SiO2 Dielectrics Research Articles

X-ray radiation damage effects on double-SOI pixel detectors for the future astronomical satellite FORCE

We have been developing the monolithic active pixel detector XRPIX onboard the future x-ray astronomical satellite FORCE. XRPIX is composed of complementary metal-oxide-semiconductor pixel circuits, SiO2 insulator, and Si sensor by utilizing the silicon-on-insulator (SOI) technology. When the semiconductor detector is operated in orbit, it suffers from radiation damage due to x-rays emitted from celestial objects as well as cosmic rays. From previous studies, positive charges trapped in the SiO2 insulator are known to cause degradation of the detector performance. To improve the radiation hardness, we developed XRPIX equipped with a double-SOI (D-SOI) structure, introducing an additional silicon layer in the SiO2 insulator. This structure is aimed at compensating for the effect of the trapped positive charges. Although the radiation hardness of the D-SOI detectors to cosmic rays has been evaluated, the radiation effect due to x-ray irradiation has not been evaluated. Thus, we then conduct an x-ray irradiation experiment using an x-ray generator with a total dose of 10 krad at the SiO2 insulator, equivalent to 7 years in orbit. As a result of this experiment, the energy resolution in full-width half maximum for the 5.9 keV x-ray degrades by 17.8 % ± 2.8 % and the dark current increases by 89 % ± 13 % . We also investigate the physical mechanism of the increase in the dark current due to x-ray irradiation using technology computer-aided design simulation. It is found that the increase in the dark current can be explained by the increase in the interface state density at the Si / SiO2 interface.

Improvement in nonvolatile memory operations for metal–ferroelectric–insulator–semiconductor capacitors using HfZrO2 and ZrO2 thin films as ferroelectric and insulator layers

Metal–ferroelectric–insulator–semiconductor (MFIS) capacitors were characterized to elucidate the optimum design schemes for the ferroelectric field-effect transistor applications. The Hf1−x Zr x O2 (HZO) thin films (18 nm) were prepared on the SiO2 and ZrO2 insulator layers (ILs) with different film thicknesses. The choice of 10 nm thick ZrO2 IL was found to be an optimum condition to properly balance between the values of electric fields applied to the HZO (E HZO) and ZrO2 (E IL) layers, leading to effective improvement in capacitance coupling ratio and to suppression of charge injection for the MFIS capacitors. Furthermore, the crystalline natures of the crystallized HZO films were also found to be strategically controlled on the ZrO2 ILs, which can additionally enhance the E HZO with reducing the E IL. As consequences, the MFIS capacitors using 10 nm thick ZrO2 IL exhibited the ferroelectric memory window as large as 2.5 V at an application of ±5 V, which corresponds to 2.7 times wider value, compared to that obtained from the device using 2 nm thick SiO2 IL. Long-time memory retention and robust program endurance were also verified for the fabricated MFIS capacitors.

Precision fabrication of diamond micro-optic elements with hybrid SiO2/Cr etching masks

Diamond is opted for high-power optical systems due to excellent optical transparency, radiation, and thermal resistance, while the fabrication of micro-structures on diamond falls behind. Here we report a reliable fabrication method of diamond and fabricate a laminar grating with 2.90 μm period and 3.08 μm groove depth by directly laser writing(DLW) and reactive ions etching (RIE). We presented a micro-masks-less and high-temperature hybrid masks of diamond etching with dielectric SiO2 mask and Cr adhesive layer. We developed a statistical analysis method using Hough transform on SEM images, which could provide the quantitative results and monitor the variation of structures during fabrication process. The grating presents 28% diffraction efficiency in the 0th order and 9% in the ±1st order at 405 nm wavelength. The results of diffraction experiment are in close agreement with the rigorous coupled wave (RCWA) simulation.

Porous N-doped Ni@SiO2/graphene network: Three-dimensional hierarchical architecture for strong and broad electromagnetic wave absorption

