Bilayer Capacitor Research Articles

Study on theoretical model for electrical explosion resistivity of Al/Ni reactive multilayer foil

Al/Ni reactive multilayer foil (RMF) possesses excellent comprehensive properties as a promising substitute for traditional Cu bridge. A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization of EFIs. Al/Ni RMF with different bilayer thicknesses and bridge dimensions were prepared by MEMS technology and electrical explosion tests were carried out. According to physical and chemical reactions in bridge, the electrical explosion process was divided into 5 stages: heating of condensed bridge, vaporization and diffusion of Al layers, intermetallic combination reaction, intrinsic explosion, ionization of metal gases, which are obviously shown in measured voltage curve. Effects of interface and grain boundary scattering on the resistivity of film metal were considered. Focusing on variations of substance and state, the resistivity was developed as a function of temperature at each stage. Electrical explosion curves were calculated by this model at different bilayer thicknesses, bridge dimensions and capacitor voltages, which showed an excellent agreement with experimental ones.

Electrochemical micromachining based on sinusoidal signals with variable resistance

ABSTRACT Reducing pulse duration is the sole effective strategy to improve the processing accuracy in ultra-short pulse electrochemical microfabrication. High cost and unsuitability in practical production also restrain its development. This study aims to propose a method based on sinusoidal signals with variable resistance. The bilayer capacitor cannot be fully charged to achieve a transient machining state. An equivalent circuit differential equation is established, and the resistance becomes an effective parameter to control the machining accuracy. The experimental result shows that the machining accuracy increases significantly with the increase in resistance. The approach is applied to machine microstructures and achieves sub-micron scale accuracy on a pure nickel sheet. The same superior machining accuracy can be obtained by machining microstructures on hard-to-cut superalloy plates.

A method of controlling the imprint effect in hafnia ferroelectric device

Recently, hafnia-based ferroelectrics are currently being investigated as next-generation memory devices due to their excellent CMOS process compatibility and functionality. However, some of the ferroelectric devices commonly exhibit an imprint effect due to charged defects around the interfacial layer, which has negative impacts on the ferroelectric memory devices. However, it can be applied to various applications as long as the imprint field is carefully adjusted. In this work, we introduced a strategy to control the imprint field in bilayer capacitors by utilizing tantalum oxide (TaO) interfacial layers and various Zr contents in Hf0.83Zr0.17O2 (HZO) films. The TaO layer (1 nm) was inserted into the bilayer capacitors to alter the imprint field's (positive or negative) direction. Whereas to control the imprint fields, we adjusted the Zr doping content (17%–83%) in the ferroelectric HZO films (8 nm). As the Zr content increased, reduced imprint fields were observed in those bilayer capacitors. In addition, it was found that a high imprint field (+2.43 MV/cm) was observed in Hf-rich films (Hf0.83Zr0.17O2) due to the higher amount of oxygen vacancies. In addition, we examined those oxygen vacancies through x-ray photoelectron spectroscopy depth profile analysis by considering sub-oxide fractions in the tantalum, which further confirms the root cause of the imprint field variations in the bilayer capacitors. Our study will contribute to a deeper understanding of imprinted hafnia-based ferroelectrics and will provide an insight into devices that utilize the imprint effect.

The Investigation for Thickness-Dependent Electrical Performance on BaTiO3/BiFeO3 Bilayer Ferromagnetic Capacitors

Bilayer barium titanate (BaTiO3, BTO)/bismuth ferrite (BiFeO3, BFO) capacitive devices were fabricated and systematically analyzed from the aspects of thin-film material crystallography and electrical characterization. The tetragonal phase (T) of BTO with the reducing thickness (150 nm) was demonstrated through carefully adjusting the conditions of sputtering process and post-thermal treatments. The thickness dependence of polarization, energy density, permittivity, and leakage current was investigated in the BTO/BFO bilayer system. It showed that 150-nm BFO film is an optimal thickness, which led to the substantial increase in energy density up to 920 mJ/cm3 with the charge/discharge efficiency of 79.7% at 10 V. The permittivity of 150-nm BFO bilayer device was found to be 258, which is much higher than the single -layer BFO and other BTO/BFO devices with different BFO thicknesses. Leakage current could be reduced by three orders with the increasing thickness of BFO layer from 30 to 225 nm. In addition, the leakage current of BTO/BFO bilayer capacitors was 102 times lower than BFO single layer with the same total thickness. The result showed that the leakage current of BFO material could be significantly reduced in the bilayer system. The performance of BTO/BFO bilayer capacitors indicates that it is a promising technique for the implementation of nanoscale, lead-free, and nonelectrochemical thin-film energy storage-related applications.

