N-channel Transistors Research Articles

Measurements of the field-effect electron mobility of the acceptor ITIC

We report on the fabrication and characterization of organic field-effect transistors using the small molecule electron acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis (4-hexylphenyl)-dithieno [2,3-d:2′,3′-d’]-s-indaceno [1,2-b:5,6-b’]dithiophene (ITIC). These experiments carried out in unipolar n-channel transistors yield an average field-effect electron mobility value of 1.4 × 10−2 cm2/Vs.

High-Performance Visible-Blind UV Phototransistors Based on n-Type Naphthalene Diimide Nanomaterials.

This study investigates the performance of single-crystalline nanomaterials of wide-band gap naphthalene diimide (NDI) derivatives with methylene-bridged aromatic side chains. Such materials are found to be easily used as high-performance, visible-blind near-UV light detectors. NDI single-crystalline nanoribbons are assembled using a simple solution-based process (without solvent-inclusion problems), which is then applied to organic phototransistors (OPTs). Such OPTs exhibit excellent n-channel transistor characteristics, including an average electron mobility of 1.7 cm2 V-1 s-1, sensitive UV detection properties with a detection limit of ∼1 μW cm-2, millisecond-level responses, and detectivity as high as 1015 Jones, demonstrating the highly sensitive organic visible-blind UV detectors. The high performance of our OPTs originates from the large face-to-face π-π stacking area between the NDI semiconducting cores, which is facilitated by methylene-bridged aromatic side chains. Interestingly, NDI-based nanoribbon OPTs exhibit a distinct visible-blind near-UV detection with an identical detection limit, even under intense visible light illumination (for example, 104 times higher intensity than UV light intensity). Our findings demonstrate that wide-band gap NDI-based nanomaterials are highly promising for developing high-performance visible-blind UV photodetectors. Such photodetectors could potentially be used for various applications including environmental and health-monitoring systems.

Direct observation of inversion capacitance in p-type diamond MOS capacitors with an electron injection layer

The electrical properties of Al2O3/p-type diamond (111) MOS capacitors were studied with the goal of furthering diamond-based semiconductor research. To confirm the formation of an inversion layer in the p-type diamond body, an n-type layer for use as a minority carrier injection layer was selectively deposited onto p-type diamond. To form the diamond MOS capacitors, Al2O3 was deposited onto OH-terminated diamond using atomic layer deposition. The MOS capacitor showed clear inversion capacitance at 10 Hz. The minority carrier injection from the n-type layer reached the inversion n-channel diamond MOS field-effect transistor (MOSFET). Using the high-low frequency capacitance method, the interface state density, Dit, within an energy range of 0.1–0.5 eV from the valence band edge energy, Ev, was estimated at (4–9) × 1012 cm−2 eV−1. However, the high Dit near Ev remains an obstacle to improving the field effect mobility for the inversion p-channel diamond MOSFET.

Photolithographically patterned N-channel organic thin film transistors using sensitized polyvinyl alcohol

Abstract The fabrication of n-channel thin-film transistors N,N′-Ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13) using conventional photolithography has been demonstrated. Sensitized polyvinyl-alcohol (PVA) was spin coated on top of the organic semiconductor (OSC) film followed by UV exposure and reactive ion etching in oxygen to form the desired active channels. The highest mobility obtained was 1.65 cm2/Vs for these photolithographically patterned devices with on-to-off current ratio of greater than 106. The electronic performances of these devices were comparable to the ones fabricated using stencil mask. These devices were also put under bias stressed in the linear regime where the drain current decayed as a function of time. This patterning method indicates that we are a step closer to the realization of a high performance large-scale fabrication of organic complementary metal-oxide-semiconductor (O-CMOS) circuits.

Impact of bulky phenylalkyl substituents on the air-stable n-channel transistors of birhodanine analogues.

By introducing bulky 2-phenylethyl groups into sulfur-rich electron acceptors, 5,5′-bithiazolidinylidene-2,2′-dione-4,4′-dithione and 5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathione, electron transport with the mobility of 0.27 cm2 V−1 s−1 with ambient and long-term stability is achieved in thin-film transistors. Bulky groups destroy the intermolecular S–S network, but the long-term transistor stability is maintained. Here, benzyl groups realize one-dimensional stacking structures, whereas 2-phenylethyl groups lead to herringbone structures.

