Dielectric Film Thickness Research Articles

Principles of Measuring Thickness and Refractive Index of Thin Dielectric Film by Using Multiresonance Archimedean Spiral Metasurfaces with C Resonator in the Terahertz Frequency Range

Metasurfaces are an excellent platform for terahertz (THz) sensing applications, enabling highly efficient light–matter interaction and overcoming the fundamental disadvantage of the relatively long-wavelength THz range (30–3000 μm), which limits sensing of small features. The current focus in developing metasurfaces is mostly directed toward single-resonance metasurfaces and reconstruction of the dielectric constants of analyte from the saturation mode induced by the limited sensing volume of the metasurface. This paper presents a numerical demonstration of using a multiresonance metasurface to extract the thickness and refractive index of a deposited film without saturation of the sensor. It was shown that the multiresonance property enables determination of the analyte characteristic via measurements with two different thicknesses and tracking changes in two resonances. High-accuracy parameter retrieval is achieved when there are large differences in the thicknesses. In contrast to the established approach, this method provides an efficient way to avoid using relatively thick films.

Terahertz Sensing of Å‐scale Thin Dielectric Film Via Electron Tunnelling

AbstractPrecise sensing of ultrathin dielectric films is paramount in various fields including nanoscale dielectric characterization, advanced material development, and quality control in microelectronics manufacturing. However, achieving this with conventional detection techniques within the terahertz (THz) frequency range has remained challenging due to their limited sensitivity and resolution. In this study, a novel approach is reported that utilizes Fowler‐Nordheim (FN) tunnelling at a metal‐dielectric junction, which drastically improves the sensitivity to changes in dielectric film thickness down to the Angstrom scale. Through a detailed analysis of both experimental and simulated data, it is demonstrated that the FN tunnelling‐based THz sensing technique exhibits exceptional sensitivity. This finding not only overcomes the limitations of traditional detection techniques, but also paves the way for novel ultrathin film sensing capabilities in the rapidly advancing field of THz technology.

Conversion of Dielectric Surface Effect into Volume Effect for High Output Energy.

Improving the output energy and durability of triboelectric nanogenerators (TENGs) remains a considerable challenge for their practical applications. Owing to the interface effect of triboelectrification and electrostatic induction, thinner films with higher dielectric constants yield a higher output; however, they are not durable for practical applications. Herein, the dielectric surface effect is changed into a volume effect by adopting a millimeter-thick dielectric film with an inner porous network structure so that charges can hop in the surface state of the network. Charge migration inside the dielectric film is the key factor affecting the output of the triboelectric nanogenerator (TENG)with a thick film, based on which each working stage follows the energy-maximization principle in the voltage-charge plot. The maximum peak and average power densities of the TENG with polyurethane foam film in 1mm thickness reach 40.9 and 20.7Wm-2 Hz-1 , respectively, under environmental conditions, and the output charge density is 5.14times that of TENGs with a poly(tetrafluoroethylene) film of the same thickness. Superdurability is achieved in the rotary-mode TENGafter 200000 operation cycles. This study identifies the physical mechanism of the thick dielectric film used in TENGs and provides a new approach to promote the output and durability of TENGs.

Scattering and ion emission from insulator films

To determine the effect of the surface potential of dielectric samples on the yield of positive ions during ion irradiation, we studied the dependence of the current of secondary particles on the thickness of dielectric films. It is shown that the yield of positive secondary particles increases significantly with increasing thickness if the film charging potential does not exceed the breakdown value determined by the electrical strength of the film. An indirect confirmation of the film charging in these experiments is the time dependence of the current from the sample holder. An experimental evaluation of the apparatus effect caused by the emission of secondary electrons from a hemispherical collector has been carried out. Possible mechanisms of the observed phenomena are discussed.

