Transmittance Of Thin Films Research Articles

Broadband 300-GHz Power Amplifier MMICs in InGaAs mHEMT Technology

In this article, we report on compact solid-state power amplifier (SSPA) millimeter-wave monolithic integrated circuits (MMICs) covering the 280–330-GHz frequency range. The technology used is a 35-nm gate-length InGaAs metamorphic high-electron-mobility transistor (mHEMT) technology. Two power amplifier MMICs are reported, based on a compact unit amplifier cell, which is parallelized two times using two different Wilkinson power combiners. The Wilkinson combiners are designed using elevated coplanar waveguide and air-bridge thin-film transmission lines in order to implement low-loss 70-Ω lines in the back-end-of-line of this InGaAs mHEMT technology. The five-stage SSPA MMICs achieve a measured small-signal gain around 20 dB over the 280–335-GHz frequency band. State-of-the-art output power performance is reported, achieving at least 13 dBm over the 286–310-GHz frequency band, with a peak output power of 13.7 dBm (23.4 mW) at 300 GHz. The PA MMICs are designed for a reduced chip width while maximizing the total gate width of 512 μm in the output stage, using a compact topology based on cascode and common-source devices, improving the output power per required chip width significantly.

Synthesis and Characterization of Physical Properties of MgO Thin Films by Various Concentrations

Abstract In this work, magnesium oxide was elaborated on a glass substrate at 450°C by a pneumatic spray technique. The structural, optical, and electrical properties were studied at different MgO concentrations (.05, .10, .15, and .2 mol L−1). Poly-crystalline MgO films with a cubic structure with a strong (002) preferred orientation were observed at all sprayed films, with a maximum crystallite size of 21.4 nm attained by the sprayed film at .2 mol L−1. Good transmission was found in the deposited MgO thin films with lowest molarity. The transmission of MgO thin films decreases rapidly as the wavelength increases in the range of 300–400 nm and then increases slowly at higher wavelengths. The bandgap of MgO thin films decreases as the molarity increases, and the band gap values range between 4.8 and 4.3 eV. The Urbach energy values range between 375 and 519 meV. The electrical resistance of our films is on the order of 2 × 107Ω. The prepared MgO thin films were suitable for electronic packaging; they are capable to provide very stable and high secondary electron emission combined with low bandgap energy and low electrical resistance.

Crystalline dependence of spin transmission in Cr2O3 thin films

Spin transmission in Cr2O3 films of different crystalline textures is studied experimentally. With Y3Fe5O12/Cr2O3/Pt trilayer devices, a spin current is injected into Cr2O3 by spin pumping from Y3Fe5O12, and the spin transmission is monitored by the inverse spin Hall voltage (VISHE) in Pt. For (0001) plane textured Cr2O3 films, VISHE vanishes quickly below the Néel temperature. However, the VISHE shows a broad shoulder below the Néel temperature for (112‾0) and (112‾3) plane co-textured Cr2O3. Such a difference in the temperature dependence of Cr2O3 can be understood by the different Néel vector orientations with respect to the injected spin moment direction.

The effect of film thickness on the structural, optical and electrical properties of ZnO thin films deposited by ultrasonic spray deposition

Zinc oxide (ZnO) thin films were deposited by ultrasonic spray deposition at different film thicknesses at 420 °C. The ZnO solution was obtained with a concentration of 0.1 mol.l−1, it was deposited on glass substrate at various times. The structural, optical and electrical properties of ZnO thin films were studied at different film thicknesses. In the results, the XRD shows that the ZnO thin films having a hexagonal structure with (002) and (101) diffraction peaks, which were observed in al deposited films. The minimum crystallite size of (002) and (101) phases are 43.6 nm for 460 nm and 32.2 nm for 350 nm, respectively. The optical transmission of ZnO thin film is about 80% approach the wavelength of 800 nm in the visible region. The optical band gap energy of ZnO thin films was decreased from 3.26 to 2.91 with increasing the film thickness from 250 to 460 nm. The highest Urbach energy was obtained at 460 nm. The ZnO thin films have an electrical conductivity was increased from 0.19 to 6.74 (Ω.cm)−1 when film thickness increases from 250 to 460 nm. The best crystalline structure, optical band gap and electrical conductivity are achieved at 460 nm.

