Atomic Layer Deposition Of ZrO2 Research Articles

Atomic layer deposition of epitaxial ZrO2 coating on LiMn2O4 nanoparticles for high-rate lithium ion batteries at elevated temperature

Epitaxial ZrO2 coating on LiMn2O4 nanoparticles using atomic layer deposition (ALD) shows high conformality, uniformity and precise thickness control at atomic scale. The thickness of ZrO2 coating can be precisely tailored at 2Å per ALD cycle. Cycling performance of ZrO2 ALD-modified LiMn2O4 cathode material is optimized by tuning the coating thickness via varying ALD growth cycles. The optimal thickness of ZrO2 coating for maximized electrochemical performance of LiMn2O4 is ∼1.2nm grown via 6 ZrO2 ALD layers. LiMn2O4 nanoparticles coated with 6 ZrO2 ALD layers deliver a very high initial discharge capacity of 136.0mAh/g at 1C at 55°C, significantly higher than that of bare LiMn2O4 (124.1mAh/g). The effect of ZrO2 ALD coating on improving capacity retention of LiMn2O4 is even more distinct at high charge/discharge rate at elevated temperature. LiMn2O4 nanoparticles coated with 6 ZrO2 ALD layers after heat treatment retain a discharge capacity of 90.3mAh/g after 100 cycles at 5C at 55°C, while bare LiMn2O4 nanoparticles exhibit a final capacity of 58.8mAh/g. ZrO2-ALD-modified LiMn2O4 nanoparticles show significantly improved specific capacity and enhanced cycleability at high rate at elevated temperature due to the protective effect of ultrathin and high-quality ALD surface coatings.

Surface Modifications of Li-Ion Battery Electrodes with Ultrathin Amphoteric Oxide Coatings for Enhanced Elevated-Temperature Cycleability

ABSTRACTTo enhance cycleability of LiMn2O4 at elevated-temperature we use atomic layer deposition (ALD) method to deposit a variety of ultrathin and highly conformal amphoteric oxide (ZnO, ZrO2, Al2O3) coatings for surface modification of LiMn2O4 electrodes. High-resolution transmission electron microscopic (HRTEM) images of ZnO, ZrO2 and Al2O3 ALD coated LiMn2O4 particles demonstrate the high qualities of ALD coatings with respect to remarkable conformity, homogeneity and uniformity. Two types of ALD-modified LiMn2O4 electrodes are fabricated: one is ALD-coated LiMn2O4 composite electrode, the other is electrode composed of ALD-coated LiMn2O4 particles and uncoated carbon/poly-vinylidenefluoride (PVDF) network. All LiMn2O4 electrodes modified with 6 oxide ALD layers (as thin as ∼1 nm) reveal significantly enhanced electrochemical performances than bare electrodes at both 25°C and 55°C. After 100 electrochemical cycles at 1 C at 55°C, the electrode consisting of LiMn2O4 particles coated with 6 ZnO ALD layers remains the highest capacity of 56.1 mAh/g, higher than 51.1 mAh/g of ZrO2 coated LiMn2O4 particles, 45.8 mAh/g of Al2O3 coated LiMn2O4 particles and 27.0 mAh/g of the bare composite electrode as well as 44.5 mAh/g of the composite electrode coated with 6 ZnO ALD layers. These results indicate that ZnO ALD coating is the most effective protective film for improved cycling stability, followed by ZrO2 and Al2O3. It is also found that amphoteric oxide coating on LiMn2O4 particles is more effective to enhance the cycleability of LiMn2O4 than coating on composite electrode. Furthermore, for coating either on composite electrode or on LiMn2O4 particles, the effect of ALD coating on improving capacity retention and increasing specific capacity of LiMn2O4 is more phenomenal at elevated temperature than at room temperature.

