Recent developments in thin film electro-acoustic technology for biosensor applications

The article reviews recent developments of the thin film electro-acoustic (TEA) technology in view of the design and fabrication of micro-acoustic transducers for biosensor applications. The use of the TEA technology leads to transducer miniaturisation, compatibility with the IC technology, possibility for multiplexing, decrease in fabrication cost, reduction of consumables, mass fabrication, etc. Focus lies on the design, fabrication and evaluation of the transducer performance in liquid media as judged by electro-acoustic behaviour and ultimately by mass and viscosity resolution. The analysis draws the conclusion that the thickness excited quasi-shear thin film bulk acoustic resonator technology is far ahead in its development with regard to other alternative approaches in terms of both performance and level of maturity. Consequently, the main aspects of the quasi-shear thin film bulk acoustic resonator (FBAR) technology from film synthesis and fabrication through to performance evaluation and demonstration are reviewed in detail.     

Imparting cell adhesion to poly(vinyl alcohol) hydrogel by coating with hydroxyapatite thin film

To impart good cell adhesion to poly(vinyl alcohol) hydrogel (PVA-H) as an artificial articular cartilage, hydroxyapatite thin film 300 nm thick was deposited by a pulsed laser deposition technique on PVA-H, which has virtually no cell adhesion. A cell culture method was used to study the effect of hydroxyapatite deposition on PVA-H upon cell adhesion among mouse fibroblasts. The cell adhesion of water content 33% PVA-H coated with the amorphous hydroxyapatite film showed a maximum as high as that of commonly used tissue culture dishes. This technique was also effective for improving cell adhesion, even on a higher water content (53%) PVA-H. This is a novel technique to improve the biocompatibility and attachment of PVA-H and with the underlying bone and natural cartilage.     

An energy method to analyze through thickness thin film fracture during indentation

Nanoindentation was utilized to induce fracture of brittle thin oxide films on compliant substrates. The energies were calculated from integrating the resulting load-depth curves from indentation. The total energy applied to the system is a superposition of the energy to deform the substrate and the energy to fracture the film. The applied energy to deform the compliant substrate was separated from the energy applied to the film/substrate system resulting in the energy to fracture the film. The energy for fracture was then converted to a crack extension force and a stress intensity using linear elastic fracture mechanics. The toughness of thermally grown aluminum oxides is between 0.37 and 0.83 MPa m^0.5, and tends to decrease as film thickness increases over the range of 25 to 63 nm.     

Plasma assisted and manipulated deposition of thin film electrodes for micro batteries

The properties of the thin film electrodes have been the main factors for the performances of lithium or lithium ion micro batteries, i.e. thin film batteries. In this paper, plasma assisted and manipulated techniques have been developed for the fabrication of polycrystalline thin film cathodes, and of amorphous/nano-crystalline thin film anodes. The thin film electrodes were deposited by magnetron sputtering under precisely controlled plasma conditions. The deposition apparatuses were designed to obtain the desired film properties by equipping a long anode-shield or an inductive coil. Polycrystalline LiMn₂O₄ thin film cathodes with a smooth surface were deposited, which greatly reduced the cathode/electrolyte interface resistances. Amorphous/nano-crystalline Sn thin film anodes were obtained free of plasma induced large grains, which enhanced the cycling stability. The results have demonstrated that by careful designs of deposition apparatus the plasma conditions can be precisely controlled and therefore the thin film electrodes of desired properties can be obtained.     

Effect of thickness of ZnO active layer on ZnO-TFT's characteristics

We have investigated the electrical characteristics of ZnO thin film transistors with respect to the thickness of ZnO active layers. The ZnO layers with the thickness of 30 nm to 150 nm were deposited on bottom gate patterned Si substrate by RF sputtering at room temperature. The low-temperature oxide served as gate dielectric. As ZnO channel layer got thicker, the leakage current at V_DS = 30 V and V_G = 0 V greatly increased from 10^− 10 A to 10^− 6 A, while the threshold voltage decreased from 15 V to 10 V. On the other hand, the field effect mobility got around 0.15 cm²/V s except for the 30-nm-thick channel. Overall, the 55-nm-thick ZnO channel layer showed the best performance.     

Effects of dielectric thickness and contact area on current-voltage characteristics of thin film metal-insulator-metal diodes

Planar asymmetric Ni-NiO-Cr/Au thin film Metal-Insulator-Metal (MIM) tunnel diodes were fabricated for use in an ultra-sensitive infrared detector operating at room temperature. MIM diodes with contact areas of 100 μm² and 1 μm² were fabricated using standard Micro-Electro Mechanical Systems techniques. A linear relationship between the thickness of reactively sputtered Nickel Oxide (NiO) and the breakdown voltage was experimentally determined, and the diode performance was verified using a theoretical approach. Current-Voltage measurements of the MIM diode revealed an increase in the current from 1.5 nA to 0.8 mA, when the thickness of the dielectric and the contact area of the detector decreased. Also, the rectification ratios of the detectors were determined, exhibiting an asymmetry of 4.5 at 1 V and 6 at 0.2 V for detectors A and B, respectively. Further, the ratio was observed to be increasing with bias voltage suggesting a strong asymmetric behavior. The results are in agreement with the theoretical predictions confirming conduction via tunneling. The nonlinearity and asymmetry exhibited by these diodes suggests their viability in infrared applications.     