Electromagnetic wave absorber is critical for reducing increasingly serious electromagnetic wave pollution, however, the development of lightweight and broadband microwave absorbers remains a pressing challenge. We report here the rational design and synthesis of N-doped [email protected]2/graphene composite constructed from 3D interconnected porous graphene network and [email protected]2 core-shell architecture, which fulfills lightweight and broadband requirements while exhibiting highly efficient electromagnetic wave absorption. The porous graphene network, functioning both as lightweight support and dielectric mediator, was synthesized via NaCl template-assisted high-temperature calcination method. Upon uniformly attached with core-shell [email protected]2 on the surface, the resulting abundant heterogeneous interfaces constructed by graphene-Ni and Ni-SiO2 strongly reinforce polarization loss. The presence of low dielectric SiO2 allows facile tuning of the complex permittivity of ternary composite by adjusting coating thickness to balance the attenuation ability and impedance matching. Moreover, further N-doping of graphene assists in the optimization of dielectric loss ability. Taking account of the advantages arising from the porous hierarchical architecture, multiple absorption centers and diverse interfaces, the lightweight composite exhibits an ultra-strong reflection loss (RL) value of - 71.13 dB at 13.76 GHz with a thickness of 2.46 mm and broad effective absorption bandwidth of 7.04 GHz at a low filler content of 15 wt.%. More importantly, the effective absorption range covers 13.28 GHz (4.72–18 GHz) with the optimized thickness of 1.6–5 mm, representing 83% of the whole range of frequencies. Our results demonstrate that the novel 3D porous N-doped [email protected]2/graphene network with hierarchical architecture is a promising candidate for high-performance electromagnetic wave absorption.

Insights into the Effect of Heat Treatment and Carbon Coating on the Electrochemical Behaviors of SiO Anodes for Li‐Ion Batteries

AbstractThe use of SiO as an anode material has attracted significant interest due to its high capacity and long cycling life. Many promising approaches, including structural design and carbon coating at high temperatures, effectively improve its intrinsic low electrical conductivity and poor Coulombic efficiency. However, the “heat treatment process‐composition and microstructure‐electrochemical properties” relationship of the SiO anode is not fundamentally understood. Here the structure and composition evolution in amorphous SiO and graphene‐coated SiO is investigated using different heat‐treatment conditions. X‐ray absorption near‐edge structure techniques are also employed to analyze the surface and bulk composition change during the initial lithiation process, supplemented by physical or chemical characterization and electrochemical testing. The results reveal the structural transition of SiO during heat treatment, from amorphous to disproportionated hierarchical structure, where the as‐formed dielectric exterior SiO2 shell and interior SiO2 matrix severely polarizes electrodes, hindering the lithiation process. Carbon coating on SiO effectively restricts the growth of the SiO2 shell and facilitates charge transfer, leading to improved electrochemical performance. A schematic model is proposed to reveal the relationship between the treatments, the resultant structural evolutions, and corresponding electrochemical behaviors.

A simple route to prepare SiO2 insulation film by atmospheric pressure plasma jet

SiO2 insulation film was rapidly prepared by the atmospheric pressure plasma jet (APPJ) technology, which could be applied to the substrate with large size and/or complex surface morphology. Si and O sources were the hexamethyldisiloxane and nature air, respectively. The optical emission spectrum results revealed that Si+, Si, and O were the main species in APPJ. The relative content of Si and O in APPJ could influence the insulation resistance of SiO2 film. With the excessive Si in APPJ, the insulation resistance of SiO2 film could be improved to 3.35×106 Ω/μm.

Miniaturized pH‐Sensitive Field‐Effect Capacitors with Ultrathin Ta2O5 Films Prepared by Atomic Layer Deposition

Miniaturized electrolyte–insulator–semiconductor capacitors (EISCAPs) with ultrathin gate insulators have been studied in terms of their pH‐sensitive sensor characteristics: three different EISCAP systems consisting of Al–p‐Si–Ta2O5(5 nm), Al–p‐Si–Si3N4(1 or 2 nm)–Ta2O5 (5 nm), and Al–p‐Si–SiO2(3.6 nm)–Ta2O5(5 nm) layer structures are characterized in buffer solution with different pH values by means of capacitance–voltage and constant capacitance method. The SiO2 and Si3N4 gate insulators are deposited by rapid thermal oxidation and rapid thermal nitridation, respectively, whereas the Ta2O5 film is prepared by atomic layer deposition. All EISCAP systems have a clear pH response, favoring the stacked gate insulators SiO2–Ta2O5 when considering the overall sensor characteristics, while the Si3N4(1 nm)–Ta2O5 stack delivers the largest accumulation capacitance (due to the lower equivalent oxide thickness) and a higher steepness in the slope of the capacitance–voltage curve among the studied stacked gate insulator systems.

A Modified SiO2-Based Memristor with Reliable Switching and Multifunctional Synaptic Behaviors.