Photoresist Absorption Measurement at Extreme Ultraviolet (EUV) Wavelength by Thin Film Transmission Method

Photoresist Absorption Measurement at Extreme Ultraviolet (EUV) Wavelength by Thin Film Transmission Method

Effect of annealing on the structural, morphological, optical and electrical properties of Al-Zn co-doped SnO2 thin films

ABSTRACTAluminum–Zinc co-doped SnO2 thin films were successfully synthesised onto glass substrates by spray-pyrolysis processing. The structural, morphological, optical and electrical properties of co-doped thin films as deposited at 400˚C, 500˚C, and 600˚C and were studied using various techniques. The XRD results show the films possessed polycrystalline SnO2 with tetragonal rutile structure. The average crystallite size found to be 39 (pure) and 31 nm (co-doped). AFM images showed the annealing temperature effects surface morphology of the films. The transmittance of thin films is up to 80 to 85% in the visible region. The bandgap of the films has been calculated for different annealing temperature and they lie within the range of 3.87 – 4.21 eV. Electrical properties of co-doped thin films were studied through Hall measurement. Furthermore, the prepared co-doped thin films will be useful in optoelectronics and gas sensing applications.

Low-loss cable-to-cable parallel connection method for thin-film superconducting flexible microwave transmission lines

We describe a superconducting (SC) cable-to-cable connection method for thin-film flexible (Nb/polyimide) parallel transmission line cables that exhibits low loss from DC to microwave frequencies. Design, fabrication procedures, assembly methods and characterization results are reported. The connector assembly incorporates a monolithic array of short superconductive bridging traces that function as a ganged electrical splice between two ribbon cables. The assembly is micro-mechanically self-aligned and uses pressure to make simultaneous electrical contacts between multiple 50 μm wide microstrip signal traces, as well as between ground planes. Each contacting surface comprises thin SC Nb overcoated with ultra-thin Au, providing nearly zero DC resistance and very good RF performance. A simulation model of the microwave performance of microstrip-to-microstrip interconnections at 4.2 K was successfully matched to measurement results. This new cable-to-cable connection approach exhibited an insertion loss <0.12 dB and a return loss >15 dB up to 14 GHz. The connections performed reproducibly throughout multiple thermal cycles and multiple disassembly/reassembly cycles.

Electrodynamic resonance of surface conduction and THz transmission through arrays of rectangular apertures in opaque metallic thin films.

A modal method is developed analytically to investigate the THz optical transmission and reflection of a metallic thin film perforated by a 2D array of rectangular apertures. For subwavelength apertures, this optical model is interpreted in terms of passive electrical circuits, with interface admittances accounting for the THz surface conduction properties of the metallic film. The reactive component of the admittance of the evanescent diffraction cloud is shown to exhibit resonant behavior governed by the shape factors of the array. Interaction of such an electrodynamic resonance with the Rayleigh diffraction orders may alter their standard Fano profiles. Experimental evidence of the resonance is obtained owing to lineshape analysis of transmittance measurements in the THz range on metallic thin films deposited on a dielectric substrate, both above and below the first Wood-Rayleigh anomaly.

Structural and physical properties of NbO2 and Nb2O5 thin films prepared by magnetron sputtering

