Ta2O5 Layer Research Articles

Ultrathin Indium Tin Oxide Accumulation Mode Electrolyte‐Gated Transistors for Bioelectronics

AbstractElectrolyte‐gated field effect transistors and electrochemical transistors have emerged as powerful components for bioelectronic sensors and biopotential recording devices. A set of parameters must be considered when developing devices to amplify weak electrophysiological signals. These include maximum transconductance values, cut‐off frequencies, and large on/off current ratios. Organic polymer‐based devices have recently dominated the field, especially when considering flexibility as a key factor. Oxide semiconductors may also offer these features, as well as advantages like higher mobility. Herein, flexible, ultrathin, indium tin oxide (ITO) electrolyte‐gated transistors are reported. These accumulation‐mode devices combine n‐type operation with µe = 9.5 cm2 Vs−1, high transconductance (gm = 44 mS), and on/off ratios (105) as well as optically transparent layouts. While oxides are normally considered brittle, mechanically flexible ITO layers are obtained by room temperature deposition of amorphous layers onto parylene C. This process results in low strain, producing devices that survive bending. ITO electrochemically degrades, however, with cycling. To overcome this, the surface is passivated with high dielectric constant inert capping layers of Ta2O5 or Ta2O5/AlN. This greatly improves stability while preserving low gate voltages. Based on their overall performance, ITO‐based EGFETs are promising for bioelectronics.

Comparison of mechanical and tribological performance of the ZrB2 to (Ta, Zr, Ti, V, Hf)B2 borides system

Borides are promising wear-resistant materials. The mechanical and tribological properties of ZrB2, (Ta, Zr)B2, (Ta, Zr, Ti)B2, (Ta, Zr, Ti, V)B2 and (Ta, Zr, Ti, V, Hf)B2 synthesized by spark plasma sintering were compared to examine the elemental dependence. The results indicated that the hardness and fracture toughness of borides increased with the increase of entropy. (Ta, Zr, Ti, V, Hf)B2 obtained the highest hardness and fracture toughness of 23.14 GPa and 5.13 Mpa·m1/2 due to the pores and second phases that change the path of crack propagation. In terms of wear, all the Ta-contained borides have a lower wear rate than that of ZrB2. It is almost one order of magnitude lower for (Ta, Zr, Ti, V, Hf)B2 than that of ZrB2. This is mainly due to the formation and action of tribofilm rich of amorphous Ta2O5. Thermodynamic calculation indicates that the Ta atoms in borides are more prone to being oxidized resulting in the formation of a layer of Ta2O5 on the surface, which is beneficial to wear resistance improvement. This work provides guidelines for the composition-design of high-entropy borides for wear-resistant material applications.

Electrolytic Micro‐Capacitors Based on Tantalum Films for High Voltage Applications

AbstractElectrolytic capacitors are known to be fast devices with very low time constant and able to deliver high power. This class of capacitors is then an interesting technology to power miniaturized embedded electronics for Internet of Things applications. However, the current electrolytic capacitor suffers from its bulky size that does not fit with the miniaturization. To solve this issue, a proof‐of‐concept consisting of miniaturizing an electrolytic capacitor based on tantalum materials to give rise to a new class of electrolytic micro‐capacitors is proposed. To reach this ambitious objective, thin films (<100 nm) of tantalum metal (Ta), tantalum nitride (TaN), and tantalum oxide (Ta2O5) are deposited on a Si substrate by sputtering deposition method. After a careful optimization of the deposition parameters, Ta/Ta2O5 and TaN/Ta2O5 electrodes (Ta and TaN ≈45 nm and Ta2O5 ≈25 nm) and study their behaviors when biased at high voltage (>20 Volts) in aqueous electrolyte are produced. The Ta/Ta2O5 and TaN/Ta2O5 interfaces when the electrode is polarized near and beyond the breakdown voltage of the dielectric layer are carefully investigated. Polarizing the electrodes beyond the breakdown voltage are shown to result in anodization‐like mechanisms. In the case of the TaN/Ta2O5 electrode, an N‐rich porous layer grew within the Ta2O5 layer as polarization increased. A comparative study on the 2 stacked layers electrodes with different compositions (Ta/Ta2O5 and TaN/Ta2O5) but similar thicknesses (45/25 nm) is carried out: both electrodes show excellent capacitance retention of over 90% over 300 000 cycles. The frequency behavior of Ta/Ta2O5 and TaN/Ta2O5 electrodes shows that both are potential candidates in electrolytic micro‐capacitors for powering miniaturized electronics.

