Transistor Characteristics Research Articles

Characteristics of Vertical Transistors on a GaN Substrate Fabricated via Na‐Flux Method and Enlargement of the Substrate Surpassing 6 Inches

Characteristics of Vertical Transistors on a GaN Substrate Fabricated via Na‐Flux Method and Enlargement of the Substrate Surpassing 6 Inches

High-Temperature Characterization of AlGaN Channel High Electron Mobility Transistor Based on Silicon Substrate

In this paper, it is demonstrated that the AlGaN high electron mobility transistor (HEMT) based on silicon wafer exhibits excellent high-temperature performance. First, the output characteristics show that the ratio of on-resistance (RON) only reaches 1.55 when the working temperature increases from 25 °C to 150 °C. This increase in RON is caused by a reduction in optical phonon scattering-limited mobility (μOP) in the AlGaN material. Moreover, the device also displays great high-performance stability in that the variation of the threshold voltage (ΔVTH) is only 0.1 V, and the off-state leakage current (ID,off-state) is simply increased from 2.87 × 10−5 to 1.85 × 10−4 mA/mm, under the operating temperature variation from 25 °C to 200 °C. It is found that the two trap states are induced at high temperatures, and the trap state densities (DT) of 4.09 × 1012~5.95 × 1012 and 7.58 × 1012~1.53 × 1013 cm−2 eV−1 are located at ET in a range of 0.46~0.48 eV and 0.57~0.61 eV, respectively, which lead to the slight performance degeneration of AlGaN HEMT. Therefore, this work provides experimental and theoretical evidence of AlGaN HEMT for high-temperature applications, pushing the development of ultra-wide gap semiconductors greatly.

Photoinduced modulation and the effect of CNT loading on field effect transistor characteristics of CNT/ZnO/PVDF composite.

CNT/ZnO/PVDF polymer composite phototransistor is studied for the effect of CNT loading and the photoinduced modulation on its transfer characteristics. XRD study shows that the induced strain in the composite is due to the addition of CNT to the ZnO/PVDF composite. The percentage of β-phase present in PVDF is estimated through Raman spectroscopy and the composite's spectral response is determined by UV-Vis absorbance spectroscopy. From the DC electrical conductivity study it is found that the percolation threshold for the composites is obtained for 0.3 wt% of CNT, and 0.44 wt % of CNT loading makes the composite conductive. On adding 1 wt% of CNT, the electrical conductivity of the ZnO/PVDF composite increases 40 times (~ 0.2 μS/m). The temperature-dependent DC conductivity shows that the conductivity of the composites changes from variable range hopping (VRH) to band conductance upon an increase in CNT loading above the percolation threshold and exhibits a negative temperature coefficient (NTC). Two terminal photoconductivity studies are done to understand the photo enhancement and sensitivity of all the devices. PE hysteresis studies show that the polarization of the composites increases drastically from 0.05 μC/cm2 below the percolation threshold to 10 - 30 μC/cm2 above the percolation threshold of CNT in the composite. To study the effect of interfacial polarization on photoconductivity, the composite is studied in a three-terminal device format using SiO2 as a gate dielectric. A band diagram analysis of the oxide-composite and CNT/ZnO interface is done to understand the mechanism behind the photoinduced field effect on transfer characteristics and the effect of CNT loading. The switching behavior and decay time under UV illumination are studied to understand the effect of CNT loading and photoinduced polarization. The persistent photoconductivity decreases and the charge collection efficiency of the FET increases as the CNT loading increases.

Strain-dependent charge trapping and its impact on the operational stability of polymer field-effect transistors

Despite recent dramatic improvements in the electronic characteristics of stretchable organic field-effect transistors (FETs), their low operational stability remains a bottleneck for their use in practical applications. Here, the operational stability, especially the bias-stress stability, of semiconducting polymer-based FETs under various tensile strains is investigated. Analyses on the structure of stretched semiconducting polymer films and spectroscopic quantification of trapped charges within them reveal the major cause of the strain-dependent bias-stress instability of the FETs. Devices with larger strains exhibit lower stability than those with smaller strains because of the increased water content, which is accompanied by the formation of cracks and nanoscale cavities in the semiconducting polymer film as results of the applied strain. The strain-dependence of bias-stress stability of stretchable OFETs can be eliminated by passivating the devices to avoid penetration of water molecules. This work provides new insights for the development of bias-stable stretchable OFETs.