Atomic Layer Deposition of Al-Doped ZrO2 Thin Films as Gate Dielectric for In0.53Ga0.47As

We have investigated the atomic layer deposition (ALD) on SiO2 and III-V (i.e., In0.53Ga0.47As) substrates of Al-doped ZrO2 (Al-ZrO2) films. The aim is to benefit from trimethylaluminum-based chemistry as adopted in the ALD of Al2O3 while concomitantly obtaining an improvement in the value of the dielectric constant of the gate stack. An in situ monitoring of the process with spectroscopic ellipsometry was carried out in order to address the formation of the first few monolayers of the films. The correlation with the structural and chemical characterization provides insights about the interface composition upon ALD. A k value of 19 ± 2 is demonstrated for Al-ZrO2 films deposited on SiO2. The electrical performances of capacitors fabricated on In0.53Ga0.47As including Al-ZrO2 as gate dielectric exhibit encouraging properties compared to those acquired for Al2O3. However, a further optimization of the interface reactivity in order to prevent the formation of undesired In, Ga and As oxidized species appears still needed for the combination of the Al2O3 and ZrO2 ALD processes.

Stability of La2O3 and GeO2 passivated Ge surfaces during ALD of ZrO2 high-k dielectric

La2O3 grown by atomic layer deposition (ALD) and thermally grown GeO2 are used to establish effective electrical surface passivations on n-type (100)-Ge substrates for high-k ZrO2 dielectrics, grown by ALD at 250°C substrate temperature. The electrical characterization of MOS capacitors indicates an impact of the Ge-surface passivation on the interfacial trap density and the frequency dependent capacitance in the inversion regime. Lower interface trap densities can be obtained for GeO2 based passivation even though a chemical decomposition of the oxidation states occur during the ALD of ZrO2. As a consequence the formation of a ZrGeOx compound inside the ZrO2 matrix and a decline of the interfacial GeO2 are observed. The La2O3 passivation provides a stable amorphous lanthanum germanate phase at the Ge interface but also traces of Zr germanate are indicated by X-ray-Photoelectron-Spectroscopy and Transmission-Electron-Microscopy.

The Competitive Reactions in Atomic Layer Deposition of HfO<sub>2</sub>, ZrO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> on Hydroxylated Si(100) Surfaces: A Density Functional Theory Study

The competitive reactions in atomic layer deposition (ALD) of HfO2, ZrO2 and Al2O3 on the hydroxylated Si(100) surfaces are investigated by using density functional theory. The surface reactions in ALD of HfO2 and ZrO2 show large similarities in energetics and geometrical structures. However, both of them show discrepancies with the surface reactions in ALD of Al2O3. In addition, by comparing with the self-termination reactions, we could find that the further growth reactions are both kinetically and thermodynamically more favorable in ALD of HfO2, ZrO2 and Al2O3.

Investigation of Surface Channel InGaAs MOSFETs with Al2O3 and ZrO2 ALD Gate Dielectric

This paper studies In0.53Ga0.47As and In0.7Ga0.3As surface channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) with atomic layer deposition (ALD) of Al2O3 and ZrO2. This work systematically compared performance of InGaAs channel device with different Indium percentage. This includes drain current, transconductance, subthreshold swing, interface trap density and reliability. For both oxide systems, In0.53Ga0.47As channel MOSFETs show better subthreshold swing (125mV/dec versus 160mV/dec for Al2O3 EOT=4.4nm) and higher transconductance than In0.7Ga0.3As channel MOSFETs. Interface trap density measured by conductance method (1.08×1012 eV-1cm-2 versus 3.24×1012 eV-1cm-2 for Al2O3) also suggests that interface between In0.53Ga0.47As substrate and Al2O3 (or ZrO2) high-k dielectric is better than that of In0.7Ga0.3As.

Oxidative Removal of Self-Assembled Monolayers for Selective Atomic Layer Deposition

Using atomic force microscopy (AFM) lithography and self-assembled monolayer (SAM), selective atomic layer deposition (ALD) of ZrO2 was performed to fabricate nanostructures. SAM layer was used for a chemical mask for ZrO2 ALD process and AFM lithography for a nano-scale patterning method. AFM anodic oxidation process was applied to create oxide patterns on ODTS-coated silicon substrates. Subsequent HF etching locally removes oxide, exposing silicon layer underneath. After 100 cycles of ZrO2 ALD process and an oxygen plasma etching, ZrO2 ALD nanostructure of 4~7 nm in height and ~130 nm in line width were fabricated. A growth rate of 0.4~0.7 Aå per cycle is estimated from the AFM scanning at each step, which is slightly less than the typical ALD growth rates of ZrO2.

