Thick Atomic Layer Deposition Research Articles

Examination of nonideal film growth in batch atomic layer deposition for plasma-resistant coatings

Atomic layer deposition (ALD) can be used to fabricate protective coatings including moisture barrier layers for organic light emitting diodes, anticorrosion layers for photoelectrodes, and plasma-resistant coating for semiconductor manufacturing equipment, which necessitates the deposition of large and thick ALD films via batch ALD. However, batch ALD for the fabrication of large-area and thick coatings exhibits nonideal film growth, a phenomenon that cannot solely be explained by transient concentration distribution within the deposition chamber. This paper describes the application of precursor “exposure” (in the unit of Langmuir, or Pa s), defined as the integral of concentration over time, as a metric to assess the growth per cycle (GPC) distribution under nonideal ALD conditions, demonstrating that the local GPC correlates well with the cumulative precursor exposure at that site. Consequently, this measure can effectively predict the nonuniformity (NU) distribution of film thickness and facilitate the determination of optimal operating conditions that ensure maximal uniformity of exposure. Under this condition, the intrafilm NU of ALD-grown Al2O3 film (nominal thickness 300 nm) was reduced to 1.2%, and the interfilm NU is diminished to as low as 3.3%. These values represent reductions of 40% and 45%, respectively, compared to the NU levels observed under nonideal conditions (insufficient trimethylaluminum, TMA exposure downstream). The plasma etch rate of ALD-deposited films is merely 4.3 nm/min, representing a reduction of one-half compared to films deposited under nonideal conditions (9.8 nm/min) with overload TMA exposure downstream leading to chemical vapor deposition-like reactions.

Atomically Precise Graphene Nanoribbon Transistors with Long-Term Stability and Reliability.

Atomically precise graphene nanoribbons (GNRs) synthesized from the bottom-up exhibit promising electronic properties for high-performance field-effect transistors (FETs). The feasibility of fabricating FETs with GNRs (GNRFETs) has been demonstrated, with ongoing efforts aimed at further improving their performance. However, their long-term stability and reliability remain unexplored, which is as important as their performance for practical applications. In this work, we fabricated short-channel FETs with nine-atom-wide armchair GNRs (9-AGNRFETs). We revealed that the on-state (ION) current performance of the 9-AGNRFETs deteriorates significantly over consecutive full transistor on and off logic cycles, which has neither been demonstrated nor previously considered. To address this issue, we deposited a thin ∼10 nm thick atomic layer deposition (ALD) layer of aluminum oxide (Al2O3) directly on these devices. The integrity, compatibility, electrical performance, stability, and reliability, of the GNRFETs before and/or after Al2O3 deposition were comprehensively studied. The results indicate that the observed decline in electrical device performance is most likely due to the degradation of contact resistance over multiple measurement cycles. We successfully demonstrated that the devices with the Al2O3 layer operate well up to several thousand continuous full cycles without any degradation. Our study offers valuable insights into the stability and reliability of GNR transistors, which could facilitate their large-scale integration into practical applications.

Measuring Local Atomic Structure Variations through the Depth of Ultrathin (<20 nm) ALD Aluminum Oxide: Implications for Lithium-Ion Batteries

Understanding the atomic structure of ultrathin (<20 nm) atomic layer deposition (ALD) coatings is critical to establish structure–property relationships and accelerate the application of ALD films to stabilize battery interfaces. Previous studies have measured the atomic structure of nanoscale ALD films using cryogenic electron diffraction with a large (∼200 nm) beam diameter. However, for ultrathin ALD coatings, these measurements provide only ensemble average structural information and cannot be used to directly measure differences in atomic structure through the depth of the ALD film. In this study, we localize the electron beam to a small (∼5 nm) spot size using cryogenic scanning transmission electron microscope (STEM), and we collect electron diffraction data at multiple points along the depth of a 12 nm thick ALD AlOx film deposited onto a carbon nanotube (CNT) substrate without a contribution from the substrate. We couple these diffraction measurements with pair distribution function (PDF) analysis and iterative reverse Monte Carlo-molecular statics (RMC-MS) modeling to compare atomic structure metrics at different positions in the film depth. We interpret the modeling results considering the three-dimensional (3D) concentric cylindrical sample geometry of a CNT with uniform AlOx coating. These measurements confirm a two-phase bulk/interface structural model proposed previously for ALD AlOx and indicate that the interfacial layer at the CNT–AlOx interface is 2.5 nm thick─5 times larger than previously reported. This report demonstrates direct measurement of atomic structural variations across nanoscale material interfaces that is of broad interest for electrochemical applications and will help inform the use of ALD coatings to stabilize lithium-ion battery interfaces.

