Post-deposition Annealing In Oxygen Research Articles

Charge Storage and Reliability Characteristics of Nonvolatile Memory Capacitors with HfO2/Al2O3-Based Charge Trapping Layers.

Flash memories are the preferred choice for data storage in portable gadgets. The charge trapping nonvolatile flash memories are the main contender to replace standard floating gate technology. In this work, we investigate metal/blocking oxide/high-k charge trapping layer/tunnel oxide/Si (MOHOS) structures from the viewpoint of their application as memory cells in charge trapping flash memories. Two different stacks, HfO2/Al2O3 nanolaminates and Al-doped HfO2, are used as the charge trapping layer, and SiO2 (of different thickness) or Al2O3 is used as the tunneling oxide. The charge trapping and memory windows, and retention and endurance characteristics are studied to assess the charge storage ability of memory cells. The influence of post-deposition oxygen annealing on the memory characteristics is also studied. The results reveal that these characteristics are most strongly affected by post-deposition oxygen annealing and the type and thickness of tunneling oxide. The stacks before annealing and the 3.5 nm SiO2 tunneling oxide have favorable charge trapping and retention properties, but their endurance is compromised because of the high electric field vulnerability. Rapid thermal annealing (RTA) in O2 significantly increases the electron trapping (hence, the memory window) in the stacks; however, it deteriorates their retention properties, most likely due to the interfacial reaction between the tunneling oxide and the charge trapping layer. The O2 annealing also enhances the high electric field susceptibility of the stacks, which results in better endurance. The results strongly imply that the origin of electron and hole traps is different—the hole traps are most likely related to HfO2, while electron traps are related to Al2O3. These findings could serve as a useful guide for further optimization of MOHOS structures as memory cells in NVM.

Fixed-charge generation in SiO2/GaN MOS structures by forming gas annealing and its suppression by controlling Ga-oxide interlayer growth

A recent study has shown that anomalous positive fixed charge is generated at SiO2/GaN interfaces by forming gas annealing (FGA). Here, we conducted systematic physical and electrical characterizations of GaN-based metal-oxide-semiconductor (MOS) structures to gain insight into the charge generation mechanism and to design optimal interface structures. A distinct correlation between the amount of FGA-induced fixed charge and interface oxide growth indicated the physical origins of the fixed charge to be defect formation driven by the reduction of the Ga-oxide (GaO x ) interlayer. This finding implies that, although post-deposition annealing in oxygen compensates for oxygen deficiencies and FGA passivates defect in GaN MOS structures, excessive interlayer GaO x growth leads to instability in the subsequent FGA treatment. On the basis of this knowledge, SiO2/GaO x /GaN MOS devices with improved electrical properties were fabricated by precisely controlling the interfacial oxide growth while taking advantage of defect passivation with FGA.

Impacts of oxygen sensitization methods on the deposition and microstructure of ternary lead chalcogenide alloys

Oxygen sensitization and incorporation of ternary lead chalcogenide PbSe1-xTex thin films was investigated with two methods: adding oxygen via PbO to the bulk source alloy and post-deposition oxygen annealing. Characterization of the composition, structure, and morphology of these films confirmed that they follow Vegard's law for lattice parameter, and adding PbO to the source alloy did not impact the lattice parameter. However, adding PbO changed the electrical carrier properties observed in Hall effect measurements without forming any new oxide phase. Conversely, post-deposition annealing increased the lattice parameter due to oxygen incorporation into the lattice via interstitials in samples with appropriate grain boundary orientations. Morphological analysis revealed that PbSe0.8Te0.2 films demonstrated (100) texture, while PbSe0.6Te0.4 films demonstrated (111) texture with resulting grain boundary orientations more favorable to oxygen diffusion and incorporation. This varying oxygen incorporation from PbO source and oxygen annealing methods reveals trends that can lead to improved photodetector performance.

Radiation Tolerance and Charge Trapping Enhancement of ALD HfO2/Al2O3 Nanolaminated Dielectrics.

High-k dielectric stacks are regarded as a promising information storage media in the Charge Trapping Non-Volatile Memories, which are the most viable alternative to the standard floating gate memory technology. The implementation of high-k materials in real devices requires (among the other investigations) estimation of their radiation hardness. Here we report the effect of gamma radiation (60Co source, doses of 10 and 10 kGy) on dielectric properties, memory windows, leakage currents and retention characteristics of nanolaminated HfO2/Al2O3 stacks obtained by atomic layer deposition and its relationship with post-deposition annealing in oxygen and nitrogen ambient. The results reveal that depending on the dose, either increase or reduction of all kinds of electrically active defects (i.e., initial oxide charge, fast and slow interface states) can be observed. Radiation generates oxide charges with a different sign in O2 and N2 annealed stacks. The results clearly demonstrate a substantial increase in memory windows of the as-grown and oxygen treated stacks resulting from enhancement of the electron trapping. The leakage currents and the retention times of O2 annealed stacks are not deteriorated by irradiation, hence these stacks have high radiation tolerance.

