Dielectric Thin Films Research Articles

SiNx/SiO2-Based Fabry-Perot Interferometer on Sapphire for Near-UV Optical Gas Sensing of Formaldehyde in Air.

Fabry-Perot interferometers (FPIs), comprising foundry-compatible dielectric thin films on sapphire wafer substrates, were investigated for possible use in chemical sensing. Specifically, structures comprising two vertically stacked distributed Bragg reflectors (DBRs), with the lower DBR between a sapphire substrate and a silicon-oxide (SiO2) resonator layer and the other DBR on top of this resonator layer, were investigated for operation in the near-ultraviolet (near-UV) range. The DBRs are composed of a stack of nitride-rich silicon-nitride (SiNx) layers for the higher index and SiO2 layers for the lower index. An exemplary application would be formaldehyde detection at sub-ppm concentrations in air, using UV absorption spectroscopy in the 300-360 nm band, while providing spectral selectivity against the main interfering gases, notably NO2 and O3. Although SiNx thin films are conventionally used only for visible and near-infrared optical wavelengths (above 450 nm) because of high absorbance at lower wavelengths, this work shows that nitride-rich SiNx is suitable for near-UV wavelengths. The interplay between spectral absorbance, transmittance and reflectance in a FPI is presented in a comparative study between one FPI design using stoichiometric material (Si3N4) and two designs based on N-rich compositions, SiN1.39 and SiN1.49. Spectral measurements confirm that if the design accounts for phase penetration depth, sufficient performance can be achieved with the SiN1.49-based FPI design for gas absorption spectroscopy in near-UV, with peak transmission at 330 nm of 64%, a free spectral range (FSR) of 20 nm and a full-width half-magnitude spectral resolution (FWHM) of 2 nm.

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.

Nucleation and growth of plasma sputtered silver nanoparticles under acoustic wave activation

Early results on the plasma deposition of dielectric thin films on acoustic wave (AW) activated substrates revealed a densification pattern arisen from the focusing of plasma ions and their impact on specific areas of the piezoelectric substrate. Herein, we extend this methodology to tailor the plasma deposition of metals onto AW-activated LiNbO3 piezoelectric substrates. Our investigation reveals the tracking of the initial stages of nanoparticle (NP) formation and growth during the submonolayer deposition of silver. We elucidate the specific role of AW activation in reducing particle size, enhancing particle circularity, and retarding NP agglomeration and account for the physical phenomena making these processes differ from those occurring on non-activated substrates. We provide a comparative analysis of the results obtained under two representative plasma conditions: diode DC sputtering and magnetron sputtering. In the latter case, the AW activation gives rise to a 2D pattern of domains with different amounts of silver and a distinct size and circularity for the silver NPs. This difference was attributed to the specific characteristics of the plasma sheath formed onto the substrate in each case. The possibilities of tuning the plasmon resonance absorption of silver NPs by AW activation of the sputtering deposition process are discussed.

High-efficiency green light emission from InGaN/GaN using localized surface plasmon resonance tuned by combination of Ag nanoparticles and dielectric thin film

We achieved significant enhancements in green light emission (550 nm) from InGaN/GaN quantum wells (QWs) by tuning the localized surface plasmon resonance (LSPR) of self-assembled Ag nanoparticles (NPs) through the application of a SiO2 thin film. The LSPR wavelength of Ag NPs was shifted towards shorter wavelengths by 80 nm using a 5 nm SiO2 layer to separate Ag NPs from GaN surface, thereby aligning it effectively with the green region. This strategic placement of Ag NPs and a 5 nm SiO2 film resulted in significant enhancements of photoluminescence (PL) by 15- and 8.8-fold with 5 and 11 nm GaN cap layers, respectively. The LSPR of Ag NPs on a SiO2 thin film facilitated a longer possible distance for the coupling between surface plasmons (SPs) and excitons in a QW. Traditionally, the distance between SPs-generating metal and a QW has been maintained at 10 nm to achieve substantial enhancements. Remarkably, even with a 25 nm cap layer, Ag NPs on a 5 nm SiO2 film boosted PL by 3.1-fold. The enhancements attributable to Ag NPs on SiO2 films were superior, reaching up to 4.8 times greater than those of Ag NPs on GaN surfaces. Additionally, the PL enhancement factors calculated using the finite differential time domain (FDTD) method aligned closely with experimental results.