Dielectric SiO2 has possible uses as an active layer for emerging memory due to its high on/off ratio and low operation voltage. However, SiO2-based memory that relies on the conducting filament still has limited endurance and stability. Here, we have constructed a passivated layer of SiO2 using Ag-doped SrTiO3, which serves as a Ag ion reservoir for the control of filament formation. It is demonstrated that the modified memristor presents an excellent endurance switching and could stably be operated in an ambient environment for 20 days without visible degradation. Based on the reliable switching, the synaptic functions such as excitatory postsynaptic current, paired-pulse facilitation, transition from short-term memory to long-term memory, and potentiation/depression have also been implemented. Furthermore, a 7 × 7 pixel array made from memristors has successfully mimicked simple learning and forgetting behavior. The experimental results offer an alternative approach for SiO2-based memristors and a possibility to be applied in neuromorphic computing.

Determination of a quantitative relationship between deposition duration and magnetic performance of soft ferromagnetic composites via data-analysis and theoretical models

The industrial production of soft ferromagnetic composites demands a quantitative description of process parameters and magnetic performance. Here, Fe–Si/SiO2 soft ferromagnetic composites were prepared via a two-step method combining chemical vapour deposition and hot-pressed sintering. Investigations of surface and section morphology, phase composition and crystal structure were undertaken to characterise the deposition duration-dependence of SiO2 insulation coating thickness in Fe–Si/SiO2 soft ferromagnetic composites. A vibrating sample magnetometer, a resistivity tester and a B–H analyser were used to study the magnetic behaviours of Fe–Si/SiO2 soft ferromagnetic composites. Based on curves of deposition duration-dependence of SiO2 insulation coating thickness and other theoretical models, quantitative relationships between deposition duration and magnetic performance were determined for Fe–Si/SiO2 soft ferromagnetic composites. These results demonstrate that the coating and crystallisation of SiO2 insulation coatings had no influence on the crystal structure of Fe–Si substrate particles and that SiO2 insulation coating thickness increased linearly with deposition duration. Total core loss of Fe–Si/SiO2 soft ferromagnetic composites was strongly predicted by SiO2 insulation coating thickness. A quantitative equation relating magnetisation intensity to Fe–Si/SiO2 soft ferromagnetic composite deposition duration was derived on the basis of experimental data and subsequent model selection. Additional quantitative equations relating electrical resistivity and eddy current loss to Fe–Si/SiO2 soft ferromagnetic composite deposition duration were determined according to electromagnetic theory. These results establish a precise adjustment mechanism for magnetic behaviour in Fe–Si/SiO2 soft ferromagnetic composites and promote the industrialisation of a new preparation process combining chemical vapour deposition and hot-pressed sintering.

3-Layer stacked pixel-parallel CMOS image sensors using hybrid bonding of SOI wafers

We report 3-layer stacked pixel-parallel CMOS image sensors developed for the first time. The hybrid bonding of silicon-on-insulator wafers through damascened Au electrodes in a SiO2 insulator on the front and backside realizes both face-to-face and face-to-back bonding, developing a multi-layer stacked device. A 3-layered pixel circuit is developed to confirm the linear response of 16-bit digital signal output. A prototype sensor with 160 × 120 pixels successfully captures video images, demonstrating the feasibility of multi-layered sensors of high performance as well as multi-functions including signal processing, memory, and computing for applications such as high-quality video cameras, measurements, recognition, robots, and various IoT devices.

Effects of channel length and gate dielectric material on electrical properties of an IGZO TFT

In this paper, the variation of threshold voltage, transconductance, and on/off current ratio of bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs) with different channel lengths and gate dielectric substrate has been investigated. Bottom gate configuration was simulated using SILVACO TCAD Software. Electrical parameters such as threshold voltage, transconductance, and on/ off current ratio were analyzed with an active layer thickness of 30 nm and the variation of length of channel from 5 μm to 25 μm and gate dielectric substrate of high dielectric constant. Threshold voltage increased and transconductance decreased with the increase of the channel length but there was no big change in IOn/IOff ratio. The threshold voltage around 0.64 V, transconductance around 44.2 μs, and On/Off current ratio around 8.13x108 were observed at a channel length of 5 μm. When the dielectric material SiO2 was replaced by Si3N4, the threshold voltage was 0.76 V, transconductance was 85.64, and On/Off current ratio was 1.58x109 and for Al2O3 threshold voltage was 0.77 V transconductance was 199.8 μs and On/Off current ratio was 4.3x109.Transconductance, Threshold voltage, and On/Off current ratio were increased for high K gate dielectric materials.