Hole and electron trapping in HfO2/Al2O3 nanolaminated stacks for emerging non-volatile flash memories

HfO2/Al2O3 nanolaminated stacks prepared by atomic layer deposition have been investigated in terms of their charge storage characteristics for possible application in charge trapping memories. It is shown that the memory window, electron and hole trapping and leakage currents depend strongly on Al2O3 thickness and post-deposition oxygen annealing. Depending on the Al2O3 thickness, post-deposition annealing in O2 creates different electrically active defects (oxide charge and traps) in the stacks. O2 annealing increases electron trapping, thus giving rise to a larger memory window and enhanced charge storage characteristics, i.e. 65% of charge is retained after ten years and the memory window decreases by 6% after 2.5 × 104 program/erase cycles.

Preparation and characterization of RF magnetron sputtered CuO/CaTi4O9 thin films with enhanced third-order nonlinear optical properties

The titanate, is a material of interest for various energy applications, including photovoltaics, catalysts, and high-rate energy storage devices. Herein, its related materials, CuO/CaTi4O9 [CCTO] thin films, were successfully fabricated on SrTiO3 (100) substrates by RF magnetron sputtering assisted with subsequent oxygen annealing. This obtained CCTO thin films were then systemically studied by X-ray powder diffraction (XRD), atomic force microscopy (AFM), scan electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). It was found that CuO and CaTi4O9 (001) particles were closely accumulated together on the surface of the substrate in the annealing process after comparing with that of the as-prepared thin film, which was verified by SEM and AFM results. Furthermore, we investigated the third-order nonlinear optical (NLO) properties of the as-prepared and annealed CCTO thin film by means of the Z-scan technique using 650nm femtosecond laser pulse. Post-deposition oxygen annealing was found to modify the morphological characteristics of the films, resulting in enhancing their NLO properties. The observation of NLO performance of annealed CCTO thin film indicates that RF magnetron sputtering is a feasible method for the fabrication of optical thin films, which can be expanded to fabricate other NLO materials from the corresponding dispersions. Naturally, we concluded that the CCTO thin film occupy a better NLO property, and thus enlarge its application in nonlinear optics.

Amorphous InGaMgO Ultraviolet Photo-TFT with Ultrahigh Photosensitivity and Extremely Large Responsivity.

Recently, amorphous InGaZnO ultraviolet photo thin-film transistors have exhibited great potential for application in future display technologies. Nevertheless, the transmittance of amorphous InGaZnO (~80%) is still not high enough, resulting in the relatively large sacrifice of aperture ratio for each sensor pixel. In this work, the ultraviolet photo thin-film transistor based on amorphous InGaMgO, which processes a larger bandgap and higher transmission compared to amorphous InGaZnO, was proposed and investigated. Furthermore, the effects of post-deposition annealing in oxygen on both the material and ultraviolet detection characteristics of amorphous InGaMgO were also comprehensively studied. It was found that oxygen post-deposition annealing can effectively reduce oxygen vacancies, leading to an optimized device performance, including lower dark current, higher sensitivity, and larger responsivity. We attributed it to the combined effect of the reduction in donor states and recombination centers, both of which are related to oxygen vacancies. As a result, the 240-min annealed device exhibited the lowest dark current of 1.7 × 10−10 A, the highest photosensitivity of 3.9 × 106, and the largest responsivity of 1.5 × 104 A/W. Therefore, our findings have revealed that amorphous InGaMgO photo thin-film transistors are a very promising alternative for UV detection, especially for application in touch-free interactive displays.

