To understand electrical/dielectric phenomena and the origins of bistable resistive switching, impedance spectroscopy was applied to NiO thin films prepared through atomic layer deposition. The dc current-voltage characteristics of the NiO thin films were also determined. Frequency-dependent characterizations indicated that the switching and memory phenomena in NiO thin films did not originate from the non-Ohmic effect at the electrode/NiO interfaces but from the bulk-related responses, i.e., from an electrocomposite where highly conducting components are distributed in the insulating NiO matrix. Low dielectric constants and bias-independent capacitance appeared to corroborate the bulk-based responses in resistive switching in NiO thin films.

A precursor originally synthesized for the chemical vapor deposition of metallic nickel, Ni(dmamp)2 (dmamp=1-dimethylamino-2-methyl-2-propanolate, -OCMe2CH2NMe2), has been adopted as a nickel source for the atomic layer deposition of nickel oxide (NiO) using water (H2O) as the oxygen source. The precursor is a solid at room temperature, but readily sublimes at 90 °C. The self-limiting atomic layer deposition (ALD) process by alternate surface reactions of Ni(dmamp)2 and H2O was confirmed from thickness measurements of the NiO films grown with varying Ni(dmamp)2 supply times and numbers of the Ni(dmamp)2-H2O ALD cycles. The ALD temperature window for this precursor was found to be between 90 and 150 °C. Under optimal reaction conditions, the growth rate of the NiO films was ∼0.8Å∕cycle. The NiO films deposited on Si(001) at 120 °C were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The x-ray diffraction patterns showed no distinct peaks for NiO, indicating that the films deposited at this temperature were amorphous. X-ray photoelectron spectroscopy analysis showed the films to be stoichiometric with no detectable amount of carbon impurities. For a film with the thickness of 810 Å (with 1000 ALD cycles) the root-mean-square surface roughness was only ∼4Å as measured by atomic force microscopy. To elucidate the ALD mechanism of the Ni precursor with water, a quadrupole mass analyzer was employed with D2O as the oxygen source in lieu of H2O. Interestingly, unlike the usual ALD fashion, the Ni(dmamp)2 precursor does not seem to decompose but only coordinatively bond to the OH-terminated surface when it was introduced. Next, the Ni(dmamp)2-surface species decompose to produce a hydroxylated nickel oxide surface and the alcohol dmampH when water was supplied.

Articles you may be interested inCharacterization of plasma-enhanced atomic layer deposition of Al2O3 using dimethylaluminum isopropoxide J. Vac. Sci. Technol. A 32, 021514 (2014); 10.1116/1.4866378 Atomic scale characterization of Hf O 2 ∕ Al 2 O 3 thin films grown on nitrided and oxidized Si substrates J. Appl. Phys. 96, 6113 (2004); 10.1063/1.1808245Growth of cubic SiC thin films on Si(001) by high vacuum chemical vapor deposition using 1,3-disilabutane and an investigation of the effect of deposition pressure Dimethylaluminum isopropoxide ͑DMAI͒, (CH 3 ) 2 AlOCH(CH 3 ) 2 , a precursor originally developed for the metalorganic chemical vapor deposition of alumina, was adopted as a new precursor for growing aluminum oxide thin films on HF-treated Si͑001͒ substrates by atomic layer deposition ͑ALD͒. This precursor is stable for a prolonged period of storage time under inert atmosphere ͑such as in nitrogen or argon͒ and does not react vigorously in air, and therefore is easy to handle and safe, without causing hazards. The self-limiting ALD process by alternate surface reactions of DMAI and H 2 O was confirmed by thicknesses of the grown aluminum oxide films measured as functions of the DMAI pulse time and the number of DMAI-H 2 O cycles. A maximum growth rate of ϳ1.06 Å/cycle was achieved in the substrate temperature range ϳ120-150°C. Growth of stoichiometric Al 2 O 3 thin films without appreciable carbon incorporation was verified by Rutherford backscattering spectrometry. Atomic force microscopy images showed atomically flat and uniform surfaces. In particular, a cross-sectional high-resolution transmission electron microscopy image of an Al 2 O 3 film shows that there is no distinguishable interfacial oxide layer between the Al 2 O 3 film and the Si substrate. These results prove the validity of DMAI as a new ALD source for aluminum oxide.

The crystallization of amorphous Si ͑a-Si͒ thin films was performed using atomic layer deposition ͑ALD͒ of nickel oxide. Nickel oxide layers were deposited using nickel aminoalkoxide as a precursor in Ni and water as a precursor in oxygen. The presence of nickel oxide caused significant crystallization to occur in a-Si at 575°C under a reducing atmosphere. Even one single ALD layer of nickel oxide was high enough to crystallize the a-Si thin films. Self-limiting layer controllability in ALD is useful in providing a catalytic layer for formation of polycrystalline Si thin films for application to large-scale flat panel displays.

