Search

Mechanical energy harvesters have not much benefited from the significant advantages of additive manufacturing techniques because the functional materials are not compatible with most printable schemes. In this work, a triboelectric nanogenerator is designed and demonstrated only by additive manufacturing methods. The all-printed triboelectric nanogenerator (AP-TENG) combines the advantages of 2D and 3D printing technologies. The structural frame is formed by 3D printing as a core-shell structure, which effectively converts external vibrations into continuous sliding motion. The contact layers are created by 2D inkjet printing with precisely patterned grating structure. The nanoscale printed contact layers made on nanocellulose paper assure high output power and abrasion durability. The un-optimized AP-TENG here produces a maximum instantaneous voltage of 98.2 V and a maximum instantaneous current of 13.7 μA, with a threshold vibration amplitude of 1 mm and an optimum frequency range of 30–60 Hz. The AP-TENG can be autonomously manufactured by printers at the point-of-demand anywhere, making it particularly attractive in remote locations including other planets and the International Space Station where the logistics is complex and expensive. [ABSTRACT FROM AUTHOR]

To date, the high energy storage performances observed in the field-induced ferroelectric HfO 2 - or ZrO 2 -based films have had an obstacle to scale-up due to the involvement of low-k monoclinic phase at the large thickness (> ~ 10 nm). Considering that the monoclinic phase formation is closely related with the in-situ (partial) crystallization during the atomic layer deposition (ALD) process, in this work, the ALD temperature of Hf 0.5 Zr 0.5 O 2 thin films was lowered, and its influence on the energy storage performances was systematically examined. Carbon and nitrogen dopants incorporated at a low deposition temperature in combination with grain size decrease change the polymorphism of Hf 0.5 Zr 0.5 O 2 thin film from the genuine ferroelectric to field-induced (incipient) ferroelectric crystal structure. The Hf 0.5 Zr 0.5 O 2 thin film deposited at 210 °C shows improved resistance to degradation by monoclinic phase involvement up to ~ 40 nm compared to the previously-reported Hf 0.3 Zr 0.7 O 2 thin films. By investigating Hf 0.5 Zr 0.5 O 2 thin films with wide ALD temperature and thickness ranges, energy storage density of ~ 55 J cm −3 with an efficiency of ~ 57% can be achieved at the ~ 7.1 nm Hf 0.5 Zr 0.5 O 2 thin films deposited at 215 °C. The performance can be retained even after 10 10 bipolar switching cycles, and the film endures thermal stress up to 175 °C without severe degradation, demonstrating notable reliability. [ABSTRACT FROM AUTHOR]

Antiferroelectric Hf x Zr 1− x O 2 (HZO, x =0.1–0.3) films are reported herein as new Si-compatible materials for monolithic devices for pyroelectric energy harvesting, electrocaloric cooling, electrostatic energy storage, and infrared sensing. Hf 0.2 Zr 0.8 O 2 and Hf 0.3 Zr 0.7 O 2 films could work as pyroelectric energy harvesters using the Olsen cycle with the harvested energy densities of 11.5 and 5.7 J cm −3 cycle −1 , which are ~7.6 and ~3.7 times larger than the largest value ever reported. The electrocaloric effect (ECE) of HZO films was also firstly examined, and the maximum Δ T values of the Hf 0.2 Zr 0.8 O 2 and Hf 0.3 Zr 0.7 O 2 films were 13.4 (at 307 K) and 9.8 K (at 448 K), respectively. The wide temperature range for the large ECE of the HZO films was highly promising for the actual cooling cycle with large reversible work values. Moreover, the large capacitance of the HZO films due to the field-induced phase transition between the poled and anti-poled states can be used for electrostatic energy storage and high-charge capacitors. The k 2 and F v values, which are the figures of merit for conventional pyroelectric energy conversion and infrared detection for thermal imaging, of the Hf 0.2 Zr 0.8 O 2 film were 24.4×10 −3 and 32.0×10 −2 m 2 C −1 , respectively, which prove that Hf 0.2 Zr 0.8 O 2 is also a promising material for these applications. [ABSTRACT FROM AUTHOR]

Abstract: Chemically conformal deposition of SrTiO3 (STO) thin films was successfully achieved by ALD using conventional metal organic precursors and remote-plasma activated H2O. It was found that the ALD behavior of the STO film was critically dependent on the Sr(thd)2 source bubbling temperature. When the Sr-source bubbling temperature was <∼200 °C (Sr(thd)2 melting temperature), the deposition proceeded in a genuine ALD mode and stoichiometric STO films were deposited with a good process reliability. Relatively good electrical properties were obtained from a planar capacitor structure with Pt top and Ru bottom electrodes. A 19.5-nm-thick STO film showed an equivalent oxide thickness (EOT) of 0.8 nm and a leakage current density of 1.98×10−6 A/cm2 at 1V after post-annealing. [Copyright &y& Elsevier]

