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CuO grown by room-temperature direct current reactive magnetron sputtering is introduced to realize p-type thin-film transistors (TFTs) with a high-k HfO2 gate dielectric fabricated by atomic layer deposition. The devices work in an accumulation mode (AM) with two apparent threshold voltages corresponding to the formation of a buried channel and an accumulation layer, respectively. A CuO AM TFT with a channel length of 25 μm exhibit a competitive on-off ratio (Ion/Ioff) of 1.3 × 102, a subthreshold swing (SS) of 1.04 V dec−1, and a field-effect mobility (μFE) of 1.1 × 10−3 cm2 V−1 s−1 at room temperature. By measuring a CuO metal oxide semiconductor (MOS) capacitor at room temperature, a high acceptor doping density (NA) of ∼5 × 1017 cm−3, a high positive effective fixed surface charge density (Qf) of ∼9 × 1012 cm−2, and a low interfacial trap charge density (Dit) of ∼6 × 1010 eV−1 cm−2 at the HfO2/CuO interface are estimated. The μFE extracted from the accumulation regime appears lower than the Hall mobility measured for a similarly processed CuO layer on glass due to the increased hole concentration in CuO TFTs, compared to a Hall concentration of ∼1014 cm−3, following the MOS process. SS appears limited by the decreased channel to gate capacitance (Ccg) related to the buried channel in AM TFTs, parasitic capacitance to ground, and potentially very high interfacial traps at the non-passivated CuO/air interface. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskites have been widely studied in high-performance optoelectronic devices. Long-term stability is a key limitation to date in restricting their further development and commercial application. In general, interface properties between a semiconductor and an electrode highly affect device performance and stability. Herein, contact characteristics between the perovskite and electrode varying with illumination status have been first investigated. The results suggest that device's contact resistance (RC), obtained from a transfer length method, decreases as the incident light intensity increases. The RC under a higher irradiation intensity (1.26 mW/cm2) is about one-tenth of that at a lower density (0.08 mW/cm2). Simulation has been performed and shows a similar trend with experimental results. The interface physical model has been discussed based on an energy band theory. The band bending and barrier modulation at the interface under light illumination are originated from the surface states and the localized charges. This work explains the interface in determining device's fundamental properties, including stability, RC variation, and charge carrier transport process. It is significant in understanding the device working mechanism and providing a potential way for perovskite optoelectronic devices with enhanced stability and performance. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive backstepping sliding mode control method based on a nonlinear disturbance observer (NDO) to solve the problem that the tracking performance of the motion system of a permanent magnet spherical motor (PMSpM) is degraded due to the influence of external nonlinear disturbance. First, the dynamic model of the PMSpM under the compound interference is established. Second, an NDO and an adaptive backstepping sliding mode controller are designed to compensate for the external disturbances and modeling uncertainties, and the stability of the closed-loop system using the proposed method is confirmed through the Lyapunov theorem. Then, compared with the results of proportion differentiation control and conventional sliding mode control, the simulation results show that the proposed method can significantly reduce input signal chattering and improve the trajectory tracking performance of the PMSpM. Finally, experimental results are provided to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, negative transconductance (NTC) behavior in molybdenum disulfides (MoS2) field effect transistors (FETs) is investigated. Combining experimental observation and numerical analysis, we demonstrate that positive shift in the device transfer curves results from the electron trapping/de-trapping processes, where the defect densities at the MoS2/SiO2 interface are reduced when the temperature T decreases from 300 to 200 K. Moreover, the main types of defects that affect the device electrical performance are the interface defect and bulk sulfur vacancy VS in which VS induces the p-type doping effect. While decreasing T below 100 K, NTC occurs when their active layer thickness t (=41 and 35 nm) is larger than the Debye length λ (28 nm). Considering the n-type doping effect induced by the interface defects and the p-type doping caused by the bulk S vacancies, these two opposite doping regions are carefully implemented in simulation at T = 70 K. A vertical barrier induced by the inhomogeneous electron distribution enlarges with the increased gate bias VGS and, thereafter, leads to the unconventional increase in the contact and total resistances with t > λ. While t ≦ λ, the barrier and NTC behavior disappear. The current IDS and transconductance g obtained from the simulation confirm the low-temperature NTC mechanism related to the defects as discussed above. The material defects and physical origin of NTC discussed in the multilayer MoS2 transistors provide the theoretical foundation for designing and realizing novel structures of functional devices via defect engineering in the two-dimensional FET. [ABSTRACT FROM AUTHOR]

The permanent magnet spherical actuator (PMSA) is a multi-variable featured and strongly coupled nonlinear system, and its motion control will unavoidably be affected by various factors. In order to reduce the influence of model uncertainty, friction, and external disturbance on the actual control during the position tracking of PMSA, this paper proposes a novel adaptive friction compensation robust control method under compound disturbance to improve the motion stability of PMSA. In this method, an adaptive compensator is designed to compensate for the unmodeled friction with unknown but constant parameters, and a robust compensator is used to deal with friction parameter variation and non-parametric interference factors that cannot be modeled. The combination of the two controllers can achieve better friction compensation and interference suppression with smaller feedback gain, thus reducing the trajectory tracking errors. In addition, in order to add the smoothness of the velocity value during the experiment, a first-order filter is introduced into the controller. Finally, the stability of the designed controller for the closed-loop system is proved by the Lyapunov method. Furthermore, a simulation model is established and experiments are conducted on the research prototype, and the feasibility and effectiveness under compound disturbance of the proposed control method are verified by comparing with the simulation and experimental results of other controllers. [ABSTRACT FROM AUTHOR]

