Dielectric Film Thickness Research Articles

Influence of dielectric layer thickness on charge injection, accumulation and transport phenomena in thin silicon oxynitride layers: a nanoscale study

Charge injection and retention in thin dielectric layers remain critical issues due to the great number of failure mechanisms they inflict. Achieving a better understanding and control of charge injection, trapping and transport phenomena in thin dielectric films is of high priority aiming at increasing lifetime and improving reliability of dielectric parts in electronic and electrical devices. Thermal silica is an excellent dielectric but for many of the current technological developments more flexible processes are required for synthesizing high quality dielectric materials such as amorphous silicon oxynitride layers using plasma methods. In this article, the studied dielectric layers are plasma deposited SiO x N y . Independently on the layer thickness, they are structurally identical: optically transparent, having the same refractive index, equal to the one of thermal silica. Influence of the dielectric film thickness on charging phenomena in such layers is investigated at nanoscale using Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy. The main effect of the dielectric film thickness variation concerns the charge flow in the layer during the charge injection step. According to the SiO x N y layer thickness two distinct trends of the measured surface potential and current are found, thus defining ultrathin (up to 15 nm thickness) and thin (15–150 nm thickness) layers. Nevertheless, analyses of KPFM surface potential measurements associated with results from finite element modeling of the structures show that the dielectric layer thickness has weak influence on the amount of injected charge and on the decay dynamics, meaning that pretty homogeneous layers can be processed. The charge penetration depth in such dielectric layers is evaluated to 10 nm regardless the dielectric thickness.

Clusters of protein pores in phospholipid bilayer membranes can be identified and characterized by electrochemical impedance spectroscopy

Cluster formation is a widely-observed phenomenon, which results in unique sets of properties both in physical, chemical and biological domains of nature. Here, we present a qualitative description of clustering of membrane defects, specifically ion-conducting protein pores in tethered phospholipid bilayers, a versatile biomimetic model of biological membranes accomplished on chemically modified gold films. By invoking the Voronoi tessellation concept we demonstrate the possibility to distinguish between random and sparsely clustered patterns both in computer generated and real-world systems using one single parameter σ, the standard deviation of the normalized Voronoi sector areas distribution. For random systems, σ ≈ 0.54, for sparsely clustered patterns σ > 0.54. Because of a specific structure and dielectric properties of tethered bilayers, they can be characterized by an alternating current technique, electrochemical impedance spectroscopy (EIS). EIS measures macroscopic parameters of dielectric systems and it is not a structural technique per se. However, we found the EIS spectra-derived quantitative metric ζ to be a diagnostic parameter that allows assessment of the distribution type (homogeneous, random or clustered) of defects at nanometer level. One of the most interesting findings of the current study is the fact that the EIS derived ζ parameter is sensitive to an average size of the defects thus enabling a purely electrochemical methodology to access fine structural information such as size of incomplete protein pores in phospholipid bilayers. Overall, our results demonstrate a fundamental property of the macroscopic technique, electrochemical impedance spectroscopy, to probe structural arrangement of defects with sizes between 0.5 nm to 25.5 nm located in a thin, 2 nm thick phospholipid dielectric layer. Our findings can be utilized in designing precision electrochemical biosensors, and/or solving specific physical, biochemical or electrochemical problems related to other types of nanometer thick dielectric films on conducting surfaces.

Enabling bottom-up nanoelectronics fabrication by selective sol–gel dielectric-on-dielectric deposition

Self-aligned patterning schemes for microelectronics fabrication require area-selective deposition processes. In this context, a sol–gel-based selective dielectric-on-dielectric deposition with respect to metal is reported. The selective deposition is achieved by first de-wetting a solution from the lyophobic surface areas and second ensuring uniform organosilicate polymer deposition during a droplet drying on the lyophilic surface regions. The de-wetting occurs when a critical volume for de-wetting is reached as a result of capillary solution draining. De-wetting from 1 µm wide lyophobic copper area separating lyophilic rectangular dielectric (SiO2) regions with a width as narrow as 4 µm is demonstrated. The subsequent solution drying results in a 200 nm thick dielectric film.