The Influence of Rapid Heat Treatment During the Formation of Aluminum-Polysilicon Contacts on the Electrical Parameters of CMOS Microcircuits

The influence of rapid heat treatment (450 °C, 7 s) on the electrical parameters of CMOS integrated circuits during the formation of ohmic contact between aluminum metallization and polysilicon is considered. The following volt-ampere characteristics of the dependence of drain current on voltage were chosen as the analyzed parameters of n- and p-channel transistors: at the gate when diode-connected; on the drain at different gate voltages; on the drain in the channel breakdown mode without applying potential to the gate. A comparison of these parameters was carried out with respect to microcircuits manufactured using standard technology (450 °C, 20 min) to form these contacts. Analysis of the results showed that the use of rapid heat treatment to form an ohmic aluminum-polysilicon contact can significantly improve the above characteristics of n-MOS and p-MOS transistors. From the current-voltage characteristics of n- and p-channel transistors it follows that in the region of gate voltages greater than 0.65 V, the drain current after long-term heat treatment is higher than after quick heat treatment. Analysis of the current-voltage characteristics of the drain current versus the drain voltage showed that the drain current when using long-term heat treatment is significantly higher than after rapid heat treatment. In this case, for long-term heat treatment, there is a decrease in the channel breakdown voltage only for n-channel transistors and an increase in the drain current in the region of more than 5 V for both n- and p-channel transistors. Such improvements occur by eliminating the formation of polysilicon conglomerates in the aluminum contact, significantly reducing the epitaxial recrystallization of silicon doped with aluminum on the silicon surface, as well as reducing the microrelief of the interface of this contact and reducing the growth in the size of contact windows due to the lateral interaction of aluminum with polysilicon.

Molecular Reconfiguration of Disordered Tellurium Oxide Transistors with Biomimetic Spectral Selectivity.

Reconfigurable devices with field-effect transistor features and neuromorphic behaviors are promising for enhancing data processing capability and reducing power consumption in next-generation semiconductor platforms. However, commonly used 2D materials for reconfigurable devices require additional modulation terminals and suffer from complex and stringent operating rules to obtain specific functionalities. Here, a p-type disordered tellurium oxide is introduced that realizes dual-mode reconfigurability as a logic transistor and a neuromorphic device. Due to the disordered film surface, the enhanced adsorption of oxygen molecules and laser-induced desorption concurrently regulate the carrier concentration in the channel. The device exhibits high-performance p-type characteristics with a field-effect hole mobility of 10.02 cm2 V-1 s-1 and an Ion/Ioff ratio exceeding 106 in the transistor mode. As a neuromorphic device, the vision system exhibits biomimetic bee vision, explicitly responding to the blue-to-ultraviolet light. Finally, in-sensor denoising and invisible image recognition in static and dynamic scenarios are achieved.

Demonstration of aluminum nitride metal oxide semiconductor field effect transistor on sapphire substrate

Abstract Aluminum nitride (AlN) is a promising ultrawide bandgap material with significant advantages for power electronics and optoelectronic applications due to its high breakdown voltage, mobility, and thermal conductivity. AlN Schottky barrier diodes (SBDs) and metal semiconductor field effect transistors (MESFETs) have shown potential but are limited by issues such as high off-state leakage current and complex structures to achieve ohmic contacts. To address these challenges, we report on the fabrication and characterization of an AlN metal oxide semiconductor field effect transistor (MOSFET) with a recessed gate structure. The source and drain contacts were fabricated on n-doped AlN epitaxy using Ti-based contacts with a Ti/Al/Ti/Au metal stack. To evaluate the performance of these contacts, a circular transmission line model (CTLM) was employed, and contacts were annealed at various temperatures ranging from 750 to 950 °C in a nitrogen ambient. Our results reveal that unannealed Ti-based contacts on AlN showed no current conduction. However, annealing these contacts at 950 °C for 30 s significantly reduced the specific contact resistance to 0.148 Ω·cm2, achieving an ~80% reduction compared to samples annealed at 750 °C. Utilizing these optimized contact conditions, we fabricated, to the best of our knowledge, the first AlN MOSFET. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, an effective mobility of 2.95 cm2/Vs, an on-off current ratio spanning two orders of magnitude, and a reverse breakdown voltage of approximately ~250 V in air without a field plate. 