NbOx thin films have been deposited on silicon (100) and quartz substrates by magnetron sputtering using a metallic Nb target in an optimized argon–oxygen atmosphere. This work investigates the dependence of structure–property relations on the key deposition parameters towards establishing optimum deposition conditions for the growth of NbOx polycrystalline films. It is found that a sputtering condition corresponding to DC power density 9.87 W cm−2, a substrate temperature of 720 °C, low gas pressures of 8 mtorr, a target to substrate distance of 45 mm gives thin films with good homogeneity and a high degree of crystallinity in the case of both NbO2 and Nb2O5. X-ray diffraction (XRD) and Raman spectroscopy confirmed the tetragonal phase of NbO2 and orthorhombic phase of Nb2O5 for similar deposition temperatures. Scanning electron microscopy (SEM) observations indicate that NbO2 has a unique nanoslice structure while Nb2O5 has a flake-like structure. The optical transmittance of the films has been investigated and found to be dependent on the oxygen gas content during deposition; the optical transmittance decreases with increasing O2 gas content. Optical constants of the films were calculated by fitting a suitable thin film transmittance model to experimental transmittance spectra using a modified Swanepoel technique. The nanohardness and stress in the films were measured by nanoindentation and an optical profilometer respectively. Nanohardness and stress in the film show no large dependence on the oxygen gas content except at high oxygen gas content. The nanohardness value of NbO2 films is approximately 6 GPa, and the Young’s modulus is 150 GPa. The Nb2O5 films exhibit a nanohardness of 5.8–13 GPa and a Young’s modulus of 137–161 GPa.

Cu sputtered Cu/ZnO Schottky diodes on fluorine doped tin oxide substrate for optoelectronic applications

In the present work, ZnO thin films were deposited on fluorine doped tin oxide (FTO) and soda lime glass substrates using sol-gel spin coating technique. Cu thin films were deposited on ZnO by the sputtering technique through a shadow mask for the Schottky diode application. The effect of solution concentration on the structural, morphological, optical and electrical properties of the deposited thin films were investigated. X-ray diffraction pattern shows that all thin films have a wurtzite structure with (002) orientation. Scanning electron micrographs revealed concentration dependent surface morphology. The transmittance of thin films were measured in the wavelength range 300 nm–800 nm and it was found that the optical bandgap decreased from 3.28 eV to 3.21 eV as molarity increased. For optoelectronic applications of the thin film samples, the current-voltage (I-V) measurements were performed for optimizing molar concentrations. The electronic parameters of the Cu/ZnO schottky diode such as ideality factor (η) and barrier height (ΦB) were obtained using I-V curve. The highest stauration current was obtained 8.67 × 10−4 A for 0.5 M thin film sample at 5 V bias voltage. The obtained results indicate that the electrical properties of the Cu/ZnO Schottky diodes can be tuned by molar concentrations.

New Transparent Bandpass Filter Using Aluminum Thin-Film Micromesh Structure

In this study, we present the new transparent coplanar waveguide (CPW) bandpass filter using aluminum (Al) thin film micromesh structure. The filter is prepared by the semiconductor process of dc sputtering and standard lift-off technology. In order to achieve the high-performance transparent bandpass filter, the new aluminum thin film micromesh structure with low resistivity to 10 -8 Ω-cm, uniform Al thin film thickness to 3μm, high optical transparent to 78% and simple manufacturing process has been proposed. The transparent bandpass filter is designed at 2.4 GHz with 3-dB fractional bandwidth (FBW) of 5%, the minimum insertion loss (-20 log |S 21 |) of 1.8 dB and the return losses (-20 log |S 11 |) of 25 dB. The simulated and measured results of the transparent bandpass filter are in good agreement. The proposed transparent bandpass filter is showing a simple coplanar waveguide configuration, low thin film resistivity, high thin film transmittance, high filter performance, and small circuit size.

The SPECTRAL Ice Chamber: Application to Titan’s Stratospheric Ice Clouds

Abstract An ice chamber for obtaining thin-film transmission spectra of Titan-relevant organic ices between 50 and 11,700 cm−1 (200–0.85 μm) is described in detail in this work. The ice chamber, called the SPECtroscopy of Titan-Related ice AnaLogs chamber, is located in the Spectroscopy for Planetary ICes Environments laboratory at NASA Goddard Space Flight Center. Organic vapors are typically deposited between 30 and 150 K via a variable leak valve onto a chemical vapor deposition diamond substrate, where condensation directly into the solid state occurs. Quantitative thin-film infrared transmission spectra of the given ice or ice mixture are then measured, from which optical constants (complex indices of refraction) are computed. These optical constants in turn provide the necessary input for interpreting radiative transfer analyses of Cassini’s Composite InfraRed Spectrometer observations of Titan’s organic stratospheric ice clouds to determine their chemical compositions, abundances, and vertical distributions as functions of Titan latitude and season.