A method for measuring plasma parameters and dielectric film thickness by analyzing transient voltages for deposition plasma processing monitoring

An electrical method is proposed to measure the dielectric film thickness, electron temperature, and plasma density for deposition plasmas. In this method, a square voltage is applied to a flat probe coated with a dielectric film, and the transient voltage of a series capacitor connected to the probe is measured. The thickness of the dielectric film is obtained from the transient voltage because the applied voltage is divided across the dielectric film and the series capacitor. The deposited dielectric film causes a change in transient voltage of the series capacitor. A circuit model with a nonlinear sheath, a series capacitor, and the dielectric films is suggested to obtain plasma density and electron temperature. The time response of transient voltage is related to plasma density, electron temperature and total capacitance of the series capacitor and the dielectric film. Two square voltages with different amplitudes were applied to measure plasma density and electron temperature. Experiments were conducted in inductively coupled plasma. Various capacitors were used to replace the dielectric films, and a flat probe coated with Al2O3 was used to verify the measurement of dielectric film thickness, showing the high accuracy of our method. In addition, the electron temperature from our method is in good agreement with that from electron energy distribution functions, and the plasma density is in good agreement with that from orbital motion limited theory. Therefore, this method would be useful for monitoring plasma parameters and deposited film thickness in industrial plasma processing.

Synthesis, Optical, and Morphological Studies of ZnO Powders and Thin Films Fabricated by Wet Chemical Methods.

Zinc oxide nanoparticles were prepared from Zn5(CO3)2(OH)6 precursor, capped with poly(vinylpyrrolidone) (PVP), and annealed at 600 °C. The obtained powders were characterized by a powder X-ray diffraction (PXD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–visible spectroscopy (UV–vis), Raman spectroscopy, infrared spectroscopy (IR), thermal analysis (TGA/DTA), and third-order nonlinear (NL) optical measurement. Morphological evaluation by TEM and SEM measurements indicated that the precursor micro-particles are ball-shaped structures composed of plates with a thickness of approximately 10 nm. ZnO thin films, as well as ZnO/polymer multilayer layouts, were obtained by wet chemical methods (spin- and dip-coating). Surface topography and morphology of the obtained films were studied by SEM and AFM microscopy. Films with uniformly distributed ZnO plates, due to the erosion of primary micro-particles were formed. The fabricated specimens were also analyzed using a spectroscopic ellipsometry in order to calculate dielectric function and film thickness.

Anisotropic topological magnetoelectric effect in axion insulators

Three-dimensional topological insulators or axion insulators exhibit the topological magnetoelectric effect, which is isotropic with a universal coefficient of proportionality quantized in units of $e^2/2h$. Here we study the finite-size effect of topological magnetoelectric effect, and find the magnetoelectric coefficients are anisotropic, namely $\alpha_{xx}\neq\alpha_{zz}$. Both of them are shown to converge to a quantized value when the thickness of topological insulator film $d$ increases reaching the three-dimensional bulk limit. The nonzero value of $(\alpha_{xx}-\alpha_{zz})\propto1/d$ could be measured by using the gyrotropic or nonreciprocal birefringence of terahertz light. The unique $1/d$ dependence on film thickness of the rotation angle of optical principle axes is the manifestation of topological magnetoelectric effect, which may also serve as a smoking gun signature for axion insulators.

Finite element analysis and EMA predictions of the dielectric and pyroelectric properties of 0-3 Pz59/PVDF-TrFE composites with experimental validation

Dielectric and pyroelectric thick film materials are of growing interest for applications in medicine, advanced sensors, energy storage and energy harvesting. In the present work, thick 0–3 composite films consisting of particles of a relaxor material embedded in the ferroelectric co-polymer PVDF-TrFE are characterized in terms of dielectric and pyroelectric properties. The experimentally measured properties are compared with the predictions of analytical models and finite element analysis (FEA). A three-dimensional numerical model has been developed via FEA to calculate the effective dielectric constant as a function of the volume fraction (0–30%) of the ceramic particles. An electro-thermal coupled model is proposed to calculate the pyroelectric coefficient. Furthermore, the distribution of the pyroelectric coefficient in different layers of the ferroelectric composite with 30 % ceramic volume fraction together with the component-resolved spatial distribution of the pyroelectric response are analyzed. Overall, simulation and experiment results show very good agreement. In particular, by analyzing the temperature distribution in the thick film, it is demonstrated that the pyroelectric coefficient increases from top to bottom surfaces. Ceramic particle distribution also affects the pyroelectric current.

