High Charge Storage Density Research Articles

Investigation of ion desolvation in aqueous electrolyte with carbon electrode via electrochemical in-situ Raman

Energy storage is an essential means to stabilize the fluctuation of renewable energy generation. Based on desolvation of electrolyte ions, high density charge storage in nanoporous electrodes has attracted widespread attention. The mechanism of ion transport within nanopores is currently under exploration. In this work, electric double layer capacitor was established using porous carbon electrode. Electrolytes with different hydrated/desolvatd ion radii were selected. The ion desolvation process was observed indirectly and concisely by using electrochemical in situ Raman technique on the carbon electrode. It was found that for ion with bigger solvation shells, its Raman intensity fluctuated with the cell charging voltage, which was caused by the desolvation of electrolyte ions. The desolvated ion has a strong polarization effect on the electron cloud of carbon. The influence of electrolyte concentrations on desolvation was also explored. High concentration electrolyte exhibits greater increase in Raman peak intensity. Our approach provides a way to study the physical mechanism and interface behavior of ion desolvation in electrochemical devices.

Energy storage and dielectric properties of a novel Bi1.5MgNb1.5O7-Bi2Mg2/3Nb4/3O7 thin film

Lead-free Bi1.5MgNb1.5O7-Bi2Mg2/3Nb4/3O7 (BMN1.5-BMN2) thin films have been deposited on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. A very low loss tangent of ~0.005 with a high dielectric constant of 158 is achieved in a BMN1.5-BMN2 thin film annealed in an oxygen pressure of 0.03 MPa. The BMN1.5-BMN2 thin film possesses superior energy storage properties due to its slim P-E loops, large maximum polarization (Pmax~36.97 μC/cm2) and high charge storage density (Pmax-Pr~32.25 μC/cm2), with an energy storage density of 40.59 J/cm3 and an energy conversion efficiency of 61.67% at 2.91 MV/cm. The energy storage density is superior to other the reference ferroelectric thin films. In addition, the BMN1.5-BMN2 thin film exhibits a large power density of 16.34 MW/cm3 due to the low dielectric loss. More importantly, BMN1.5-BMN2 as a new system provides new ideas for the design of lead-free linear dielectrics with ultrahigh energy storage density, indicating it is a very promising candidate for electrostatic energy storage capacitors.

Lithiation-induced fracture of silicon nanowires observed by in-situ scanning electron microscopy

Silicon is expected to be a useful anode material in lithium ion batteries for future energy storage applications, because of its high theoretical charge storage density of Li+ ions. However, volume expansion due to lithiation fractures the Si anode material, leading to poor cycle stability of battery operation. The approaches to overcome the problem include using Si nanowires to relieve the stress induced by volume expansion and coating a protective layer on the Si anode to prevent delamination. In this study, we use in-situ scanning electron microscopy to monitor the morphological changes of 90 nm thick pristine Si nanowires and the Si nanowires coated with amorphous TiO2, respectively, during electrochemical lithiation. The results of in-situ observation show that both kinds of Si nanowires exhibit a larger thickness after 10 h lithiation and suffer fracture after 25 h. It is also found that the TiO2 layer is not strong enough to prevent Si nanowires from fracture. Since the TiO2 layer can not be elastically deformed, this surface shell fractures earlier in the lithiation process than pristine Si nanowires. Transformation of the crystalline Si nanowires to an amorphous phase and lithium composition detected in the nanowires support that the observed fracture indeed results from lithiation.

Organic Pigment Electrode in Aqueous Magnesium Ion Batteries

Lithium-ion batteries (LIBs) have made tremendous successes in powering electronics and electric vehicles. Yet, LIBs face an insurmountable challenge in sustainability for large-scale stationary applications. Lithium, without effective recycling strategies, is too rare to be used at the current pace, rendering a concern over this great technology. Efforts are, therefore, guaranteed to pursue inexpensive and sustainable energy storage solutions. As of today, Na-ion batteries have received tremendous attention; however, it faces its own hurdle before commercialization, which originated from the choice of anodes. Alike sodium and potassium, magnesium is a benign and extremely Earth abundant element. So far, most electrodes for Mg2+ ion storage have been studied in non-aqueous electrolytes, where intrinsic properties of Mg2+ ion storage might be covered up by factors, including instability of the electrolyte and large overpotentials of Mg metal counter/reference electrode. To date, Mg2+ ion electrodes are still limited to Chevrel compounds or metal oxides. Here, we, for the first time, report reversible Mg2+ ion storage properties in 3,4,9,10-perylenetetracaboxilicdianhydride (PTCDA) in an aqueous electrolyte. In the potential range of -0.6 to 0.2 V vs Ag/AgCl reference electrode, PTCDA is able to deliver a reversible specific capacity of 125 mAh g-1, a good rate capability with 75 mAh g-1 at 500 mA g-1 and a reasonable cycling stability for 100 cycles. This work opens up a new avenue to harvest high-density charge storage for Mg2+ ions in an aqueous medium, which presents a large potential in magnesium ion batteries.