MOSFETs on (110) C–H Diamond: ALD Al₂O₃/Diamond Interface Analysis and High Performance Normally-OFF Operation Realization

Hole concentration of 2-D hole gas (2DHG) on (110) diamond is higher than that on other faces, making it the best choice for power device application. Detailed analysis of atomic layer deposition (ALD) Al₂O₃/(110) C&#x2013;H diamond interface structure is of vital importance. MOSFETs with thin (10 nm) and thick (100 nm) ALD Al₂O₃ layer were made in this study. The microstructure of Al₂O₃ on (110) C&#x2013;H diamond was analyzed. Abrupt interface of ALD Al₂O₃/C&#x2013;H diamond was observed through high resolution transmission electron microscope (HRTEM). Cascode structure using diamond MOSFETs and enhancement mode silicon MOSFET is fabricated and its high performance is confirmed.

On the corrosion, stress corrosion and cytocompatibility performances of ALD TiO2 and ZrO2 coated magnesium alloys

Magnesium alloys are increasingly studied as materials for temporary implants. However, their high corrosion rate and susceptibility to corrosion-assisted cracking phenomena, such as stress corrosion cracking (SCC), continue to prevent their mainstream use. Recently, coatings have been considered to provide an effective solution to these issues and researchers have focused their attention on Atomic Layer Deposition (ALD). ALD stands out as a coating technology due to the outstanding film conformality and density achievable, and has shown encouraging preliminary results in terms of reduced corrosion rate and reduced SCC susceptibility. Here, we contribute to the ongoing interest in ALD-coated Mg alloys, providing a comprehensive characterisation of the effect of 100 nm thick ALD TiO2 and ZrO2 coatings on the corrosion behaviour and SCC susceptibility of AZ31 alloy. Moreover, we also investigate the effect of these coatings on the induced biological response. Our results suggest that the ALD coatings can improve the corrosion and SCC resistance of the Mg alloy, with the ZrO2 ALD coating showing the best improvements. We suggest that the different corrosion behaviours are the cause of the cytocompatibility results (only the ZrO2 ALD coating was found to meet the demands for cellular applications). Finally, we leverage on considerations about the coatings’ wettability, electrochemical stability and surface integrity to justify the different results.

On the evaluation of ALD TiO2, ZrO2 and HfO2 coatings on corrosion and cytotoxicity performances

Magnesium alloys have been widely studied as materials for temporary implants, but their use has been limited by their corrosion rate. Recently, coatings have been proven to provide an effective barrier. Though only little explored in the field, Atomic Layer Deposition (ALD) stands out as a coating technology due to the outstanding film conformality and density achievable. Here, we provide first insights into the corrosion behavior and the induced biological response of 100 nm thick ALD TiO 2 , HfO 2 and ZrO 2 coatings on AZ31 alloy by means of potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), hydrogen evolution and MTS colorimetric assay with L929 cells. All three coatings improve the corrosion behavior and cytotoxicity of the alloy. Particularly, HfO 2 coatings were characterized by the highest corrosion resistance and cell viability, slightly higher than those of ZrO 2 coatings. TiO 2 was characterized by the lowest corrosion improvements and, though generally considered a biocompatible coating, was found to not meet the demands for cellular applications (it was characterized by grade 3 cytotoxicity after 5 days of culture). These results reveal a strong link between biocompatibility and corrosion resistance and entail the need of taking the latter into consideration in the choice of a biocompatible coating to protect degradable Mg-based alloys.

Anodic TiO2 nanotube walls reconstructed: Inner wall replaced by ALD TiO2 coating

A reconstruction process of TiO2 nanotube (TNT) layers towards their superior photoelectrochemical performance and photocatalytic activity is presented. At first, TNT layers (~5 μm thick, ~250 nm in diameter) were prepared via electrochemical anodization to obtain double-wall (DW) TNT layers. Second, a selective chemical treatment was conducted to etch the inner wall, yielding single-wall (SW) TNT layers. Third, TNT layers were coated by an additional approx. 5.5 nm, 11 nm, and 16 nm thick TiO2 coatings, respectively, using Atomic Layer Deposition (ALD). A pronounced increase in the incident photon-to-electron conversion efficiency (reaching ~85% at λ = 350 nm) was achieved on SW TNT layers coated with 11 nm thick ALD coatings compared to SW without coating (~35% at λ = 350 nm). This is due to the optimal thickness of the ALD TiO2 coating that passivates surface states and improves the separation of the photogenerated charge carriers. Photocatalytic performance of SW TNT layers with 11 nm thick ALD coatings (rate constant; k = 0.1156 min−1) was increased by approx. 10-times compared to that of the nowadays most reported blank DW TNT layers (rate constant; k = 0.0119 min−1).

