Gadolinium Oxide Thin Films Research Articles

Influence of power on the physical and electrical properties of magnetron sputtered gadolinium oxide thin films for MOS capacitors

The effect of variation in sputtering power on the structural, morphological, compositional and electrical characteristics of Gadolinium oxide (Gd2O3) thin films deposited on Silicon (Si) substrate using RF magnetron sputtering is presented in this paper. All the deposited films were characterized using X-ray diffractometer (XRD), Atomic Force Microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The obtained results indicated that the crystallinity of the films increased with increase in sputtering power and the films deposited at higher power showed the lower rms roughness value. Stoichiometry of the films is closer to the ideal value at a sputtering power of 40 W and further increase in power leads to the formation of an excess concentration of oxygen within the films. Al/Gd2O3/p-Si metal-insulator-semiconductor (MOS) structures were fabricated and the performance of the devices was analyzed using capacitance-voltage (C-V) and current-voltage (J-V) studies. The minimum flat band voltage shift and lowest effective oxide charge density values were obtained from the MOS capacitor with Gd2O3 grown at 40 W power. J-V characterization suggests Schottky and Poole-Frenkel are the dominant conduction in the deposited Gd2O3 films.

Hopping conduction distance of bipolar switching GdOx resistance random access memory thin films devices modified by different constant compliance current

Bipolar switching properties and electrical conduction mechanism of the gadolinium oxide thin film prepared by rf sputtering technology for applications in resistive random access memory devices was investigated in different constant compliance current. The electrical and physical properties of gadolinium oxide thin film were determined by current versus applied voltage (I-V) and XPS measurement. To discuss the electrical conduction mechanism for different constant compliance current, the typical electrical switching curves of gadolinium oxide thin films RRAM devices for different temperature was transferred to fitting. Finally, the activation barrier energy, hopping conduction distance and non-volatile characteristics between the electrons transmission switching behavior in initial metallic filament forming path of the gadolinium oxide thin film RRAM devices was described and explained in physical diagram model.

Characterization of gadolinium oxide thin films with CF4 plasma treatment for resistive switching memory applications

The effect of the CF4 plasma treatment on the gadolinium oxide (GdxOy) thin films for the resistive random access memory (RRAM) applications was investigated. The material properties of the fluorine incorporated GdxOy films were analyzed by the X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and ultraviolet–visible spectroscopy (UV–VIS). Further, the set and reset voltages of the Pt/GdxOy/W RRAM devices with the CF4 plasma treatment were effectively reduced to −1.15 and 2.1V respectively owing to the low Schottky barrier height. The formation of GdF bonds can prevent the oxygen atoms from out-diffusing through Pt grain boundaries into the atmosphere, leading to the superior retention characteristics for over 104s. The CF4 plasma treated GdxOy RRAMs can sustain a resistance ratio of 102 for more than 800 times stable set/reset cycling, suitable for future low-voltage and high-performance nonvolatile memory operation.

Optimization of in situ plasma oxidation of metallic gadolinium thin films deposited by high pressure sputtering on silicon

Gadolinium oxide thin films were deposited on silicon by a two-step process: high pressure sputtering from a metallic gadolinium target followed by an in situ plasma oxidation. Several plasma conditions for metal deposition and oxidation were studied in order to minimize the growth of a SiOx layer at the interface between the high permittivity dielectric and the silicon substrate and to avoid substrate damage. Plasma emission was studied with glow discharge optical spectroscopy. The films were structurally characterized by Fourier transform infrared spectroscopy. Metal–insulator–semiconductor capacitors were fabricated with two different top metals (titanium and platinum) to analyze the influence of deposition conditions and the metal choice. Pt gated devices showed an interfacial SiOx regrowth after a forming gas annealing, while Ti gates scavenge the interface layer.

Plasma-enhanced atomic layer deposition and etching of high-k gadolinium oxide

Atomic layer deposition (ALD) of high-quality gadolinium oxide thin films is achieved using Gd(iPrCp)3 and O2 plasma. Gd2O3 growth is observed from 150 to 350 °C, though the optical properties of the film improve at higher temperature. True layer-by-layer ALD growth of Gd2O3 occurred in a relatively narrow window of temperature and precursor dose. A saturated growth rate of 1.4 Å/cycle was observed at 250 °C. As the temperature increases, high-quality films are deposited, but the growth mechanism appears to become CVD-like, indicating the onset of precursor decomposition. At 250 °C, the refractive index of the film is stable at ∼1.80 regardless of other deposition conditions, and the measured dispersion characteristics are comparable to those of bulk Gd2O3. XPS data show that the O/Gd ratio is oxygen deficient at 1.3, and that it is also very hygroscopic. The plasma etching rate of the ALD Gd2O3 film in a high-density helicon reactor is very low. Little difference is observed in etching rate between Cl2 and pure Ar plasmas, suggesting that physical sputtering dominates the etching. A threshold bias power exists below which etching does not occur; thus it may be possible to etch a metal gate material and stop easily on the Gd2O3 gate dielectric. The Gd2O3 film has a dielectric constant of about 16, exhibits low C–V hysteresis, and allows a 50 × reduction in gate leakage compared to SiO2. However, the plasma enhanced atomic layer deposition (PE-ALD) process causes formation of an ∼1.8 nm SiO2 interfacial layer, and generates a fixed charge of −1.21 × 1012 cm−2, both of which may limit use of PE-ALD Gd2O3 as a gate dielectric.