Positively Charged Defects in Ta2O5 and Nb2O5: Are They Correlated with Sodium Ions?

In the present study, capacitance–voltage and triangular voltage sweep (TVS) measurements reveal mobile positively charged defects in both Ta2O5 and Nb2O5 layers deposited on thin SiO2 layers . These defects are not detected in the SiO2 layers before the deposition of high‐k oxides and their concentration depends significantly on the purity of the targets. The electrical properties of these defects are found to be similar to those of positively charged Na+ in SiO2. Vapor‐phase decomposition‐inductively coupled plasma‐mass spectrometry (VPD‐ICPMS) measurements show that Na is a dominant signal besides Ta and Nb after the deposition of Ta2O5 and Nb2O5, respectively. Considering these findings, the origin of the positively charged defects is discussed with an emphasis on their correlation with Na+.

SURFACE PLASMON RESONANCE ANALYSIS FOR BENZENE SENSING MEDIA USING SILVER AND Ta2O5 THIN FILMS

The increasing demand for optical sensors is driven by their wide applications, making surface plasmon resonance (SPR) play a crucial role in this field. In this study, a multilayered thin film consisting of tantalum pentoxide (Ta2O5) and silver (Ag) deposited on a glass prism was used to study SPR. The Ag layer thickness was fixed at 50 nm, while the Ta2O5 layer thickness varied from 0 to 70 nm. The Kretschmann configuration was employed to assess the sensitivity of air and gases with different refractive indices. Therefore, different layer thicknesses along with different wavelengths and angles were investigated. MATLAB software was employed to simulate and analyze SPR with a half-sphere prism to extend the incident angle. The simulation conditions with Fresnel equations were used to calculate the reflectivity and transmittance coefficients for the studied sample. The results revealed that the best output was at a Ta2O5 thickness of 50 nm to get optimal full width at half maximum of 2.4 and sensitivity factor of 162.5. This device works in the visible and infrared regions.

Ultrahigh-reflective optical thin films prepared by reactive magnetron sputtering with RF-induced substrate bias.

Optical thin films with high-reflectivity (HR) are essential for applications in quantum precision measurements. In this work, we propose a coating technique based on reactive magnetron sputtering with RF-induced substrate bias to fabricate HR-optical thin films. First, atomically flat SiO2 and Ta2O5 layers have been demonstrated due to the assistance of radio-frequency plasma during the coating process. Second, a distributed Bragg reflector (DBR) mirror with an HR of ∼99.999 328% centered at 1397nm has been realized. The DBR structure is air-H{LH}19-substrate, in which the L and H denote a single layer of SiO2 with a thickness of 237.8nm and a single layer of Ta2O5 with a thickness of 171.6nm, respectively. This novel coating method would facilitate the development of HR reflectors and promote their wide applications in precision measurements.

Comparative study on the oxidation behavior of Si2BC3N/Ta4HfC5 ceramics at 1000 °C and 1500 °C: Microstructural evolution and kinetics consideration

The oxidation kinetics and oxide scale morphology of the Si2BC3N/Ta4HfC5 ceramics sintered by hot-pressing were explored at 1000 °C and 1500 °C in flowing air. Dense Si2BC3N/Ta4HfC5 ceramic sintered at 1900 °C with fine grain sizes shows the optimal oxidation resistance both at 1000 °C and 1500 °C. When oxidized at 1000 °C, the formation of a porous oxide layer of Ta2O5, Hf6Ta2O17 and HfO2 containing amorphous SiO2 are primarily responsible for the unsatisfying oxidation resistance of the composite. A highly oxidation resistance component like Si2BC3N can promote the oxidation resistance of Ta4HfC5 at 1500 °C, thanks to the formation of a dense and continuous tantalum-hafnium silicate glass. The oxidation kinetic curve at 1500 °C can be described by a parabolic law whilst the oxidation process is controlled by the diffusion rate of oxygen through the oxide layer; however, the oxidation reaction rate governs the oxidation progress at 1000 °C via a linear oxidation kinetics.