A Low-Power and In Situ Annealing Technique for the Recovery of Active Devices After Proton Irradiation

In this paper, we study the recovery of onmembrane semiconductor components, such as N-type Field-Effect Transistors (FETs) available in two different channel widths and a Complementary Metal-Oxide-Semiconductor (CMOS) inverter, after the exposure to high dose of proton radiation. Due to the ionizing effect, the electrical characteristics of the components established remarkable shifts, where the threshold voltages showed an average shift of -480 mV and -280 mV respectively for 6 μm and 24 μm N-channel transistors, likewise the inversion point of the inverter showed an important shift of -690 mV. The recovery concept is based mainly on a micro-hotplate, fabricated with backside MEMS micromachining structure and a Silicon-On-Insulator (SOI) technology, ensuring rapid, low power and in situ annealing technique, this method proved its reliability in recent works. Annealing the N-channel transistors and the inverter for 16 min with a temperature of the heater up to 385 °C, guaranteed a partial recovery of the semiconductor based components with a maximum power consumption of 66 mW.

Hydrogen Sensing Characteristics of AlGaInP/InGaAs Complementary Co-Integrated Pseudomorphic Doping-Channel Field-Effect Transistors

In this article, the hydrogen sensing device and logic characteristics of the Al0.25Ga0.25In0.5P/In0.1Ga0.9As complementary co-integrated pseudomorphic doping-channel field-effect transistors are demonstrated. Due to the existence of a relatively large conduction (valence) band discontinuity at Al0.25Ga0.25In0.5P/In0.1Ga0.9As heterojunction and the employment of a small energy-gap In0.1Ga0.9As channel layer, it could provide a high gate barrier height to avoid electrons (holes) injection form channel into gate region in the studied n-channel (p-channel) device. With respect to the n-channel (p-channel) transistor under hydrogen ambient, hydrogen molecules are adsorbed and dissociated on the Pd catalytic metal surface, followed by rapid diffusion of hydrogen atoms into the MS interface where the dipoles are formed to lower (elevate) the gate barrier height and enhance (decrease) the drain current. In the n-channel (p-channel) device, the threshold voltages at drain current of 0.1 mA/mm are of 0.67 (0.05) and 0.38 (−0.26) V in air and at hydrogen concentration of 9800 ppm, respectively. As hydrogen is detected, the characteristics of inverters shift left obviously, and the VOH and VIH values are decreased.

Roll-to-Roll Production of Layer-Controlled Molybdenum Disulfide: A Platform for 2D Semiconductor-Based Industrial Applications.

A facile methodology for the large-scale production of layer-controlled MoS2 layers on an inexpensive substrate involving a simple coating of single source precursor with subsequent roll-to-roll-based thermal decomposition is developed. The resulting 50 cm long MoS2 layers synthesized on Ni foils possess excellent long-range uniformity and optimum stoichiometry. Moreover, this methodology is promising because it enables simple control of the number of MoS2 layers by simply adjusting the concentration of (NH4 )2 MoS4 . Additionally, the capability of the MoS2 for practical applications in electronic/optoelectronic devices and catalysts for hydrogen evolution reaction is verified. The MoS2 -based field effect transistors exhibit unipolar n-channel transistor behavior with electron mobility of 0.6 cm2 V-1 s-1 and an on-off ratio of ≈10³. The MoS2 -based visible-light photodetectors are fabricated in order to evaluate their photoelectrical properties, obtaining an 100% yield for active devices with significant photocurrents and extracted photoresponsivity of ≈22 mA W-1 . Moreover, the MoS2 layers on Ni foils exhibit applicable catalytic activity with observed overpotential of ≈165 mV and a Tafel slope of 133 mV dec-1 . Based on these results, it is envisaged that the cost-effective methodology will trigger actual industrial applications, as well as novel research related to 2D semiconductor-based multifaceted applications.

