Bulk and surface micromachined MEMS in thin film SOI technology

Silicon-on-insulator (SOI) technology is emerging as a major contender for heterogeneous microsystems applications. In this work, we demonstrate the advantages of SOI technology for building thin film sensors on membranes as well as three-dimensional (3D) surface micromachined sensors and actuators. The flatness and robustness of the thin membrane as well as the self-assembling of 3D microstructures rely on the chemical release of the microstructures and on the control of the residual stresses building up in multilayered structures undergoing a complete thermal process. The deflection of multilayered structures made of both elastic and plastic thin films results from the thermal expansion coefficient mismatches between the layers and from the plastic flow of a metallic layer. The proposed CMOS-compatible fabrication processes were successfully applied to suspended sensors on thin dielectric membranes such as gas-composition, gas-flow and pressure sensors and to 3D self-assembled microstructures such as thermal and flow sensors.     

SrTiO3薄膜的自组装生长

利用激光分子束外延技术在LaAlO3(100)单晶基片表面生长SrTiO3(STO)薄膜。通过反射式高能电子衍射原位实时监测STO薄膜自组装生长过程，采用原子力显微镜分析自组装生长演化过程，并利用X射线衍射分析薄膜结构及其生长方向。对不同生长条件下薄膜的生长的研究发现：在较低生长温度时，STO薄膜在(200)方向上以三维岛状模式进行生长，小岛在单位原胞尺度呈波浪状周期性排列，即出现自组装生长；而在较高的生长温度时，薄膜以层状模式进行生长自组装行为被抑止。并据此讨论了STO多元氧化物薄膜自组装生长条件及生长机理。     

Growth and characteristics of metal-containing diamond-like carbon using a self-assembled process

A recently developed self-assembled method, involving the use of a single metal target and a fixed substrate in a sputter deposition chamber, was used for the growth of various metal-containing diamond-like carbon thin films. The metals used include, Cu, Pt, and Ni. The resulting films consist of self-assembled alternating dark and bright layers, both of which constitute a period. The dark layer was found to always have a higher metal concentration than the bright layer in a period. Effects of the growth condition on the growth rate, periodicity, and film structure were examined. The relation between the growth condition and the film characteristics is discussed.     

Interface-layer-assisted reliable ferroelectricity in BiFeO3 thin films by chemical solution deposition

BiFeO₃ thin films, specifically those fabricated by chemical solution deposition, suffer from severe leakage that hinder the acquirements of their intrinsic high polarizations and are thus normally not considered for use in practical electronics. The controlled fabrication of thin films with reduced leakage is of vital importance. In the present work, BiFeO₃ films (with thicknesses below ~300 nm), assisted by an interfacial amorphous layer, were fabricated by chemical solution deposition on Pt/Ti/SiO₂/Si substrates. This facile method facilitates the growth of the mentioned amorphous layer, and the ferroelectric properties of the obtained films were greatly enhanced. The conducting mechanisms of both types of thin films were systematically investigated to understand the impact of the designed interface. The results not only advance the potential use of BiFeO₃ thin films in electromechanical devices but also promote chemical solution deposition as a promising methodology for the fabrication of high-quality ferroelectric films with compressed leakage.     

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.     

Gallium oxide films deposition by RF magnetron sputtering; a detailed analysis on the effects of deposition pressure and sputtering power and annealing

In this study, gallium oxide (Ga₂O₃) thin films were deposited on sapphire and n-Si substrates using Ga₂O₃ target by radio frequency magnetron sputtering (RFMS) at substrate temperature of 300 °C at variable RF power and deposition pressure. The effects of deposition pressure and growth power on crystalline structure, morphology, transmittance, refractive index and band gap energy were investigated in detail. X-ray diffraction results showed that amorphous phase was observed in all the as-deposited thin films except for the thin films grown at low growth pressure. All the films showed conversion to poly-crystal β-Ga₂O₃ phase after annealing process. When the deposition pressure increased from 7.5 mTorr to 12.20 mTorr, change in the 2D growth mode to 3D columnar growth mode was observed from the SEM images. Annealing clearly showed formation of larger grains for all the thin films. Lower transmission values were observed as the growth pressure increases. Annealing caused to obtain similar transmittance values for the thin films grown at different pressures. It was found that a red shift observed in the absorption edges and the energy band gap values decrease with increasing growth pressure. For as-deposited and annealing films, increasing sputtering power resulted in the increase refractive index.     