Boosted energy-storage efficiency by controlling conduction loss of multilayered polymeric capacitors

Among the organic dielectrics, polyvinylidene fluoride PVDF-based polymers present the highest level of polarizability with permittivity >35. Nonetheless, their applications in advanced electronics and industrial uses are limited by significant leakage current under high voltage, which is considered the principal cause of device energy consumption and short lifetime. Therefore, the main objective of this paper was to focus on alternative capacitor structure-based polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene (PVDF-TrFE-CTFE) terpolymers to efficiently limit the leakage current and lead to enhanced electrical breakdown with negligible degradation of polarization level. The novel bilayer capacitor was constructed by depositing a thin barrier layer of high polar PVDF-HFP copolymer on the terpolymer via a rapid solution-casting technique. The relationship between leakage current, dielectric strength and conduction mechanisms was investigated. Implementation of such a barrier layer led to a significant reduction (70%) in leakage current and ferroelectric losses (approximately 90%), thus boosting the performance of multilayered material up to 50% of enhanced energy-storage efficiency. Experimental results are very promising, allowing to confirm that combining both terpolymer and copolymer in a hybrid multilayer design makes a possibility to achieve the best compromise in terms of energy efficiency, dielectric properties, and breakdown strength.

Switching On/Off Negative Capacitance in Ultrathin Ferroelectric/Dielectric Capacitors.

Ferroelectric (FE) and dielectric (DE) insulator bilayer stacks provide a promising gate for low-power microelectronic devices. To fully realize the FE polarization switching, the DE layer must be ultrathin in the FE/DE bilayer stack. Motivated by this, this work presents the first successful fabrication and characterization of Fe/FeOx/Al2O3/Fe FE/DE bilayer capacitors using in vacuo atomic layer deposition (ALD) with a total FE/DE stack thickness <3-4 nm. A key tuning parameter in generating the FE/DE bilayer capacitors is the thickness of an Al wetting layer between the bottom Fe electrode and the ALD-Al2O3 DE layer. At a large thickness in exceeding 1.0 nm, high-quality conventional DE capacitors of 2.2 nm thick ALD-Al2O3 were obtained with dielectric constant (εr) ∼8.0 that is close to εr ∼ 9.2 for the Al2O3 bulk single crystal with an effective oxide thickness of 1.0 nm. By reducing the Al wetting layer thickness to below 1.0 nm, a thin ferroelectric FeOx interfacial layer of a thickness of 1-2 nm forms, enabling the achievement of a FeOx/Al2O3 FE/DE bilayer capacitor with static negative capacitance. Since all ferroelectric materials are piezoelectric, we show that a dynamic switching on/off of the negative capacitance can be achieved under the application of an external force on the ultrathin FE/DE capacitors through manipulation of the electric dipoles. This result not only provides a viable approach for generating ultrathin FE/DE bilayer capacitors but also offers a promising solution to low-power consumption microelectronics.

Mechanism and characteristics on the electric explosion of Al/Ni reactive multilayer foils

Al/Ni multilayer foils were integrated with high voltage initiators using conventional microelectronic processing techniques and electrically exploded at an extremely high heating rate. In order to increase the knowledge about the electric explosion process of Al/Ni foils, several samples with different bilayer thicknesses, bridge dimensions, and capacitor voltages were tested. Time dependent voltage and current waveforms, energy depositions, and average flier velocities were measured and compared. The application of Al/Ni multilayers significantly increased the flier velocity and energy deposition of the device. The stored chemical energy of Al/Ni multilayer foils indeed contributed to the flier velocity increase, according to the experimental observations that the 225 nm bilayer bridges with the largest heat of reaction resulting in the highest flier velocities of all. Analysis of the experimental results allows us to prove that the electric explosion process of Al/Ni foils consisted of three stages. First, the Al layers were heated to vaporize. Then, the condensed AlNi grains started to nucleate due to exothermic mixing and subsequently evaporated with continuous energy deposition. Finally, the metal vapors ionized and formed plasma. These results provide fundamental understanding about electric explosion of Al/Ni reactive multilayer foils, and also enable us to improve the reliability and energy efficiency of electrically exploded Al/Ni multilayers for specific applications.