Study of Internal Stress in Conductive and Dielectric Thick Films

This paper is focused on the study of internal stress in thick films used in hybrid microelectronics. Internal stress in thick films arises after firing and during cooling due to the differing coefficients of thermal expansion in fired film and ceramic substrates. Different thermal expansions cause deflection of the substrate and in extreme cases, the deflection can lead to damage of the substrate. Two silver pastes and two dielectric pastes, as well as their combinations, were used for the experiments, and the internal stress in the thick films was investigated using the cantilever method. Further experiments were also focused on internal stress changes during the experiment and on the influence of heat treatment (annealing) on internal stress. The results were correlated with the morphology of the fired thick films. The internal stress in the thick films was in the range of 8 to 21 MPa for metallic films and in the range from 12 to 16 MPa for dielectric films. It was verified that the cantilever method can be successfully used for the evaluation of internal stress in thick films. It was also found that the values of deflection and internal stress are not stable after firing, and they can change over time, mainly for metallic thick films.

Impact of dielectric film thickness on field emission in MEMS capacitive switches

This study presents experimental evidence of field emission in MEMS capacitive switches. Devices with dielectric layers of silicon nitride of different thicknesses between 50 and 200 nm were investigated by current-voltage (I-V) measurements. These measurements were performed at room temperature and under a controlled atmosphere pressure of 3 × 10−2 mbar at bias levels below breakdown and corresponding electric fields encountered in MEMS capacitive switches during pull-in (1-2 × 106 V/cm). Field emission although was not always clearly observed, it occurred in all devices and clearly manifested at electric fields larger than 106 V/cm.

Sensitivity improvement of aluminum-based far-ultraviolet nearly guided-wave surface plasmon resonance sensor

An aluminum (Al) based nearly guided-wave surface plasmon resonance (NGWSPR) sensor is investigated in the far-ultraviolet (FUV) region. By simultaneously optimizing the thickness of Al and dielectric films, the sensitivity of the optimized Al-based FUV-NGWSPR sensor increases from 183°/RIU to 309°/RIU, and its figure of merit rises from 26.47 RIU−1 to 32.59 RIU−1 when the refractive index of dielectric increases from 2 to 5. Compared with a traditional FUV-SPR sensor without dielectric, the optimized FUV-NGWSPR sensor can realize simultaneous improvement of sensitivity and figure of merit. In addition, the FUV-NGWSPR sensor with realistic materials (diamond, Ta2O5, and GaN) is also investigated, and 137.84%, 52.70%, and 41.89% sensitivity improvements are achieved respectively. This work proposes a method for performance improvement of FUV-SPR sensors by exciting nearly guided-wave, and could be helpful for the high-performance SPR sensor in the short-wavelength region.

Optical sensing based on classical analogy of double Electromagnetically induced transparencies

Electromagnetically induced transparencies (EITs) in metallic nanostructures and metamaterials have attracted increasing attentions in recent years, because of many applications such as optical sensing. In this work, we study theoretically the classical analogy of double EITs in a peridic array of metal nanodisks on a dielectric film. It is found that the double EITs arise from the interactions between the localized surface plasmons (LSPs) of metal nanodisks and the waveguide modes within dielectric film. The resonance positions of double EITs can be predicted analytically by the well-known waveguide theory, and can be also largely tuned by varying the array period of metal nanodisks or the thickness of dielectric film. With the help of theoretical model of Fano interference, the EITs profile is approximately reproduced. The double EITs may hold potential in refractive index sensing.

Label-Free Fluorescent Nanofilm Sensor Based on Surface Plasmon Coupled Emission: In Situ Monitoring the Growth of Metal-Organic Frameworks.

We have proposed a universal label-free fluorescent nanofilm sensor based on surface plasmon coupled emission (SPCE). A metal-dye-dielectric (MDD) structure was fabricated to mediate the label-free monitoring based on SPCE. The nonfluorescent dielectric film smartly borrowed the fluorescence signal from the bottom dye layer and led to a new SPCE response through the adjacent metal film. The fluorescence emission angle and polarization strongly depended on the thickness of the nonfluorescent dielectric film on the MDD structure. As a demonstration, the growth of a two-dimensional zeolitic imidazolate framework film (ZIF-L) was in situ monitored in the liquid phase by MDD-SPCE for the first time. The label-free fluorescent sensors are facilely prepared by a spin coating technique, with the potential to be widely spread for in situ studies, especially toward nanomaterial growth processes.