A comparative analysis of fiber-based surface plasmonic resonance sensors utilizing various fluoride glass cores and the influence of different oxide layers on the sensor performance in near-infrared

In a fiber-based surface plasmon resonance (SPR) sensor, with multiple layers, including fluoride glass core, cladding, metal (Ag), graphene and alcohols as the analyte, we focused on comparing the effects of 12 different types of fluoride glass cores from three main groups of fluorozirconate (ZrF4-based), fluoroaluminate (AlF3-based) and fluoroindate (InF3-based). The comparison was conducted to evaluate the sensor’s sensitivity and figure of merit (FOM) at specific near infrared (NIR) wavelengths (785 nm, 852 nm, 895 nm and 980 nm) while keeping other parameters constant. The highest FOM was consistently observed at the wavelength of 980 nm for all three categories of fluoride glass cores. Among them, the fluoride glass core IZBSC (40 InF3-20 ZnF2-15 BaF2-20 SrF2-5 CaF2) from InF3-based group presented the largest FOM = 1459.15 RIU−1. Furthermore, we observed that the FOM of the fiber types belonging to the ZrF4-based and InF3-based categories increased with the wavelength. However, the fluoroaluminate fibers showed different trend and they also exhibited the smallest FOM values at 852 nm, 895 nm and 980 nm wavelengths. To enhance the sensor’s performance, we explored the incorporation of an oxide layer into the to the SPR sensor with a ZBLAN (55.8 ZrF4-14.4 BaF2-5.8 LaF3-3.8 AlF3-20.2 NaF) core. We analyzed the effects of various oxide coatings (Sc2O3, Lu2O3, Al2O3, GeO2, TeO2, Ta2O5, MgO, TiO2, and ZnO) on the Ag layer, which has not previously studied, to the best of our knowledge. Among the different oxide coatings, the Ta2O5 layer, with optimized thickness, exhibited a significant enhancement, achieving FOM of 1631.43 RIU−1.

Influence of Annealing on Mechanical Behavior of Alumina-Tantala Nanolaminates.

Mechanical properties of thin films are significant for the applicability of nanodevices. Amorphous Al2O3-Ta2O5 double and triple layers were atomic layer-deposited to the thickness of 70 nm with constituent single-layer thicknesses varying from 40 to 23 nm. The sequence of layers was alternated and rapid thermal annealing (700 and 800 °C) was implemented on all deposited nanolaminates. Annealing caused changes in the microstructure of laminates dependent on their layered structure. Various shapes of crystalline grains of orthorhombic Ta2O5 were formed. Annealing at 800 °C resulted in hardening up to 16 GPa (~11 GPa prior to annealing) in double-layered laminate with top Ta2O5 and bottom Al2O3 layers, while the hardness of all other laminates remained below 15 GPa. The elastic modulus of annealed laminates depended on the sequence of layers and reached up to 169 GPa. The layered structure of the laminate had a significant influence on the mechanical behavior after annealing treatments.

Enabling rotary atomic layer deposition for optical applications.

Atomic layer deposition (ALD) has been proven as an excellent method for depositing high-quality optical coatings due to its outstanding film quality and precise process control. Unfortunately, batch ALD requires time-consuming purge steps, which leads to low deposition rates and highly time-intensive processes for complex multilayer coatings. Recently, rotary ALD has been proposed for optical applications. In this, to the best of our knowledge, novel concept, each process step takes place in a separate part of the reactor divided by pressure and nitrogen curtains. To be coated, substrates are rotated through these zones. During each rotation, an ALD cycle is completed, and the deposition rate depends primarily on the rotation speed. In this work, the performance of a novel rotary ALD coating tool for optical applications is investigated and characterized with S i O 2 and T a 2 O 5 layers. Low absorption levels of <3.1p p m and <6.0p p m are demonstrated at 1064nm for around 186.2nm thick single layers of T a 2 O 5 and 1032nm S i O 2, respectively. Growth rates up to 0.18nm/s on fused silica substrates were achieved. Furthermore, excellent non-uniformity is also demonstrated, with values reaching as low as ±0.53% and ±1.07% over an area of 135×60m m for T a 2 O 5 and S i O 2, respectively.

