Flexible Ultrathin Chip-Film Patch for Electronic Component Integration and Encapsulation using Atomic Layer-Deposited Al2O3-TiO2 Nanolaminates

Plasma-enhanced atomic layer deposition (PEALD) is utilized to improve the barrier properties of an organic chip-film patch (CFP) when it is used as an implant to prevent moisture and ions from migrating into the embedded electronic circuits. For this purpose, surface condition and material properties of eight modifications of Al2O3-TiO2 nanolaminates sequentially deposited on polyimide PI-2611 films are evaluated in detail. The effect of stress-induced warpage of the deposited Al2O3-TiO2 on the wafer level is calculated with the Stoney equation and reveals higher tensile stress values while increasing the thickness of Al2O3-TiO2 nanolaminates from 20 up to 80 nm. Contact angle measurement and atomic force microscopy are used to investigate the surface energy and wettability, as well as the surface morphology of polyimide-Al2O3-TiO2 interfaces. We show that plasma treatment of pristine polyimide leads to an enhanced adhesion force of the PEAL-deposited layer by a factor of 1.3. The water vapor transmission rate (WVTR) is determined by exposing the coated polyimide films to 85% humidity and 23 °C and yields down to 1.58 × 10-3 g(H2O)/(m2 d). The data obtained are compared with alternative coating processes using the polymers parylene-C and benzocyclobutene (BCB). The latter shows higher WVTR values of 1.2 × 10-1 and 1.7 × 10-1 g(H2O)/(m2 d) compared to the PEALD-PI-2611 systems, indicating lower barrier properties. Two Al2O3-TiO2 modifications with low WVTR values have been chosen for encapsulating the CFP substrates and exposing them in a long-time experiment to chemical and mechanical loads in a chamber filled with phosphate-buffered saline at 37 °C, pH 7.3, and a cyclically applied pressure of 160 mbar (∼120 mm Hg). The electrical leakage behavior of the CFP systems is measured and reveals reliable electrical long-term stability far beyond 11 months, highlighting the great potential of PEALD-encapsulated CFPs.

Membrane Fabrication and Modification by Atomic Layer Deposition: Processes and Applications in Water Treatment and Gas Separation

Membrane-based separation processes are part of most water purification plants worldwide. Industrial separation applications, primarily water purification and gas separation, can be improved with novel membranes or modification to existing ones. Atomic layer deposition (ALD) is an emerging technique that is proposed to upgrade certain kinds of membranes independent of their chemistry and morphology. ALD deposits thin, defect-free, angstrom-scale, and uniform coating layers on a substrate's surface by reacting with gaseous precursors. The surface-modifying effects of ALD are described in the present review, followed by a description of various types of inorganic and organic barrier films and how these can be used in combination with ALD. The role of ALD in membrane fabrication and modification is categorized into different membrane-based groups according to the treated medium, i.e., water or gas. In all membrane types, the ALD-based direct deposition of inorganic materials, mainly metal oxides, on the membrane surface can improve antifouling, selectivity, permeability, and hydrophilicity. Therefore, the ALD technique can broaden the applications of membranes to the treatment of emerging contaminants in water and air. Finally, the advancement, limitations, and challenges of ALD-based membrane fabrication and modification are compared to provide a comprehensive guideline for developing next-generation membranes with improved filtration and separation performance.

Plasma-Assisted Nanofabrication: The Potential and Challenges in Atomic Layer Deposition and Etching

The growing need for increasingly miniaturized devices has placed high importance and demands on nanofabrication technologies with high-quality, low temperatures, and low-cost techniques. In the past few years, the development and recent advances in atomic layer deposition (ALD) processes boosted interest in their use in advanced electronic and nano/microelectromechanical systems (NEMS/MEMS) device manufacturing. In this context, non-thermal plasma (NTP) technology has been highlighted because it allowed the ALD technique to expand its process window and the fabrication of several nanomaterials at reduced temperatures, allowing thermosensitive substrates to be covered with good formability and uniformity. In this review article, we comprehensively describe how the NTP changed the ALD universe and expanded it in device fabrication for different applications. We also present an overview of the efforts and developed strategies to gather the NTP and ALD technologies with the consecutive formation of plasma-assisted ALD (PA-ALD) technique, which has been successfully applied in nanofabrication and surface modification. The advantages and limitations currently faced by this technique are presented and discussed. We conclude this review by showing the atomic layer etching (ALE) technique, another development of NTP and ALD junction that has gained more and more attention by allowing significant advancements in plasma-assisted nanofabrication.