Electrical characteristics of multilayered HfO2-Al2O3 charge trapping stacks deposited by ALD

Electrical and charge trapping properties of atomic layer deposited HfO2-Al2O3 multilayer stacks with two different Al2O3 sublayer thicknesses were investigated regarding their implementation in charge trapping non-volatile memories. The effect of post deposition annealing in oxygen at 600°C is also studied. The decreasing Al2O3 thickness increases the stack's dielectric constant and the density of the initial positive oxide charge. The initial oxide charge increases after annealing to ∼6×1012 cm-2 and changes its sign to negative for the stacks with thicker Al2O3. The annealing enhances the dielectric constant of the stacks and reduces their thickness preserving the amorphous status. Nevertheless the annealing is not beneficial for the stacks with thicker Al2O3 as it considerably increases leakage currents. Conduction mechanisms in stacks were considered in terms of hopping conduction at low electric fields, and Fowler- Nordheim tunnelling, Schottky emission and Poole-Frenkel effect at higher ones. Maximum memory windows of about 12 and 16V were obtained for the as-grown structures with higher and lower Al2O3 content, respectively. In latter case additional improvement (the memory window increase up to 23V) is achieved by the annealing.

Gold Nanoparticles Effect on (Bi,Pb)-2223 Superconducting Thin Films

<p class="1Body">Superconductor samples were prepared by a conventional solid-state reaction method and systematically studied for their superconducting properties. The Au nanoparticles concentration x varied from 0.0 to 1.0 wt% of the sample's total mass. Those samples were used as targets to prepare Au<sub>x</sub>–Bi<sub>1.7</sub>Pb<sub>0.3</sub>Sr<sub>2</sub>Ca<sub>2</sub>Cu<sub>3</sub>O<sub>10+δ</sub> thin films by pulsed laser deposition (PLD), deposited on Si (111) substrates and post-deposition oxygen annealing have been achieved. The effect of Au nanoparticles (20 nm) on the physical properties of superconducting phase was studied. The phase identification/gross structural characteristics of synthesized bulk and thin films samples explored through powder X-ray diffractometer and reveals that all the samples crystallize in orthorhombic structure In addition, phase examination by XRD indicated that Au nanoparticles enhanced the (Bi,Pb)-2223 phase formation. The critical transition temperature (<em>T<sub>c</sub></em>) measured by the standard DC four-probe method and was found to have optimal value at x=1.0 wt%, which had a maximum enhancement in <em>T<sub>c</sub></em> for both bulk and thin films samples. The surface morphology investigated through scanning electron microscope (SEM) and atomic force microscopy (AFM), the granular investigation showed that both number and size of voids decreased while grains size increased as x increases to 1.0 wt%.</p>

Platinum-assisted post deposition annealing of the n-Ge/Y2O3 interface

The impact of annealing temperature and annealing duration on the interface properties of n-Ge/Y2O3/Pt MOS-capacitors is investigated employing an ultrathin catalytically acting Pt-layer. X-ray photoelectron spectroscopy analysis has been used to verify an enhanced growth of GeO2 and thermally stabilizing yttrium germanate at the n-Ge/Y2O3 interface induced by an oxygen post deposition annealing (PDA). Especially at 500 °C and 550 °C high quality Ge/Y2O3 interfaces have been achieved resulting in very low interface trap density of 7.41*1010 eV−1 cm−2. It is shown that either a short oxygen annealing at higher temperatures (550 °C) or a long time annealing at lower temperatures (450 °C) are appropriate to realize low interface trap density (Dit). It turns out that a Pt-assisted PDA in combination with a final PMA are needed to reduce hysteresis width significantly and to bring flat band voltages toward ideal values.

Synthesis and Characterization of Ag Nanoparticles Addition on BPSCCO Superconducting Thin Films

The growth of epitaxial Ag nanoparticles doped (Bi, Pb)-2223 thin films on Si (111) substrates by pulsed laser deposition (PLD) and post-deposition oxygen annealing have been achieved. The phase identification and gross structural characteristics of synthesized films explored through X-ray diffractometer reveal that all the samples crystallize in orthorhombic structure. DC electrical resistivity measurements were done by the standard four-probe method and the results showed improvement in Tc by increasing Ag nanoparticles to 1.0 wt% which had a maximum enhancement in Tc for all investigated films. The surface morphology investigated through scanning electron microscope (SEM) and atomic force microscopy (AFM) results showed that an increase in Tc with the appropriate Ag nanoparticles addition in the samples is associated with the enhancement of Bi (Pb)-2223 phase formation.

A revisit to ultrathin NiO(0 0 1) film: LEED and valence band photoemission studies

LEED and photoemission measurements have been performed on ultrathin NiO films to reinvestigate its surface quality and valence electronic structures, respectively. On Ag(001) substrate, the best epitaxial order was observed for high temperature deposition with sufficient oxygen flux associated with a post-deposition oxygen annealing. The effect of the substrate vicinity on valence band electronic structure, in case of interfacial NiO layers, has been explained. The variation of Ni 3d to O 2p photoemission cross-section with photon energy (hν) has been demonstrated in this work.