Development of Highly Stable and Sensitive SAW UV Sensor Based on Ta2O5 Coated 1D ZnO/SnO2 Core–Shell Nanostructures

AbstractDespite extensive research on ultraviolet (UV) sensors based on core–shell heterostructures, most of them exhibit low sensitivities, slow response/recovery times, and unsatisfactory long‐term stabilities, thereby limiting their use in real‐time applications. To solve these problems, a highly sensitive and stable surface acoustic wave (SAW) UV sensor based on novel tantalum pentoxide (Ta2O5) coated 1D zinc oxide (ZnO)/tin dioxide (SnO2) core–shell nanostructures is introduced. The fabricated SAW‐based UV sensor system, including sensor interface electronics, exhibits a high UV response, fast response/recovery time, and long‐term stability. Prior to device fabrication, coupling of mode (COM) modeling is performed to calculate the optimal parameters for the SAW device. Photoluminescence and X‐ray photoelectron spectroscopy measurements reveal that the Ta2O5 layer coating effectively suppresses the recombination of photogenerated carriers, leading to an increase in the carrier density and improvement in the UV sensing properties. The evaluated sensitivity and linearity of the proposed sensor are 120.36 ppm (mW cm−2)−1 and 0.988, respectively, in the range of 1–60 µW cm−2. The sensing mechanism of the proposed UV sensor is discussed in detail. Using COMSOL simulations and photo‐corrosion experiments, it is found that the Ta2O5 coated ZnO/SnO2 core–shell heterostructure minimizes the effects of humidity and improves stability.

Multilayer thin films of aluminum oxide and tantalum oxide deposited by pulsed direct current magnetron sputtering for dielectric applications

This research describes the synthesis of multilayer thin films of aluminum oxide and tantalum oxide for dielectric applications. The multilayer thin films are made of two, four, or eight oxide layers produced by physical vapor deposition (PVD), specifically mid-frequency pulsed direct current magnetron sputtering. The oxide layers are stoichiometric Al2O3 and Ta2O5 with two specific morphologies observed from cross-section images obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Al2O3 layers exhibit a columnar structure whereas the Ta2O5 layers are uniform and dense. However, the morphology of the Ta2O5 layers changes progressively in the four-layer and eight-layer systems under the influence of the morphology of the Al2O3 layer below. This behavior is induced by the morphological continuity of the interface between two oxide layers. X-ray diffraction (XRD) shows the low crystallinity of these oxide layers due to the experimental conditions used during the magnetron sputtering process, particularly the low deposition temperature. The dielectric behavior of the multilayer thin films is studied by dielectric strength measurements. The results are compared to the values obtained for single layers of Al2O3 and Ta2O5 produced under the same experimental conditions. The two-layer system shows an intermediate value compared to the single layers, higher than Al2O3 and lower than Ta2O5. The dielectric strengths of the four-layer and the eight-layer systems are higher than those measured for the single layers of Al2O3 and Ta2O5. Finally, the morphology and the crystallinity of the multilayer thin films are changed by thermal annealing of these samples at 850 °C under vacuum. The thermal annealing induces crystallization of the Ta2O5 layers and the loss of morphological continuity at the interface between the oxide layers. These modifications result however in a lower dielectric strength for all the multilayer thin films.