Water vapor and hydrogen gas diffusion barrier characteristics of Al2O3-alucone multi-layer structures for flexible OLED display applications

Organic light emitting diodes (OLEDs) and amorphous oxide semiconductors (AOSs), which are very important technologies in high performance flexible displays, have issues related to degradation due to diffusion of water and hydrogen, respectively. To solve these issues, gas diffusion barrier properties were evaluated with aluminum oxide deposited by atomic layer deposition (ALD) and alucone deposited by molecular layer deposition (MLD) using trimethylaluminum (TMA) as a metal precursor and H₂O and hydroquinone (HQ) as co-reactants, respectively. The water vapor transmission rate (WVTR) and hydrogen gas permeability (HGP) were measured for the fabricated films via electrical calcium tests and vacuum time-lag, respectively. To enhance the diffusion barrier properties, Al₂O₃/alucone hybrid multi-layer structures were successfully deposited through an in situ ALD/MLD process. The 4.5 dyads of the Al₂O₃/alucone structure showed improved barrier properties compared to the single Al₂O₃ film with a WVTR of 8.24 × 10^-5 g m^-2 day^-1 and a HGP of 9.93 × 10^-5 barrer, and factors related to gas diffusion in multi-layer structures were discussed. The stability to external stress was also evaluated based on the WVTR change rate after the bending test, and we confirmed that the stability of the multi-layer structures was improved due to the flexibility of inserted alucone layers. All the developed structures had a high optical transmittance of >80% in the 300-800 nm wavelength region based on UV-vis measurements.

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers

High-density SnO_x and SiO_x thin films were deposited via atomic layer deposition (ALD) at low temperatures (100 °C) using tetrakis(dimethylamino)tin(IV) (TDMASn) and di-isopropylaminosilane (DIPAS) as precursors and hydrogen peroxide (H₂O₂) and O₂ plasma as reactants, respectively. The thin-film encapsulation (TFE) properties of SnO_x and SiO_x were demonstrated with thickness dependence measurements of the water vapor transmission rate (WVTR) evaluated at 50 °C and 90% relative humidity, and different TFE performance tendencies were observed between thermal and plasma ALD SnO_x. The film density, crystallinity, and pinholes formed in the SnO_x film appeared to be closely related to the diffusion barrier properties of the film. Based on the above results, a nanolaminate (NL) structure consisting of SiO_x and SnO_x deposited using plasma-enhanced ALD was measured using WVTR (H₂O molecule diffusion) at 2.43 × 10^-5 g/m² day with a 10/10 nm NL structure and time-lag gas permeation measurement (H₂ gas diffusion) for applications as passivation layers in various electronic devices.

Optical bandgap control in Al2O3/TiO2 heterostructures by plasma enhanced atomic layer deposition: Toward quantizing structures and tailored binary oxides

Atomically thin heterostructures and superlattices are promising candidates for various optoelectronic and photonic applications. Different combinations of Al₂O₃/TiO₂ composites are obtained by plasma enhanced atomic layer deposition (PEALD). Their growth, composition, dispersion relation, and optical bandgap are systematically studied by means of UV/VIS spectrophotometry, spectroscopic ellipsometry (SE), x-ray reflectometry (XRR), scanning transmission electron microscopy(STEM) and x-ray photoelectron spectroscopy (XPS). Besides, an effective medium approximation (EMA) approach is applied to model the heterostructures theoretically. The refractive index and the indirect bandgap of the heterostructures depend on the ratio of the two oxides, while the bandgap is very sensitive to the thicknesses of the barrier and quantum well layers. A large blue shift of the absorption edge from 400 nm to 320 nm is obtained by changing the TiO₂ (quantum well) thickness from ~2 nm to ~0.1 nm separated by ~2 nm of Al₂O₃ (barrier) layers. PEALD unfolds the possibility of achieving optical quantizing effects within complex heterostructures enabling control of their structures down to atomic scale. It enables a path towards atomic scale processing of new 'artificial' materials with desired refractive indices and bandgap combinations by precise control of their compositions.

