Properties Of Field-effect Transistors Research Articles

Organic/inorganic interfaced field-effect transistor properties with a novel organic semiconducting material

A novel 1,3,4-oxadiazole-substituted benzo[b]triphenylene was synthesized by three-step synthetic procedure and OFET device design was successfully designed after theoretical calculations made using Gaussian software. For investigating the field-effect properties of designed organic electronic device, a SiO2 (300 nm) was thermally grown on p-Si wafer at 1000 °C as a dielectric layer and gate, source and drain contacts have been deposited using Au metal with physical vapour deposition. 1,3,4-Oxadiazole-substituted benzo[b]triphenylene was spin coated on the source and drain electrodes of our device, forming organic/inorganic interfaced field-effect transistors. Surface morphology and thin film properties were investigated using AFM. All electrical measurements were done in air ambient. The device showed a typical p-type channel behaviour with increasing negative gate bias voltage values. Our results have surprisingly shown that the saturation regime of this device has high mobility (μFET), excellent on/off ratio (Ion/Ioff), high transconductance (gm) and a small threshold voltage (VTh). The values of μFET, Ion/Ioff, gm and VTh were found as 5.02 cm2/Vs, 0.7 × 103, 5.64 μS/mm and 1.37 V, respectively. These values show that our novel organic material could be a potential candidate for organic electronic device applications in the future.

Phosphonic acid self-assembled monolayer improved the properties of n-type organic field-effect transistors in air ambient

The electron mobilities of NDI-C14 based thin film transistors get a great improvement by vapor deposition on the surface of three SAMs modified SiO2 dielectric. This is associated with its close packing arrangement of NDI-C14 film on these SAMs.

Synthesis and field-effect transistor properties of a diseleno[3,2-b:2′,3′-d]silole-based donor–acceptor copolymer: investigation of chalcogen effect

We have designed and synthesized a tricyclic diseleno[3,2-b:2′,3′-d]silole (DSS) wherein the 3,3′-position of a biselenophene is bridged by a dioctylsilyl moiety.

Subthreshold slope as a measure of interfacial trap density in pentacene films

Electrical properties in organic field effect transistors (FETs) are dominated by charge transport in the accumulation layer, few molecular layers close to the gate dielectric. Through comparison of the subthreshold slope between monolayer (ML) and thick pentacene FETs, formation of the second layer islands on top of the complete first layer is found to be crucial in determining the charge transport in ML pentacene FETs. It is demonstrated that a pentacene ML field effect transistor (FET) is an excellent probe that can detect electronic states of organic semiconductors interfacing with the gate dielectric at nanometer scale. Far higher sub-threshold slope in ML FETs, as a measure of interfacial charge trap density, than that in thick pentacene FETs is translated that the path of the induced carriers in ML FETs is limited into the molecular layer interfacing with the gate dielectric with a high density of charge traps, while carriers in thicker films have alternative pathways through more electrically conductive layer above the first layer with much less trap density.

Pyrene Derivate Functionalized with Acetylene for Organic Field Effect Transistors

A new X-shaped compound (SiPy) functionalized with acetylene bonds in the 1-, 3-, 6-, and 8-positions of the pyrene core has been synthesized by Sonogashira coupling reactions. Its photophysical, thermal, and organic field effect transistor (OFET) properties as well as the film morphologies have been investigated. SiPy exhibits high stability which is evidenced by thermal gravimetric analysis. The atomic force microscopy images reveal that the morphology of thin films depends on the substrate temperature. The film OFET devices based on SiPy were constructed and exhibited p-type performances.

Plasma treatment introduced memory properties in MoS2 field-effect transistors

We present a facile method to obtain MoS2-based nonvolatile memory field-effect transistors by oxygen plasma treatment on the MoS2 surface that is in contact with a dielectric. The oxygen plasma treatment provides a way of introducing deep defects into the MoS2 surface. Only those deep defects located at the semiconductor/dielectric interface can behave as charge trapping sites to develop the memory capability. No memory properties can be observed when the MoS2 surface far from the conductive channel was treated with oxygen plasma. This method brings promising advantages to MoS2-based memory devices obtained using a simple fabrication method and small device dimensions.

Tunable single hole regime of a silicon field effect transistor in standard CMOS technology

The electrical properties of a Single Hole Field Effect Transistor (SH-FET) based on CMOS technology are analyzed in a cryogenic environment. Few electron–hole Coulomb diamonds are observed using quantum transport spectroscopy measurements, down to the limit of single hole transport. Controlling the hole filling of the SH-FET is made possible by biasing the top gate, while the bulk contact is employed as a back gate that tunes the hole state coupling with the contacts and their distance from the interface. We compare the cryogenic Coulomb blockade regime with the room temperature regime, where the device operation is similar to that of a standard p-MOSFET.