Controlling the broadband enhanced light chirality with L-shaped dielectric metamaterials

The inherently weak chiroptical responses of natural materials limit their usage for controlling and enhancing chiral light-matter interactions. Recently, several nanostructures with subwavelength scale dimensions were demonstrated, mainly due to the advent of nanofabrication technologies, as a potential alternative to efficiently enhance chirality. However, the intrinsic lossy nature of metals and the inherent narrowband response of dielectric planar thin films or metasurface structures pose severe limitations toward the practical realization of broadband and tailorable chiral systems. Here, we tackle these problems by designing all-dielectric silicon-based L-shaped optical metamaterials based on tilted nanopillars that exhibit broadband and enhanced chiroptical response in transmission operation. We use an emerging bottom-up fabrication approach, named glancing angle deposition, to assemble these dielectric metamaterials on a wafer scale. The reported strong chirality and optical anisotropic properties are controllable in terms of both amplitude and operating frequency by simply varying the shape and dimensions of the nanopillars. The presented nanostructures can be used in a plethora of emerging nanophotonic applications, such as chiral sensors, polarization filters, and spin-locked nanowaveguides.

Mid-infrared strong coupling between quasibound states in the continuum and epsilon-near-zero modes in a thin polar dielectric film

Mid-infrared strong coupling between quasibound states in the continuum and epsilon-near-zero modes in a thin polar dielectric film

Nanosecond Partial Discharge Current Waveforms with Polyethylene Naphthalate Films on IEC(b) Electrode

The polyethylene naphthalate (PEN) film has been widely applied as a heat‐resistant thin insulation film and sensor film. For the safe and long application of the film in various products, one significant characteristic is the partial discharge (PD) resistivity. In this study, a well‐known IEC(b) electrode is used to measure PD characteristics such as the maximum partial discharge, qmax and fast PD current waveforms at AC peak voltages of 1–3 kVp and 50–1000 Hz over PEN films with thicknesses of 75, 50, or 25 μm. All experiments are conducted at room temperature of ~20 °C. The positive PD current is defined as the current flowing from a high‐voltage electrode to a ground electrode. The positive and negative qmax increased rapidly with the applied voltage increase but remained almost the same for the applied voltage frequency changes. The PD current duration time was less than 40 ns for the positive current and 30 ns for the negative current at all voltages, frequencies, and film thicknesses. It was deduced that the positive current peak magnitude was approximately twice of the negative one at all applied voltages, frequencies, and film thicknesses. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Thin-Film-Assisted Photothermal Deformation of Gold Nanoparticles: A Facile and In-Situ Strategy for Single-Plate-Based Devices.

Optical-induced shape transformation of single nanoparticles on substrates has shown benefits of simplicity and regularity for single-particle device fabrication and on-chip integration. However, most of the existing strategies are based on wet chemical growth and etching, which could lead to surface contamination with limited local selectivity and device compatibility. Shape deformation via the photothermal effect can overcome these issues but has limited versatility and tunability largely due to the high surface tension of the molten droplet. Here we show gold nanoparticles (Au NPs) can drastically transform into nanoplates under the irradiation of a continuous wave laser (446 nm). We reveal the dielectric thin film underneath the molten Au is critical in deforming the NP into faceted nanoplate under the drive of photothermophoretic forces, which is sufficient to counteract the surface tension of the molten droplet. Both experimental evidence and simulations support this thin-film-assisted photothermal deformation mechanism, which is local selective and generally applicable to differently shaped Au NPs. It provides a facile and robust strategy for single-plate-based device applications.

Excitation of exchange spin waves in a magnetic insulator thin film at cryogenic temperatures

Spin waves and their quanta, magnons, are promising candidates for next-generation electronic devices, due to their low-power consumption and compatibility with radio-frequency-based electronic devices. For achieving magnon-based hybrid quantum systems for quantum memory and computation, the investigation of spin-wave propagation at cryogenic temperatures is highly required. In this article, we report the excitation and detection of exchange spin waves with wavelengths of tens of nanometers in an yttrium iron garnet (YIG) thin film at cryogenic temperatures. We find that the exchange spin waves are unidirectional in all temperature ranges, owing to the chiral dynamical dipolar coupling between the spin-wave mode in the YIG and the ferromagnetic resonance mode in the cobalt nanowire. Notably, a high exchange spin-wave group velocity of 2 km s−1 at 10 K is observed. Our results are promising for the development of high-speed and energy-efficient quantum magnonic devices operating at cryogenic temperatures.