Seeding-Layer-Free Deposition of High-k Dielectric on CVD Graphene for Enhanced Gate Control Ability

The gate insulator is one of the most crucial factors determining the performance of a graphene field effect transistor (GFET). Good electrostatic control of the conduction channel by gate voltage requires thin gate oxides. Due to the lack of the dangling bond, a seed layer is usually needed for the gate dielectric film grown by the atomic layer deposition (ALD) process. The seed layer leads to the high-quality deposition of dielectric films, but it may lead to a great increase in the thickness of the final dielectric film. To address this problem, this paper proposes an improved process, where the self-oxidized Al2O3 seed layer was removed by etching solutions before atomic layer deposition, and the Al2O3 residue would provide nucleation sites on the graphene surface. Benefiting from the decreased thickness of the dielectric film, the transconductance of the GFET using this method as a top-gate dielectric film deposition process shows an average 44.7% increase compared with the GFETs using the standard Al evaporation seed layer methods.

Synthesis and characterization of (BTO)0.2-(CCTO)0.8 nanocomposite thick films

Dual phase (Bi4Ti3O12)0.2-(CaCu3Ti4O12)0.8 {(BTO)0.2-(CCTO)0.8} nanocomposite powder was synthesized via a low cost auto-combustion method. Nancomposite powder was modified in the form of a thick layer (50 μm) over the alumina ceramic substrate using screen printing technique. The structural, morphological, functional and electrical properties of the dielectric thick film have been observed. The XRD spectra confirm the coexistence of dual phase composite systems with proper ratios. The particle size was significantly smaller and very few un-melted particles were observed from FESEM analysis of the thick film. Vibrational modes present in the composite film were confirmed with the help of FTIR spectrum. The (BTO)0.2-(CCTO)0.8 shows an unusual behaviour of high dielectric constant (∼243) and dielectric loss (∼5.9) at low frequency as well as room temperature. The understanding of this amazing dielectric behaviour opens the new way of nanocomposite thick films which can be used as a dielectric substrate for microstrip antenna fabrication.

Selectively electroless deposited Ag nanoparticles embedded in the dielectric layer to tune the rear color of bifacial solar cells

In this paper, a simple method to grow silver nanoparticles (Ag-NPs) onto a thin dielectric layer on silicon substrates is presented by using a wet-based chemical technique. The mechanism of Ag-NPs in-situ growth on dielectric films, and the influence of the dielectric materials, the thickness of dielectric film and the reaction time on the morphologies of Ag-NPs were investigated. Moreover, the Ag-NPs have been integrated into the rear dielectric layers (Al2O3/SiNx) of bifacial monocrystalline silicon passivated-emitter–rear-contact (mono-Si PERC) solar cells. The cells show not only the acceptable electrical performance, i.e. the average efficiency gain ~0.04% and the highest efficiency of 22.71%, but also the tunable rear colors. The research in this paper provides a feasible approach for tunning the rear color of the solar cells, which has potential to be applied in building integrated photovoltaics (BIPV) in terms of aesthetical aspects.

The simulation of thermal deformation on lightweight optics with thick coatings

Lightweight optics utilized in high-power laser system can dissipate heat better and reduce system weight. Dielectric films can be designed for laser pulse modulation, high reflect rate and wide bandwidth. However, the deformation caused by coating residual stress will be large due to the large thickness of dielectric films and low stiffness of lightweight mirror, which brings a large bending deformation with the temperature variation. The traditional surface compensation technology is double-sided coating, but it is not suitable for lightweight mirrors. In this study, we construct a finite shell-element model to estimate the surface shape error caused by dielectric film coating residual stress on a lightweight mirror for surface pre-processing. Thermal deformation and bimetal effect deformation are also simulated.