Effects of anodisation parameters on thin film properties: a review

Electrochemical anodisation is a well-received method in the complementary metal-oxide-semiconductor field as it is advantageous; best performed at room temperature which translates into being more affordable and a simple alternative to form nano-structured oxide films for different metals. The quintessential parameters involved allow numerous formations of metal oxide films according to desired morphology and thickness. Therefore, this paper aims to review the effects of anodising parameters such as applied voltage, concentration, temperature, time, current density and post-anodisation annealing among them.     

纳米薄膜研究的进展

介绍了纳米材料研究的产生、现状以及这类材料的特性。着重介绍了几种具有不同用途的纳米薄膜的结构特性、制备方法和性能特点。     

Structure, morphology and magnetic properties of Fe-B-Si-Nb glassy alloy thin film prepared by a pulsed laser deposition method

With the aim of applying to a soft magnetic underlayer of the double-layered perpendicular magnetic recording media, an Fe_74.9B_17.5Si_2.5Nb_5.1 alloy thin film was fabricated on Si substrate by a pulsed laser deposition method. The Fe-based alloy thin film of 200 nm in thickness was confirmed as a glassy structure. The thermal properties of the thin film have similar features to those for the melt-spun glassy alloy ribbon. The glassy alloy thin film exhibits good soft magnetic properties, i.e., high B_s of 1.2 T and in-plane low H_c of 134 A/m. The Fe-B-Si-Nb glassy alloy thin film is expected to be suitable for the soft magnetic underlayer material in the double-layered perpendicular magnetic recording media.     

Boron thin film deposition by using Thermionic Vacuum Arc (TVA) technology

In this paper a new technology for boron thin film deposition is presented. The film in high vacuum conditions is condensing on the sample from the plasma state of the vapor phase of the anode material, generated by a Thermionic Vacuum Arc (TVA). Boron coating is one of the technologies recently considered to be of special interest due to the qualities of boron. The aim of this paper is to present the use of TVA technology for boron coating.     

Development of a hybrid inverter through integration of organic and inorganic thin film transistors

In this paper, complementary thin-film transistor (TFT) inverter is fabricated with organic-inorganic hybrid channels. By adopting p-channel pentacene and n-channel ZnO, we have fabricated a device of hybrid complementary TFT inverter by using same electrode in organic-inorganic hybrid channels. To be accomplished Ohmic-contact in organic-inorganic hybrid channels, we adapted to n-channel staggered TFT and p-channel coplanar TFT. In results, a hybrid inverter built through integration of organic and inorganic TFT shows that the typical inverter response to stage switching is clearly observed between 0 and 40 V, for both input directions, displaying a high voltage gain — (dV_OUT/dV_IN) > 16.     

Initiated chemical vapor deposition of poly(2-hydroxyethyl methacrylate) hydrogels

Initiated chemical vapor deposition (iCVD), a low temperature variant of hot-wire chemical vapor deposition (HWCVD) is a solvent-free polymerization technique. It was used to synthesize thick, free-standing films of the hydrogel poly(2-hydroxyethyl methacrylate) (PHEMA). In this work, we show that the iCVD technique can yield PHEMA which is free from residual entrained monomer, has low non-specific protein adsorption and is capable of supporting good cell adhesion and proliferation.     

Effects of cetyltrimethylammonium bromide on redox deposition and rectification properties of silicon oxide thin film

Silicon oxide (SiO_x) thin film was deposited onto fluorine-doped tin oxide (FTO) and silicon wafer substrate by the reduction of an aqueous solution containing ammonium hexafluorosilicate, dimethylamine borane and cetyltrimethylammonium bromide (CTAB). Characterization of the films by X-ray photoelectron spectroscopic depth profile and infrared spectroscopy proved that the addition of CTAB into the film enhanced the aggregation of silica particles and the growth rate. The SiO_x films (resistivity: 3.2 × 10⁸ Ω cm) remarkably improved the rectification properties of FTO/SiO_x/poly(3,4-ethylenedioxythiophene) derivative diodes. A rectification mechanism based on conduction of electron and ions was investigated.     

Numerical modeling of SiH4 discharge for Si thin film deposition for thin film transistor and solar cells

Amorphous and microcrystalline silicon thin films are used in solar cells as a multi-junction photovoltaic device. Plasma enhanced chemical vapor deposition is used and high deposition rate of a few nm/s is required while keeping film quality. SiH₄ is used as a precursor diluted with H₂. Electron impact processes give complex interdependent plasma chemical reactions. Many researchers suggest keeping high H/SiH_x ratio is important. Numerical modeling of this process for capacitively coupled plasma and inductively coupled plasma is done to investigate which process parameters are playing key roles in determining it. A full set of 67 volume reactions and reduced set are used. Under most of conditions, CCP shows 100 times higher H/SiH₃ ratio over ICP case due to its spatially localized two electron temperature distribution. Multi hollow cathode type CCP is also modeled as a 2 × 2 hole array. For Ar, the discharge is well localized at the neck of the hole at a few Torr of gas pressure. H₂ and SiH₄ + H₂ needed higher gas pressure and power density to get a multi hole localized density profile. H/SiH₃ was calculated to be about 1/10.     