In Situ Reaction Mechanism Studies on Atomic Layer Deposition of ZrO2 from (CpMe)2Zr(OMe)Me and Water or Ozone

Reaction mechanisms in the atomic layer deposition of ZrO2 from (CpMe)2Zr(OMe)Me and deuterated water or ozone were studied in situ with a quadrupole mass spectrometer and a quartz crystal microbalance at 350 °C. In the D2O process the detected reaction byproducts were as expected MeD, MeOD, and DCpMe. About 80% of the MeD, 40% of the MeOD, and 60% of the DCpMe were formed during the (CpMe)2Zr(OMe)Me pulse in reactions with surface −OD groups and the rest during the D2O pulse. In the ozone process the most important reaction byproducts were CO2 and H2O. Interestingly, about 20% of both of these were released already during the (CpMe)2Zr(OMe)Me pulse and the rest during the O3 pulse. In addition, some MeH and HCpMe were formed during the (CpMe)2Zr(OMe)Me pulse. Furthermore, D2O was used to probe the state of the surface after the (CpMe)2Zr(OMe)Me pulse in the O3 process. Thereby, it could be stated that about 50% of the Me− ligands, 40% of the MeO− ligands, and 60% of the −CpMe ligands were eliminated duri...

In0.53Ga0.47As based metal oxide semiconductor capacitors with atomic layer deposition ZrO2 gate oxide demonstrating low gate leakage current and equivalent oxide thickness less than 1nm

The paper demonstrates properties of metal oxide semiconductor capacitors fabricated on molecular beam epitaxial In0.53Ga0.47As wafers with the atomic layer deposition ZrO2 gate oxide. The equivalent oxide thickness of 0.8nm was obtained for 5nm thick ZrO2, while the gate leakage current density at VFB+1V was as low as 0.1A∕cm2. Sensitivity of capacitance-voltage characteristics to the metal gate work function along with low frequency dispersion of ∼5%/decade served as a strong evidence of a nonpinned Fermi level at the oxide-InGaAs interface. Both electrical and structural properties remain stable up to 800°C.

Selective Atomic Layer Deposition of ZrO2 and Cu Using Soft Lithography

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Self-assembled monolayer resist for atomic layer deposition of HfO2 and ZrO2 high-κ gate dielectrics

A molecular layer resist for HfO2 and ZrO2 atomic layer deposition (ALD) was demonstrated by using self-assembled monolayers (SAMs). X-ray photoelectron spectroscopy and transmission electron microscopy indicated that silicon samples terminated with octadecyltrichlorosilane (ODTS) were deactivated with respect to subsequent ALD of metal oxide gate dielectrics, under conditions in which standard chemical oxide passivated substrates are highly effective templates for ALD film growth. A time-dependent investigation of SAM formation showed that the efficiency of deactivation depends strongly on the quality of the SAMs, with a high-quality, closely packed ODTS film crucial for achieving complete blocking of the HfO2 and ZrO2 ALD process.

A Quantum Chemical Study of the Atomic Layer Deposition of Al2O3 Using AlCl3 and H2O as Precursors

Atomic layer deposition (ALD) of alumina (Al2O3) using water and aluminum trichloride (AlCl3) is studied using density functional theory (DFT). The atomistic mechanisms of the two deposition half-cycles on Al2O3−OH* and Al2O3−Cl* surface sites include the formation of stable intermediates and result in high barriers for HCl formation. Increasing the temperature reduces the stability of the intermediates but also increases the desorption rate of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ALD of HfO2 and ZrO2 from H2O and HfCl4 and ZrCl4, respectively, but differ significantly from the reactions of ALD of Al2O3 from Al(CH3)3 and H2O. Although the high electronegativity of Cl increases the stability of the dative-bonded trapped intermediates in the Zr and Hf chloride cases, the inductive effect is stronger for AlCl3, increasing the stability of adsorbed AlCl3 by 29 kcal/mol relative to the adsorption energy of Al(CH3)3. Furthermore, the ligand-exchang...