Optimised Spintronic Emitters of Terahertz Radiation for Time-Domain Spectroscopy

Spintronic metal thin films excited by femtosecond laser pulses have recently emerged as excellent broadband sources of terahertz (THz) radiation. Unfortunately, these emitters transmit a significant proportion of the incident excitation laser, which causes two issues: first, the transmitted light can interfere with measurements and so must be attenuated; second, the transmitted light is effectively wasted as it does not drive further THz generation. Here, we address both issues with the inclusion of a high-reflectivity (HR) coating made from alternating layers of SiO2 and Ta2O5. Emitters with the HR coating transmit less than 0.1% of the incident excitation pulse. Additionally, we find that the HR coating increases the peak THz signal by roughly 35%, whereas alternative attenuating elements, such as cellulose nitrate films, reduce the THz signal. To further improve the emission, we study the inclusion of an anti-reflective coating to the HR-coated emitters and find the peak THz signal is enhanced by a further 4%.

A Surface-Scattering-Based Composite Optical Waveguide Sensor for Aerosol Deposition Detection

Aerosol is a suspension of fine chemical or biological particles in the air, and it is harmful, easily causing air pollution, respiratory diseases, infrastructure corrosion, and poor visibility. Therefore, the development of advanced optical sensors for real-time detection of aerosol deposition is of great significance. In this work, a prism-coupled composite optical waveguide (COWG) sensor for aerosol deposition detection based on surface scattering is proposed and demonstrated theoretically and experimentally. The COWG consists of a single-mode slab glass waveguide locally covered with a tapered thin film of high-index metal oxide. The tapered film can greatly enhance the evanescent field through the adiabatic transition of the fundamental transverse electric (TE0) mode between the uncovered and film-covered regions, thereby enabling the COWG to serve as a simple yet highly sensitive evanescent-wave scattering sensor for sensitive detection of aerosol deposition. The COWG with a tapered layer of Ta2O5 was prepared by masked sputtering, aerosol salt particle deposition on the COWG was successfully detected, and the influence of surface water droplets on the COWG sensor performance was analyzed. The experimental results indicate that the sensitivity of the COWG is 30 times higher than that of the bare glass waveguide.

Reactive co-sputtering of ternary Au–Ta–O films with tunable electrical resistivity

Heavy-metal-based films with high electrical resistivity are needed for hohlraums for magnetically assisted inertial confinement fusion. Here, we study ternary Au–Ta–O films deposited by reactive direct-current magnetron co-sputtering from elemental Au and Ta targets in an oxygen containing atmosphere. By varying the O content, the electrical resistivity of films can be tuned in a wide range of ∼100–40 000 μΩ cm. With increasing O content, a drastic increase in resistivity occurs at ∼45 at. % of O, separating regimes with two different dominant conduction mechanisms attributed to metallic conduction through the Au–Ta alloy matrix (for ≲45 at. % of O) and tunneling across insulating Ta2O5 layers separating conducting islands (for ≳45 at. % of O). Post-deposition annealing at 300 °C leads to the segregation of Au into ∼50-nm islands, sharply decreasing the resistivity for films with ≳45 at. % of O but not for the metal-like films with lower O content.

Wear-out and breakdown of Ta2O5/Nb:SrTiO3 stacks

Tantalum oxide (Ta2O5) is widely used in electronics, with important applications in backend capacitors and memristors. However, major technological challenges have to be faced and solved. Also, concerns related to the reliability of these new stacks have to be taken into consideration. We report the reliability of Ta2O5 films focusing on the dynamics of the charge trapping and their leakage behavior under a constant voltage stress. We leverage the use of Nb:SrTiO3 back electrodes as a clean, well-defined surface, allowing the study of the Ta2O5 layer with no significant interface effects. The main features of the breakdown Ta2O5/Nb:SrTiO3 stacks are presented and analyzed in terms of an electromigration-based model. Our results outline the performance limits of Ta2O5 films, providing guidelines for development and integration of current and future devices.

Milk-Ta2O5 Hybrid Memristors with Crossbar Array Structure for Bio-Organic Neuromorphic Chip Applications.

