Transistor Measurements Research Articles

New metallophthalocyanines including benzylphenoxy groups and investigation of their organic-field effect transistor (OFET) features

In this study, metal and metal-free novel phthalocyanines containing peripheral and non-peripheral tetra 2-benzylphenoxy groups were synthesized. The compounds were characterized by UV–Vis, FT-IR, 1H NMR, and MALDI-TOF mass spectrometry as well as elemental analysis. These new phthalocyanines exhibited excellent solubility in most organic solvents, and their redox behavior was investigated in different solvents such as dimethyl sulfoxide (DMSO) and dichloromethane (DCM). The redox behavior of the peripheral and non-peripheral phthalocyanine compounds 1a-c and 2a-c was determined by cyclic voltammetry and in situ spectroelectrochemistry. According to organic field-effect transistors (OFETs) measurements, the peripheral and non-peripheral phthalocyanine-cobalt complexes which have higher mobility than others were utilized top-gate bottom-contact OFETs fabrication. The output characteristics of the device show that its mobility is approximately 5 × 10−2 cm2/Vs with p-type accumulation.

Heat sink efficiency investigation of silicon-on-diamond composite substrates for gallium nitride-based devices

In this work, thermometric measurements of gallium nitride-based ungated transistors on silicon-on-diamond composite substrates are performed. Their heat sink efficiency is compared with transistors made by standard technology on a silicon carbide substrates. Reducing of the surface temperature by more than 50oC using new type of silicon-on-diamond composite substrates at dissipation power above 7 W is shown. The proposed approach is promising for increasing the output power and reliability of gallium nitride-based devices. Keywords: gallium nitride, heat sink, diamond, dissipation power.

Изучение эффективности теплоотвода композитных подложек "кремний на алмазе" для устройств на основе нитрида галлия

In this work, thermometric measurements of gallium nitride-based ungated transistors on silicon-on-diamond composite substrates are performed. Their heat sink efficiency is compared with transistors made by standard technology on a silicon carbide substrates. Reducing of the surface temperature by more than 50°C using new type of silicon-on-diamond composite substrates at dissipation power above 7 W is shown. The proposed approach is promising for increasing the output power and reliability of gallium nitride-based devices.

P-Type Thin Film Transistor-Like Effects in Organic Light-Emitting Diodes Array: The Origin of Lateral Leakage

The presence of lateral leakage through organic semi-conductive layers in organic light-emitting diodes (OLEDs) array prevents excellent performance of display application especially in high resolution one. To mitigate the impact of lateral leakage and figure out the detailed mechanism, an accurate model involving simultaneous measurements of OLED and organic thin film transistor (OTFT) is proposed. The results establish that the lateral leakage generates to the adjacent off-state devices due to a p-type thin film transistor-like effects with the cathode playing a gate function. The proposed technique reveals that higher gate voltage and source voltage brings in more serious lateral leakage, corresponding to the electric field effect. It also shows a temperature dependence when the environment has changed. The research opens the possibility of considering the influences of semi-conductive layers and parallel structural devices on more self-luminous arrays for their actual application.

Charge transport in semiconducting carbon nanotube networks

Efficient and controlled charge transport in networks of semiconducting single-walled carbon nanotubes is the basis for their application in electronic devices, especially in field-effect transistors and thermoelectrics. The recent advances in selective growth, purification, and sorting of semiconducting and even monochiral carbon nanotubes have enabled field-effect transistors with high carrier mobilities and on/off current ratios that were impossible a few years ago. They have also allowed researchers to examine the microscopic interplay of parameters such as nanotube length, density, diameter distribution, carrier density, intentional and unintentional defects, dielectric environment, etc., and their impact on the macroscopic charge transport properties in a rational and reproducible manner. This review discusses various models that are considered for charge transport in nanotube networks and the experimental methods to characterize and investigate transport beyond simple conductivity or transistor measurements. Static and dynamic absorption, photoluminescence and electroluminescence spectroscopy, as well as scanning probe techniques (e.g., conductive atomic force microscopy, Kelvin probe force microscopy), and their unique insights in the distribution of charge carriers in a given nanotube network and the resulting current pathways will be introduced. Finally, recommendations for further optimization of nanotube network devices and a list of remaining challenges are provided.