Structural, optical, and mechanical properties of TiO2 nanolaminates

The structural, optical, and mechanical properties of TiO₂ nanolaminate films grown by plasma-enhanced atomic layer deposition are discussed. Several TiO₂/Al₂O₃ and TiO₂/SiO₂ compositions have been investigated to study the effect of the relative number of ALD oxide cycles on the film properties to obtain a high refractive index coating with low optical losses, low roughness, and low mechanical stress. The formation of crystalline TiO₂ observed at high deposition temperature, or film thickness was inhibited by periodically introducing ultra-thin amorphous layers into the film. Only 4 ALD cycles of Al₂O₃ (corresponding to ca. 0.5 nm) between 335 ALD cycles of TiO₂ (ca. 11 nm) form a closed, distinct layer suppressing the crystallization in TiO₂ film. Consequently, the roughness of the pure TiO₂ film is reduced from ca. 20 nm rms to 1 nm rms in the 335/4 nanolaminate, with only a slight decrease of the refractive index from 2.46 to 2.44 in 100 nm pure TiO₂ and the nanolaminate, respectively. The refractive indices of the nanolaminates in various compositions vary between 2.38 and 2.50 at 632 nm, and the corresponding optical losses from the films are low. The mechanical stress was reduced to about 140 MPa in several TiO₂/Al₂O₃ nanolaminates; however, lower mechanical stress has not been obtained with the studied compositions. The nanolaminate structure is preserved up to 600 °C annealing temperature. After annealing at 800 °C, the individual layers interdiffuse into each other so that no distinct nanolaminate structure is detected. By using TiO₂/Al₂O₃ nanolaminates with reduced mechanical stress, a narrow bandpass filter was realized on various substrates, including half-ball and aspherical lenses.

Sub-10 nm Nanolaminated Al2O3/HfO2 Coatings for Long-Term Stability of Cu Plasmonic Nanodisks in Physiological Environments

By supporting localized plasmon modes, metal-based plasmonic nanostructures can confine optical fields at deep-subwavelength scale in various applications, such as biological and chemical sensing, nanoscale light emission, and solar energy harvesting. While Cu is a low-cost complementary metal oxide semiconductor (CMOS) compatible material, its poor chemical stability limits the use of Cu plasmonic nanodevices in corrosive biochemical aqueous environments. In this paper, we demonstrate that sub-10 nm Al₂O₃/HfO₂ nanolaminated coatings can significantly extend the lifetime of Cu nanodisk arrays from ∼5 h to ∼180 days in the physiological environment of 1× phosphate-buffered saline (PBS) at 37 °C. Cu nanodisk arrays are fabricated using freestanding Au nanohole array films as the physical vapor deposition masks and sub-10 nm nanolaminated coatings composed of alternating Al₂O₃ and HfO₂ nanolayers are grown on Cu nanodisk arrays by atomic layer deposition (ALD). Time-dependent optical extinction measurements of Cu nanodisk arrays are conducted in 1× solutions at 37 °C to investigate the anticorrosion performance for different pure and nanolaminated ALD coatings. We observe a linear relationship between the lifetime of Cu nanodisk arrays in 1× PBS at 37 °C and the nanolaminated coating thickness, and ∼1.3 nm nanolaminated coatings of ∼10 ALD cycles can extend the lifetime of Cu plasmonics up to ∼20 days. Furthermore, we find that the anticorrosion performance of Al₂O₃/HfO₂ nanolaminated ALD coatings strongly depends on the processing and the geometric parameters, such as the annealing temperature and the nanolaminated backbone unit size.