Effective reduction of trap density at the Y2O3/Ge interface by rigorous high-temperature oxygen annealing

The impact of thermal post deposition annealing in oxygen at different temperatures on the Ge/Y2O3 interface is investigated using metal oxide semiconductor capacitors, where the yttrium oxide was grown by atomic layer deposition from tris(methylcyclopentadienyl)yttrium and H2O precursors on n-type (100)-Ge substrates. By performing in-situ X-ray photoelectron spectroscopy, the growth of GeO during the first cycles of ALD was proven and interface trap densities just below 1 × 1011 eV−1 cm−2 were achieved by oxygen annealing at high temperatures (550 °C–600 °C). The good interface quality is most likely driven by the growth of interfacial GeO2 and thermally stabilizing yttrium germanate.

Microstructure, magnetism and magnetotransport of epitaxial Sm0.45Nd0.08Sr0.47MnO3 thin films

The growth of low bandwidth manganite thin films having optical magnetic and transport properties has been found to be extremely difficult. In the present study we have prepared thin films of a low bandwidth manganite Sm0.45Nd0.08Sr0.47MnO3 and carried out detailed study of microstructural and magnetotransport properties. Thin films (thickness ∼36 nm and ∼80 nm) of Sm0.45Nd0.08Sr0.47MnO3 were grown by dc magnetron sputtering on (001) oriented LaAlO3 single-crystal substrate and post-annealed in oxygen. The x-ray diffraction (θ–2θ) shows that the as grown films, irrespective of the thickness are under extremely high compressive strain, which is only partially relaxed by post deposition annealing in oxygen. High resolution x-ray diffraction (ω–2θ scans) shows the occurrence of Pendellösung fringes in the ∼36 nm film, which appear to get disordered in the thicker ∼80 nm film. This shows that the films have grown epitaxially at lower thickness and at higher thickness the microstructural degradation destroys its global nature. The epitaxial growth is confirmed by occurrence of step-terrace morphology in the 36 nm film, which, however, appears to be less prominent at higher film thickness of ∼80 nm. The as-grown films do not show any insulator metal transition and only weak paramagnetic-to-ferromagnetic transition is observed. The O2 annealed 36 nm film shows a broad paramagnetic to ferromagnetic transition at ≈100 K but no insulator–metal transition is seen. Magnetic field (H) produces insulator metal transition and colossal decrement in the resistivity (ρ) in the 36 nm film. At T < TC, ρ–H curves show strong hysteresis, which is a signature of a first-order phase transition. In the 80 nm a paramagnetic insulator to ferromagnetic metal transition occurs at TC ≈ 145 K but magnetic field induced colossal decrease in resistivity and the ρ–H hysteresis is reduced considerably. Our results clearly show that the electrical transport is strongly influenced by the phase separation in these films. The differences in the magnetic properties and magnetic field dependent electrical transport behaviours are attributed to the modulation of the phase separated state due to the strain induced variation in the fraction of the competing ferromagnetic metallic and antiferromagnetic-charge ordered insulating phases.

Atomic layer deposition of Zn(O,S) thin films with tunable electrical properties by oxygen annealing

Zinc oxysulfide, Zn(O,S), films grown by atomic layer deposition were annealed in oxygen to adjust the carrier concentration. The electron carrier concentration of Zn(O,S) can be reduced by several orders of magnitude from 1019 to 1015 cm−3 by post-deposition annealing in oxygen at temperatures from 200 °C to 290 °C. In the case of Zn(O,S) with S/Zn = 0.37, despite the considerable change in the electron carrier concentration, the bandgap energy decreased by only ∼0.1 eV, and the crystallinity did not change much after annealing. The oxygen/zinc ratio increased by 0.05 after annealing, but the stoichiometry remained uniform throughout the film.

Effects of Oxygen and Forming Gas Annealing on ZnO TFTs

ABSTRACTZnO TFTs with bottom gate top S/D contact architecture were fabricated by sputtering of ZnO with layer thicknesses from 30 nm to 100 nm. The effect of post deposition annealing in oxygen and forming gas atmospheres at 400°C to 500°C on the devices was investigated. The tendencies of a lower threshold voltage Vth and a higher saturation mobility μsat for higher annealing temperature can be observed for both oxygen and forming gas annealing. Reduction of trap density in oxygen annealing and additional hydrogen incorporation in forming gas annealing play an important role for these electrical parameters. Morphological changes of increased grain size and fewer grain boundaries in the channel also contribute to tendencies in electrical characteristics of ZnO TFTs.

