developed by TCAD. An inverter model has been developed for n- and p-type prototypes with an optimized radius ratio of 0.76. At control voltages of 0.6 V and a frequency of 25 GHz, the model predicts a maximum switching delay of 1.0 ps, an active power limit of 0.22 µW, and a static power of 72 pW. The electrophysical characteristics of the n-type prototype with dielectric stacks of gate oxide SiO2-Al2O3 and SiO2-HfO2 are analyzed numerically. The simulation results show that the use of high k stacks has a noticeable effect on key transistor characteristics. Thus, a parabolic nanotransistor architecture with an optimized radius ratio can potentially become a replacement for a cylindrical structure for high-speed low-voltage applications.

An area-efficient sub-10 nW temperature-to-digital converter for thermopile temperature sensors

A 6.29 nW temperature-to-digital converter for IR radiation-based thermopile temperature sensors was designed and fabricated on the chip area of 0.068 mm2 using 90 nm CMOS technology. The sub-mV voltage produced by the sensor is nearly proportional to the temperature difference between the object and the environment and is converted to sub-nA current using the gate-leakage characteristics of PMOS transistors. The ratio of the sub-nA current and the reference current proportional to the sub-mV voltage difference is converted to the frequency ratio of the two current-to-frequency oscillators. Then, the digital output proportional to the tiny voltage difference can be obtained by the counters. After the two-point calibrated digital outputs are mapped to the object temperatures, the average resolution is 0.11 °C with a conversion time of 348 ms, which results in the figure of merit of 0.026 nJ × °C2. The inaccuracy of the object temperature is +0.26/−0.95 °C from −10 °C to 100 °C at the ambient temperature of 25 °C.

Investigating the Mobility-Compressibility Properties of Conjugated Polymers by the Contact Film Transfer Method with Prestrain.

Up to now, researches on the mobility-stretchability of semiconducting polymers are extensively investigated, but little attention was paid to their morphology and field-effect transistor characteristics under compressive strains, which is equally crucial in wearable electronic applications. In this work, a contact film transfer method is applied to evaluate the mobility-compressibility properties of conjugated polymers. A series of isoindigo-bithiophene conjugated polymers with symmetric carbosilane side chains (P(SiSi)), siloxane-terminated alkyl side chains (P(SiOSiO)), and combined asymmetric side chains (P(SiOSi)) are investigated. Accordingly, a compressed elastomer slab is used to transfer and compress the polymer films by releasing prestrain, and the morphology and mobility evolutions of these polymers are tracked. It is found that P(SiOSi) outperforms the other symmetric polymers including P(Si─Si)andP(SiO─SiO), having the ability to dissipate strain with its shortened lamellar spacing and orthogonal chain alignment. Notably, the mechanical durability of P(SiOSi) is also enhanced after consecutive compress-release cycles. In addition, the contact film transfer technique is demonstrated to be applicable to investigate the compressibility of different semiconducting polymers. These results demonstrate a comprehensive approach to understand the mobility-compressibility properties of semiconducting polymers under tensile and compressive strains.

Plasma processing technique by combination of plasma-assisted reactive sputtering and plasma annealing for uniform electrical characteristics of InGaZnO thin film transistors formed on large-area substrates

The homogeneous formation of high-mobility oxide semiconductor thin films over large areas at low temperatures was accomplished by optimizing both the film formation process and the low-temperature post-processing via plasma annealing. Increasing the substrate-to-target distance (D ST) and the applied target voltage was found to produce more uniform deposition. The results of the field-effect mobility distributions of IGZO TFTs processed using plasma annealing were founded that plasma annealing generated essentially uniform distributions with μ FE values in the range of 32–35 cm2 V−1 s−1.

Comparative Study between Sulfurized MoS2 from Molybdenum and Molybdenum Trioxide Precursors for Thin-Film Device Applications.