Thermal stability and interfacial charge trap properties of the multi-metal (Ir/Pt/Au) top electrode of a metal–insulator–metal cathode for field emission display applications were examined. The thin (∼5 nm) multi-metal electrode did not show sufficient thermal stability during the post-annealing stage, which is needed to obtain good emission properties of the cathode, due to inter-diffusion and agglomeration of the layers. Reactively sputtered IrO2 thin films as the top electrode were examined considering their excellent thermal stability and low work function. However, the proper sputtering conditions of thin IrO2 (<10 nm) films were different from those of thick films (>100 nm) and should be optimized again due to the serious resputtering of the substrate at the initial deposition stage. Increasing the oxygen concentration (25%) during sputtering, which is the condition that results in a non-uniform film when the film is thick (>100 nm), was essential to ensure that the film was a well oxidized IrO2 when the film was very thin (<10 nm). Excellent thermal stability in terms of the non-varying resistivity and surface roughness of the 8-nm-thick IrO2 films compared to the multi-metal electrode film were confirmed. [Copyright &y& Elsevier]

The resistive switching (RS) behavior of a gallium oxide (Ga 2 O 3) thin film for use in resistive random access memory (RRAM) was investigated. Ta/Ga 2 O 3 /Pt memory devices exhibited favorable RS behavior, such as a small distribution of switching parameters and switching cycles of more than 3 × 106. X-ray photoelectron spectroscopy and the current transport mechanism indicated that that the RS behavior was attributed to the local variation on the Schottky barrier near the Pt electrode interface due to oxygen vacancies. A hybrid system for self-powered data storage and deletion was built by combining the RRAM device with a commercial Pb(Zr 1-x Ti x)O 3 piezoelectric ceramic as a pressure sensor/power generator. The excellent anti-interference and reuse performance of the system indicated promising potential for the application of this memory device. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure of amorphous semiconductor InGaO3(ZnO)0.5 thin films, which were deposited by radio-frequency magnetron sputtering process, was investigated using X-ray photoelectron spectroscopy and O K-edge X-ray absorption spectroscopy. The overall features of the valence and conduction bands were analyzed by comparing with the spectra of Ga2O3, In2O3, and ZnO films. The valence and conduction band edges are mainly composed of O 2p and In 5sp states, respectively. The bandgap of the films determined by spectroscopic ellipsometry was approximately 3.2 eV. Further, it is found that the introduction of oxygen gas during the sputter-deposition does not induce significant variations in the chemical states and band structure. [Copyright &y& Elsevier]

This paper investigates the effect of an oxygen (O 2 ) plasma treatment on multi-layer tungsten diselenide (WSe 2 ) field-effect transistor (FET) by forming tungsten trioxide (WO 3 ) layers. Palladium (Pd), which is known to form an Ohmic contact with WSe 2 , is used for the source and drain (S/D) contact electrodes as a control group for metal variables. And then, Nickel (Ni), which is thought to form a Schottky contact with WSe 2 experimentally, is used as an experimental group. For both cases of the control group and the experimental group, the electrical characteristics including drain current ( I D ), on/off ratio ( I ON / I OFF ), subthreshold swing ( SS ) and field effect mobility ( μ eff ) are analyzed according to the presence or absence of WO 3 . In case of adopting the WO 3 contact layer between the WSe 2 and the Ni for the S/D contact electrode, we observe a remarkable improvement in I D , I ON / I OFF , μ eff , and SS compared to the case without the WO 3 contact layer. The analyzed electrical characteristics show that an efficient hole-injection contact was achieved for the multi-layer WSe 2 FET by the O 2 plasma treatment, which leads to the formation of an Ohmic-like contact at an electrode/WSe 2 interface. [ABSTRACT FROM AUTHOR]

A metal-oxide-semiconductor field-effect transistor (MOSFET)-based gas sensor having a floating gate (FG) is fabricated and its sensing property is characterized. The gas sensor has 10 nm thick ZnO as a sensing layer prepared by atomic layer deposition (ALD). The FG, the sensing layer and the control gate (CG) are formed horizontally so that diverse sensing materials can be applied to the structure of the sensor without contamination. The gas-sensing performance of the sensor is investigated for seven target gases. Drain currents in NO 2 and H 2 S ambiences are changed by 176% and 58%, respectively, for given NO 2 (20 ppm) and H 2 S (20 ppm) concentrations. Whereas the changes of drain current for NH 3 , SO 2 , CO 2 , CH 4 and C 3 H 8 gases are less than 5%. Response and recovery times for NO 2 are 90 s and 580 s, respectively, at 180 °C. The responses with working temperature and gas concentration are also studied. The sensing mechanisms for NO 2 and H 2 S gases are explained. [ABSTRACT FROM AUTHOR]

Surface sulfur (S) passivation on InP substrate was performed using a dry process – rapid thermal annealing under H 2 S atmosphere for III–V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO 2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process – (NH 4 ) 2 S solution treatment. The H 2 S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH 4 ) 2 S solution treatment, although S profiles at the interface of HfO 2 /InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H 2 S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H 2 S annealing. [ABSTRACT FROM AUTHOR]