Some recent developments in the MOCVD and ALD of high-κ dielectric oxides

A range of high-permittivity (κ) dielectric oxides are currently being investigated as alternatives to SiO2 as the dielectric insulating layer in sub-0.1 μm CMOS technology. Metalorganic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are promising techniques for the deposition of these high-κ dielectric oxides. Some recent developments in precursors for the MOCVD and ALD of ZrO2, HfO2, Zr- and Hf-silicate and the rare earth oxides M2O3 (M = Pr, La, Gd, Nd) are discussed.

Growth and electrical properties of atomic-layer deposited ZrO2/Si-nitride stack gate dielectrics

We deposited ZrO2 thin films by atomic-layer deposition (ALD) using zirconium tertiary–butoxide [Zr(t-OC4H9)4, (ZTB)] and H2O source gases on Si substrates at low temperatures. We grew ZrO2 films layer by layer in a temperature range of 175–250 °C to minimize surface roughness. The deposited ZrO2 film thickness had self-limiting properties with the exposure time of ZTB and vapor pressures of ZTB and H2O. The deposition rate per cycle was independent of the vapor pressure of ZTB from 0.01 kPa to 0.04 kPa. Transmission electron microscopy revealed that the formation of an SiOx interfacial layer could be suppressed by using an ALD ZrO2/ALD Si-nitride (∼0.5 nm) stack structure. We found the fixed charge, interface trap density, and leakage current density in the ALD ZrO2/ALD Si-nitride stack dielectrics to be less than those in ALD ZrO2 dielectrics. In spite of the same equivalent oxide thickness of 1.6 nm, the relative dielectric constant εr (11.5) of the ALD ZrO2/ALD Si-nitride stack capacitor was higher than that (10.5) of the ALD ZrO2 capacitor due to the suppression of formation of the interfacial SiOx layer (1.0–1.5 nm) by an ultrathin ALD Si nitride (∼0.5 nm). The current conduction mechanism is identified as direct tunneling of electron except at very low dielectric fields. Comparing structural and electrical properties, ALD ZrO2/ALD Si-nitride stack dielectrics are promising candidates for sub-0.1-μm metal–oxide–semiconductor field-effect transistors.

Atomic layer deposition of hafnium oxide: A detailed reaction mechanism from first principles

Atomic layer deposition (ALD) of hafnium oxide (HfO2) using HfCl4 and H2O as precursors is studied using density functional theory. The mechanism consists of two deposition half-reactions: (1) HfCl4 with Hf-OH sites, and (2) H2O with Hf-Cl sites. Both half-reactions exhibit stable intermediates with energies lower than those of the final products. We show that increasing the temperature reduces the stability of the complex. However, increasing temperature also increases the dissociation free-energy barrier, which in turn results in increased desorption of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ZrO2 ALD using ZrCl4 and H2O.

Iodide-Based Atomic Layer Deposition of ZrO2: Aspects of Phase Stability and Dielectric Properties

This study is an investigation into the influence of temperature, substrate, and thickness on the properties of ZrO2 thin films grown by atomic layer deposition (ALD). ZrI4 and H2O2 were used as so ...

Modelling of ZrO2 deposition from ZrCl4 and H2O on the Si(1 0 0) surface: initial reactions and surface structures

The mechanism of initial reactions and atomic structures arising in ZrO2 atomic layer deposition (ALD) on a Si(100) substrate using ZrCl4 and H2O as precursors have been studied using first-principle DFT plane-wave and quantum-chemical cluster calculations. The wet oxidation of silicon and reactions corresponding to the first two ZrO2 ALD steps have been examined, and energy characteristics of these reactions have been calculated in the cluster approximation. The results of cluster and periodic calculations have been compared. The growth of amorphous ZrO2 films has been explained based on a simple chemical mechanism.