Single-target sputter deposition and post-processing of perovskite lead titanate thin films

The growth of ferroelectric lead titanate (PT) thin films by RF magnetron sputtering using a single mixed-oxide target is described. This study has been focused on producing perovskite thin (2000 Å) films with the desired composition on different substrates. Depositions were performed at room temperature and the process gas is pure argon. The effects of deposition and post-annealing conditions on film composition and microstructure were evaluated. Optimization of process conditions is discussed in terms of stoichiometry, structure and reproducibility. The optical properties of the films have also been characterized.     

Silver nanoparticle deposition on hydrophilic multilayer film surface and its effect on antimicrobial activity

Silver nanoparticles were deposited on the surface of the external polyamide 6 (PA6) layer of a multilayer film, by spraying and ultrasound‐assisted methods. The effect of silver nanoparticles content and deposition method on the mechanical and optical properties of the multilayered films as well as the efficiency of silver ion release and their fungicidal characteristics were evaluated. Itaconic (IA) and Maleic anhydride (MA) were used as adhesion promoter agents for preventing the agglomeration of the silver nanoparticles and for improving the adhesion to the PA6 polymer surface. With IA, a homogeneous distribution of silver nanoparticles on the PA6 surface was achieved. The silver ion release and biocide effect of the multilayered films was found to be dependent on the anhydride type and on the deposition method used. The multilayer films with a layer of PA6‐silver nanocomposite demonstrated good fungicidal activity, specifically against fungus Aspergillius niger. The observed results could be applied in the design of industrial films for packaging. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrospray deposition of polymer thin films for organic light-emitting diodes

Electrospray process was developed for organic layer deposition onto polymer organic light-emitting diode [PLED] devices in this work. An electrospray can be used to produce nanometer-scale thin films by electric repulsion of microscale fine droplets. PLED devices made by an electrospray process were compared with spin-coated ones. The PLED device fabricated by the electrospray process showed maximum current efficiency of 24 cd/A, which was comparable with that of the spin-coating process. The electrospray process required a higher concentration of hole and electron transport materials in the inks than spin-coating processes to achieve PLED maximum performance. Photoluminescence [PL] at 407 nm was observed using electrosprayed poly(N-vinyl carbazole) films, whereas a peak at 410 nm was observed with the spin-coated ones. Similar difference in peak position was observed between aromatic and nonaromatic solvents in the spin-coating process. PLED devices made by the electrospray process showed lower current density than that of spin-coated ones. The PL peak shift and reduced current of electrosprayed films can therefore be attributed to the conformation of the polymer.     

Growth of carbon nanotube forests between a bi-metallic catalyst layer and a SiO2 substrate to form a self-assembled carbon–metal heterostructure

A special nanostructure was formed by the growth of carbon nanotubes (CNTs) between a substrate and a thin bi-metallic catalyst layer using a thermal chemical vapor deposition process. The catalyst layer is composed of adjacently disposed Cr and Ni phases formed prior to CNT growth. The Cr/Ni layer serves as a bi-metallic catalyst layer, which is pushed away from the substrate as a thin and continuous nanomembrane with the growth of CNTs. The self-assembled CNT–catalyst heterostructure possesses a smooth surface (RMS = 2.9 nm) with a metallic shine. Directly interlinked to the Cr/Ni layer, dense and vertically aligned multi-walled CNTs are found. Compared to conventional CNT films, the structure has significant advantages for CNT integration. From technology point of view, the structure allows further processing without impact on the CNTs as well as transfer of pristine vertically aligned CNTs to arbitrary substrates. Moreover, the as-grown CNT films provide an interface ideal for further electrical, thermal and mechanical contacting of CNT films. We present structural investigations of this special CNT–metal heterostructure. Furthermore, we discuss possible interface mechanisms during catalyst layer formation and CNT growth.     