Efficient charge transport of a radical polyether/SWCNT composite electrode for an organic radical battery with high charge-storage density

A fast and reversible charge storage capability was established for the radical polyether/SWCNT composite layer with a large layer thickness of several tens of micrometres despite the low SWCNT content of 10%.

空気電池：有機負極を目指したポリマー膜の設計

Energy storage by organic redox-active molecules is based on the electromotive force produced from a couple of molecules which are different in redox potentials. Reversible and high-density charge storage by redox polymers ( [Red/Ox]polym ) require charge transport and electroneutralization by electrolyte ions throughout the polymer layer populated in high density with the redox-active groups. Charging/discharging capabilities are accomplished by fabricating organic rechargeable air batteries ((-) M | [Red]polym ↔ [Ox]polym | KOH, H2O | C (catalyst), O2 (+)), using polymer layers as the anode-active material which undergo reversible charging at potentials more negative than that of O2. Nonconjugated polymers with various types of main chains populated with anthraquinone derivatives per repeating unit have been synthesized with a view to unravel their charge transport and storage properties based on the n-type redox reactions. Anthraquinone-functionalized polymers have been proposed as a new class of anodeactive materials with negative charge storage properties and large redox capacities, as a result of the capability of using almost all of the redox sites in the polymer. The polymer/carbon composite layer allowed efficient swelling of the polymer in aqueous electrolyte solutions, giving rise to the rechargeable air battery effect with more than 500 charge/discharge cycle performances.

Nonvolatile floating gate memory containing AgInSbTe–SiO2 nanocomposite layer and capping the HfO2/SiO2 composite blocking oxide layer

An extremely large memory window shift of about 30.7 V and high charge storage density = 2.3 × 1013 cm−2 at ±23 V gate voltage sweep were achieved in the nonvolatile floating gate memory (NFGM) device containing the AgInSbTe (AIST)–SiO2 nanocomposite as the charge trap layer and HfO2/SiO2 as the blocking oxide layer. Due to the deep trap sites formed by high-density AIST nanocrystals (NCs) in the nanocomposite matrix and the high-barrier-height feature of the composite blocking oxide layer, a good retention property of the device with a charge loss of about 16.1% at ±15 V gate voltage stress for 104 s at the test temperature of 85 °C was observed. In addition to inhibiting the Hf diffusion into the programming layer, incorporation of the SiO2 layer prepared by plasma-enhanced chemical vapor deposition in the sample provided a good Coulomb blockade effect and allowed significant charge storage in AIST NCs. Analytical results demonstrated the feasibility of an AIST-SiO2 nanocomposite layer in memory device fabrication with a simplified processing method and post-annealing at a comparatively low temperature of 400 °C in comparison with previous NC-based NFGM studies.

Synthesis and Charge Transport Properties of Redox-Active Nitroxide Polyethers with Large Site Density

To maximize the theoretical redox capacity of polymers containing cyclic nitroxides as redox-active pendant groups for high-density charge storage application, a compact five-membered ring with the smallest equivalent weight among the robust cyclic nitroxides was directly bound to a poly(ethylene oxide) chain. 2,2,5,5-Tetramethyl-3-oxiranyl-3-pyrrolin-1-oxyl was synthesized and polymerized via anionic coordinated ring-opening polymerization utilizing diethyl zinc/H2O as an initiator. The unpaired electron in the monomer survived during the polymerization, giving rise to a high density redox polymer with a weight-specific theoretical capacity of 147 mA h/g. Cyclic voltammetry of the polymer layer confined at the surface of an electrode revealed a large redox capacity comparable to the theoretical capacity, which was ascribed to the efficient swelling and yet insoluble properties of the polyether in electrolyte solutions by virtue of the high molecular weight of >105 and adhesive properties allowing immobilization of the layer on the electrode surface. The redox capacity also indicated that the ionophoric polyether matrix accommodated electrolyte anions through the polymer/electrolyte interface to neutralize positive charges produced by the oxidation of the neutral radicals at the polymer/electrode interface. The diffusion coefficient for the redox gradient-driven charge hopping process corresponded to a large second-order rate constant in the order of 107 M−1 s−1, which suggested an efficient electron self-exchange reaction throughout the polymer layer due to the large redox site population and hence to the small intersite distance. Test cells fabricated with a polymer/carbon fiber composite layer on an aluminum current collector as the cathode and a Li anode sandwiching an electrolyte layer were capable of charging and discharging as a secondary battery with an output voltage near 3.7 V and were durable for more than 103 charging−discharging cycles without substantial degradation.