Direct integration of dielectric all-ceramic thick films on a polymer substrate using room temperature fabrication

Direct integration of all-ceramic thick films and a polymer substrate has been realized for the first time without high temperature processing using the Room Temperature Fabrication method.Printable Li2MoO4-BaTiO3 composite pastes with 0, 10, and 20 vol.% of BaTiO3 were fabricated from the respective ceramic powders and water without organic additives or vehicles. The pastes were stencil printed on a polyimide substrate and dried at 120 °C without pressing or lamination.Using scanning electron microscopy, the films were observed to be in seamless contact with the substrate and to have a uniform microstructure. Relative permittivities of the ceramic films increased from 4.2 to 7.2 (at 2.5 GHz) and 4.5 to 7.5 (at 9.9 GHz) according to the vol.% content of the added BaTiO3, with corresponding dielectric losses from 10−3 to 10-2.The results show that the room temperature fabrication method enables 2D printing of all-ceramic thick films on temperature-sensitive substrates.

A Review of SiC Wafers In-Line Detection Method in Power Device Fabrication

Silicon carbide (SiC) has outstanding advantages such as wide band gap, high electron saturation drift speed, high thermal conductivity, high voltage and high temperature resistance. It is particularly suitable for making high-power devices. The in-line detection of wafers in the manufacturing process of SiC devices can reflect the quality of incoming materials and process quality. It is a very important part of the manufacturing process. SiC wafer’s in-line inspections involves characterization of the epilayer thickness, surface defects and contamination, wafer warping, dielectric and metal film thickness, etching morphology, etc. Various test methods are compared and discussed in this paper and suggestions are given on detection method selection.

Two voltages in contact-separation triboelectric nanogenerator: From asymmetry to symmetry for maximum output

The output voltage is an important parameter to evaluate performance of triboelectric nanogenerator (TENG). However, the voltage for contact-separation TENG is hardly to reach a higher value and commonly gives an asymmetric alternating voltage (current). When the upper electrode operates from separation to contact state, the voltage is mainly related to dielectric film thickness (Low voltage), while it operates from contact to separation state, the voltage is mostly depended on separate distance (High voltage). It is found that the output voltage is limited by the asymmetrical voltages because the Low voltage hardly pushes charges fully from one electrode to another electrode in large load situation. Two strategies are found. By increasing dielectric film thickness symmetrical output voltages are obtained and 2.7 times output energy are achieved. By using half-wave circuit to eliminate the low voltage restriction, 16.5 kV high voltage and 5 times output energy (1.862 mJ per cycle) are achieved. The improved voltage mechanism of contact-separation TENG in this work provides a basic scientific method for maximum energy output, which also can be used in other device improvement.

Determination of the fundamental absorption and optical bandgap of dielectric thin films from single optical transmittance measurements.

In this work, we propose a method to retrieve the thickness and optical constants of dielectric thin films from single optical transmittance measurements. The method is based on the envelope method and requires a simple dispersion model for the real part of the refractive index with few fitting parameters, while the absorption coefficient can be determined without the aid of a dispersion model. The wavelength-dependent optical constants can be obtained even from spectra that exhibit few interference fringes. We have tested the method with simulated and real transmittance data from thin films in the spectral range covering the fundamental absorption. In order to assess the method's reliability to retrieve the optical constants and optical bandgap, a comparison is performed with the method by Chambouleyron, known as the Pointwise Unconstrained Minimization Approach, and a fit using the Cody-Lorentz dispersion model. We evaluate the methods' capability to retrieve the fundamental absorption and optical bandgap, and their compromise with film thickness accuracy. Finally, the methods are tested and contrasted using optical transmittance of three different semiconductor material thin films.