Ultra-broadband thermal radiator for daytime passive radiative cooling based on single dielectric SiO2 on metal Ag

Passive radiative cooling plays an essential role in global energy conservation and environment preservation. We designed a single medium cone SiO2 on Ag, which reflects more than 96% sunlight and emits near-unity infrared between 8–25μm. Under direct sunlight of 103 W/m2, the designed cooler can effectively achieve a predicted steady-state temperature of 261 K, which is 39 K below ambient at 300 K without consideration of thermal convection and conduction. When considering the significant influence of external conduction and convection (10 W/m2/K), the net cooling power of the cooler is about 121 W/m2 at T=300 K, and the predicted steady-state temperature is 9 K below ambient. When sunlight is shielded, the net cooling power is 160 W/m2 and the predicted steady-state temperature is 244 K at hc=0 W/m2/K and 288 K at hc=10 W/m2/K. It benefits from the zero transmission of Ag, the particular extinction coefficient of SiO2 and the optimized structure. Furthermore, we explored the inner mechanism through studying the dependences of spectra on structure, geometry parameters as well as electromagnetic field distributions. The excellent performances of passive cooling with simple and compatible structure and mature SiO2 can effectively enhance the efficiency of the cooling system, and promote the practical application for radiative cooling greatly.

Ultra-low energy threshold engineering for all-optical switching of magnetization in dielectric-coated Co/Gd based synthetic-ferrimagnet

A femtosecond laser pulse is able to switch the magnetic state of a 3d-4f ferrimagnetic material on a pico-second timescale. Devices based on this all-optical switching (AOS) mechanism are competitive candidates for ultrafast memory applications. However, a large portion of the light energy is lost by reflection from the metal thin film as well as transmission to the substrate. In this paper, we explore the use of dielectric coatings to increase the light absorption by the magnetic metal layer based on the principle of constructive interference. We experimentally show that the switching energy oscillates with the dielectric layer thickness following the light interference profile as obtained from theoretical calculations. Furthermore, the switching threshold fluence can be reduced by at least 80% to 0.6 mJ/cm2 using two dielectric SiO2 layers sandwiching the metal stack, which scales to 15 fJ of incident energy for a cell size of 502 nm2.

Effect of dielectric surface passivation on organic field-effect transistors: spectral analysis of the density of trap-states

The semiconductor/dielectric interface is arguably the most important region in field-effect transistors. This article investigates the performance-enhancing effects of passivation of the dielectric surface by a self-assembled layer (SAM) of silanes on organic field-effect transistors. Apart from conventional figures of merit for the devices, the energetic distribution of the density of the in-gap trap-states (trap-DOS) and the contact resistance are evaluated using numerical methods. The investigation reveals that the surface passivation of the dielectric SiO2 has a dual effect on device operation. Firstly, it establishes quantitatively that the surface passivation leads to a significant reduction in the density of both shallow and deep traps in the organic semiconductor PBTTT-C14. This effect outweighs the impact of the SAM dipoles on the device turn-on. Secondly, the contact resistance gets lowered by a factor of more than 10 due to the improved top-surface morphology of the PBTTT-C14 thin film. The lower contact resistance in devices is corroborated by lower contact potential difference between PBTTT-C14 and gold, measured using scanning kelvin probe microscopy.

High‐Sensitivity Tunable Bloch Surface Waves’ Biosensor Using Nanocomposite Cap Layer

The advantage of the high versatility of the nanocomposite (Nc) materials in modeling photonic structure devices is exploited to design an optical biosensor based on Bloch surface waves (BSWs) to probe different biomolecular species. The suggested biosensor is constituted by two periods of low and high refractive indices (RIs) of alternate dielectric materials SiO2 and TiO2 capped by Ag−TiO2 Nc layer operating under the Kretschmann configuration and using p‐polarized incident light. Herein, the biosensor performances are theoretically investigated in a wide range of the sensing medium RI [1.33, 1.61] using selected operating wavelengths 455, 465, 480, 500, and 600 nm to deviate a large dielectric loss of the Ag−TiO2 Nc layer. The results show that the structure sustains BSW for each wavelength in separate domains of the sensing medium RI conferring to the proposed biosensor a potential for the high‐sensitive multiwavelength detection of different biomolecular entities.