Transient Negative Capacitance Effect in Atomic‐Layer‐Deposited Al2O3/Hf0.3Zr0.7O2 Bilayer Thin Film

AbstractThe negative capacitance (NC) effect is now attracting a great deal of attention in work towards low‐power operation of field effect transistors and extremely large capacitance density in dynamic random access memory. However, to date, observation of the NC effect in dielectric/ferroelectric bilayer capacitors has been limited to the use of epitaxial ferroelectric thin films based on perovskite crystal structures, such as Pb(Zr,Ti)O3 and BaTiO3, which is not compatible with current complementary metal oxide semiconductor technology. This work, therefore, reports on the transient NC effect in amorphous‐Al2O3/polycrystalline‐Hf0.3Zr0.7O2 bilayer systems prepared using atomic layer deposition. The thin film processing conditions are carefully tuned to achieve the appropriate ferroelectric performances that are a prerequisite for the examination of the transient NC effect. Capacitance enhancement is observed in a wide voltage range in 5–10 nm thick Al2O3/Hf0.3Zr0.7O2 bilayer thin films. It is found that the capacitance of the dielectric layer plays a critical role in the determination of additional charge density induced by the NC effect. In addition, inhibition of the leakage current is important for stabilization of nonhysteretic charge–discharge behavior of the bilayers. The mean‐field approximation combined with classical Landau formalism precisely reproduces the experimental results.

Photovoltaic Cell with High-Capacity Energy Storage Based on LiCoO2 and Carbon Materials

A hybrid electrochemical storage cell is suggested as an energy storage unit in autonomous photovoltaic systems. The developed setup combines the advantages of lithium-ion batteries and bilayer capacitors. The increase in energy capacity is achieved by increasing the mass ratio of the positive and negative electrodes.

Negative Capacitance in BaTiO3/BiFeO3 Bilayer Capacitors.

Negative capacitances provide an approach to reduce heat generations in field-effect transistors during the switch processes, which contributes to further miniaturization of the conventional integrated circuits. Although there are many studies about negative capacitances using ferroelectric materials, the direct observation of stable ferroelectric negative capacitances has rarely been reported. Here, we put forward a dc bias assistant model in bilayer capacitors, where one ferroelectric layer with large dielectric constant and the other ferroelectric layer with small dielectric constant are needed. Negative capacitances can be obtained when external dc bias electric fields are larger than a critical value. Based on the model, BaTiO3/BiFeO3 bilayer capacitors are chosen as study objects, and negative capacitances are observed directly. Additionally, the upward self-polarization effect in the ferroelectric layer reduces the critical electric field, which may provide a method for realizing zero and/or small dc bias assistant negative capacitances.

Time-Dependent Negative Capacitance Effects in Al2O3/BaTiO3 Bilayers.

The negative capacitance (NC) effects in ferroelectric materials have emerged as the possible solution to low-power transistor devices and high-charge-density capacitors. Although the steep switching characteristic (subthreshold swing < sub-60 mV/dec) has been demonstrated in various devices combining the conventional transistors with ferroelectric gates, the actual applications of the NC effects are still some way off owing to the inherent hysteresis problem. This work reinterpreted the hysteretic properties of the NC effects within the time domain and demonstrated that capacitance (charge) boosting could be achieved without the hysteresis from the Al2O3/BaTiO3 bilayer capacitors through short-pulse charging. This work revealed that the hysteresis phenomenon in NC devices originated from the dielectric leakage of the dielectric layer. The suppression of charge injection via the dielectric leakage, which usually takes time, inhibits complete ferroelectric polarization switching during a short pulse time. It was demonstrated that a nonhysteretic NC effect can be achieved only within certain limited time and voltage ranges, but that these are sufficient for critical device applications.