Low-temperature (330 °C) crystallization and dopant activation of Ge thin films via AgSb-induced layer exchange: Operation of an n-channel polycrystalline Ge thin-film transistor

Ge thin films have been prepared by layer-exchange metal-induced crystallization using AgSb alloy as a catalyst. Not only the crystallization of Ge, but also the incorporation of Sb atoms into the crystalline Ge layer and their activation have been realized during the process at a temperature as low as 330 °C. Thin-film transistors have been fabricated using the Ge thin films as channel layers and the operation of an n-channel transistor with an on/off ratio of over 300 has been demonstrated.

Electron energy dissipation model of gate dielectric progressive breakdown in n- and p-channel field effect transistors

We report the data and a model showing that the energy loss experienced by the carriers flowing through breakdown spots is the primary cause of progressive breakdown spot growth. The experiments are performed in gate dielectrics of metal-oxide-semiconductor (MOS) devices subjected to accelerated high electric field constant voltage stress under inversion conditions. The model is analytical and contains few free parameters of clear physical meaning. This is compared to a large set of data on breakdown transients at various oxide thicknesses, stress voltages, and temperatures, both in cases of n-channel and p-channel transistors and polycrystalline Si/oxynitride/Si and metal gate/high k dielectric/Si gate stacks. The basic idea is that the breakdown transient is due to the growth of one or more filaments in the dielectric promoted by electromigration driven by the energy lost by the electrons traveling through the breakdown spots. Both cases of polycrystalline Si/oxynitride/Si and metal gate/high-k dielectric/Si MOS structures are investigated. The best fit values of the model to the data, reported and discussed in the paper, consistently describe a large set of data. The case of simultaneous growth of multiple progressive breakdown spots in the same device is also discussed in detail.

High-mobility air-stable n-type field-effect transistors based on large-area solution-processed organic single-crystal arrays

Solution-processed n-type organic semiconductor micro/nanocrystals (OSMCs) are fundamental elements for developing low-cost, large-area, and all organic logic/complementary circuits. However, the development of air-stable, highly aligned n-channel OSMC arrays for realizing high-performance devices lags far behind their p-channel counterparts. Herein, we present a simple one-step slope-coating method for the large-scale, solution-processed fabrication of highly aligned, air-stable, n-channel ribbon-shaped single-crystalline N,N′-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) arrays. The slope and patterned photoresist (PR) stripes on the substrate are found to be crucial for the formation of large-area submicron ribbon arrays. The width and thickness of the BPE-PTCDI submicron ribbons can be finely tuned by controlling the solution concentration as well as the slope angle. The resulting BPE-PTCDI submicron ribbon arrays possess an optimum electron mobility up to 2.67 cm2·V–1·s–1 (with an average mobility of 1.13 cm2·V–1·s–1), which is remarkably higher than that of thin film counterparts and better than the performance reported previously for single-crystalline BPE-PTCDI-based devices. Moreover, the devices exhibit robust air stability and remain stable after exposing in air over 50 days. Our study facilitates the development of air-stable, n-channel organic field-effect transistors (OFETs) and paves the way towards the fabrication of high-performance, organic single crystal-based integrated circuits.

Graphene electrode with tunable charge transport in thin-film transistors

Graphene, a single atomic layer of sp2-hybridized carbon, has immense potential as a transparent conducting material in electronic applications owing to its superior properties, including optical transparency and high conductivity. Particularly, the tunable work function of graphene enables the integration of graphene electrodes with various electronic devices. To achieve high performance in graphene-based devices, effective charge transport between the graphene electrode and the semiconducting material needs to be optimized; this is closely related to the modulation of the Schottky barrier (SB). In this study, we investigate the tunable charge transport properties as a function of graphene doping in n-channel thin-film transistors (TFTs) in terms of the electrical characteristics and low-frequency noise (LFN) behaviors. Alkali metal carbonates tuned the work function of graphene, resulting in a dramatic decrease in the SB and an improvement of the carrier injection in n-channel TFTs. The electrical performance of the TFTs was evaluated by extraction of the field-effect mobilities and ratio of contact resistance to total resistance. Furthermore, the level of contact noise created by the barrier height fluctuation and relative contribution of channel noise and contact noise in the TFTs was investigated by LFN measurements to demonstrate the tunable charge transport. Our findings therefore provide new insights into the tunable charge transport mechanism in graphene-based devices and reveal the immense potential of graphene as electrodes in high performance flexible and transparent displays.