In this study, a high-performance bio-organic memristor with a crossbar array structure using milk as a resistive switching layer (RSL) is proposed. To ensure compatibility with the complementary metal oxide semiconductor process of milk RSL, a high-k Ta2O5 layer was deposited as a capping layer; this layer enables high-density, integration-capable, photolithography processes. The fabricated crossbar array memristors contain milk–Ta2O5 hybrid membranes, and they exhibit bipolar resistance switching behavior and uniform resistance distribution across hundreds of repeated test cycles. In terms of the artificial synaptic behavior and synaptic weight changes, milk–Ta2O5 hybrid crossbar array memristors have a stable analog RESET process, and the memristors are highly responsive to presynaptic stimulation via paired-pulse facilitation excitatory post-synaptic current. Moreover, spike-timing-dependent plasticity and potentiation and depression behaviors, which closely emulate long-term plasticity and modulate synaptic weights, were evaluated. Finally, an artificial neural network was designed and trained to recognize the pattern of the Modified National Institute of Standards and Technology (MNIST) digits to evaluate the capability of the neuromorphic computing system. Consequently, a high recognition rate of over 88% was achieved. Thus, the milk–Ta2O5 hybrid crossbar array memristor is a promising electronic platform for in-memory computing systems.

Methods of controlling operation modes in Pt/TaO x /Ta2O5/Pt resistive switching cells

Forming and resistive switching (RS) characteristics of Pt/TaO x /Ta2O5/Pt cells were investigated when the TaO x thickness was varied. With an increase in the TaO x thickness, a semi-forming process, which is defined as a transition from an initial state to high resistance states more than 1 kΩ, occurs more frequently. The semi-forming can be understood as the formation of an incomplete filament with a gap or a constricted part in the Ta2O5 layer. Moreover, in a single cell after the semi-forming, selective control of RS operation modes was achieved by simply adjusting the range of the applied voltage. In a complementary RS mode where both set and subsequent reset processes occur at both positive and negative voltages, analog RS characteristics can be observed. The control of the RS operation modes could be useful for the improvement of the multi-leveled controllability of resistance.

Thickness dependent resistive switching behaviors in Ta2O5 layer at low temperature: Towards flexible, invisible, cryo-electronic applications in aerospace

The role of Ta2O5 resistive switching (RS) layer thickness on transparent resistive random-access memories (TRRAMs) is systematically investigated. Ta2O5 TRRAMs (t-TRRAMs) exhibits not only high optical transmittance (82%) in the visible region but also bipolar resistive switching behavior with RON/ROFF ratio of ≈103, SET voltage of (0.37 ± 0.08)V, RESET voltage of -(2.83 ± 0.42)V, good endurance of ≈103 cycles and retention over 104s at room temperature (RT) as well as 80 °C. The temperature-dependent RS properties for t-TRRAMs are experimentally validated from low temperature (150 K) to elevated temperature (333 K). Furthermore, t-TRRAMs are implemented on ITO-coated flexible polyethylene terephthalate (PET) substrates. The flexible t-TRRAMs demonstrate RON/ROFF ratio of ≈102, reasonable endurance of ≈500 cycles, and retention over 104s at RT. The experimental results indicate that t-TRRAMs can be a potential candidate for flexible, invisible, cryo-electronic applications.

Tantalum Oxide as an Efficient Alternative Electron Transporting Layer for Perovskite Solar Cells.

Electron transporting layers facilitating electron extraction and suppressing hole recombination at the cathode are crucial components in any thin-film solar cell geometry, including that of metal–halide perovskite solar cells. Amorphous tantalum oxide (Ta2O5) deposited by spin coating was explored as an electron transport material for perovskite solar cells, achieving power conversion efficiency (PCE) up to ~14%. Ultraviolet photoelectron spectroscopy (UPS) measurements revealed that the extraction of photogenerated electrons is facilitated due to proper alignment of bandgap energies. Steady-state photoluminescence spectroscopy (PL) verified efficient charge transport from perovskite absorber film to thin Ta2O5 layer. Our findings suggest that tantalum oxide as an n-type semiconductor with a calculated carrier density of ~7 × 1018/cm3 in amorphous Ta2O5 films, is a potentially competitive candidate for an electron transport material in perovskite solar cells.