Passivation of black phosphorus saturable absorbers for reliable pulse formation of fiber lasers

Black phosphorus (BP) has attracted increasing attention due to its unique electrical properties. In addition, the outstanding optical nonlinearity of BP has been demonstrated in various ways. Its functionality as a saturable absorber, in particular, has been validated in demonstrations of passive mode-locked lasers. However, normally, the performance of BP is degraded eventually by both thermal and chemical damage in ambient conditions. The passivation of BP is the critical issue to guarantee a stable performance of the optical devices. We quantitatively characterized the mode-locked lasers operated by BP saturable absorbers with diversified passivation materials such as polydimethylsiloxane (PDMS) or Al₂O₃, considering the atomic structure of the materials, and therefore the hydro-permeability of the passivation layers. Unlike the BP layers without passivation, we demonstrated that the Al₂O₃-passivated BP layer was protected from the surface oxidation reaction in the long-term, and the PDMS-passivated one had a short-term blocking effect. The quantitative analysis showed that the time-dependent characteristics of the pulsed laser without passivation were changed with respect to the pulse duration, spectral width, and time-bandwidth product displaying 550 fs, 2.8 nm, and 0.406, respectively. With passivation, the changes were limited to <43 fs, <0.3 nm, and <0.012, respectively.

Quantum confinement induced ultra-high intensity interfacial radiative recombination in nanolaminates

Al₂O₃/ZnO, Al₂O₃/TiO₂, TiO₂/ZnO and MgO/ZnO nanolaminates (NLs) were prepared using atomic layer deposition to explore the dependence of luminescence characterization on the sublayer width and constituents. When the ZnO sublayer width is larger than the Bohr radius in Al₂O₃/ZnO NLs, the UV luminescence arising from ZnO is reduced and even quenched with decreasing the ZnO width due to the nonradiative recombination (NR) caused by the existence of interface states, while for the ZnO width smaller than the Bohr radius, a visible luminescence rather than UV emission is observed and further enhanced with decreasing the ZnO width. It is also found that the visible luminescence needs a certain width of Al₂O₃ and is extinguished by the replacement of Al₂O₃ with TiO₂. A theoretical model based on the configuration coordination and quantum confinement effect is proposed to understand the physical origin underlying the intriguing optical behaviour. The mechanism has generality and is applicable for other NLs as well, such as Al₂O₃/TiO₂ and MgO/ZnO NLs with ultra-thin sublayers in which similar luminescence enhancements are also observed. This work may provide a promising approach for realizing high performance luminescence with various wavelengths for electro- and photo-luminescence applications in NLs.

Effects of Bilayer Thickness on the Morphological, Optical, and Electrical Properties of Al2O3/ZnO Nanolaminates

This report mainly focuses on the investigation of morphological, optical, and electrical properties of Al₂O₃/ZnO nanolaminates regulated by varying bilayer thicknesses. The growth mechanism of nanolaminates based on atomic layer deposition and Al penetration into ZnO layer are proposed. The surface roughness of Al₂O₃/ZnO nanolaminates can be controlled due to the smooth effect of interposed Al₂O₃ layers. The thickness, optical constants, and bandgap information of nanolaminates have been investigated by spectroscopic ellipsometry measurement. The band gap and absorption edge have a blue shift with decreasing the bilayer thickness on account of the Burstein-Moss effect, the quantum confinement effect and the characteristic evolution of nanolaminates. Also, the carrier concentrations and resistivities are found to be modified considerably among various bilayer thicknesses. The modulations of these properties are vital for Al₂O₃/ZnO nanolaminates to be used as transparent conductor and high resistance layer in optoelectronic applications.

Performance improvement by alumina coatings on Y3Al5O12:Ce3+ phosphor powder deposited using atomic layer deposition in a fluidized bed reactor

To improve the thermal stability, Al₂O₃ has been successfully coated on a Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor powder host by using the Atomic Layer Deposition (ALD) approach in a fluidized bed reactor.