Simultaneous determination of the thickness and refractive index dispersion of dielectric films by the Paul wavelet transform

The continuous wavelet transform with Paul wavelet was proposed as a method for the simultaneous determination of physical thickness and refractive index dispersion of dielectric films in the visible and near infrared region. Transmittance spectrums, acquired at two different incident angles, were used for the calculations. By this way refractive index dispersion was obtained without knowing the film thickness. The method was tested with simulated data and experimentally applied to a sample of borosilicate glass. The obtained thickness and refractive index dispersion values were compared to the values obtained by the envelope method and the ones provided by the manufacturer.

Determination of the threshold sensitivity of a deposited dielectric film thickness control method based on surface plasmon resonance effect

The lower boundaries of the real time measuring range of the dielectric film thickness on the sensor surface, the principle of which is based on the effect of the excitation of surface electromagnetic waves (SEW), are determined. The simulation was performed for materials with high and low refractive index.

Modeling of Negative Capacitance in Ferroelectric Thin Films.

The negative capacitance (NC) effect in ferroelectric thin films has attracted a great deal of attention from the material and semiconductor device communities because it could be a possible solution to the impending problems related to field-effect transistor power consumption and dynamic random-access memory charge loss. A short discussion on the fundamental premise of the NC effect is presented. A phase-field model based on the time-dependent Ginzburg-Landau (TDGL) formalism in conjunction with the Chensky-Tarasenko (C-T) formalism for multidomain configuration is then developed to reveal the subtle correlation between the domain wall motion and NC effect for different thicknesses of ferroelectric and dielectric films. When a ferroelectric film becomes thin enough, a stripe domain structure can be achieved through competition between the electrostatic energy and domain wall energy. This stripe domain structure is quite resilient to transition to a homogeneous polarization state, making it very useful for (quasi-)static NC operation. Finally, the physical implications of the numerical results are explored with analytical modeling. It is identified that the domain wall motion in the stripe domain structure remains dominated by the external field, even when the entire film is in the (quasi-)static NC state.

Research on thick copper CMP based on multilayer wiring of radio frequency microsystem

To cope with the special requirements of RF microsystem for ultra-thick wiring layer and large-size line width of microwave signal, based on the damascene process in CMOS manufacturing, the dishing phenomenon and causes of thick copper CMP dishing were discussed. Through using the radio frequency module wiring layout, dishing generated by different line width in copper CMP was studied and compared. The influence of the thickness of electroplated copper on dishing is discussed, and a method to reduce dishing is proposed. In addition, in order to reduce the dishing generated by the Ta-CMP process, the removal rates of Ta, Cu and SiO2 were tested, and a polishing selection ratio close to 1:1:1 were obtained. Dishing was reduced to 1000 Å. Finally, a three-layer thick copper wiring consisting of a thick dielectric film deposition and etching, thick copper plating and CMP was successfully developed with a total thickness of 10μm.

Tunnel current model of asymmetric MIM structure levying various image forces to analyze the characteristics of filamentary memristor

Electro-formation in metal insulator metal (MIM) structure causes the emergence of the conductive filament and also leaves a tiny insulating gap amid upper electrode and conductive filament. Since the material property of conductive filament is unlike that of the upper electrode, it is vital to consider these dissimilarities of electrodes in tunneling phenomena. In this paper, the trapezoidal potential barrier of an insulating film sandwiched between two dissimilar electrodes (asymmetric MIM) is accounted for and superimposed with triangular, parabolic and rectangular image force potentials, to derive the corresponding mean barrier heights. Then, the impact of the insulating film thickness, metal’s work function difference, and the dielectric constant of the insulating film on tunneling current density are investigated, employing the same mean barrier potential. Finally, the obtained results are implemented in conductive filament-based memristor model to analyze its physical behavior through pinched hysteresis I–V characteristics. It is ascertained that symmetric results are obtained in forward and reverse biased conditions. The incorporation of triangular image potential suppresses the barrier foremost, whereas parabolic image potential (PIP) has moderate effects on barrier lowering and rectangular image potential exhibits least lowering of the potential barrier, which renders minimum current. The switching dynamics of memristor apprises that PIP manifests only 0.5% deviation with experimental results in OFF switching and also shows good agreement in ON switching. The design is endorsed by comparing the outcomes with experimental and simulated data. This model enables reconfigurable and neuromorphic computing applications of the memristor.