Two-dimensional (2D) materials have been studied as an emerging class of nanomaterials owing to their attractive properties in nearly every field of science and technology. Molybdenum disulfide (MoS2) is one of the more promising candidates of these atomically thin 2D materials for its technological potential. The facile synthesis of MoS2 remains a matter of broad interest. In this study, MoS2 was synthesized by chemical vapor deposition sulfurization at various temperatures (550 °C, 650 °C, and 750 °C) of either precursor molybdenum metal (Mo) or molybdenum trioxide (MoO3) deposited on silicon/silicon dioxide (Si/SiO2) via e-beam evaporation. Monolayer, bilayer, and few layers sulfurized samples have been grown and verified by Raman, photoluminescence spectroscopy, XRD, XPS, and AFM. MoO3 sulfurization provided monolayer growth in comparison to Mo sulfurization under the same conditions and precursor thicknesses. Optical microscopy showed the homogeneous nature of grown samples. A main finding of this work is that MoO3 sulfurization produced higher quality MoS2 as compared to those grown by an Mo precursor. Device characteristics based on monolayer MoO3 sulfurized MoS2-x include nonvolatile resistive switching with Ion/Ioff ≈ 104 at a relatively low operating bias of ±1 V. In addition, field-effect transistor characteristics revealed p-type material growth with a carrier mobility ∼ 41 cm2 V-1 s-1, which is in contrast to typically observed n-type characteristics.

Design of Class F Power Amplifier for Sub 6 GHz

Class F power amplifiers increasingly have widespread use cases in the modern portable mobile communications and higher efficiency operation due to base station. This paper focuses on the design of sub 6 GHz class-F Power Amplifiers (PA) to ensure maximum output power and gain using Gallium nitride– High Electron Mobility Transistor (GaN HEMT). The work also aims to analyze stability and Power Added Efficiency (PAE) using Advanced Design System (ADS) software. Simulations for DC characteristics of the GaN HEMT transistor are performed, stability circles are simulated, and stability factor values have been noted, using ADS software. Stability analysis involves measurements to examine the conditions that may lead to unstable behavior of the PA. The load pull analysis followed by impedance matching is done to transfer maximum power from amplifier stage to load. The input and output network has been designed using transmission lines and incorporated in the final circuit of the PA design. Using the LineCalc tool, the values of electrical parameters are used in the respective MLIN and TLIN circuits, and the respective matching networks are designed at the input side and output side. The amplifier stability factor is 2.276 and the maximum PAE is 65.75%. The maximum output is 39.83 dBm. The layout for the PA network using ADS software has been obtained.

Effect of Surface Modification on the Fundamental Electrical Characteristics of Solution-Gated Indium Tin Oxide-Based Thin-Film Transistor Fabricated by One-Step Sputtering.

Our solution-gated indium tin oxide (ITO)-based thin-film transistor (TFT) produced by single-step sputtering has great future potential in bioelectronics. In particular, chemical modifications of the ITO channel surface are expected to contribute to biomolecular recognition with ultrahigh sensitivity owing to a remarkably steep subthreshold slope (SS). In this study, we investigate the effect of a chemical modification of an aptamer as a receptor molecule at the ITO channel surface on the electrical characteristics of the solution-gated TFT. In this case, a SARS-CoV-2 aptamer is immobilized using a spacer molecule on an aryl diazonium monolayer that is electrochemically deposited with a radical scavenger. The monolayer is expected to not only passivate the ITO channel surface but also change the electron density in the ITO channel owing to the reduction reaction of aryl diazonium salts. Indeed, the electrochemical deposition of aryl diazonium salts decreases the leakage current through the ITO channel surface and provides a steep SS, which is near the thermal limit at 300 K, owing to the decrease in depletion layer capacitance. After the aptamer immobilization, the leakage current and SS unexpectedly return close to their original values before the surface modifications. This finding indicates that aptamer molecules should be carefully used because their negative charges would attract cations around the detection interface. Eventually, the solution-gated ITO-based TFT with the SARS-CoV-2 aptamer clearly responds to inactivated SARS-CoV-2 particles owing to the successful surface modification.