A Simulation Study for Enhancing the Performance of Luminescent Organic Transistor Using Reduced Voltage and Hole Blocking Layer

Abstract Eco-friendly and biodegradable technology forms the basis of organic electronics. A luminescent organic transistor (LOT) is a device created using this technology, which is capable of emission of light and acting as switch functions in a single unit. This research seeks to develop and model a nonplanar contact heterostructure-based LOT by employing the defect density of states (DOS) to accurately simulate the amorphous nature of organic semiconductors. This study evaluates two high-k dielectric materials, hafnium oxide (HfO2) and poly(vinylidene fluoride-trifluoroethylene)P(VDF-TrFe), to achieve low-voltage operation at (-10V). Furthermore, this study investigated the influence of a hole blocking material, 1,3,5-Tris(3-pyridyl-3-phenyl)benzene(TmPyPB), on device performance. Simulations revealed p-channel transistor characteristics with a maximum source-drain current of (-1.6 mA) and an on-off current ratio exceeding 104 for HfO2, compared to (-0.75 mA) and approximately 104 for P(VDF-TrFe). The model also demonstrated exceptional electrical properties, including a peak hole mobility of (1.96 cm2 v-1 s-1), a threshold voltage of (-0.85 V), and a sub-threshold voltage of 492 mV/dec in saturation. The recombination zone exhibited an electron concentration of 18.0 cm-3, a hole concentration of 19.3 cm-3, and a Langevin recombination rate of 24.7 cm-3s-1 near the drain electrode. This model serves as an ideal platform for testing newly developed molecules to enhance the performance of luminescent transistor.

Characterization of AI-enhanced magnetophoretic transistors operating in a tri-axial magnetic field for on-chip bioparticle sorting.

We demonstrate two general classes of magnetophoretic transistors, called the "trap" and the "repel-and-collect" transistors, capable of switching single magnetically labeled cells and magnetic particles between different paths in a microfluidic chamber. Compared with prior work on magnetophoretic transistors operating in a two-dimensional in-plane rotating field, the use of a tri-axial magnetic field has the fundamental advantages of preventing particle cluster formation and better syncing of single particles with the general operating clock. We use finite element methods to investigate the energy distribution on the chip surface and to predict the particle behavior at various device geometries. We then fabricate the proposed transistors and compare the experimental results with the simulation predictions. We found that with gate electrical currents of ~ 40mA for a transistor with proper geometry, complete switching of magnetic particles with diameters in the range of 8-15μm is achieved. We show that the device is reliable and works well at different magnetic field strengths (50-100 Oe) and frequencies (0.05-0.5Hz). We also employed an image processing code with a trained convolutional neural network to automate the proposed transistors for identifying and sorting particles with various sizes and magnetic susceptibilities with accuracies higher than 98%. The proposed transistors can be used in designing novel magnetophoretic circuits for important applications in biomedical microdevices and single-cell biology.

Facile strategy for uniform gold coating on silver nanowires embedded PDMS for soft electronics

Silver nanowires-embedded polydimethylsiloxane (AgNWs/PDMS) electrodes are promising components for various soft electronics, but face energy mismatch with organic semiconductors. Attempts at galvanic replacement, involving spontaneous gold (Au) formation on the electrodes, often result in non-uniform and particulate Au coatings, compromising device performance and stability. In this study, we introduce a novel approach for achieving a uniform and complete Au coating on AgNWs/PDMS electrodes by adding NaCl to the Au complex solution. This addition slows down the galvanic replacement process and prevents precipitation, enabling a uniform and complete Au coating on the AgNWs surface. Such coating significantly reduces contact resistance (RC), thereby enhancing the electrical characteristics of p-type organic transistors. Furthermore, the development of high-performance, fully soft organic transistors was achieved incorporating an organic semiconductor-elastomer blend. Additionally, reliable, mechanically stable soft glucose sensor was developed, taking advantage of the complete Au coating, which protects against oxidation during the glucose sensing process.

Quantitative Spermidine Detection in Cosmetics using an Organic Transistor-Based Chemical Sensor.