Gadolinium oxide thin films by atomic layer deposition

Gadolinium oxide thin films have been deposited on Si(1 0 0) by atomic layer deposition (ALD) using as precursors either a β-diketonate-type chelate, namely Gd(thd) 3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione) and ozone or a true organometallic (CpCH 3) 3Gd (Cp=cyclopentadienyl, −C 5H 5) together with water. Self-limiting ALD growth mode was detected for the Gd(thd) 3/O 3 process at 300 °C with a growth rate of 0.3 Å/cycle. In the case of the (CpCH 3) 3Gd/H 2O process, partial decomposition of the metal precursor affected the film growth mechanism. However, at 250 °C, the uniform films obtained from (CpCH 3) 3Gd and H 2O showed almost an ideal stoichiometry with low impurity contents (e.g. 0.5 at% of C) as analyzed by time-of-flight elastic recoil detection analysis (TOF-ERDA). X-ray diffraction data indicated that Gd 2O 3 films obtained by the Cp-based process were crystalline with cubic C-type structure when deposited even at 150 °C. The strongest reflection changed from (4 0 0) to (2 2 2) at deposition temperatures around 200 °C. Oxygen-rich films grown by the Gd(thd) 3/O 3 process were amorphous at deposition temperatures below 250 °C but crystalline with (4 0 0) dominant reflection at temperatures exceeding 250 °C. The films were smooth with both processes at the optimized deposition temperatures. In addition, the dielectric properties were analyzed showing effective permittivity of about 13 for the (CpCH 3) 3Gd/H 2O-processed Gd 2O 3 films.

Characterization of microroughness parameters in gadolinium oxide thin films: A study based on extended power spectral density analyses

Spectral microroughness is a performance-limiting factor for optical thin films like Gd 2O 3, which have dedicative applications in ultraviolet or deep ultraviolet region of the electromagnetic spectrum. Such a morphological parameter of a thin film surface can be very well characterized by power spectral density (PSD) functions. The PSD provides a more reliable description to the topography than the RMS roughness and imparts several useful information of the surface including fractal and superstructure contributions. Through the present study it has been noticed that deposition parameters like evaporation rate and oxygen pressure can play very definite, dominant and predictable roles in the evolution of fractal and superstructures in thin film topographies recorded through atomic force microscopy (AFM). In this work, the PSD functions derived from morphologies of various gadolinia thin films have been fitted with a novel multi peak-shifting Gaussian model along with fractal and k-correlation functions, to extract characteristic parameters of the precision surfaces. Using such information, roughness contributions of the fractal components (substrate dominated), pure film and the aggregates have been successfully extracted. Higher spectral fractal strengths have depicted lower refractive index values. The microroughness and grain sizes of the pure film have been influenced very differently with deposition rate and oxygen pressure. The oxygen pressure strongly influenced the grain sizes where as the deposition rate influenced the microroughness of the gadolinia films.

Properties of high k gate dielectric gadolinium oxide deposited on Si (1 0 0) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100–500eV. The films had a monoclinic Gd2O3 structure with preferred orientation (4¯02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700°C, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented.

Photoluminescence behaviors from stoichiometric gadolinium oxide films

Stoichiometric gadolinium oxide thin films have been grown on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Gadolinium oxide shares Gd2O3 structures although the ratio of gadolinium and oxygen in the film is about 2:1 and a lot of oxygen deficiencies exist. Photoluminescence (PL) measurements have been carried out within a temperature range of 5–300 K. The detailed characters of the PL emission integrated intensity, peak position, and peak width at different temperature were reported and an anomalous photoluminescence behavior was observed. The character of PL emission integrated intensity is similar to that of some other materials such as porous silicon and silicon nanocrystals in silicon dioxide. Four peaks relative to α band and β band were observed also. Therefore we suggest that the nanoclusters with the oxygen deficiencies contribute to the PL emission and the model of singlet-triplet exchange splitting of exciton was employed for discussion.

Correlation of optical and microstructural properties of Gd 2O 3 thin films through phase-modulated ellipsometry and multi-mode atomic force microscopy

Gadolinium oxide thin films have been prepared by electron beam evaporation with different reactive oxygen pressures at low ambient substrate temperature. These thin films have been analyzed with phase-modulated spectroscopic ellipsometry and multi-mode atomic force microscopy (AFM). The distinct influences of oxygen pressure on surface topographies, microstructures and refractive indices of the thin films have been observed from the results of these advanced measurements. Both these techniques have displayed very strong co-relationships in the characterisation results acquired through respective modes of measurements and data analysis. Unequivocally, these two techniques indicated an optimum value of the oxygen pressure leading to best optical and structural properties of such a novel optical coating material.

Studies of the photoconductivity of gadolinium oxide films

The results of experimental studies of the photoconductivity of gadolinium oxide thin films are reported. Metal/Gd2O3/Al structures were obtained by the vacuum evaporation technique. Gd2O3 films of various thicknesses were prepared in an oxygen atmosphere by electron beam evaporation. One electrode was always aluminium, the other was aluminium, copper, chromium, silver or gold. Under illumination the photocurrent ΔI = I − I0 yields a straight line in a plot of log ΔIversus V12 and shows a very weak temperature dependence between 300 and 77 K.