Ultraviolet laser damage properties of single-layer SiO2 film grown by atomic layer deposition

Optical properties and ultraviolet laser damage of single-layer atomic layer deposition (ALD) SiO2 films were investigated. ALD SiO2 films of high transparency shows weak absorption at 355nm. The absorption at 355 nm measured by laser calorimeter varies linearly with the film thickness with absorption coefficient of ∼0.76 ppm/nm. Such absorption is considered originating from various point defects in ALD SiO2 film. Fourier transform infrared (FTIR) spectra confirm the presence of point defects in ALD SiO2 films including non-bridging oxygen atoms and residual OH groups. Nanosecond laser-induced damage of ALD SiO2 film at 355 nm was investigated. The damage threshold and damage morphology suggest that laser-induced damage of ALD film is associated with point defect clusters which can absorb enough laser energy to initiate micro-explosion in ALD films. Furthermore, the ALD films were conditioned with sub-nanosecond ultraviolet laser. Significant improvement in damage resistance has been demonstrated after sub-nanosecond laser conditioning. After laser conditioning to 3 J/cm2, the damage threshold of 535 nm thick ALD film increased from 5.5 J/cm2 to 14.9 J/cm2 and improved about 170%. Annealing of point defects by sub-nanosecond ultraviolet laser is supposed to be the reason for the improvement of the damage resistance.

Bidirectional Self-Folding with Atomic Layer Deposition Nanofilms for Microscale Origami.

Origami design principles are scale invariant and enable direct miniaturization of origami structures provided the sheets used for folding have equal thickness to length ratios. Recently, seminal steps have been taken to fabricate microscale origami using unidirectionally actuated sheets with nanoscale thickness. Here, we extend the full power of origami-inspired fabrication to nanoscale sheets by engineering bidirectional folding with 4 nm thick atomic layer deposition (ALD) SiNx-SiO2 bilayer films. Strain differentials within these bilayers result in bending, producing microscopic radii of curvature. We lithographically pattern these bilayers and localize the bending using rigid panels to fabricate a variety of complex micro-origami devices. Upon release, these devices self-fold according to prescribed patterns. Our approach combines planar semiconductor microfabrication methods with computerized origami design, making it easy to fabricate and deploy such microstructures en masse. These devices represent an important step forward in the fabrication and assembly of deployable micromechanical systems that can interact with and manipulate micro- and nanoscale environments.

In vacuo atomic layer deposition and electron tunneling characterization of ultrathin dielectric films for metal/insulator/metal tunnel junctions

Metal-insulator-metal tunnel junctions (MIMTJs) are an enabling technology for future electronics including advanced computing, data storage, sensors, etc. MIMTJs are formed by inserting an ultrathin insulating layer, known as the tunnel barrier (TB), between metal electrodes. Devices based on MIMTJs have advantages of enhanced quantum coherent transport, fast speed, small size, and energy efficiency. The performance of MIMTJs depends critically on the thickness and quality of the tunnel barrier. Specifically, the tunneling current, for example, the superconducting critical current in superconductor-insulator-superconductor Josephson junctions (JJs) or the spin tunneling current in ferromagnetic-insulator-ferromagnetic magnetic tunnel junctions (MTJs), decreases exponentially with the TB thickness. This means thinner TBs would enable stronger coherent tunneling in MIMTJs. In addition, the defects in the TBs can degrade the quantum coherence of electrons (spins) of JJs and MTJs, respectively, resulting in decoherence and degraded performance of the MIMTJs. This justifies the urgent need in research and development of ultrathin (subnanometers to 1 nm) pinhole-free and defect-free TBs beyond the current state-of-the-art TBs of larger thickness (&amp;gt;1–2 nm) and high defect concentration made using thermal diffusion of oxygen or physical vapor deposition (PVD) including magnetron sputtering and molecular beam epitaxy. Atomic layer deposition (ALD) can provide a unique resolution to achieving ultrathin and defect-free dielectric TBs for high-performance MIMTJs for future electronics. In this article, a review on their recent effort in the development of in vacuo ALD for the fabrication of ultrathin TBs for JJs and MTJs is presented. A custom-designed system that integrates high-vacuum/ultrahigh-vacuum PVD, ALD, and scanning probe microscopy was established for in vacuo fabrication of MIMTJs and characterization of the electronic properties of ALD TBs including Al2O3, MgO, and Al2MgO4 on both superconductor metals (Al) and ferromagnetic metals (Fe and FeCoB). Capacitors with ALD dielectric of thickness in the range of 1–5 nm were also constructed for the characterization of the dielectric properties of the ALD TBs. The authors have found that the metal-insulator interface plays a critical role in controlling the quality of the ALD TBs including the tunnel barrier height, dielectric constant, electric breakdown, and uniformity. They have shown that JJs and MTJs with 0.1–1.0 nm thick ALD Al2O3 TBs can be obtained with highly promising performance. The result obtained suggests that the in vacuo ALD may provide a unique approach toward MIMTJs with an atomic-scale control of the device structure required for high-performance future electronics.