VCSEL Wavelength Setting by Intra-Cavity Phase Tuning — Numerical Analysis and Experimental Verification

Monolithic multi-wavelength VCSEL arrays, with wavelengths of individual VCSELs precisely set in a post-epitaxial growth process, would enable compact multi-color light sources and transmitters for various sensing and datacom applications. Here we report on a numerical study of the requirements of spectral matching and balancing of DBR reflectances, optical confinement factor, and optical gain for uniformity of threshold current and slope efficiency over wavelength with wavelength set by intra-cavity phase tuning. The requirements are verified by an experimental demonstration of intra-cavity phase tuned VCSELs in the spectral range 1043–1067 nm with a wavelength spacing of 8 ± 1 nm enabled by precise Ar ion-beam etching. Small variations of threshold current and slope efficiency are achieved by close to ideal spectral matching and balancing. The VCSELs are GaAs-based with a dielectric SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> top-DBR. We conclude that high uniformity of threshold current and slope efficiency is demanding in terms of spectral matching and balancing and requires not only very precise etching for intra-cavity phase tuning and precise thickness of the layers in the dielectric top-DBR, but also precise thickness and composition of the layers in the epitaxial semiconductor part.

Hybrid Metal-Dielectric-Metal Sandwiches for SERS Applications.

The development of efficient plasmonic nanostructures with controlled and reproducible surface-enhanced Raman spectroscopy (SERS) signals is an important task for the evolution of ultrasensitive sensor-related methods. One of the methods to improving the characteristics of nanostructures is the development of hybrid structures that include several types of materials. Here, we experimentally investigate ultrathin gold films (3–9 nm) near the percolation threshold on Si/Au/SiO2 and Si/Au/SiO2/graphene multilayer structures. The occurring field enhanced (FE) effects were characterized by a recording of SERS signal from Crystal Violet dye. In this geometry, the overall FE principally benefits from the combination of two mechanisms. The first one is associated with plasmon excitation in Au clusters located closest to each other. The second is due to the gap plasmons’ excitation in a thin dielectric layer between the mirror and corrugated gold layers. Experimentally obtained SERS signals from sandwiched structures fabricated with Au film of 100 nm as a reflector, dielectric SiO2 spacer of 50 nm and ultrathin gold atop could reach SERS enhancements of up to around seven times relative to gold films near the percolation threshold deposited on a standard glass substrate. The close contiguity of the analyte to graphene and nanostructured Au efficiently quenches the fluorescent background of the model compound. The obtained result shows that the strategy of combining ultrathin nano-island gold films near the percolation threshold with gap plasmon resonances is promising for the design of highly efficient SERS substrates for potential applications in ultrasensitive Raman detection.

Admittance of Pentacene- Based Mis-Structures with Two-Layer Insulator SiO2–Al2O3

Admittance of Pentacene- Based Mis-Structures with Two-Layer Insulator SiO2–Al2O3

Interlayer engineering for enhanced ferroelectric tunnel junction operations in HfO x -based metal-ferroelectric-insulator-semiconductor stack

Ferroelectric tunnel junction (FTJ) has been considered as a promising candidate for next-generation memory devices due to its non-destructive and low power operations. In this article, we demonstrate the interlayer (IL) engineering in the FTJs to boost device performances. Through the analysis on the material and electrical characteristics of the fabricated FTJs with engineered IL stacks, it is clearly found that the insertion of an Al2O3 layer between the SiO2 insulator and the pure-HfO x FE improves the read disturbance (2V c = 2.2 V increased), the endurance characteristics (tenfold improvement), and the cell-to-cell TER variation simultaneously without the degradation of the ferroelectricity (less than 5%) and the polarization switching speeds through grain size modulation. Based on these investigations, the guidelines of IL engineering for low power ferroelectric devices were provided to obtain stable and fast memory operations.

Low activation energy field-effect transistors fabricated by bar-assisted meniscus shearing

Here, we study the temperature-dependent transport properties of OFETs with the prototypical OSC 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) co-processed with polystyrene (PS) as the active layer. The active layer is deposited directly on SiO2 using the bar-assisted meniscus shearing (BAMS) method. The co-processing with PS favors a consequential decrease in interfacial trap densities as previously reported. Furthermore, we demonstrate how this processing method leads to devices exhibiting activation energies well below the current state of the art for TIPS-pentacene on SiO2 or other dielectrics. Altogether, our study reports on TIPS-pentacene thin films exhibiting an activation energy (Ea) as low as 15 meV when the active material is blended with PS and processed via BAMS. Such an unprecedentedly low value originates not only from a decrease in the interfacial trap densities but also from trapping energies much shallower than previously reported elsewhere for the same material. This allows us to clarify the previously reported notion that significant passivation of interfacial traps occurs following the separation of PS from TIPS-pentacene into an individual layer at the interface with the insulator and to confirm that the enhanced transport originates from a synergistic effect wherein both trapping density and depth are reduced.