Phase-gradient atomic layer deposition of TiO2 thin films by plasma-induced local crystallization

Atomic layer deposition (ALD) is a thin-film fabrication method that can be used to deposit films with precise thickness controllability and uniformity. The low deposition temperature of ALD, however, often interrupts the facile crystallization of films, resulting in inferior optical and electrical properties. In this study, the extremely localized crystallization of TiO₂ thin films was demonstrated by per-cycle plasma treatment during the plasma-enhanced ALD process. By layering crystalline and amorphous films, a phase-gradient TiO₂ film with precisely modulated optical and electrical properties was fabricated. Moreover, the ratio between the amorphous and crystalline layer thicknesses for a high dielectric constant and low leakage current density was optimized.     

Dynamics and control of thin film surface microstructure in a complex deposition process

In this work, a complex deposition process, which includes two types of macromolecules whose growth behaviors are very different, is investigated. This deposition process is influenced by both short- and long-range interactions. The study of this process is motivated by recent experimental results on the growth of high-κ dielectric thin films using plasma-enhanced chemical vapor deposition. A multi-component kinetic Monte-Carlo (kMC) model is developed for the deposition. Both single- and multi-component cases are simulated and the dependence of the surface microstructure of the thin film, such as island size and surface roughness, on substrate temperature and gas phase composition is studied. The surface morphology is found to be strongly influenced by these two factors and growth regimes governed by short- and long-range interactions are observed. Furthermore, two kMC model-based feedback control schemes which use the substrate temperature to control the final surface roughness of the thin film are proposed. The closed-loop simulation results demonstrate that robust deposition with controlled thin film surface roughness can be achieved under a kMC estimator-based proportional integral (PI) feedback controller in the short-range interaction dominated growth regime, while a kMC model-predictive controller is needed to control the surface roughness in the long-range interaction dominated growth regime.     

衬底温度对HfO_xN_y薄膜相关物性的影响

采用射频反应磁控溅射法制备了HfOxNy栅介质薄膜,并研究了HfOxNy栅介质薄膜的化学特性和界面结构随淀积温度的变化而发生的变化规律。光电子能谱测试表明,随着衬底温度的升高,薄膜中的氮含量也随之增加。傅立叶红外吸收光谱研究表明,随着淀积温度的增加,界面层SiO2的厚度也逐渐增高。     

Electrodeposition of Ru by atomic layer deposition (ALD)

Studies are presented describing attempts to form a cycle for the growth of Ru nanofilms using the electrochemical form of atomic layer deposition (ALD). Au substrates have been used to form Ru nanofilms, based on layer by layer growth of deposits, using surface limited reactions. These deposits were formed using surface limited redox replacement (SLRR), where an atomic layer of a sacrificial element is first deposited by underpotential deposition (UPD), and is then exchanged for the element of interest. The use of the UPD atomic layer limits subsequent growth by limiting the number of electrons available for deposition. In the present study, Pb atomic layers were used, and exposed to solutions of Ru³⁺ ions at open circuit. This process can then be repeated to grow films of the desired thickness. It was shown that less than an at.% of Pb was evident in the deposits, using electron probe microanalysis (EPMA), and even that could be removed if a stripping step was added to the ALD cycle. The deposits displayed the expected Ru voltammetry, as well as the Ru hcp XRD pattern. There were some differences in the first 20 cycles, compared with subsequent, suggesting some nucleation process that must be investigated. However, after 20 cycles, the deposit showed the linear growth with the number of cycles expected for an ALD process. The morphology of Ru films, deposited on template-stripped Au was studied using ex situ scanning tunneling microscopy (STM), and showed no evidence of 3D growth.     

Fabrication of a new type of organic-inorganic hybrid superlattice films combined with titanium oxide and polydiacetylene

We fabricated a new organic-inorganic hybrid superlattice film using molecular layer deposition [MLD] combined with atomic layer deposition [ALD]. In the molecular layer deposition process, polydiacetylene [PDA] layers were grown by repeated sequential adsorption of titanium tetrachloride and 2,4-hexadiyne-1,6-diol with ultraviolet polymerization under a substrate temperature of 100°C. Titanium oxide [TiO₂] inorganic layers were deposited at the same temperatures with alternating surface-saturating reactions of titanium tetrachloride and water. Ellipsometry analysis showed a self-limiting surface reaction process and linear growth of the nanohybrid films. The transmission electron microscopy analysis of the titanium oxide cross-linked polydiacetylene [TiOPDA]-TiO₂ thin films confirmed the MLD growth rate and showed that the films are amorphous superlattices. Composition and polymerization of the films were confirmed by infrared spectroscopy. The TiOPDA-TiO₂ nanohybrid superlattice films exhibited good thermal and mechanical stabilities.     