Simulating the Effect of Field Electron Emission from a Cathode with a Thin Dielectric Film on Its Sputtering in a Gas Discharge in an Argon and Mercury Vapor Mixture

Simulating the Effect of Field Electron Emission from a Cathode with a Thin Dielectric Film on Its Sputtering in a Gas Discharge in an Argon and Mercury Vapor Mixture

The effect of surface-step-terrace on energy storage density and working temperature of BaZr0.2Ti0.8O3 epitaxial films

Dielectric film capacitors have been widely used in various electronic devices due to the high energy storage density and high charge–discharge speed. The energy storage performances are highly determined by the strain status of the films. Herein, we improved the energy storage performances of epitaxial BaZr0.2Ti0.8O3 film through surface-step-terrace in the vicinal substrate. It is found that the terraces in the vicinal substrate create an additional strain parallel to the terraces and a compressive strain along the out-of-plane direction. The strains result in the increase in the energy storage density of the BZT film up to 66.9 J/cm3 with an energy storage efficiency of 73.2% at room temperature, which is 2.2 times as high as that of the films on regular substrates. Moreover, the strains also lead to the reduction of the hysteresis loss and increase in the up-limited working temperature from 125 to 225 °C with an energy storage density of 52.35 J/cm3 and an efficiency of 70.25%, exhibiting excellent thermal stability. Our work demonstrates that the strains generated by vicinal substrates can improve the energy storage performance greatly and provide a method to improve the energy storage performances of dielectric thin film capacitors.

Enhancing dielectric-silicon interfaces through surface electric fields during firing

Minimising charge losses at silicon interfaces is a major development area for highly efficient solar cells. Here we report on the interface improvements achieved by establishing a surface electric field during low-temperature firing of dielectric thin films. By inducing a corona electric field on the surface of a thin film stack, we observe significant modifications to the silicon-dielectric interface upon annealing, which correlate with the characteristics of interface defects. The passivation properties of the interfaces strongly depend on the polarity and strength of the electric field during firing, as well as the dielectric materials in the layer stack. We show that the surface electric fields not only influence surface carrier population but also affect the resulting chemical interface properties post-annealing. It is postulated that hydrogen migration plays a role in these observed effects. Leveraging the corona-induced electric field enables fine-tuning of both the chemical and field-effect passivation in thin film surface dielectrics, resulting in recombination current densities as low as 2.8 fA cm−2 in research-grade float zone silicon, and 14 fA cm−2 in industrial-grade textured silicon. The simplicity and versatility of the thin film electric polarisation enable a new strategy for controlling and exploiting the chemical enhancement of interfaces in solar cell devices, from current TOPCon and PERC devices to future multijunction silicon-based cells.

Ultra-high performance hafnium-based capacitors: Synergistic achievement of high dielectric constant and low leakage current

The relationship between the dielectric constant and leakage current of materials often exhibits a negative correlation. However, to sustain Moore's Law, the semiconductor industry necessitates novel materials that simultaneously possess a high dielectric constant and low leakage current, meeting the shrinking demands of electronic components. In this study, a high-performance hafnium-based thin film capacitor achieved through the collaborative effects of bottom electrode engineering and ion doping. Tungsten (W) as the bottom electrode, with its chemically inert nature and low thermal expansion coefficient, proves advantageous in improving interface quality and promoting the generation of the high-k phase in HfO2. Concurrently, yttrium (Y) ion doping contributes to stabilizing the high-k phase of HfO2, reducing non-lattice oxygen, and enhancing the disorderliness of the dielectric thin film. By synergistically integrating these factors, the hafnium-based thin film capacitor achieves a high dielectric constant of 36.6 while maintaining minimal leakage current (Electric field ∼ 6 MV/cm, J ∼ 10−8 A/cm2) and a high charge storage capacity (Urec ∼ 104.4 J/cm³). These research findings open a promising pathway for the development of novel hafnium-based materials with broad applicability and exceptional dielectric performance.

Bridging the gap between surface physics and photonics.