Numerical simulation of laser-induced thin film delamination

Laser-induced thin film spallation has been developed to be one of the most powerful tools for quantitative measurement of thin film interfacial adhesion. High-energy laser pulse absorption generates stress pulse that can be used to delaminate a thin film-substrate interface. Interfacial strength is obtained from the measured surface motion of the thin film using elastic wave mechanics. Due to the short duration of the stress pulses, the dynamic interfacial debonding process usually happens within nanosecond duration, thus the interfacial strength measurement pertains to the intrinsic adhesion of the interface. In this paper, we performed detailed numerical simulations on various aspects of this experimental technique. Combining with experimental observations, the simulation results provide explanations of various phenomena and insights on the fundamental mechanisms of the laser-induced interface debonding process.     

Formation and characterization of Y : 247 film through spray pyrolysis technique

The synthesis of high temperature superconducting films of Y : 247 (T _c ～ 73 K) have been successfully achieved. The difficulty in synthesis owing to narrow range of stability of Y : 247 has been taken care of through several quenching modes, e.g. quenching of the films synthesized at ～850°C, in air or in liquid nitrogen. The energy dispersive analysis of X-rays (EDAX) and transmission electron microscopy (TEM) studies of the as processed film, Y₂Ba₄Cu₇O_14+x, exhibit nearly correct cationic stoichiometry of 2 :4 :7; also narrow regions (< 50 Å) of minority Y : 124 phase and stacking faults capable of working as flux pinning sites have been invariably found to be present. In addition to Y : 247, Ag admixed films have also been investigated. TheT _c here is ～ 70–75 K which is similar to that of the film without silver. Representative estimates of transport critical current density (J _c) for Y : 247 films is ～10³ A/cm², and with silver corresponding to Y₂Ba₄Cu₇O_14+x (Ag_0.1) is found to be ～ 10⁴ A/cm².     

Direct simulation Monte Carlo modeling of metal vapor flows in application to thin film deposition

Thin films of metal for electronics, nano/microelectromechanical systems and optical coatings are often prepared by various vacuum deposition techniques. Modeling such metal vapor flows using methods such as the direct simulation Monte Carlo (DSMC) can aid in the design and analysis of deposition systems and accelerate development of films with desired properties. The determination of suitable variable hard sphere (VHS) molecular model parameters for DSMC simulations using measured growth rate distribution is demonstrated with aluminum vapor as an example. Axisymmetric DSMC simulations using a VHS model corresponding to a reference diameter of 0.8 nm and a viscosity-temperature exponent of 1 are shown to agree well with available experimental data. The model is then used in two-dimensional DSMC simulations to study the interaction of plumes from multiple sources. An expression for substrate mass flux assuming no interaction between sources agrees well with DSMC simulations for a mass flow rate of 0.1 g/min corresponding to a Knudsen number (Kn) of about 0.1. The non-additive interaction of plumes at a higher flow rate of 1 g/min corresponding to a Kn of about 0.01 results in a higher mass flux non-uniformity in the DSMC simulations which is not captured by the simplified analytical expression.     

Nanocrystalline silicon fabrication by conventional plasma enhanced chemical vapor deposition for bottom gate thin film transistor

Nanocrystalline silicon was successfully fabricated using conventional plasma enhanced chemical vapor deposition (PECVD) for bottom gate thin film transistor. This was accomplished by promoting nucleation rate in the initial stage of silicon growth by H₂ or SF₆ plasma treatment of the surface of silicon nitride (SiN_x) films. Microstructure of hydrogenated nanocrystalline silicon (nc-Si:H) films confirmed the crystallization of silicon, and nanocrystalline silicon thin film transistor exhibited excellent stability.     

On the lower thickness boundary of sputtered TiNi films for shape memory application

In this paper, we study the effects of film thickness on phase transformation of constrained Ti_50.2Ni_49.8 films deposited onto silicon substrates. When the film is too thin, surface oxide and interfacial diffusion layers exert dominant constraining effect that renders high residual stress and low recovery capabilities in the film. The surface oxide and inter-diffusion layer restricts the phase transformation, alters stoichiometry of the remaining TiNi film, and reduces volume of the material available for phase transformation. As a result, a lower thickness boundary (about 100 nm) exists for TiNi films to remain “shape remembering”. Results indicate that a maximum recovery stress and actuation speed can be realized with a thickness of about 800 nm. Based on the curvature measurement results, the relationship between the relative stress and strain of the films (during phase transformation with change of temperature) can be derived.