Plasma-Assisted ALD of LiPO(N) for Solid State Batteries

All solid state 3D batteries are pursued for their increased safety and high power capabilities. At present conformal coating of the solid electrolyte remains one of the key hurdles for the implementation of such devices. In the present work we investigate atomic layer deposition (ALD) as means of conformal deposition of lithium phosphate (Li3PO4) and nitrogen doped lithium phosphates (LiPON). These processes are characterized here to obtain the highest possible Li-ion conductivity. Li3PO4 is shown to yield a conductivity of 10−10 S/cm at 25°C. On the other hand, an optimized LiPON process gave rise to a Li-ion conductivity of 5⋅10−7 S/cm at 25°C. In addition, good conformality of the LiPON process was shown on high aspect ratio pillars. Furthermore, a solid state battery device was fabricated comprising a Li4Ti5O12 cathode, a 70 nm thick ALD LiPON solid electrolyte and a metallic lithium anode. This finding indicates that a layer down to 70 nm can be made pinhole free.

In situ atomic layer deposition and electron tunneling characterization of monolayer Al2O3 on Fe for magnetic tunnel junctions

Magnetic tunnel junctions (MTJs), formed through sandwiching an ultrathin insulating film (so-called tunnel barrier or TB), with ferromagnetic metal electrodes, are fundamental building blocks in magnetoresistive random access memory (MRAM), spintronics, etc. The current MTJ technology employs physical vapor deposition (PVD) to fabricate either amorphous AlOx or epitaxial MgO TBs of thickness around 1 nm or larger to avoid leakage caused by defects in TBs. Motivated by the fundamental limitation in PVD in, and the need for atomically thin and defect-free TBs in MTJs, this work explores atomic layer deposition (ALD) of 1-6 Å thick Al2O3 TBs both directly on Fe films and with an ultrathin Al wetting layer. In situ characterization of the ALD Al2O3 TB was carried out using scanning tunneling spectroscopy (STS). Despite a moderate decrease in TB height Eb with reducing Al wetting layer thicknesses, a remarkable Eb of ∼1.25 eV was obtained on 1 Å thick ALD Al2O3 TB grown directly on an Fe electrode, which is more than twice of that of thermal AlOx TB (∼0.6 eV). Achieving such an atomically thin low-defect TB represents a major step towards improving spin current tunneling in MTJs.

Urchin-inspired ZnO-TiO2 core-shell as building blocks for dye sensitized solar cells

We applied the core-shell concept to an urchin-inspired ZnO nanowire photoanode building block as a means to increase the electron transport and reduce recombination between nanowire and electrolyte. Dye-sensitized solar cells (DSSCs) were prepared, for the first time, from arrays of urchin-like ZnO nanowire building blocks covered with a thin layer of anatase TiO2 by atomic layer deposition (ALD). An increase in the cell open-circuit voltage (VOC) and an improvement in the conversion efficiency were observed when the urchin-like ZnO building blocks were coated with 10nm thick TiO2 ALD shells in combination with 10μm thick top layer of TiO2 nanoparticles of 15.8nm size. Using urchin-like ZnO nanowires as building blocks can improve the light-scattering and provide a higher surface area with a great control of the nanowire dimensions to increase the dye loading and reduce the electron collection path. The addition of a thin TiO2 blocking layer decreases the recombination of charges in such a high surface area nanostructure.