Femtosecond pulsed laser deposition of silicon thin films

Optimisation of femtosecond pulsed laser deposition parameters for the fabrication of silicon thin films is discussed. Substrate temperature, gas pressure and gas type are used to better understand the deposition process and optimise it for the fabrication of high-quality thin films designed for optical and optoelectronic applications.     

Nonlinear growth of zinc tin oxide thin films prepared by atomic layer deposition

Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO₂ processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO_x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV.     

Control of Microstructure and Orientation in Solution-Deposited BaTiO3 and SrTiO3 Thin Films

Columnar and highly oriented (100) BaTiO₃ and SrTiO₃ thin films were prepared by a chelate-type chemical solution deposition (CSD) process by manipulation of film deposition conditions and seeded growth techniques. Randomly oriented columnar films were prepared on platinum-coated Si substrates by a multilayering process in which nucleation of the perovskite phase was restricted to the substrate or underlying layers by control of layer thickness. The columnar films displayed improvements in dielectric constant and dielectric loss compared to the fine-grain equiaxed films that typically result from CSD methods. Highly oriented BaTiO₃ and SrTiO₃ thin films were fabricated on LaAlO₃ by a seeded growth process that appeared to follow a standard "two-step" growth mechanism that has been previously reported. The film transformation process involved the bulk nucleation of BaTiO₃ throughout the film, followed by the consumption of this matrix by an epitaxial overgrowth process originating at the seed layer. Both BaTiO₃ and PbTiO₃ seed layers were effective in promoting the growth of highly oriented (100) BaTiO₃ films. Based on the various processing factors that can influence thin film microstructure, the decomposition pathway involving the formation of BaCO₃ and TiO₂ appeared to dictate thin film microstructural evolution.     

Low temperature atomic layer deposition of nickel sulfide and nickel oxide thin films using Ni(dmamb)2 as Ni precursor

Nickel(II) 1-dimethylamino-2-methyl-2-butoxide (Ni(dmamb)₂) with water and hydrogen sulfide as oxygen and sulfur sources was employed in atomic layer deposition (ALD) of nickel oxide (NiO) and nickel sulfide (NiS) thin films. Both NiO and NiS thin films demonstrate temperature-independent growth rates per cycle of 0.128?nm/cycle and 0.0765?nm/cycle, at 130–150?°C and 80–160?°C, respectively. Comparison of two nickel-based thin film materials demonstrates dissimilar deposition features depending on the reactivity of the Ni precursor, i.e., Ni(dmamb)₂ with anion sources provided by the water and hydrogen sulfide reactants. Difference in reactivity observed for NiO and NiS ALD processes is further investigated by density functional theory (DFT) simulations of surface reactions, which indicated that H₂S demonstrate higher reactivity with surface-adsorbed Ni precursor than H₂O. The material properties of ALD NiO and NiS thin films including stoichiometry, crystallinity, band structure, and electronic properties were analyzed by multiple experimental techniques, showing potential of ALD NiS as electrode or catalyst for energy-oriented devices.     

Effect of annealing on SiC thin films prepared by pulsed laser deposition

Crystalline cubic SiC thin films were successfully fabricated on Si(100) substrates by using laser deposition combined with a vacuum annealing process. The effect of annealing conditions on the structure of the thin films was investigated by X-ray diffraction and Fourier transform infrared spectroscopy. It was demonstrated that amorphous SiC films deposited at 800°C could be transformed into crystalline phase after being annealed in a vacuum and that the annealing temperature played an important role in this transformation, with an optimum annealing temperature of 980°C. Results of X-ray photoelectron spectroscopy revealed the approximate stoichiometry of the SiC films. The characteristic microstructure displayed in a scanning electron microscope image of the films was indicative of epitaxial growth along the (100) plane.