Spermidine is an essential biomarker related to antiaging. Although the detection of spermidine levels is in high demand in life science fields, easy-to-use analytical tools without sample purification have not yet been fully established. Herein, we propose an organic field-effect transistor-based chemical sensor for quantifying the spermidine concentration in commercial cosmetics. An extended-gate structure was employed for organic field-effect transistor (OFET)-based chemical sensing in aqueous media. A coordination-bond-based sensing system was introduced into the OFET device to visualize the spermidine detection information through changes in the transistor characteristics. The extended-gate-type OFET has shown quantitative responses to spermidine, which indicates sufficient detectability (i. e., the limit of detection for spermidine: 2.3 μM) considering actual concentrations in cosmetics. The applicability of the OFET-based chemical sensor for cosmetic analysis was validated by instrumental analysis using high-performance liquid chromatography. The estimated recovery rates for spermidine in cosmetic ingredient products (108-111 %) suggest the feasibility of cosmetic analysis based on the OFET-based chemical sensor.

High-voltage kV-class AlN metal-semiconductor field-effect transistors on single-crystal AlN substrates

This letter reports the demonstration and electrical characterization of high-voltage AlN metal-semiconductor field-effect transistors (MESFETs) on single-crystal AlN substrates. Compared with AlN MESFETs on foreign substrates, the AlN-on-AlN MESFETs showed high breakdown voltages of over 2 kV for drain-to-gate spacing of 15 μm and one of the highest average breakdown fields among reported AlN MESFETs. Additionally, the devices also exhibited decent drain saturation current and on/off ratio without complicated regrown or graded contact layers, which are several times higher than those of reported AlN-on-sapphire MESEFTs. This work is beneficial for the future development of ultrawide bandgap AlN power electronics.

Multi-Functional Molybdenum Oxide Doping to Improve the Electrical Characteristics of Indium Oxide Thin Film Transistors

Multi-Functional Molybdenum Oxide Doping to Improve the Electrical Characteristics of Indium Oxide Thin Film Transistors

Improving bias stability of IGZO field-effect transistors through CF4 plasma treatment of Al2O3 dielectrics

In this study, the effects of the CF4 plasma treatment on the amorphous indium gallium zinc oxide (IGZO) material were explored. The electrical characteristics of the IGZO-based field-effect transistor (FET) were also thoroughly examined to analyze the influence of the plasma treatment. Excellent adhesion of the sol-gel-based IGZO semiconducting film was achieved owing to the strong dipole moment of the AlOxFy layer created by the surface treatment. In particular, X-ray photoelectron spectroscopy depth profiles and transmission electron microscopy electron energy loss spectroscopy analyses provided clear evidence that fluorine atoms diffused into the Al2O3 surface via the CF4 plasma treatment. The formation of an AlOxFy layer at the IGZO/Al2O3 interface is expected to be advantageous for reducing the interface trap density, thereby enhancing the critical transistor parameters. Additionally, the plasma-treated IGZO transistor demonstrated strong electrical bias stability under continuous gate bias stress conditions. Therefore, surface modification via CF4 plasma treatment is proposed to boost the stability and performance of the device, offering a straightforward approach for integrated thin-film transistor circuitry in advanced display applications.

Thieno[3,2-b]thiophene flanked para-azaquinodimethane π-extended aromatic-quinoidal polymers

A series of thieno[3,2-b]thiophene (TT) flanked para-azaquinodimethane (p-AQM) based quinoidal conjugated polymers PAQM2TT-T, PAQM2TT-BT and PAQM3TT were designed in a strategy to extend the aromatic-quinoidal π-system. The three polymers were synthesized by Stille polycondensation, and their opto-electronic properties and device performance in field-effect transistors have been explored. From absorption spectroscopy, the polymers show low bandgaps (1.54–1.57 eV) and high HOMO energy levels. They exhibit typical p-type behavior according to the results of the characterization of the field-effect transistors with average charge carrier mobilities of 0.08 cm2 V−1 s−1 for PAQM2TT-T, 0.12 cm2 V−1 s−1 for PAQM2TT-BT and 0.05 cm2 V−1 s−1 for PAM3TT. This report presents an alternative π-extended quinoidal-donor strategy to control the molecular design and properties of new p-AQM-based conjugated polymers.