Use and performance criteria of photonic devices increase in various application areas such as information and communication, lighting, and photovoltaics. In many current and future photonic devices, surfaces of a semiconductor crystal are a weak part causing significant photo-electric losses and malfunctions in applications. These surface challenges, many of which arise from material defects at semiconductor surfaces, include signal attenuation in waveguides, light absorption in light emitting diodes, non-radiative recombination of carriers in solar cells, leakage (dark) current of photodiodes, and light reflection at solar cell interfaces for instance. To reduce harmful surface effects, the optical and electrical passivation of devices has been developed for several decades, especially with the methods of semiconductor technology. Because atomic scale control and knowledge of surface-related phenomena have become relevant to increase the performance of different devices, it might be useful to enhance the bridging of surface physics to photonics. Toward that target, we review some evolving research subjects with open questions and possible solutions, which hopefully provide example connecting points between photonic device passivation and surface physics. One question is related to the properties of the wet chemically cleaned semiconductor surfaces which are typically utilized in device manufacturing processes, but which appear to be different from crystalline surfaces studied in ultrahigh vacuum by physicists. In devices, a defective semiconductor surface often lies at an embedded interface formed by a thin metal or insulator film grown on the semiconductor crystal, which makes the measurements of its atomic and electronic structures difficult. To understand these interface properties, it is essential to combine quantum mechanical simulation methods. This review also covers metal-semiconductor interfaces which are included in most photonic devices to transmit electric carriers to the semiconductor structure. Low-resistive and passivated contacts with an ultrathin tunneling barrier are an emergent solution to control electrical losses in photonic devices.

Study on Bulk-Surface Transport Separation and Dielectric Polarization of Topological Insulator Bi1.2Sb0.8Te0.4Se2.6.

This study successfully fabricated the quaternary topological insulator thin films of Bi1.2Sb0.8Te0.4Se2.6 (BSTS) with a thickness of 25 nm, improving the intrinsic defects in binary topological materials through doping methods and achieving the separation of transport characteristics between the bulk and surface of topological insulator materials by utilizing a comprehensive Physical Properties Measurement System (PPMS) and Terahertz Time-Domain Spectroscopy (THz-TDS) to extract electronic transport information for both bulk and surface states. Additionally, the dielectric polarization behavior of BSTS in the low-frequency (10-107 Hz) and high-frequency (0.5-2.0 THz) ranges was investigated. These research findings provide crucial experimental groundwork and theoretical guidance for the development of novel low-energy electronic devices, spintronic devices, and quantum computing technology based on topological insulators.

Continuously variable Fourier filters fabricated using varying angle glancing angle deposition for chip-scale spectroscopy.

Low-cost spectroscopy has received a great deal of attention in recent years in applications such as food inspection, disease detection, and manufacturing. Current spectroscopic systems rely on multiple optical components, making them mechanically fragile systems. In our previous work, we demonstrated the use of Fourier filtering using thin dielectric films. The sampling effect from the cavity resonances can be used to decompose a signal into its Fourier components. Although the thin films were deposited directly on the face of the detectors, filters of varying thicknesses were needed, which required multiple lithographic processes. To overcome this challenge, in this work, we use a continuously variable filters deposited by a single-step electron-beam evaporation technique. We demonstrate a novel, to our knowledge, method that utilizes the glancing angle deposition technique with a continuously varying angle in order to produce tens of variable Fourier filters in a single deposition run. To prove this technique, we deposit this variable filter on a 38-channel linear detector and show the results from this device.

Optimizing the Crystallinity of a ZrO2 Thin Film Insulator for InGaZnO‐Based Metal–Insulator–Semiconductor Capacitors

AbstractThe utilization of a zirconium oxide (ZrO2) thin film as the insulator in a metal–insulator–semiconductor (MIS) capacitor to enhance the characteristics of thin‐film transistors is investigated. Although the high crystallinity of ZrO2 is favorable to achieving higher capacitance density in metal–insulator–metal capacitors with ZrO2 thin films, it decreases the capacitance with increasing applied bias in Mo/ZrO2/InGaZnO (IGZO)‐structured MIS capacitors. Through comprehensive physical, chemical, and electrical characterizations, this study investigated the mechanism underlying the decreasing capacitance with increasing the applied bias in the accumulation state of the Mo/ZrO2/IGZO‐structured MIS capacitor depending on the crystallinity of ZrO2. Furthermore, the investigation identifies the optimal crystal structure of ZrO2 thin films for IGZO‐based MIS capacitors, highlighting the importance of forming meso‐crystalline structures in high dielectric constant (k) materials to enhance the k value and mitigating the decrease in capacitance caused by the accumulated carrier loss through grain boundaries of ZrO2.