Investigation of Threshold Voltage Shift in Gamma Irradiated N-Channel and P-Channel MOS Transistors of CD4007

Investigation of Threshold Voltage Shift in Gamma Irradiated N-Channel and P-Channel MOS Transistors of CD4007

Influences of silicon-rich shallow trench isolation on total ionizing dose hardening and gate oxide integrity in a 130 nm partially depleted SOI CMOS technology

The influences of silicon-rich shallow trench isolation (STI) on total ionizing dose (TID) hardening and gate oxide integrity (GOI) in a 130nm partially depleted silicon-on-insulator (SOI) complementary metal-oxide semiconductor (CMOS) technology are investigated. Radiation-induced charges buildup in STI oxide can invert the parasitic sidewall channel of the n-channel transistor, which will increase the off-state leakage current and decrease the threshold voltage for the main transistor. Compared with the general STI process, the silicon-rich STI process can significantly suppress the increase in leakage current and negative shifts in subthreshold region induced by the total dose radiation, implying TID hardening for STI trench oxide. However, the silicon-rich STI process has a deleterious impact on GOI. It leads to the thin gate oxide thickness at trench corner and lowers the gate oxide breakdown voltage. Issues of gate oxide integrity induced by silicon-rich STI are investigated in this paper, and an optimized process to solve this problem is proposed and examined. Finally, the TID response of the optimized silicon-rich STI process is presented in comparison to the general and silicon-rich STI processes.

Floating Gate Nonvolatile Memory Using Individually Cladded Monodispersed Quantum Dots

This paper presents nonvolatile memory characteristics of a quantum dot gate floating gate nonvolatile memory (QDNVM) that employs SiOx-cladded silicon quantum dots as discrete charge storage nodes of the floating gate. The cladding of Si quantum dots and control of their size are shown to result in a faster access and improved retention time. The floating gate is formed by site-specific self-assembly of SiOx-Si quantum dots on the tunnel oxide layer over the p-region between source and drain of an n-channel field-effect transistor (FET). Experimental data on fabricated long channel devices show threshold voltage shift as a function of duration and magnitude of the electrical stress applied during the “Write” operation. Current–voltage characteristics ( $I_{\mathrm {D}}$ – $V_{\mathrm {D}}$ and $I_{D}$ – $V_{G})$ are presented before and after stress. The electrical characteristics are explained using a quantum dot gate FET model which includes the threshold voltage shift ( $\Delta \text{V}_{\mathrm { {TH}}})$ as a function of charge on the floating gate quantum dots due to applied electrical stress.

In-situ thermal annealing of on-membrane silicon-on-insulator semiconductor-based devices after high gamma dose irradiation

In this paper, we investigate the recovery of some semiconductor-based components, such as N/P-type field-effect transistors (FETs) and a complementary metal–oxide–semiconductor (CMOS) inverter, after being exposed to a high total dose of gamma ray radiation. The employed method consists mainly of a rapid, low power and in situ annealing mitigation technique by silicon-on-insulator micro-hotplates. Due to the ionizing effect of the gamma irradiation, the threshold voltages showed an average shift of −580 mV for N-channel transistors, and −360 mV for P-MOSFETs. A 4 min double-cycle annealing of components with a heater temperature up to 465 °C, corresponding to a maximum power of 38 mW, ensured partial recovery but was not sufficient for full recovery. The degradation was completely recovered after the use of a built-in high temperature annealing process, up to 975 °C for 8 min corresponding to a maximum power of 112 mW, which restored the normal operating characteristics for all devices after their irradiation.