Radiation-hardened property of single-walled carbon nanotube film-based field-effect transistors under low-energy proton irradiation

Strong C–C bonds, nanoscale cross-section and low atomic number make single-walled carbon nanotubes (SWCNTs) a potential candidate material for integrated circuits (ICs) applied in outer space. However, very little work combines the simulation calculations with the electrical measurements of SWCNT field-effect transistors (FETs), which limits further understanding on the mechanisms of radiation effects. Here, SWCNT film-based FETs were fabricated to explore the total ionizing dose (TID) and displacement damage effect on the electrical performance under low-energy proton irradiation with different fluences up to 1 × 1015 p/cm2. Large negative shift of the threshold voltage and obvious decrease of the on-state current verified the TID effect caused in the oxide layer. The stability of the subthreshold swing and the off-state current reveals that the displacement damage caused in the CNT layer is not serious, which proves that the CNT film is radiation-hardened. Specially, according to the simulation, we found the displacement damage caused by protons is different in the source/drain contact area and channel area, leading to varying degrees of change for the contact resistance and sheet resistance. Having analyzed the simulation results and electrical measurements, we explained the low-energy proton irradiation mechanism of the CNT FETs, which is essential for the construction of radiation-hardened CNT film-based ICs for aircrafts.

A Study on the Effect of Base‐Reactant in Low‐Temperature Atomic Layer Deposition of Zinc Oxide

During the low‐temperature atomic layer deposition (ALD) process, residual carbon from the unreacted ligand of precursors causes deterioration in the properties of grown materials. Herein, a simple approach using a base solution as a reactant to reduce residual carbon and improve the low‐temperature ALD reaction is proposed. NaOH dissolved in H2O is used as the reactant base solution and diethyl zinc is used as a reactant. The effects of the base‐reactant on the ZnO film growth are analyzed using X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), photoluminescence (PL), and thin‐film transistor (TFT) measurements. The crystallinity, grain size, and Zn and O contents of the ZnO thin films gradually increased as the concentration of NaOH increased (0, 10, 20, and 30 wt%). Residual carbon occupying Zn sites is reduced as NaOH concentrations increased. The unintended heavily doped state induced by the residual carbon during the low‐temperature ALD process is improved, and the ZnO TFT device fabricated with the NaOH/H2O solution also shows improvements in its field‐effect mobility and the on/off current ratio. This simple approach, using the base solution as the reactant during the low‐temperature ALD process, effectively improves the quality of the grown film with low carbon impurities.

Noise Performance and Thermalization of a Single Electron Transistor using Quantum Fluids

We report on low-temperature noise measurements of a single electron transistor (SET) immersed in superfluid 4He. The device acts as a charge sensitive electrometer able to detect the fluctuations of charged defects in close proximity to the SET. In particular, we measure telegraph switching of the electric current through the device originating from a strongly coupled individual two-level fluctuator. By embedding the device in a superfluid helium immersion cell, we are able to systematically control the thermalizing environment surrounding the SET and investigate the effect of the superfluid on the SET noise performance. We find that the presence of superfluid 4He can strongly suppress the switching rate of the defect by cooling the surrounding phonon bath.

Synthesis of 5‐Azatetracene and Comparison of Its Optical and Electrochemical Properties with Tetracene

AbstractA four‐step route for the synthesis of 5‐azatetracene (benzo[b]acridine) has been developed, employing a base‐catalysed Friedlander condensation reaction between 3‐amino‐2‐napthaldehyde and cyclohexanone as the key step followed by dehydrogenation of the intermediate. The optical and electrochemical properties of the 5‐azatetracene were investigated by UV‐vis and photoluminescence spectroscopy, and by cyclic voltammetry and compared with those of tetracene. It is found that 5‐azatetracene shows broader absorption in the visible region than tetracene, exhibits a higher luminescence quantum efficiency, and possesses a lower‐lying LUMO level and smaller HOMO‐LUMO band gap. Time‐resolved PL spectroscopy was used to elucidate the reasons for the more efficient luminescence of 5‐azatetracene. Field‐effect transistor measurements revealed the ambipolar nature of charge transport in 5‐azatetracene.

Toward Low-Temperature Solid-Source Synthesis of Monolayer MoS2

Two-dimensional (2D) semiconductors have been proposed for heterogeneous integration with existing silicon technology; however, their chemical vapor deposition (CVD) growth temperatures are often too high. Here, we demonstrate direct CVD solid-source precursor synthesis of continuous monolayer (1L) MoS2 films at 560 °C in 50 min, within the 450-to-600 °C, 2 h thermal budget window required for back-end-of-the-line compatibility with modern silicon technology. Transistor measurements reveal on-state current up to ∼140 μA/μm at 1 V drain-to-source voltage for 100 nm channel lengths, the highest reported to date for 1L MoS2 grown below 600 °C using solid-source precursors. The effective mobility from transfer length method test structures is 29 ± 5 cm2 V-1 s-1 at 6.1 × 1012 cm-2 electron density, which is comparable to mobilities reported from films grown at higher temperatures. The results of this work provide a path toward the realization of high-quality, thermal-budget-compatible 2D semiconductors for heterogeneous integration with silicon manufacturing.