Investigation on the gate insulator thickness dependence of ZnO–SnO2 thin film transistors

The effect of gate insulator thickness on the properties of ZnO–SnO2 (ZTO) thin film transistors (TFTs) was investigated. The ZTO TFTs with gate insulator thickness ranging from 100 to 400 nm were fabricated in a low temperature process. The drain source current sharply increased with decreasing gate insulator films thickness. Also, the field effect mobility remarkably increased and subthreshold swing decreased with decreasing gate insulator film thickness. It is found that the gate insulator thickness is important for the proper operation of ZTO TFTs in a low temperature process.

Sensitivity comparison of graphene-based nearly guided-wave surface plasmon resonance biosensors with Au, Ag, Cu, and Al

A comparative study of sensitivity of guided-wave surface plasmon resonance (NGWSPR) biosensors with Au, Ag, Cu, and Al is presented. The thicknesses of metal films in NGWSPR biosensors were optimized first to realize minimal reflectivity at resonance angle. Then, the sensitivities of NGWSPR biosensors were optimized by optimizing the thickness of dielectric film, and the peak sensitivities for different metals are determined. By comparing peak sensitivities of different metals, we find that the Ag-based NGWSPR biosensor always exhibits largest peak sensitivity for different dielectrics, followed by Cu-, Au-, and Al-based ones. When using PbS as the dielectric in the NGWSPR biosensor, the largest peak sensitivity of Ag-based NGWSPR biosensor is up to 232.48 deg / RIU at 632.8 nm wavelength, which is 45.72%, 31.58%, or 271.49% higher than the sensitivity of Au-, Cu-, or Al-based ones. In addition, the reflectance curves and electric field intensity distributions of optimized NGWSPR biosensors with different metals are studied to analyze the origin of high sensitivity achieved by Ag. Furthermore, the effect of the number of graphene layers on the peak sensitivity of an NGWSPR biosensor is also investigated. It is believed that the sensitivity comparison of graphene-based NGWSPR biosensors with Au, Ag, Cu, and Al could be helpful for highly sensitive biosensors development.

Recent advances in lead-free dielectric materials for energy storage

To better promote the development of lead-free dielectric capacitors with high energy-storage density and efficiency, we comprehensively review the latest research progress on the application to energy storage of several representative lead-free dielectric materials, including ceramics (ferroelectrics–relaxor ferroelectrics–antiferroelectrics), glass-ceramics, thin and thick films, and polymer-based composites. The results indicate that lead-free dielectric materials with large maximum polarization, high breakdown electric field, small remnant polarization, and slim polarization-electric field loops are more appropriate for developing dielectric capacitors with high energy density and efficiency. However, some significant drawbacks in current lead-free dielectric materials hinder the energy storage performance of these materials. Based on this, we review herein some new strategies to improve the energy-storage capacity of dielectric materials.

Fabrication of Fabry–Perot-cavity-based monolithic full-color filter arrays using a template-confined micro-reflow process

Transmissive color filters based on metal-dielectric-metal (MDM) Fabry–Perot (FP) resonators are of great interest for various applications due to their high stability, environmental friendliness and chemical inertia. However, it is still technically challenging to obtain a compact monolithic MDM-based color filter array (CFA) because of the difficulty in achieving microscale-pixelated stepwise dielectric films with designed thickness. In this work, we proposed a template-confined thermal reflow approach to fabricate monolithic CFA based on silver–polymethyl methacrylate–silver (Ag–PMMA–Ag) sandwich configuration. Via template-confined thermal reflow of periodic PMMA nanogratings with different filling density, the thickness of PMMA dielectric layer in each pixel can be independently controlled, enabling the spectral tunability across the whole visible light region with high transmission efficiency and narrow linewidth. Compared to conventional multiple deposition technique, the approach we proposed is able to control the thickness of dielectric film via a single exposure step and can be potentially applied in high-throughput production by combining nanoimprint lithography.