This work investigates the effect of nitrogen and hydrogen (N/H) co-doping on the performance of ZnO thin-film transistors (TFTs). Optimum N/H co-doped ZnO TFTs showed high field-effect mobility (25.5 cm2 Vs−1) and Ion/Ioff (107) and low sub-threshold slope (0.25 V/dec.) and threshold voltage (1.2 V). X-ray photo-electron spectroscopy (XPS) and low-frequency noise analysis suggest that the observed improved electrical performance may be attributed to the reduction of the defect concentration and the average interface trap density due to the occupation of the NO–H complex on the oxygen vacancy and Zn interstitials. Moreover, density functional theory calculation and XPS band structure results demonstrate that the N/H co-doped ZnO film slightly changed the valence band maximum energy offset, indicating that the N/H co-doping controlled the carrier concentration of the ZnO film due to the formation of neutral complex N–H states. The enhanced electrical performance of the N/H co-doped ZnO TFT shows significant potential for the use of low-cost thin film electronic applications. [ABSTRACT FROM AUTHOR]

Integrated mixed-dimensional (MD) van der Waals (vdWs) heterojunctions for self-powered photodetectors have attracted intense attention. Performances of these photodetectors are highly dependent on the interface properties, including the semiconductor–metal interface and the semiconductor–semiconductor interface. To date, how to balance the interface properties remains to be explored. Here, we explore a straightforward strategy to balance the interface properties of the MD-vdWs heterojunction photodetector, by tuning the Fermi level of ambipolar two-dimensional material with a gate bias. The effectiveness of gate-tunable interface properties is verified by a GaAs-WSe2 MD vdWs heterojunction self-powered photodetector with different metal contacts. Under the gate biasing, the responsivity is enhanced from 122.55 mA/W to 510.98 mA/W in the GaAs–WSe2 heterojunction photodetector with the Au/Cr electrodes, which is better than the state-of-the-art GaAs-based self-powered photodetectors. This work provides a simple and effective method to fabricate high-responsivity, self-powered heterojunction photodetectors by gate-tunable interface properties. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) has potential for fabricating p-type transistors in ultra-thin 2D-material complementary circuits. However, as the synergetic effect of water and oxygen leads to performance degradation under an ambient atmosphere, it is urgent to develop a passivation strategy for robust stability. Herein, a scalable superhydrophobic passivation layer is designed to improve the stability of BP transistors, which consists of fluoroalkylsilane-coated titanium dioxide (TiO2) nanoparticles. Due to the superhydrophobic property of the passivation layer, the BP transistors preserve intrinsic performance in extremely wet conditions, including humid air, water, HCl, and KOH. After 28 days in atmospheric conditions, the performance presents only 20% channel current degradation and the device can work even after 60 days. This work not only experimentally demonstrates robust stable BP transistors in harsh conditions but also provides a highly efficient and damage-free strategy to suppress the influence of water adsorption in atmospheric conditions for highly stable 2D materials devices. [ABSTRACT FROM AUTHOR]

This work analyses the physics of active trap states impacted by hydrogen (H) and nitrogen (N) dopings in amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and investigates their effects on the device performances under back-gate biasing. Based on numerical simulation and interpretation of the device transfer characteristics, it is concluded that the interface and bulk tail states, as well as the 2+ charge states (i.e., acceptors VO2+) related to oxygen vacancy (VO), are neutralized by the H/N dopants incorporation via an experimental plasma treatment. Moreover, the simulation reveals that an acceptor-like defect VOH has been induced by the H doping, to support the observed additional degradation of device subthreshold slope. Superior stability of the optimized a-IGZO TFTs under a proper amount of H/N doping is demonstrated by the decreased density of VO-related defects in simulation, where hole (VO0 donor) and electron trapping (Oi acceptor) occurs during the negative or positive bias stresses. This work benefit lies in an in-depth systematic understanding and exploration of the effects of the incorporation of the H and N dopants into the a-IGZO film for the TFTs improvement and optimization. [ABSTRACT FROM AUTHOR]

CuO grown by room-temperature direct current reactive magnetron sputtering is introduced to realize p-type thin-film transistors (TFTs) with a high-k HfO2 gate dielectric fabricated by atomic layer deposition. The devices work in an accumulation mode (AM) with two apparent threshold voltages corresponding to the formation of a buried channel and an accumulation layer, respectively. A CuO AM TFT with a channel length of 25 μm exhibit a competitive on-off ratio (Ion/Ioff) of 1.3 × 102, a subthreshold swing (SS) of 1.04 V dec−1, and a field-effect mobility (μFE) of 1.1 × 10−3 cm2 V−1 s−1 at room temperature. By measuring a CuO metal oxide semiconductor (MOS) capacitor at room temperature, a high acceptor doping density (NA) of ∼5 × 1017 cm−3, a high positive effective fixed surface charge density (Qf) of ∼9 × 1012 cm−2, and a low interfacial trap charge density (Dit) of ∼6 × 1010 eV−1 cm−2 at the HfO2/CuO interface are estimated. The μFE extracted from the accumulation regime appears lower than the Hall mobility measured for a similarly processed CuO layer on glass due to the increased hole concentration in CuO TFTs, compared to a Hall concentration of ∼1014 cm−3, following the MOS process. SS appears limited by the decreased channel to gate capacitance (Ccg) related to the buried channel in AM TFTs, parasitic capacitance to ground, and potentially very high interfacial traps at the non-passivated CuO/air interface. [ABSTRACT FROM AUTHOR]