Atomic layer deposited ultrathin metal nitride barrier layers for ruthenium interconnect applications

Resistance capacitance time delay in Cu interconnects is becoming a significant factor requiring further performance improvements in future nanoelectronic devices. Choice of alternate interconnect materials, for example, refractory metals, and subsequent integration with underlying barrier and liner layers are extremely challenging for the sub-10 nm nodes. The development of conformal deposition processes for alternate interconnects, liner, and barrier materials are crucial in order for implementation of a possible replacement for Cu interconnects for narrow line widths. In this study, the authors report on ultrathin (∼3 nm) chemical vapor deposition (CVD) grown ruthenium films on 0.5 and 1 nm thick metal nitride (TiN, TaN) barrier layers deposited via atomic layer deposition (ALD). Using scanning electron microscopy, the authors determined the effect of the underlying barrier layer on the coverage of the ruthenium overlayer. The authors utilized synchrotron x-ray diffraction with in situ rapid thermal annealing to investigate the thermal stability of the barrier layers and determine the effective activation energies of barrier failure leading to ruthenium monosilicide formation. For Ru films deposited directly on Si and on 0.5 nm MN (M = Ti, Ta) covered Si substrates, silicide formation proceeds via a two-step crystallization process involving lateral nucleation above ∼440 °C followed by thickening of the ruthenium monosilicide layer above ∼520 °C. This silicidation temperature of ∼440 °C could be potentially problematic in back-end-of-the-line (BEOL) processing since it is close to the typical thermal budget used. However ∼1 nm thick ALD MN (M = Ti, Ta) was found to be adequate to block silicide formation up to ∼580 and ∼620 °C for TiN and TaN, respectively, and also aided in superior coverage of the CVD ruthenium overlayer (&amp;gt;90%). The results reported here might be useful to ascertain annealing temperature and time for BEOL process and integration optimization without reaching a state where ruthenium silicides start forming.

Photodriven Oxidation of Surface-Bound Iridium-Based Molecular Water-Oxidation Catalysts on Perylene-3,4-dicarboximide-Sensitized TiO2 Electrodes Protected by an Al2O3 Layer

Improving stability and slowing charge recombination are some of the greatest challenges in the development of dye-sensitized photoelectrochemical cells (DSPECs) for solar fuels production. We have investigated the effect of encasing dye molecules in varying thicknesses of Al2O3 deposited by atomic layer deposition (ALD) before catalyst loading on both the stability and the charge transfer dynamics in organic dye-sensitized TiO2 photoanodes containing iridium-based molecular water-oxidation catalysts. In the TiO2|dye|Al2O3|catalyst electrodes, a sufficiently thick ALD layer protects the perylene-3,4-dicarboximide (PMI) chromophores from degradation over several weeks of exposure to light. The insulating capacity of the layer allows a higher photocurrent in the presence of ALD while initial charge injection is slowed by only 1.6 times, as observed by femtosecond transient absorption spectroscopy. Rapid picosecond-scale catalyst oxidation is observed in the presence of a dinuclear catalyst, IrIr, but is slo...

Plasma - Assisted ALD of Lipo(N) for Solid State Batteries

All solid state 3D batteries are pursued for their increased safety and high power capabilities. At present conformal coating of the solid electrolyte remains one of the key hurdles for the implementation of such devices. In the present work we investigate atomic layer deposition (ALD) as means of conformal deposition of lithium phosphate (Li3PO4) and nitrogen doped lithium phosphates (LiPON). These processes are characterized here to obtain the highest possible Li-ion conductivity. Li3PO4 is shown to yield a conductivity of 10-10 S/cm. On the other hand, an optimized LiPON process gave rise to a Li-ion conductivity of 5×10-7 S/cm. In addition, good conformality of the LiPON process was shown on high aspect ratio pillars. Furthermore, a solid state battery device was fabricated comprising a Li4Ti5O12 cathode, a 70 nm thick ALD LiPON solid electrolyte and a metallic lithium anode. The fabricated device is based on the thinnest solid electrolyte used so far as well as on the first ALD deposited solid electrolyte.

Chemical Protection of Polycarbonate Surfaces by Atomic Layer Deposition of Alumina with Oxygen Plasma Pretreatment

This study reports the effect of an O2 plasma pretreatment of polycarbonate (PC) films for the enhanced integration of Al2O3 films prepared by atomic layer deposition (ALD) on the PC substrate. It is revealed that the plasma treatment produces functional groups on the PC surface, which are essential for the ALD of Al2O3. Specifically, it is revealed that a significant amount of carbonyl groups, essential for the chemisorption of the precursors and covalent binding with the Al2O3 surface protection layer, are present in the plasma‐treated PC surface. To evaluate the chemical resistivity of the PC‐ALD alumina film, an acetone immersion test is conducted. As a result, a severe degradation occurs in the plasma‐untreated PCs, even with a sufficiently thick ALD alumina protection layer. In contrast, the PCs that are plasma‐treated and coated with the ALD alumina exhibit a significantly improved stability against acetone etching. Light transmittance and surface morphology analysis support this improvement.