A reliable and controllable graphene doping method compatible with current CMOS technology and the demonstration of its device applications

The modulation of charge carrier concentration allows us to tune the Fermi level (EF) of graphene thanks to the low electronic density of states near the EF. The introduced metal oxide thin films as well as the modified transfer process can elaborately maneuver the amounts of charge carrier concentration in graphene. The self-encapsulation provides a solution to overcome the stability issues of metal oxide hole dopants. We have manipulated systematic graphene p-n junction structures for electronic or photonic application-compatible doping methods with current semiconducting process technology. We have demonstrated the anticipated transport properties on the designed heterojunction devices with non-destructive doping methods. This mitigates the device architecture limitation imposed in previously known doping methods. Furthermore, we employed EF-modulated graphene source/drain (S/D) electrodes in a low dimensional transition metal dichalcogenide field effect transistor (TMDFET). We have succeeded in fulfilling n-type, ambipolar, or p-type field effect transistors (FETs) by moving around only the graphene work function. Besides, the graphene/transition metal dichalcogenide (TMD) junction in either both p- and n-type transistor reveals linear voltage dependence with the enhanced contact resistance. We accomplished the complete conversion of p-/n-channel transistors with S/D tunable electrodes. The EF modulation using metal oxide facilitates graphene to access state-of-the-art complimentary-metal-oxide-semiconductor (CMOS) technology.

Modulation-Doped In2 O3 /ZnO Heterojunction Transistors Processed from Solution.

This paper reports the controlled growth of atomically sharp In2 O3 /ZnO and In2 O3 /Li-doped ZnO (In2 O3 /Li-ZnO) heterojunctions via spin-coating at 200 °C and assesses their application in n-channel thin-film transistors (TFTs). It is shown that addition of Li in ZnO leads to n-type doping and allows for the accurate tuning of its Fermi energy. In the case of In2 O3 /ZnO heterojunctions, presence of the n-doped ZnO layer results in an increased amount of electrons being transferred from its conduction band minimum to that of In2 O3 over the interface, in a process similar to modulation doping. Electrical characterization reveals the profound impact of the presence of the n-doped ZnO layer on the charge transport properties of the isotype In2 O3 /Li-ZnO heterojunctions as well as on the operating characteristics of the resulting TFTs. By judicious optimization of the In2 O3 /Li-ZnO interface microstructure, and Li concentration, significant enhancement in both the electron mobility and TFT bias stability is demonstrated.

Enhanced performance of field-effect transistors based on C60 single crystals with conjugated polyelectrolyte

Contact resistance at the interface between metal electrodes and semiconductors can significantly limit the performance of organic field-effect transistors, leading to a distinct voltage drop at the interface. Here, we demonstrate enhanced performance of n-channel field-effect transistors based on solution-grown C60 single-crystalline ribbons by introducing an interlayer of a conjugated polyelectrolyte (CPE) composed of poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN+Br−). The PFN+Br− interlayer greatly improves the charge injection. Consequently, the electron mobility is promoted up to 5.60 cm2 V−1 s−1 and the threshold voltage decreased dramatically with the minimum of 4.90 V.

Efficient Color-Stable Inverted White Organic Light-Emitting Diodes with Outcoupling-Enhanced ZnO Layer

Inverted organic light-emitting diode (OLED) has attracted extensive attention due to the demand in active-matrix OLED display panels as its geometry enables the direct connection with n-channel transistor backplane on the substrate. One key challenge of high-performance inverted OLED is an efficient electron-injection layer with superior electrical and optical properties to match the indium tin oxide cathode on substrate. We here propose a synergistic electron-injection architecture using surface modification of ZnO layer to simultaneously promote electron injection into organic emitter and enhance out-coupling of waveguided light. An efficient inverted white OLED is realized by introducing the nanoimprinted aperiodic nanostructure of ZnO for broadband and angle-independent light out-coupling and inserting an n-type doped interlayer for energy level tuning and injection barrier lowering. As a result, the optimized inverted white OLEDs have an external quantum efficiency of 42.4% and a power efficiency of 85.4 lm W1-, which are accompanied by the superiority of angular color stability over the visible wavelength range. Our results may inspire a promising approach to fabricate high-efficiency inverted OLEDs for large-scale display panels.