Emergence of Negative Capacitance in Multidomain Ferroelectric-Paraelectric Nanocapacitors at Finite Bias.

The emergence of negative capacitance in an ultrathin ferroelectric/paraelectric bilayer capacitor under electrical bias is examined using first-principles simulation. An antiferroelectric-like behavior is predicted, and negative capacitance is shown to emerge when the monodomain state becomes stable after bias application. The polydomain-monodomain transition is also shown to be a source of capacitance enhancement.

Thin-film multi-layer capacitors using Bi2Mg2/3Nb4/3O7 (BMNO) pyrochlore thin films via radio-frequency sputtering

Thin-film multi-layer ceramic capacitors (MLCCs) were prepared using high-dielectric constant Bi2Mg2/3Nb4/3O7 thin-films deposited at room temperature via radio-frequency magnetron sputtering. The multi-layer capacitors, in sizes 0402, 0603 and 1005, were well equipped with both inner and outer Cu electrodes. The capacitances of the bi-layer capacitors were twice that of the single-layer version in sizes 0402, 0603, and 1005. The 200 nm-thick Bi2Mg2/3Nb4/3O7 thin-films would be suitable for thin-film multi-layer capacitor applications.

Multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 layers for tunable applications.

The dielectric properties and tunability of multilayer thin films with compositional PbZr0.52Ti0.48O3/Bi1.5Zn1.0Nb1.5O7 (PZT/BZN) layers (PPBLs) fabricated by pulsed laser deposition on Pt/TiO2/SiO2/Si substrate have been investigated. Dielectric measurements indicate that the PZT/BZN bilayer thin films exhibit medium dielectric constant of about 490, low loss tangent of 0.017, and superior tunable dielectric properties (tunability = 49.7% at 500 kV/cm) at a PZT/BZN thickness ratio of 3, while the largest figure of merit is obtained as 51.8. The thickness effect is discussed with a series connection model of bilayer capacitors, and the calculated dielectric constant and loss tangent are obtained. Furthermore, five kinds of thin–film samples comprising single bilayers, two, three, four and five PPBLs were also elaborated with the final same thickness. The four PPBLs show the largest dielectric constant of ~538 and tunability of 53.3% at a maximum applied bias field of 500 kV/cm and the lowest loss tangent of ~0.015, while the largest figure of merit is 65.6. The results indicate that four PPBLs are excellent candidates for applications of tunable devices.

Cellulose-Derivative-Based Gate Dielectric for High-Performance Organic Complementary Inverters.

been realized using organic thin-fi lm transistors (OTFTs) as the essential element. In the majority of these applications OTFTs are integrated either in the form of arrays or as digital logic. The fundamental building block of digital logic is the inverter, a circuit that inverts an input signal. Much work has been devoted in the last fi ve years to design unipolar inverters using p-typeonly OTFTs. [ 18‐23 ] Unfortunately, unipolar logic based on single gate OTFTs always suffers from high power consumption and low noise margin coupled with high noise margin variability and therefore impedes the fabrication of complex circuits having hundreds or more logic gates. [ 19,22,23 ] In this context, it stands

The strain capacitor: A novel energy storage device

A novel electromechanical energy storage device is reported that has the potential to have high energy densities. It can efficiently store both mechanical strain energy and electrical energy in the form of an electric field between the electrodes of a strain-mismatched bilayer capacitor. When the charged device is discharged, both the electrical and mechanical energy are extracted in an electrical form. The charge-voltage profile of the device is suitable for energy storage applications since a larger portion of the stored energy can be extracted at higher voltage levels compared to a normal capacitor. Its unique features include the potential for long lifetime, safety, portability, wide operating temperature range, and environment friendliness. The device can be designed to operate over varied operating voltage ranges by selecting appropriate materials and by changing the dimensions of the device. In this paper a finite element model of the device is developed to verify and demonstrate the potential of the device as an energy storage element. This device has the potential to replace conventional energy storage devices.