Effect of Hf x Zr1−x O2/Ge metal–ferroelectrics–insulator–semiconductor interfaces on polarization reversal behavior

To evaluate the polarization characteristics of ferroelectric-gate field-effect transistors, metal–ferroelectrics–insulator–semiconductor (MFIS) structures are often used. This study examines the influence of interface characteristics on polarization characterization in MFIS on low-impurity-concentration substrates by experimentally evaluating the ferroelectric properties of Hf x Zr1−x O2 (HZO)/Ge MFIS capacitors with different interface properties. Usually, polarization reversal behavior is not observed for MFIS capacitors on low-impurity-concentration substrates. However, it is found that, when the interface properties are poor and the interface state density is high, polarization reversal behavior can be observed even on the low-impurity concentration substrates. In lightly-doped MFIS capacitors with many interface states, the response of the interface states at low measurement frequencies suppresses the depletion layer change and voltage drop in the Ge substrate, resulting in the high electric field across the HZO films and observation of polarization reversal behavior.

Tetramethylammonium Iodide Additive for Enhancing the Charge Carrier Mobilities of Diketopyrrolopyrrole‐Based Conjugated Polymer in Ambipolar Organic Field‐Effect Transistors†

Comprehensive SummaryDiketopyrrolopyrrole (DPP) is one of the most promising building blocks for constructing polymer semiconductors with high charge‐carrier mobilities in organic field‐effect transistors (OFETs). In this study, a novel DPP‐based conjugated polymer, PDPPy‐BDD, was designed and synthesized. The ambipolar field‐effect transistor characteristics were realized with the average hole and electron mobilities of 3.5 × 10–3 and 3.07 × 10–2 cm2 V−1 s−1, respectively. Both the hole and electron mobilities could be successfully enhanced by using a tetramethylammonium iodide (NMe4I) additive. Such an enhancement was attributed to the formation of stronger interchain π–π stackings, the weakening of the face‐on packing orientation in the thin film state, and the higher channel conductivities in the OFETs.

Trap characteristics of hafnium oxide-based ferroelectric field-effect transistors measured by using a current transient method

The trap characteristics and polarization effect on the trapping behavior in Hf0.5Zr0.5O2 ferroelectric field-effect transistors were analyzed. The current transient that corresponds to the trapping/detrapping of charge carriers was measured and the exact time constant spectra were extracted. In accordance with the different time constants and activation energies as well as the dependence of the trapping behavior on the filling conditions, traps that originated from the oxygen vacancies in the Hf0.5Zr0.5O2 layer and from the Si/SiO2 interface trap states were identified. The detrapping peaks in time constant spectra showed a consistent changing trend with the variation of remanent polarization, confirming that the positive polarization enhanced the trapping of charge carriers injected from channel side to the ferroelectric layer.

Effect of Gate Bias Stress on the Electrical Characteristics of Ferroelectric Oxide Thin-Film Transistors with Poly(Vinylidenefluoride-Trifluoroethylene).

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and a large positive shift under positive gate bias stress (PBS) in transfer characteristic curves. In contrast, the FeOxTFTs show a small positive shift and a large negative shift under NBS and PBS, respectively. It was confirmed that sufficient changes in the electrical characteristics are obtained by 10 min NBS and PBS. The changed electrical characteristics such as threshold voltage shift, memory on- and memory off-current were maintained for more than 168 h after NBS and 24 h after PBS. It is deduced that, since the dipole alignment of the ferroelectric layer is maximized during GBS, these changes in electrical properties are caused by the remnant dipole moments still being retained during the gate sweep. The memory on- and memory off-current are controlled by GBS and the best on/off current ratio at 107 was obtained after NBS. By repeatedly alternating NBS and PBS, the electrical characteristics were reversibly changed. Our results provide the scientific and technological basis for the development of stability and performance optimization of FeOxTFTs.