Investigation of the dipole formation and growth behavior at In2O3|TiO2 heterojunctions using photoemission spectroscopy and atomic force microscopy

This paper discusses the investigation of the dipole formation at In2O3|TiO2 heterojunctions depending on preparation conditions, i.e., cleaning methods. In2O3 films were deposited using atomic layer deposition (ALD) onto solvent and in situ cleaned anatase and rutile film substrates. The interface dipole strength and film thickness were evaluated by photoemission spectroscopy. Our results indicate the formation of a large intrinsic and film thickness dependent interface dipole that reaches its maximum strength at monolayer thick ALD films. In addition, it was observed that UV photoelectron spectroscopy measurements introduced UV induced surface hydroxylation, which resulted in dipole potentials of −0.70 eV and −0.50 eV on solvent cleaned anatase and rutile, respectively. The overlayers also introduced small amounts of band bending (∼0.10 eV) at the interfaces. Taking these effects into account, the total dipole strength at monolayer thick In2O3 films was determined to be −0.96 eV for solvent cleaned anatase and rutile and −0.81 eV for in situ cleaned rutile. The deposition of single ALD cycles on differently cleaned rutile substrates resulted in similar work function values, suggesting little influence of the sample preparation method prior to ALD deposition on the dipole formation. This was assigned to the fact that ALD oxides benefit from ambient water related contamination by integrating the molecules into the growing ALD layer. Highest initial growth was observed on solvent cleaned rutile, followed by in-situ cleaned rutile and solvent cleaned anatase. The In2O3 growth converged at 0.3 Å/c past the nucleation regime.

Protecting silver cultural heritage objects with atomic layer deposited corrosion barriers

Silver, prized throughout history for its luster and shine, develops a black Ag2S tarnish layer that is aesthetically displeasing when exposed to atmospheric pollutants. Tarnishing, and subsequent polishing, leads to irreversible material loss and object damage. Currently, nitrocellulose coatings are often used to prevent silver from tarnishing, however non-uniform coatings and degradation over time limit their effectiveness. Atomic layer deposition (ALD) has been explored as a new method for creating dense, uniform, and conformal coatings on 3-dimensional (3D) objects that are more effective than nitrocellulose in preventing silver from tarnishing. To create high quality ALD coatings on 3D objects, slowing down the ALD process is critical to ensure proper precursor exposure. Non-ideal deposition of organo-oxy-metallic compounds can occur with fast deposition rates that do not allow sufficient flow around 3D objects. The coatings can be removed by dissolving the Al2O3 ALD films in aqueous NaOH. Thicker ALD films prevent defects from occurring on non-ideal surfaces and effectively prevent silver objects from tarnishing under ambient aging conditions. Thick ALD films, deposited with sufficiently long precursor pulse and purge times, may be effective in preventing complex, 3D non-mixed media silver cultural heritage objects from tarnishing.

Impact of La2O3 interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al2O3/La2O3/InGaAs gate stacks deposited by atomic-layer-deposition

We examine the electrical properties of atomic layer deposition (ALD) La2O3/InGaAs and Al2O3/La2O3/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La2O3/InGaAs interface provides low interface state density (Dit) with the minimum value of ∼3 × 1011 cm−2 eV−1, which is attributable to the excellent La2O3 passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La2O3. In order to simultaneously satisfy low Dit and small hysteresis, the effectiveness of Al2O3/La2O3/InGaAs gate stacks with ultrathin La2O3 interfacial layers is in addition evaluated. The reduction of the La2O3 thickness to 0.4 nm in Al2O3/La2O3/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, Dit of the Al2O3/La2O3/InGaAs interfaces becomes higher than that of the La2O3/InGaAs ones, attributable to the diffusion of Al2O3 through La2O3 into InGaAs and resulting modification of the La2O3/InGaAs interface structure. As a result of the effective passivation effect of La2O3 on InGaAs, however, the Al2O3/10 cycle (0.4 nm) La2O3/InGaAs gate stacks can realize still lower Dit with maintaining small hysteresis and low leakage current than the conventional Al2O3/InGaAs MOS interfaces.