Growth and Characterization of Na0.5Bi0.5TiO3 Thin Films with BaTiO3 Buffer Layer (Study of Au/Na0.5Bi0.5TiO3/BaTiO3/Pt Capacitor)

Lead free bilayer capacitor structure has been fabricated as a combination of sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) thin films with barium titanate, (BaTiO3) (BT) buffer layer in situ using pulsed laser deposition (PLD). PLD control parameters have been optimized using Taguchi approach to obtain good quality NBT and BT thin films. It has been observed that dielectric properties of NBT thin films enhanced by inserting BT buffer layer. This improvement in the dielectric properties of NBT thin films have been discussed in relation to the effect of the buffer layer on the structure, microstructure and interface of the NBT/BT multilayer capacitor.

Highly n‐type doped InGaN films for efficient direct solar hydrogen generation

AbstractWe report on the metal organic vapour phase epitaxy (MOVPE) and characterization of n‐type InGaN films for application in direct solar water splitting. The 40 nm thick films exhibit an In fraction of 15% and show good structural quality and a surface root mean square (RMS) roughness of only 0.7 nm. An electron concentration of 9 × 1018 cm‐3 at a mobility of 185 cm2/Vs is assessed. The emission peak in photoluminescence (PL) spectra taken at room temperature (RT) is at 2.8 eV, which is consistent to transmission data and the expected bandgap value for this composition. Illumination of the InGaN electrode with a Xe lamp in a 1 M NaOH electrolyte solution at zero external voltage induces a photocurrent (PC) of 0.13 mA/cm2 with a pronounced overshoot in the first few seconds, which we explain by the discharging of a Helmholtz bilayer capacitor. The PC linearly increases with applied voltage while the estimated total conversion efficiency peaks at 0.6 V. Although hydrogen bubbles visibly evolve from the Pt counter electrode, total conversion efficiencies are limited to 0.05%, which is ascribed to incomplete utilization of the optical excitation spectrum and low thickness of both the InGaN film and the space charge region at the semiconductor surface. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

PEN/Si3N4 bilayer film for dc bus capacitors in power converters in hybrid electric vehicles

High performance hybrid bilayer capacitor film has been developed by controlled deposition of silicon nitride (Si3N4) on polyethylene naphthalate (PEN). It was found that silicon nitride prepared with plasma-enhanced chemical vapor deposition can significantly increase the dielectric constant (K) and energy density of PEN by more than 20% and 50%, respectively. Moreover, the PEN/Si3N4 bilayer hybrid film also exhibits appropriate mechanical and thermal properties for capacitor winding. The high operating temperature and energy density of the PEN/Si3N4 bilayer dielectric film are very attractive for dc bus capacitors used in power inverters or converters found in hybrid electric vehicles, wind turbine generators, grid-tied photovoltaics, and smart grid, as well as pulsed power systems.

Improved ferroelectric property of very thin Mn-doped BiFeO3 films by an inlaid Al2O3 tunnel switch

A thin Al2O3 layer was atomic layer deposited on a 50 - or 70 nm-thick, polycrystalline Mn-doped BiFeO3 (BFMO) thin film to fabricate a dielectric/ferroelectric bi-layer capacitor. The thin Al2O3 layer worked as a tunnel switch to improve the ferroelectric performance of the BFMO films. The BFMO thin film and BiFeO3 film contains a high density of charged defects, such as oxygen vacancies, Bi vacancies, and Fe2+ ions reduced from Fe3+, which induce a large leakage current and cause instability of ferroelectric polarization in one direction. An asymmetric hysteresis loop and severe depolarization was observed in the BFMO capacitor due to the local field induced by the defect complexes that are mainly formed near the Pt/BFMO interface from interactions between charged defects. Depositing a thin Al2O3 tunnel switch layer reduced these detrimental phenomena, which could be attributed to a decrease in the amount of oxygen vacancies as well as the suppression of polarization back-switching after the polarization switching and during non-switching. The defects in the BFMO films also caused domain wall pinning during the relaxation time so the switching speed decreased with increasing relaxation time. Adopting an Al2O3 tunnel switch layer also improved this problem.