Nonvolatile memory effects of Al 2 O 3 /NiO/Al 2 O 3 nanolaminates deposited through atomic layer deposition were investigated. The memory structure was constructed without interruption in the order of Al 2 O 3 /NiO/Al 2 O 3 thin-film deposition on Si wafers. The memory characteristics were analyzed through high frequency capacitance-voltage measurement along with high resolution images of the aforementioned nanolaminates. The defective nature of nickel oxide produces a significantly large memory window; the largest memory window observed was 13.8 V. The peculiar memory characteristics were understood in terms of the constituent tunnel and charge-trapping layers in the metal gate/high-k oxide/semiconducting oxide/high-k oxide/Si memory structures. Nanoscale nonvolatile memories have been gaining widespread attention in research and development because of the advent of digital convergent and ubiquitous societies. The next-generation nonvolatile memories should meet two prerequisites, i.e., faster programming/erasing speed and longer data retention time: 10 6 programming/erasing cycles, 10 years charge retention at 85°C, and 5 V or less programming voltage. 1 Dynamic random access memories suffer from volatile data storage along with issues involving the scaling down of device structures and flash memories encountering variations in both operation voltages and oxide integrity. One alternative, polysilicon/oxide/nitride/oxide/Si ͑SONOS͒ devices, has been proposed as highly promising. Despite the continuous vertical scaling process, the SONOS structure suffers from two drawbacks, i.e., in terms of program/erase speed and charge retention. To improve the operation speed and charge retention features, replacing the blocking SiO 2 layer and the conventional nitride trapping layer with high-k materials was attempted. The applications ͑or modifications͒ incorporate TaN/Al 2 O 3 /SiN x /SiO 2 /Si, metal gate/SiO 2 /high-k dielectrics/SiO 2 /Si, and metal nitride/high-k/high-k trapping layer/high-k/Si. 2-4 Furthermore, tunnel barrier engineering was attempted using an ultrathin multiple layer instead of the SiO 2 tunnel layer in the SONOS structure, where hole direct tunneling is suppressed. 4-8 The charge-trapping memories require the artificial control conduction band offset between the tunnel layer and the charge-trapping layer to enhance the corresponding charge retention by reducing the trapped electron leakage from the charge-trapping layer. Tan et al. improved the retention issue using a hafnium oxide charge storage layer based on the energy band diagram. 9 The nonvolatile memory effect in Al 2 O 3 thin films with an embedded Al-rich layer deposited by electron-cyclotron-resonance sputtering was reported, where the Al-Al bonds with many oxygen vacancies in the Al-rich Al 2 O 3 layer provided charge-trapping centers. 10 The Al 2 O 3 thin-film structure can be interpreted to be similar to the charge-trapping nitride memories.One of the transition-metal oxides, NiO has been reported to exhibit typical resistive switchin...

Undoped and Al-doped ZnO thin films have been prepared by atomic layer deposition (ALD) using the Zn precursor methylzinc isopropoxide [MZI, (CH3)Zn(OCH(CH3)2)] with water (H2O). Dimethylaluminum isopropoxide (DMAI) was used as an Al precursor. The self-limiting ALD process via alternate surface reactions of MZI and H2O was confirmed by thickness measurements of the ZnO films with varying MZI supply time and numbers of MZI-H2O ALD cycles. Under optimal reaction conditions, the growth rate of the ZnO films was 1.9 to approximately 2.0 A/cycle in the substrate temperature range of 160 to approximately 200 degrees C and the maximum growth rate reached about 2.58 A/cycle at 240 degrees C. Room temperature photoluminescence (PL) measurements revealed a strong free excitonic peak at 3.27 eV with almost negligible deep level emission. Resistivities of ZnO films were measured to be 5 x 10(-3) to approximately 3.2 x 10(-3) omega cm depending on the substrate temperature. By Al-doping, the resistivity was minimized to approximately 1.35 x 10(-4) cm.

This paper studies a repetitive controller design scheme for a bridgeless single-ended primary inductor converter (SEPIC) power factor correction (PFC) converter to mitigate input current distortions. A small signal modeling of the converter is performed by a fifth-order model. Since the fifth-order model is complex to be applied in designing a current controller, the model is approximated to a third-order model. Using the third-order model, the repetitive controller is designed to reduce the input current distortion. Then, the stability of the repetitive controller is verified with an error transfer function. The proposed controller performance is validated by simulation, and the experiment results show that the input current total harmonic distortion (THD) is improved by applying the proposed controller for an 800 W bridgeless SEPIC PFC converter prototype.

The field emission ͑FE͒ properties of ZnO and NiO-coated ZnO ͑NiO / ZnO͒ nanorods are investigated under vacuum of 7 ϫ 10 −7 Torr and oxygen rich vacuum of 1 ϫ 10 −5 Torr. The ZnO nanorods were synthesized on a Si͑100͒ substrate by metal-organic chemical vapor deposition, and the NiO film with the thickness of ϳ15 nm was coated by using atomic layer deposition. The turn-on voltages of the NiO / ZnO nanorod and the ZnO nanorod were ϳ5.2 and ϳ3.0 V / m at 1 A / cm 2 , respectively. The electron FE stability of the NiO / ZnO nanorods to the ZnO nanorod was significantly improved in oxygen rich vacuum even.