High-k dielectric based high performance vertical organic thin film transistor for flexible low power applications

The basic performance parameters such as threshold voltage, drain current and saturation mobility play an important role for any transistor-based devices. The planar organic TFT provides a good performance but it is still not satisfactory. Therefore, in this paper, a vertical channel TFT (D5) is proposed that exhibits a significant improvement for threshold voltage V t , drain current I Dmax and saturation mobility μ sat in comparison to planar devices. The proposed vertical device (D5) is 44 and 24 times enhanced in comparison with planar device D1 in terms of I Dmax and μ sat , correspondingly. Furthermore, this paper compares five different vertical-channel device architectures (D2, D3, D4, D5, D6 & D7). Out of these structures, our proposed novel structure (D5) shows remarkable performance in terms of drain current (528 μA) and saturation mobility (80.8 cm2/V.s). As compared to the best mentioned vertical devices D2, D3 and D7, the proposed device exhibits 41.8 %, 15.6 % and 27.8 %, increment in drain current, respectively. Additionally, the proposed device exhibits about 2.7, 5.2 and 3.5 times improvement in comparison with D2, D3 and D7 correspondingly. The reasons for this better performance of the proposed device have been explained by vertical and horizontal cutline analysis.

Modulation of electrical properties of sputtered Ta2O5 films by variation of RF power and substrate temperature

Dielectric thin films are important building blocks of microelectronic devices, and hence, research on the development of high-k dielectric thin films has drawn tremendous research interest. In this research, thin films of tantalum oxide (Ta2O5), a high-k dielectric material, are deposited on the Si substrate by the radio frequency (RF) magnetron sputtering technique. During the deposition of Ta2O5 thin film, the sputtering parameters such as sputtering power and substrate temperature were systematically varied, and post-deposition structural, morphological, and electrical properties of sputtered Ta2O5 films are studied by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscope, capacitance–voltage (C-V) and current–voltage (I-V) measurement techniques. The annealed Ta2O5 thin film at the temperature of 900 °C for 1 h possesses polycrystalline nature with β—phase orthorhombic crystal structure. The film deposited at 150 W and substrate temperature at room temperature has shown comparatively lower surface roughness, which depicts the energy, and mobility of adatoms greatly influenced by RF power and substrate temperature. With the increase in sputtering power, the oxide charge density (Qox) is found to increase. On the other hand, Qox is found to decrease with the increase in substrate temperature. The film deposited at RF power of 150 W and substrate temperature of 300 °C is found to be of high dielectric constant, low oxide and interface charge density, and lower leakage current.

Investigation of laser-induced contamination on dielectric thin films in MHz sub-ps regime

High-repetition rate diode-pumped sub-ps lasers are widely used in the industrial sector for high-quality material processing applications. However, for their reliable operation, it is crucial to study the power handling capabilities of the optical components used in these systems. The optical components, such as mirrors, gratings, dichroic filters, and gain media, are designed based on dielectric thin films. When subjected to high-intensity laser radiation, the phenomenon of laser-induced contamination (LIC) can lead to the growth of a nanometric, highly absorbent layer on an irradiated optical surface, which can result in transmission or reflection loss and eventual permanent damage. In this study, we investigate LIC growth on dielectric oxide thin films in an air environment irradiated by MHz sub-ps laser at 515 nm. We examine the effect of thin film deposition method, material, and thickness on LIC growth dynamics. The irradiated spots on the surface are inspected using multiple observation methods, including white light interference microscopy and fluorescence imaging. Our results show that the LIC growth dynamics depend on the laser intensity and irradiation time and can be affected by the thin film deposition method, material, and thickness. These findings could be used to inform the development of more resistant optical components, ensuring long-term reliable laser operation required for industrial applications. The study highlights the need for validating optical components using tests that closely mimic real-world applications and provides insight into the complex processes that lead to LIC.