Wavelength-Selective Near Unity Absorber Based on Fabry-Pérot Nanoresonators

We proposed and analyzed a planar narrow-band absorber based on a bi-layer metal/dielectric structure. The planar absorber uses the Fabry-Pérot resonance and the inherent loss of the metals, for maximum light absorption in the range of the electromagnetic spectrum visible to the near infrared. The absorption resonance peak can be shifted to other regions of the spectrum by varying the dielectric film thicknesses. It is also possible to control the absorption with the angle of incidence for TE and TM polarization modes. The high absorption (near unity) and the high tolerance to fabrication errors of the proposed absorber can be explored in a large number of optoelectronic devices.

Numerical analysis of a dual-wave band guided-mode resonance filter with embedded bilayer asymmetric metallic gratings

In this paper, a novel guided-mode resonances (GMRs) based embedded dual-wavelength filter, which had the bilayer gratings located at the two sides of dielectric substrate and arranged at asymmetric position, was investigated and studied theoretically. As compared to symmetric structures that usually provided single wavelength of transmission resonance, as one normal incidence was used for transverse magnetic polarized light, the designed asymmetric structure could generate two remarkable narrow band wavelengths of transmission resonance. The parameters to affect the resonance wavelengths and the transmission resonance Q value (Q = λ/Δλ) of two bands were the distance between the two metallic gratings, the relatively lateral positions of the upper and lower gratings, the number of structure period, the thicknesses of metallic gratings, and the thickness of dielectric film. By optimizing the designed parameters, a GMR device with two resonance wavelengths located at 1239 and 1302 nm showed relative optimal performance because they had high transmission depth (99.9% and 90%) and ultra-narrow transmission bandwidth (2.8 and 1.8 nm) at the two resonance wavelengths. The presented structure can offer a potential route towards dual-band narrow-band filters and refractive index sensors in the near infrared.

Achieving a Low-Voltage, High-Mobility IGZO Transistor through an ALD-Derived Bilayer Channel and a Hafnia-Based Gate Dielectric Stack

Ultrahigh-resolution displays for augmented reality (AR) and virtual reality (VR) applications require a novel architecture and process. Atomic-layer deposition (ALD) enables the facile fabrication of indium-gallium zinc oxide (IGZO) thin-film transistors (TFTs) on a substrate with a nonplanar surface due to its excellent step coverage and accurate thickness control. Here, we report all-ALD-derived TFTs using IGZO and HfO2 as the channel layer and gate insulator, respectively. A bilayer IGZO channel structure consisting of a 10 nm base layer (In0.52Ga0.29Zn0.19O) with good stability and a 3 nm boost layer (In0.82Ga0.08Zn0.10O) with extremely high mobility was designed based on a cation combinatorial study of the ALD-derived IGZO system. Reducing the thickness of the HfO2 dielectric film by the ALD process offers high areal capacitance in field-effect transistors, which allows low-voltage drivability and enhanced carrier transport. The intrinsic inferior stability of the HfO2 gate insulator was effectively mitigated by the insertion of an ALD-derived 4 nm Al2O3 interfacial layer between HfO2 and the IGZO film. The optimized bilayer IGZO TFTs with HfO2-based gate insulators exhibited excellent performances with a high field-effect mobility of 74.0 ± 0.91 cm2/(V s), a low subthreshold swing of 0.13 ± 0.01 V/dec, a threshold voltage of 0.20 ± 0.24 V, and an ION/OFF of ∼3.2 × 108 in a low-operation-voltage (≤2 V) range. This promising result was due to the synergic effects of a bilayer IGZO channel and HfO2-based gate insulator with a high permittivity, which were mainly attributed to the effective carrier confinement in the boost layer with high mobility, low free carrier density of the base layer with a low VO concentration, and HfO2-induced high effective capacitance.