Control of Interface Traps in HfO2 Gate Dielectric on Silicon

The effects of postdeposition annealing (PDA) on the interface between HfO2 high-k dielectric and bulk silicon were studied in detail. The key challenges of successfully adopting the high-k dielectric/Si gate stack into advanced complementary metal–oxide–semiconductor (CMOS) technology are mostly due to interfacial properties. We have proposed a PDA treatment at 600°C for several different durations (5 min to 25 min) in nitrogen or oxygen (95% N2 + 5% O2) ambient with a 5-nm-thick HfO2 film on a silicon substrate. We found that oxidation of the HfO2/Si interface, removal of the deep trap centers, and crystallization of the film take place during the postdeposition annealing (PDA). The optimal PDA conditions for low interface trap density were found to be dependent on the PDA duration. The formation of an amorphous interface layer (IL) at the HfO2/Si interface was observed. The growth was due to oxygen incorporated during thermal annealing that reacts with the Si substrate. The interface traps of the bonding features, defect states, and hysteresis under different PDA conditions were studied using x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM), and leakage current density–voltage (J–V) and capacitance–voltage (C–V) techniques. The results showed that the HfO2/Si stack with PDA in oxygen showed better physical and electrical performance than with PDA in nitrogen. Therefore, PDA can improve the interface properties of HfO2/Si and the densification of HfO2 thin films.

Improvement of TDDB reliability, characteristics of HfO 2 high-k/metal gate MOSFET device with oxygen post deposition annealing

In this work, influences of oxygen effect on an Hf-based high-k gate dielectric were investigated. A post deposition annealing (PDA) including oxygen ion after high- k dielectric deposition was used to improve reliability of the Hf-based high-k/metal gate device. The basic electrical characteristics of devices were compared with and without the PDA process. Experiment results show that the oxygen PDA did not degrade the drive current and effective oxide thickness of the Hf-based gate devices. In addition, reliability issues such as positive bias instability, negative bias instability and TDDB were also improved by the oxygen PDA significantly. During the TDDB test, the charge trapping was characterized by an in situ charge pumping system, which could make us to understand the variations of interface trap during the reliability stress easily.

Fabrication and characterization of all-oxide heterojunction p-CuAlO 2 + x /n-Zn 1 − x Al xO transparent diode for potential application in “invisible electronics”

Transparent p–n heterojunction diodes have been fabricated by p-type copper aluminum oxide (p-CuAlO 2 + x ) and n-type aluminum doped zinc oxide (n-Zn 1 − x Al xO) thin films on glass substrates. The n-layers are deposited by sol-gel-dip-coating process from zinc acetate dihydrate (Zn(CH 3COO) 2·2H 2O) and aluminum nitrate (Al(NO 3) 3·9H 2O). Al concentration in the nominal solution is taken as 1.62 at %. P-layers are deposited onto the ZnO:Al-coated glass substrates by direct current sputtering process from a prefabricated CuAlO 2 sintered target. The sputtering is performed in oxygen-diluted argon atmosphere with an elevated substrate temperature. Post-deposition oxygen annealing induces excess oxygen within the p-CuAlO 2 + x films, which in turn enhances p-type conductivity of the layers. The device characterization shows rectifying current–voltage characteristics, confirming the proper formation of the p–n junction. The turn-on voltage is obtained around 0.8 V, with a forward-to-reverse current ratio around 30 at ± 4 V. The diode structure has a total thickness of 1.1 μm and the optical transmission spectra of the diode show almost 60% transmittance in the visible region, indicating its potential application in ‘invisible electronics’. Also the cost-effective procedures enable the large-scale production of these transparent diodes for diverse device applications.

Effect of in-flight annealing and deposition method on gas-sensitive SnO x films made from size-selected nanoparticles

A method which includes synthesis of SnO nanoparticles, size-selection, in-flight oxidation, film formation and post-deposition annealing in oxygen has been investigated. High-temperature in-flight annealing of SnO nanoparticles in the presence of oxygen allowed to assess the effect of this short-time annealing in comparison to post-deposition annealing at lower temperature. This high-temperature annealing was performed in-flight and allowed to keep the crystal size constant, whereas post-deposition high-temperature annealing would have led to crystal growth. Its effect on crystal structure, surface stoichiometry and normalized conductance in ethanol-containing air was investigated. Furthermore, the influence of different particle deposition methods on the crystal phase is shown. Finally, the results indicated that the form of the response transients was markedly different for different gases.