Highlights: [•] Atomic-layer-deposited HfO2 films grown at extremely low temperatures (≤100°C) were examined. [•] Growth saturation behavior of ALD was observed near to room temperatures. [•] Effects of growth temperatures and O3 concentrations on film properties are reported in detail. [•] Grown HfO2 films exhibited acceptable properties for flexible display and bio-electronic applications. [ABSTRACT FROM AUTHOR]

Abstract: Ru thin films were grown on polymorphic TiO2 thin film substrates at 230 and 250°C by atomic layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru and an O2 gas. While the Ru films grown on amorphous and rutile TiO2 substrates showed a relatively long incubation cycle number of approximately 350 and 100 at 230 and 250°C, respectively, the Ru films grown on anatase TiO2 substrates exhibited a significantly shorter incubation delay which was attributed to the catalytic activity of anatase TiO2. This difference in the incubation cycle affected the surface morphology of the Ru films on different TiO2 substrates. [ABSTRACT FROM AUTHOR]

Abstract: Metal-insulator-semiconductor capacitors were fabricated with sputtered ZnO and atomic layer deposited HfO2 as the semiconductor and gate dielectric layers, respectively. From the capacitance–voltage measurements, it was confirmed that pre-deposition annealing of the sputtered ZnO layer at 300°C in air greatly decreased the interfacial trap density (∼2×1012 cm−2 eV−1). X-ray photoelectron spectroscopy showed a decrease in the OH bonds adsorbed on the ZnO surface after pre-deposition annealing, which improved the interface property. A very small capacitance equivalent thickness of 1.3nm was achieved, which decreased the operation voltage (<5V) of the device significantly. [Copyright &y& Elsevier]

Abstract: A thin (∼ 0.5 nm) layer of Hf metal was deposited on an atomic layer deposited (ALD) HfO2 film by the DC sputtering method. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses showed that the Hf metal layer transformed into HfO2 during the post-deposition annealing process. It appears that the HfO2 layer formed by the oxidation of Hf metal provided the underlying ALD HfO2 layer with the nucleation sites necessary to decrease the grain-boundary density of the crystallized HfO2 film. The decrease in the grain-boundary density resulted in a reduction in the Hf-silicate formation and interfacial layer growth during post deposition annealing. This eventually resulted in a smaller increase in the capacitance equivalent thickness (CET) and high-k characteristics in the CET vs. leakage current density curve even after post deposition annealing at 1000 °C. [Copyright &y& Elsevier]

Abstract: High-quality GaN epitaxial films were successfully grown directly on 4H-SiC substrates. The difficulty in the nucleation as well as the overgrowth of GaN islands, which is often observed during metal-organic chemical vapor deposition, was solved using the concept of an epitaxial lateral overgrowth technique. The continuous mirror-flat GaN epitaxial film could be obtained at a reduced reactor pressure (76Torr) and a lower N/Ga supply ratio. The full-width half-maximums (FWHMs) of the (0002) and (10 3) rocking curves of the GaN epitaxial films on the 4H-SiC substrate at the optimized condition were 105 and 118arcsec, respectively, under a skew symmetric diffraction geometry. The intense bound exciton lines with a FWHM of 10meV and a free exciton peak appeared in the low-temperature photoluminescence spectrum, illustrating the very high quality of the GaN film on 4H-SiC. [Copyright &y& Elsevier]

Abstract: In this work, we have prepared metal–insulator–metal capacitors for dynamic random access memory capacitor application using atomic layer deposition of TiO2 high-κ dielectric and RuO2 bottom electrode. We compare TiO2 layers grown using TiCl4 precursor or Ti-tetra-isopropoxide precursor, and Al-doped TiO2 layers grown using Ti-tetra-isopropoxide precursor. The capacitors were analyzed in the terms of capacitance – voltage and current – voltage measurements and transmission electron microscopy imaging. [Copyright &y& Elsevier]

• A new capacitive-type FET (CFET) gas sensor based on Si FET is proposed. • Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. • The NO 2 gas-sensing characteristics are obtained by using pulse pre-bias method. • Depending on the polarity of pre-bias (V pre), the CFET gas sensor exhibits the opposite I D behaviors. • The sensing mechanism is explained by using schematic energy band diagrams. A new capacitive-type FET (CFET) gas sensor is proposed in this work and fabricated by using Si FET technology. Only five photomasks are used to prepare the CFET sensor and a ZnO thin film prepared by atomic layer deposition (ALD) is adopted as a sensing material. A diluted nitrogen dioxide (NO 2) is used as a test gas and the sensing properties of the CFET gas sensor are measured at 180℃ by using pulse pre-bias method. It is verified that the response of the CFET sensor is significantly improved as the absolute value of the difference between pre-bias (V pre) and gate read bias (V rCG) increases. However, the response is negligible when V pre = V rCG. The drain current (I D) of the CFET gas sensor increases by 44.6% at a V pre of −2 V while the I D decreases by 43.2% at a V pre of 2 V under exposure to 0.5 ppm NO 2 at a V rCG of 0 V at 180℃. The response and the recovery times are also investigated. The sensing mechanism is explained by using schematic energy band diagrams. [ABSTRACT FROM AUTHOR]