Impact of area scaling on the ferroelectric properties of back-end of line compatible Hf0.5Zr0.5O2 and Si:HfO2-based MFM capacitors

Scaling of planar HfO2-based ferroelectric capacitors is investigated experimentally by varying the capacitor area within five orders of magnitude, under the scope of a limited thermal budget for crystallization. Both Hf0.5Zr0.5O2 (HZO) and Si-doped HfO2 (HSO)-based metal/ferroelectric/metal capacitors with a 10 nm dielectric film thickness and TiN electrodes are demonstrated to be ferroelectric when integrated in a back-end of line (BEOL) of 130 nm CMOS technology, with a maximum thermal budget below 500 °C. When the area of the ferroelectric capacitors is scaled down from 7850 μm2 to 0.28 μm2, no degradation of the remanent polarization (2·PR > 10 μC/cm2 for HSO, > 30 μC/cm2 for HZO) or of the switching kinetics (down to 100 ns at 3 V) is observed. Significant improvement of the field cycling endurance is demonstrated upon area scaling, consistent with the reduction of the total number of defects when devices are shrunk. The results pave the way for future BEOL demonstrations in 130 nm and more advanced nodes with record endurance similar to perovskite ferroelectrics.

Copper Nitride Nanowire Arrays-Comparison of Synthetic Approaches.

Copper nitride nanowire arrays were synthesized by an ammonolysis reaction of copper oxide precursors grown on copper surfaces in an ammonia solution. The starting Cu films were deposited on a silicon substrate using two different methods: thermal evaporation (30 nm thickness) and electroplating (2 μm thickness). The grown CuO or CuO/Cu(OH)2 architectures were studied in regard to morphology and size, using electron microscopy methods (SEM, TEM). The final shape and composition of the structures were mostly affected by the concentration of the ammonia solution and time of the immersion. Needle-shaped 2–3 μm long nanostructures were formed from the electrodeposited copper films placed in a 0.033 M NH3 solution for 48 h, whereas for the copper films obtained by physical vapor deposition (PVD), well-aligned nano-needles were obtained after 3 h. The phase composition of the films was studied by X-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis, indicating a presence of CuO and Cu(OH)2, as well as Cu residues. Therefore, in order to obtain a pure oxide film, the samples were thermally treated at 120–180 °C, after which the morphology of the structures remained unchanged. In the final stage of this study, Cu3N nanostructures were obtained by an ammonolysis reaction at 310 °C and studied by SEM, TEM, XRD, and spectroscopic methods. The fabricated PVD-derived coatings were also analyzed using a spectroscopic ellipsometry method, in order to calculate dielectric function, band gap and film thickness.

PRISA: a user-friendly software for determining refractive index, extinction co-efficient, dispersion energy, band gap, and thickness of semiconductor and dielectric thin films

A user-friendly software PRISA has been developed to determine optical constants (refractive index and extinction co-efficient), dispersion parameters (oscillator energy and dispersion energy), absorption co-efficient, band gap and thickness of semiconductor and dielectric thin films from measured transmission spectrum, only. The thickness, refractive index, and extinction co-efficient of the films have been derived using Envelope method proposed by Swanepoel. The absorption co-efficient in the strong absorption region is calculated using the method proposed by Connel and Lewis. Subsequently, both direct and indirect bandgap of the films is estimated from the absorption co-efficient spectrum using Tauc plot. The software codes are written in Python and the graphical user interface is programmed with tkinter package of Python. It provides convenient input and output of the measured and derived data. The software has a feature to cross check the results by retrieving transmission spectrum using the values of refractive index, extinction co-efficient, and thickness obtained from Envelope method. The performance of the software is verified by analyzing numerically generated transmission spectra of a-Si:H amorphous semiconductor thin films, and experimentally measured transmission spectra of electron beam evaporated HfO2 dielectric thin films as examples. PRISA is found to be much simpler and accurate as compared to the other freely available softwares. To help researchers working on thin films, the software is made freely available at https://www.shuvendujena.tk/download.

Nanoscale film thickness measurement based on weak measurement.

In this paper, a novel method of film thickness measurement based on weak measurements is proposed by analyzing the quantitative relationship between film thickness and the weak measurement amplified shift of the photonic spin Hall effect, and the corresponding measurement system is established to verify it through experiments. This method can measure the thickness of an arbitrary dielectric film with nanometer resolution. The theoretical analysis and experimental results show that the method is reasonable, feasible, and reliable, and the structure of the measurement system is simple, easy to operate, and easy to assemble into a prototype instrument. The measurement model and method provide not only a new way for the measurement of thin film thickness but also an important reference for the precise measurement of other optical interface parameters.