Improvement of properties of an ambipolar organic field-effect transistor by using a singlet biradicaloid film

We have improved the properties of ambipolar organic field-effect transistors by chemically treating the source and drain electrodes with a vacuum-deposited biradicaloid film. Biradicaloid was a diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL). An alkane thiol self-assembled monolayer (SAM) was used as an insulator buffer layer at the Ph2-IDPL/electrode interface to prevent off-current. We confirmed the transport level alignment at the Ph2-IDPL/SAM/electrode interface by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. Although Ph2-IDPL transistors containing the SAM showed a higher on/off ratio or mobility than a previously reported device without the buffer layer, there was a trade-off between on/off ratio and mobility. Our results suggest that biradical molecules are promising candidates for use in low-power inverters.

Properties of Self-Aligned Short-Channel Graphene Field-Effect Transistors Based on Boron-Nitride-Dielectric Encapsulation and Edge Contacts

We present the characterization of ballistic graphene field-effect transistors (GFETs) with an effective oxide thickness of 3.5 nm. Graphene channels are fully encapsulated within hexagonal boron nitride, and self-aligned contacts are formed to the edge of the single-layer graphene. Devices of channel lengths (LG) down to 67 nm are fabricated, and a virtual-source transport model is used to model the resulting current-voltage characteristics. The mobility and source-injection velocity as a function of LG yields a mean-free-path, ballistic velocity, and effective mobility of 850 nm, 9.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s, and 13700 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, respectively, which are among the highest velocities and mobilities reported for GFETs. Despite these bestin-class attributes, these devices achieve transconductance (gm) and output conductance (gds) of only 600 and 300 μS/μm, respectively, due to the fundamental limitations of graphene's quantum capacitance and zero-bandgap. gm values, which are less than those of comparable ballistic silicon devices, benefit from the high ballistic velocity in graphene but are degraded by an effective gate capacitance reduced by the quantum capacitance. The gds values, which limit the effective power gain achievable in these devices, are significantly worse than comparable silicon devices due to the properties of the zero-bandgap graphene channel.

Metal to Insulator Quantum-Phase Transition in Few-Layered ReS₂.

In ReS2, a layer-independent direct band gap of 1.5 eV implies a potential for its use in optoelectronic applications. ReS2 crystallizes in the 1T'-structure, which leads to anisotropic physical properties and whose concomitant electronic structure might host a nontrivial topology. Here, we report an overall evaluation of the anisotropic Raman response and the transport properties of few-layered ReS2 field-effect transistors. We find that ReS2 exfoliated on SiO2 behaves as an n-type semiconductor with an intrinsic carrier mobility surpassing μ(i) ∼ 30 cm(2)/(V s) at T = 300 K, which increases up to ∼350 cm(2)/(V s) at 2 K. Semiconducting behavior is observed at low electron densities n, but at high values of n the resistivity decreases by a factor of >7 upon cooling to 2 K and displays a metallic T(2)-dependence. This suggests that the band structure of 1T'-ReS2 is quite susceptible to an electric field applied perpendicularly to the layers. The electric-field induced metallic state observed in transition metal dichalcogenides was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of T and n, we find that the metallic state of ReS2 results from a second-order metal-to-insulator transition driven by electronic correlations. This gate-induced metallic state offers an alternative to phase engineering for producing ohmic contacts and metallic interconnects in devices based on transition metal dichalcogenides.

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.

Effect of surfactant conjugation on structure and properties of poly(3-hexylthiophene) colloids and field effect transistors

Abstract In this work, aqueous suspensions of poly(3-hexylthiophene) (P3HT) colloids were fabricated using three different surfactants with varied degrees of conjugation. The morphology, crystalline structure and optical properties of these colloids were characterized by scanning electron microscopy, wide angle X-ray diffractometry and UV–vis spectrometry, respectively. Results indicated that the morphology and crystalline were similar for all the colloids, while the optical properties and aggregation could be tuned by surfactant conjugation. Increasing conjugation in surfactant corresponded to increased chain order, conjugation length, and red-shifted absorbance spectrum in P3HT colloids. Field effect transistors (FETs) made from these colloids showed a hole mobility on the order of 10 −3 cm 2 /Vs, also tunable by surfactant conjugation and comparable to FETs made from P3HT solution.

HfO2 dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids–Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id–Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-GFETs with different HfO2 dielectric thickness, the hole mobility shows a tendency of rise when the thickness decreases to 7 nm. The possible reason might be due to the introduced impurities into HfO2 film from atomic layer deposition process, the concentration of which varies from the thickness of HfO2 layer.

Pentacene organic ferroelectric transistors with [P(VDF-TrFE)] gate by Langmuir-Blodgett process

We report the fabrication and electrical properties of pentacene-based ferroelectric organic field-effect transistors (FeOFETs) with ultrathin poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] gate insulators. A ultrathin and uniform P(VDF-TrFE) film was successfully deposited by Langmuir-Blodgett (LB) deposition with well-defined ferroelectric microdomains at the interface between P(VDF-TrFE) films and pentacene active layers. The P(VDF-TrFE) films derived by LB deposition significantly enhance the crystallization of the upper pentacene channel films and thus the performance of our FeOFETs. Our FeOFET device achieves a threshold voltage shift of 8.56 V induced by ferroelectric polarization under different voltage sweeping directions and such enhancement indicates a great potential for future organic nonvolatile memory applications.