Correlating Charge Transport Properties of Conjugated Polymers in Solution Aggregates and Thin‐Film Aggregates

AbstractThe role of solution aggregates on the charge transport process of conjugated polymers in electronic devices has gained increasing attention; however, the correlation of the charge carrier mobilities between the solution aggregates and the solid‐state films remains elusive. Herein, three polymers, FBDOPV‐2T, FBDOPV‐2F2T, and FBDOPV‐4F2T, are designed and synthesized with distinct aggregation behavior in solution. By combining contact‐free ultrafast terahertz (THz) spectroscopy and field‐effect transistor measurements, we track the charge carrier mobility of the aggregates of these polymers from the solution to the thin‐film state. Remarkably, the mobility of these three polymers is found to follow nearly the same trend (FBDOPV‐2T>FBDOPV‐2F2T≫FBDOPV‐4F2T) in both solutions and thin‐film states. The quantitative mobility correlation indicates that the charge transport properties of solution aggregates play a critical role in determining the thin‐film charge transport properties and final device performance. Our results highlight the importance of investigating and controlling solution aggregation structures towards efficient organic electronic devices.

Correlating Charge Transport Properties of Conjugated Polymers in Solution Aggregates and Thin-Film Aggregates.

The role of solution aggregates on the charge transport process of conjugated polymers in electronic devices has gained increasing attention; however, the correlation of the charge carrier mobilities between the solution aggregates and the solid-state films remains elusive. Herein, three polymers, FBDOPV-2T, FBDOPV-2F2T, and FBDOPV-4F2T, are designed and synthesized with distinct aggregation behavior in solution. By combining contact-free ultrafast terahertz (THz) spectroscopy and field-effect transistor measurements, we track the charge carrier mobility of the aggregates of these polymers from the solution to the thin-film state. Remarkably, the mobility of these three polymers is found to follow nearly the same trend (FBDOPV-2T>FBDOPV-2F2T≫FBDOPV-4F2T) in both solutions and thin-film states. The quantitative mobility correlation indicates that the charge transport properties of solution aggregates play a critical role in determining the thin-film charge transport properties and final device performance. Our results highlight the importance of investigating and controlling solution aggregation structures towards efficient organic electronic devices.

Charge Carrier Mobility in Organic Mixed Ionic–Electronic Conductors by the Electrolyte‐Gated van der Pauw Method

AbstractOrganic mixed ionic–electronic conductors (OMIECs) combine electronic semiconductor functionality with ionic conductivity, biocompatibility, and electrochemical stability in water and are currently investigated as the active material in devices for bioelectronics, neuromorphic computing, as well as energy conversion and storage. Operation speed of such devices depends on fast electronic transport in OMIECs. However, due to contact resistance problems, reliable measurements of electronic mobility are difficult to achieve in this class of materials. To address the problem, the electrolyte‐gated van der Pauw (EgVDP) method is introduced for the simple and accurate determination of the electrical characteristics of OMIEC thin films, independent of contact effects. The technique is applied to the most widespread OMIEC blend, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS). By comparing with organic electrochemical transistor (OECT) measurements, it is found that gate voltage dependent contact resistance effects lead to systematic errors in OECT based transport characterization. These observations confirm that a contact‐independent technique is crucial for the proper characterization of OMIECs, and the EgVDP method reveals to be a simple, elegant, but effective technique for this scope.

Electrochemical p-Doping of CsPbBr3 Perovskite Nanocrystals.

Lead halide perovskite nanocrystals have drawn attention as active light-absorbing or -emitting materials for opto-electronic applications due to their facile synthesis, intrinsic defect tolerance, and color-pure emission ranging over the entire visible spectrum. To optimize their application in, e.g., solar cells and light-emitting diodes, it is desirable to gain control over electronic doping of these materials. However, predominantly due to the intrinsic instability of perovskites, successful electronic doping has remained elusive. Using spectro-electrochemistry and electrochemical transistor measurements, we demonstrate here that CsPbBr3 nanocrystals can be successfully and reversibly p-doped via electrochemical hole injection. From an applied potential of ∼0.9 V vs NHE, the emission quenches, the band edge absorbance bleaches, and the electronic conductivity quickly increases, demonstrating the successful injection of holes into the valence band of the CsPbBr3 nanocrystals.

Electrochemically functionalized single-walled carbon nanotubes for ultrasensitive detection of BTEX vapors

Single-walled carbon nanotubes (SWNTs) have been functionalized electrochemically with porphyrin and were employed as the channel to fabricate the chemical field-effect transistor. Tetraphenylporphyrin was chosen for functionalization purpose. The primary aim of this study was to evaluate the sensing performance of functionalized SWNTs for the detection of BTEX vapor and to understand the underlying mechanism for the detection. The functionalization showed a significant enhancement in the sensing response for all analytes starting from 1.25 ppm to 15 ppm of concentration. A sub-ppm limit of detection was also observed. The systematic study of field effect transistor (FET) measurements indicates that the sensing mechanism is dominated by the electrostatic gating effect.