Investigation of Nanostructure and Optical Properties of Flexible AZO Thin Films at Different Powers of RF Magnetron Sputtering

In this study Al-doped Zinc Oxide (AZO) thin films were successfully deposited on the flexible Polymethyl methacrylate (PMMA) substrate by RF magnetron sputtering. The effects of RF power on the crystal structure, morphology, thickness and optical properties of AZO thin films have been investigated. The AZO thin films were analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), DEKTAK 3 profilometer, UV–Visible spectroscopy and room temperature photoluminescence (PL) spectroscopy. The XRD patterns show that increase of RF power leads to increase in the predominant direction along (100) and crystal plane of hexagonal ZnO. Moreover, the transmittance of thin films decreased from 76% to 61% and optical bang gap varied among 3.34[Formula: see text]eV to 3.22[Formula: see text]eV with increasing RF power. The PL spectra show excellent light-emitting characteristics: 375[Formula: see text]nm, 428[Formula: see text]nm, 467[Formula: see text]nm and 505[Formula: see text]nm. The results indicate that the peak intensity increases with increasing RF power from 80[Formula: see text]W to 180[Formula: see text]W.

Characterization of CuInGeSe4 thin films and Al/n–Si/p–CuInGeSe4/Au heterojunction device

CuInGeSe4 thin films of various thicknesses were prepared on a glass substrate by thermal evaporation followed by selenization at 700 K. Energy dispersive X-ray analysis shows that the CuInGeSe4 thin films are near stoichiometric. The X-ray diffraction patterns indicate that the as-deposited CuInGeSe4 thin films are amorphous, while the CuInGeSe4 thin films annealed at 700 K are polycrystalline with the chalcopyrite phase. The structure of the films was further investigated by transmission electron microscopy and diffraction, with the results verifying the X-ray diffraction data. High-resolution scanning electron microscopy images show well-defined grains that are nearly similar in size. The surface roughness increases with film thickness, as confirmed by atomic force microscopy. The optical transmission and reflection spectra of the CuInGeSe4 thin films were recorded over the wavelength range of 400–2500 nm. The variation of the optical parameters of the CuInGeSe4 thin films, such as the refractive index n and the optical band gap Eg, as a function of the film thickness was determined. The value of Eg decreases with increasing film thickness. For the studied films, n were estimated from the Swanoepl’s method and were found to increase with increasing film thickness as well as follow the two-term Cauchy dispersion relation. A heterojunction with the configuration Al/n–Si/p–CuInGeSe4/Au was fabricated. The built-in voltage and the carrier concentration of the heterojunction was determined from the capacitance–voltage measurements at 1 MHz and were found to be 0.61 V and 3.72 × 1017 cm−3, respectively. Under 1000 W/m2 solar simulator illumination, the heterojunction achieved a conversion efficiency of 2.83%.

Optical design of perovskite solar cells for applications in monolithic tandem configuration with CuInSe2 bottom cells

Abstract:Monolithic integrated thin film tandem solar cells consisting of a high bandgap perovskite top cell and a low bandgap thin film bottom cell are expected to reach higher power conversion efficiencies (PCEs) with lower manufacturing cost and environmental impacts than the market-dominant crystalline silicon photovoltaics. There have been several demonstrations of 4-terminal and 2-terminal perovskite tandem devices with CuInGaSe2 (CIGS) or CuInSe2 (CIS) and, similar to the other tandem structures, the optimization of this device relies on optimal choice for the perovskite bandgap and thickness. Therefore, further advancement will be enabled by tuning the perovskite absorber to maximize the photocurrent limited by the current match condition. Here, we systematically study the optical absorption and transmission of perovskite thin films with varying absorber band gap. Based on these results, we model the photocurrent generations in both perovskite and CIS subcells and estimate the performances of projected tandem devices by considering the ideally functioning perovskite and CIS device. Our results show that for perovskite layers with 500 nm thickness the optimal bandgap is around 1.6 eV. With these configurations, PCEs above 20% could be achieved by monolithically integrated perovskite/CIS tandem solar cells. Also by modelling the absorption at every layer we calculate the quantum efficiency at each subcell in addition to tracking optical losses.