Reversible Switching of Light‐Gated Organic Transistors Employing Dihydroazulene/Vinylheptafulvene Photo‐/Thermochromic Molecules

AbstractAn innovative possibility to introduce additional functionality to organic field‐effect transistors (OFETs) is to employ photochromic molecules, which undergo reversible isomerization under applied stimuli such as irradiation with specific wavelengths. As a result, the transistors not only can be switched on/off by the applied voltages, they can also be programmed by alternate triggers, such as light. Here, reversible switching of OFETs is presented by blending various dihydroazulene/vinylheptafulvene photoswitches into polythiophene‐based conjugated polymers. In result, the transfer characteristics of the transistors are altered significantly through UV irradiation. In contrast to current literature on different photoswitches such as spiropyrans or diarylethenes, the backreaction is induced thermally and not via visible light irradiation and reproducibly yields the pristine transistor characteristics. This reversible switching upon alternating UV irradiation and thermal annealing is quantified by figures of merit such as the magnitude of drain current, threshold voltage, and subthreshold swing. Irradiating the devices with different doses of UV light shows that the magnitude of switching directly depends on the respective UV dose, hence enabling a multi‐level electronic system. Furthermore, long‐term cyclability over 100 steps of repeated UV light exposure and thermal annealing is demonstrated.

Small signal analysis for the characterization of organic electrochemical transistors

A method for the characterization of organic electrochemical transistors (OECTs) based on small signal analysis is presented that allows to determine the electronic mobility as a function of continuous gate potential using a standard two-channel AC potentiostat. Vector analysis in the frequency domain allows to exclude parasitic components in both ionic and electronic conduction regardless of film thickness, thus resulting in a standard deviation as low as 4%. Besides the electronic mobility, small signal analysis of OECTs also provides information about a wide range of other parameters including the conductance, transconductance, conductivity and volumetric capacitance through a single measurement. General applicability of small signal analysis is demonstrated by characterizing devices based on n-type, p-type, and ambipolar materials operating in accumulation or depletion modes. Accurate benchmarking of organic mixed ionic-electronic conductors through small signal analysis can be anticipated to guide both materials development and the design of bioelectronic devices.

Design and Characterization of an Optical 4H-SiC Bipolar Junction Transistor

In this paper, a first demonstration of the optical triggering of a 10 kV 4H-SiC Bipolar Junction Transistor is reported. A laser emitting UV (349 nm) has been used for the generation electron-hole pairs within the device. A current density of about 20 A.cm-2 has been obtained. This low value in comparison with 100 A.cm-2 for “conventional” BJT is due to the narrow pulse width (5 ns). The current waveform shows the effect of the carrier lifetime in the base and collector regions. From these measurements, we have extracted the IC (VCE) characteristics for different laser optical power and the switch-on time which is about 1 µs.

Device-level XPS analysis for physical and electrical characterization of oxide-channel thin-film transistors

Device-level XPS analysis for physical and electrical characterization of oxide-channel thin-film transistors

High Throughput Characterization of Organic Thin Film Transistors.

Automation is vital to accelerating research. In recent years,the application of self-driving labs to materials discovery and device optimization has highlighted many benefits and challenges inherent to these new technologies. Successful automated workflows offer tangible benefits to fundamental science and industrial scale-up by significantly increasing productivity and reproducibility all while enabling entirely new types of experiments. However, it's implemtation is often time-consuming and cost-prohibitive and necessitates establishing multidisciplinary teams that bring together domain-specific knowledge with specific skillsets in computer science and engineering. This perspective article provides a comprehensive overview of how the research group has adopted "hybrid automation" over the last 8 years by using simple automatic electrical testers (autotesters) as a tool to increase productivity and enhance reproducibility in organic thin film transistor (OTFT) research. From wearable and stretchable electronics to next-generation sensors and displays, OTFTs have the potential to be a key technology that will enable new applications from health to aerospace. The combination of materials chemistry, device manufacturing, thin film characterization and electrical engineering makes OTFT research challenging due to the large parameter space created by both diverse material roles and device architectures. Consequently, this research stands to benefit enormously from automation. By leveraging the multidisciplinary team and taking a user-centered design approach in the design and continued improvement of the autotesters, the group has meaningfully increased productivity, explored research avenues impossible with traditional workflows, and developed as scientists and engineers capable of effectively designing and leveraging automation to build the future of their fields to encourage this approach, the files for replicating the infrastructure are included, and questions and potential collaborations are welcomed.