Charge Transport in Networks of sp3-Functionalized Single-Walled Carbon Nanotubes

The controlled introduction of luminescent sp3 defects into semiconducting single-walled carbon nanotubes (SWCNTs) leads to narrowband, tunable emission in the near-infrared and increases their photoluminescence (PL) quantum yield for potential optoelectronic applications [ACS Nano 2019, 13, 9259]. While the spectroscopic properties of sp3-functionalized SWCNTs are already well-established, a detailed understanding of the impact of functionalization on their electrical performance especially in a network is still lacking. Here, we investigate charge transport in ambipolar, light-emitting field-effect transistors based on networks of pristine and sp3-functionalized (6,5) SWCNTs. While both hole and electron mobilities decrease with increasing degree of functionalization, the transistors remain fully operational, showing electroluminescence from the defect states. Charge-modulated PL spectroscopy, which exclusively probes the mobile charge carriers in SWCNT networks [ACS Nano 2020, 14, 2412], confirms that the defects are efficiently sampled by mobile carriers and consequently, sp3-functionalized SWCNTs actively participate in the charge transport within the network. Temperature-dependent transport measurements of transistors combined with ultrafast photoconductivity dynamics of individually dispersed SWCNTs measured by optical-pump THz-probe spectroscopy provide further insights into the impact of sp3-functionalization on charge transport within a single nanotube and within a network.

Performance comparison of RF energy harvesting rectifiers designed in CMOS FDSOI 28 nm with dynamic back gate biasing and BiCMOS 55 nm technology

AbstractA comparison between two Dickson voltage multipliers realized in two technologies, fully depleted silicon on insulator (FDSOI) 28 nm and Bipolar CMOS (BiCMOS) 55 nm is presented. The assessment is based on the I–V characteristics measurements of transistors configured as diodes; and on the measurements of one and two stages of Dickson multipliers designed for RF energy harvesting. The I–V characteristics show that FDSOI technology is profitable owing to its smaller threshold voltage (Vth), and a leakage current less than that of BiCMOS. Consequently, for the same input voltage, the output voltage acquired in FDSOI is greater than that achieved with BiCMOS. Moreover, for rectifiers designed in FDSOI, a dynamic back gate bias could be employed to enhance the performance by adjusting dynamically the Vth and the leakage current.

On the Application of Junctionless Nanowire Transistors in Basic Analog Building Blocks

In this work an evaluation of analog building blocks using junctionless nanowire transistors is presented. This analysis has been carried out through experimental measurements of junctionless nMOS transistors configured as two amplifier stages composed by single transistors, namely the common-source and the common-drain amplifiers. The performance of junctionless devices is evaluated as a function of channel length, nanowire width, doping concentration and bias condition, taking as figures of merit the voltage gain, linearity and, in the case of the common drain amplifier, the input voltage range. The obtained results indicate that these two basic analog blocks can be benefitted by the use of junctionless devices, providing nearly ideal voltage gain when configured as common-drain amplifier, and improvement on voltage gain and linearity with device narrowing in the case of the common-source amplifier.

Evidence of band filling in PbS colloidal quantum dot square superstructures.

PbS square superstructures are formed by the oriented assembly of PbS quantum dots (QDs), reflecting the facet structures of each QD. In the square assembly, the quantum dots are highly oriented, in sharp contrast to the conventional hexagonal QD assemblies, in which the orientation of QDs is highly disordered, and each QD is connected through ligand molecules. Here, we measured the transport properties of the oriented assembly of PbS square superstructures. The combined electrochemical doping studies by electric double layer transistor (EDLT) and spectroelectrochemistry showed that more than fourteen electrons per quantum dot are introduced. Furthermore, we proved that the lowest conduction band is formed by the quasi-fourth degenerate quantized (1Se) level in the PbS QD square superstructures.

Improved measurement techniques for high-power transistor modeling.

Measurement for modeling of the high-power transistors is difficult due to its high-power and low-impedance characteristics. In this paper, novel methods and devices were designed and applied to achieve precise measurements of the high-power transistors. Fixtures capable of withstanding high voltage and current were designed to replace traditional radio frequency (RF) probes for higher power capacity. To reduce the impact of capacitive and inductive components of traditional bias tees on the rising/falling edge, two wideband 90° hybrid couplers that were connected back-to-back were designed for pulsed measurements. The measurement system of stable S-parameters with the Vector Network Analyzer (VNA) was reported, which could protect the devices and laboratory equipment from damage of self-oscillation. Application of several innovative approaches enabled accurate I-V characteristic and S-parameters measurements of high-power transistors in DC or pulsed mode. Experimental results of a 30 W gallium nitride high-electron-mobility transistor verified the validity.