Effect of the number of cycles on the optical and structural properties of Mn3O4 nanostructures obtained by SILAR technique

In this study, nanostructured Mn3O4 (manganese oxide) thin films were successfully obtained by successive ionic layer adsorption and reaction (SILAR) method on the soda lime glass substrates using Manganese Nitrate (Mn(NO3)2) and Ammonium hydroxide (NH4(OH)) as cationic and anionic precursors respectively. Structural and morphological characterizations of the Mn3O4 films obtained at different cycles were determined using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The crystal structure of the thin films were also confirmed by RAMAN spectroscopy. Optical properties such as absorption, transmission, reflection, extinction coefficient and optical band gap of nanostructured Mn3O4 thin films were determined by UV–Vis spectroscopy. SEM images showed that the manganese oxide nanosheets formed uniformly on substrate surface. As the deposition cycles increased, nano-sheets structure deteriorated. The optical band gap of Mn3O4 thin films varied from 2.12 to 2.59 eV, depending on the increase in number of cycles. From contact angle measurements of thin films, it was determined that thin films had hydrophilic character.

Characterization of Thin Metal Films Using Terahertz Spectroscopy

A theoretical model is presented to simulate the transmission of thin metal films. Using terahertz spectroscopy, the two key characteristic parameters, conductivity and thickness, are determined simultaneously by fitting the experimental data to the theoretical model. Three different metal films, aluminum, copper, and silver, are investigated. The measured conductivities are significantly less than the bulk values. The sample thicknesses obtained are consistent with those estimated by the quartz thickness monitor.

Near-zero IR transmission of VO2 thin films deposited on Si substrate

Vanadium dioxide (VO2) thin films of different thickness have been deposited on Si substrates by using DC magnetron sputtering. The effects of substrate pre-treatment by means of seeding (spin coating and ultrasonic bathing) and biasing on the structure and optical properties were investigated. Seeding results in a smaller grain size in the oxide film, whereas biasing results in square-textured crystals. VO2 thin films of 150 nm thick show a near-zero IR transmission in switched state. Especially, the 150 nm thick VO2 thin film with seeding treatment shows an enhanced switching efficiency.

Electrically tuned transmission and dielectric properties of illuminated and non-illuminated barium titanate thin film in terahertz regime

Transmission and dielectric properties of non-illuminated and illuminated barium titanate thin film were investigated by time-domain terahertz spectrometer and tuned by an electric field. Compared with the sample illuminated by 532 nm laser, the electric field could realize a higher modulation in the phase of the transmission for the nonilluminated sample. Results displayed that when the sample was illuminated by green laser, optical field suppressed the effect of electric field on transmission and dielectric properties of BTO thin film, because excited carriers from the substrate and ferroelectric thin film would form a built-in electric field to shield the external electric field. In addition, optical field and electrical field would play different roles in the lattice dynamics of the ferroelectric thin film.

On the depolarization in granular thin films: a Mueller-matrix approach.

We describe a general method to disclose the information hidden in Mueller matrices experimentally obtained from depolarizing samples. Although spectroscopic Mueller-matrix ellipsometry allows for a model-free characterization of inhomogeneous samples, i.e., independently from any assumption on the sample structure, the interpretation of the obtained results is often challenging. The proposed method combines three different decomposition techniques applied to the measured Mueller matrices in transmission and reflection of granular thin films with different thicknesses and densities. We demonstrate that the comparative analysis of the respective differential-, product-, and sum-decomposition of the Mueller matrices, together with correlation effects and the visualization as a Poincaré sphere, reveals the particular underlying physical processes of depolarization. As an example, we apply this method on granular BaSO4 thin films. This method is general and can be applied to a wide variety of intrinsically inhomogeneous materials with applications in physics, industry, biology, or medicine.