(Invited) Microscopic Studies of Black Phosphorus and Its Field-Effect Transistors

In this manuscript, we report atomic scale studies of electronic direct bandgap measurement of the puckered honeycomb structure of freshly cleaved black phosphorus using a high-resolution scanning tunneling spectroscopy (STS) survey. Through a combination of STM/S measurements and first-principles calculations, a model for edge reconstruction and the related edge states are also determined. Besides, we also investigate electrical transport and optoelectronic properties of field effect transistors (FETs) made from few-layer black phosphorus (BP) crystals down to a few nanometers. In particular, we explore the anisotropic nature and photocurrent generation mechanisms in BP FETs through spatial- and polarization-dependent photocurrent measurements. Our results reveal that the anisotropic feature primarily results from the directional-dependent absorption of BP crystals.

Fabrication of SWCNT-Graphene Field-Effect Transistors

Graphene and single-walled carbon nanotube (SWCNT) have been widely studied because of their extraordinary electrical, thermal, mechanical, and optical properties. This paper describes a novel and flexible method to fabricate all-carbon field-effect transistors (FETs). The fabrication process begins with assembling graphene grown by chemical vapor deposition (CVD) on a silicon chip with SiO2 as the dielectric layer and n-doped Si substrate as the gate. Next, an atomic force microscopy (AFM)-based mechanical cutting method is utilized to cut the graphene into interdigitated electrodes with nanogaps, which serve as the source and drain. Lastly, SWCNTs are assembled on the graphene interdigitated electrodes by dielectrophoresis to form the conductive channel. The electrical properties of the thus-fabricated SWCNT-graphene FETs are investigated and their FET behavior is confirmed. The current method effectively integrates SWCNTs and graphene in nanoelectronic devices, and presents a new method to build all-carbon electronic devices.

Quantitative analysis of the density of trap states at the semiconductor-dielectric interface in organic field-effect transistors

The electrical properties of organic field-effect transistors are governed by the quality of the constituting layers, and the resulting interfaces. We compare the properties of the same organic semiconductor film, 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene, with bottom SiO2 dielectric and top Cytop dielectric and find a 10× increase in charge carrier mobility, from 0.17 ± 0.19 cm2 V−1 s−1 to 1.5 ± 0.70 cm2 V−1 s−1, when the polymer dielectric is used. This results from a significant reduction of the trap density of states in the semiconductor band-gap, and a decrease in the contact resistance.

MoS&lt;sub&gt;2&lt;/sub&gt; Field-Effect Transistors With Lead Zirconate-Titanate Ferroelectric Gating

We report back gate field-effect transistors (FETs) with few-layered MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheet controlled by lead-zirconate-titanate (PZT) ferroelectric gating. The MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> transistors with PZT gating (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -PZT FETs) exhibit reproducible hysteresis and nonvolatile memory behaviors with high stability, which can be attributed to the polarization screening from interface adsorbates and charge dynamic trapping/detrapping into the interface defect states. The ON/OFF states ratios and memory windows have little change with the channel scaling from 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> to 200 nm, revealing the channel scaling has not obvious influence on MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -PZT FET properties, which suggests MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -PZT FET a promising candidate for future non-volatile memory applications.

Optoelectrical Molybdenum Disulfide (MoS2)--Ferroelectric Memories.

In this study, we fabricated and tested electronic and memory properties of field-effect transistors (FETs) based on monolayer or few-layer molybdenum disulfide (MoS2) on a lead zirconium titanate (Pb(Zr,Ti)O3, PZT) substrate that was used as a gate dielectric. MoS2-PZT FETs exhibit a large hysteresis of electronic transport with high ON/OFF ratios. We demonstrate that the interplay of polarization and interfacial phenomena strongly affects the electronic behavior and memory characteristics of MoS2-PZT FETs. We further demonstrate that MoS2-PZT memories have a number of advantages and unique features compared to their graphene-based counterparts as well as commercial ferroelectric random-access memories (FeRAMs), such as nondestructive data readout, low operation voltage, wide memory window and the possibility to write and erase them both electrically and optically. This dual optoelectrical operation of these memories can simplify the device architecture and offer additional practical functionalities, such as an instant optical erase of large data arrays that is unavailable for many conventional memories.

1D and 2D Bi Compounds in Field‐Effect Transistors

The properties of field-effect transistors (FETs) with single crystals of Bi compounds, Bi2CuO4 and LaOBiS2, are investigated using an electric-double-layer capacitor. The observation of FET characteristics due to electrostatic carrier accumulation is very significant for the field-induced control of physical properties of these crystals, which may produce the novel physical properties such as superconductivity.