Proton redistribution and pseudoantiferroelectricity in H+ implanted Pb(Zr,Ti)O3 thin films

Hydrogen ions were implanted into 500-nm-thick Pb(Zr,Ti)O3 ferroelectric thin films with different doses and energies. An antiferroelectric behavior was confirmed in the implanted thin films with proper H+ injection energies from independent measurements of polarization-electric hysteresis loops and capacitance-voltage curves. With the increase in the H+ doping concentration and implanting energy up to 25 keV, the characteristic pseudoantiferroelectric behavior becomes more evident in the films along with the concomitant reduction in the remnant polarization. However, the above antiferroelectricity is weakened for the restoration of a preferred ferroelectric state, once the implanting energy is higher than 35 eV. The consequent “Trim94” simulation of the H+ distribution as well as the induced oxygen vacancies (VO⋅⋅) indicates the almost linear shift in the depth for the maximum charge density within the film with the enhanced implanting energy until the depth moves out of the film thickness above 40 keV. Beyond the antiferroelectric dependence on the implanting energy in thin films, the previous ferroelectric state can also be rejuvenated under a bipolar-field stressing through the redistribution of the H+ and VO⋅⋅ concentrations. The rejuvenation process is accelerated upon heating due to the increased charge mobility. The doping charges are immobile during short-time domain switching but movable under a long-time negative/positive field with the estimated activation energy of 0.23/0.29 eV. This study implies the potential application of high-density charge storage of the implanted ferroelectric capacitor with the property comparable to a genuine antiferroelectric capacitor.

Nernstian Adsorbate-like Bulk Layer of Organic Radical Polymers for High-Density Charge Storage Purposes

Redox polymer layers with 2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl (TEMPO) groups showed nernstian adsorbate-like electrochemical behaviors up to submicrometer thicknesses, based on a fast charge propagation within the bulk layer and persistency in electrolyte solutions.

Synthesis and Characterization of Radical-Bearing Polyethers as an Electrode-Active Material for Organic Secondary Batteries

In search of polymer backbones to bind organic radical pendant groups as redox centers for high-density charge storage application, polyether was employed as a flexible chain with a low glass transition temperature and affinity to electrolyte solutions. Cyclic ethers bearing nitroxide radicals were synthesized and polymerized via ring-opening polymerization utilizing various initiators. Polyethers bearing robust radical substituents such as 2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl and 2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-1-oxyl-3-yl groups with high density, i.e., per repeating unit with small equivalent weights, were prepared by the anionic polymerization of the corresponding epoxides. Cyclic voltammetry of the radical polyethers, obtained for polymer/carbon composites confined at an aluminum current collector, revealed large redox capacities comparable to the formula weight-based theoretical values, which was ascribed to the efficient swelling and yet insoluble properties of the polyethers in electrolyte solutions by virtue of their high molecular weights and adhesive properties to be held on electrode surfaces. The redox capacity also indicated that the ionophoric polyether matrix accommodated electrolyte anions to compensate positive charges produced by the oxidation of the neutral radicals at the polymer/electrode interface, allowing charge propagation deep into the polymer layer by a site-hopping mechanism. Test cells fabricated with the polymer/carbon composite as the cathode and a Li anode, sandwiching an electrolyte layer, performed as a secondary battery at output voltages near 3.6 V without substantial degradation even after 100 charging−discharging cycles.

Progress on Charge Distribution in Multiply-Stacked Si Quantum Dots/SiO2 Structure as Evaluated by AFM/KFM

Multiply-stacked structures of Si quantum dots (Si-QDs) in gate oxide are attracting much attention because of their potential importance to improve retention characteristics in a high density charge storage. In this work, we have fabricated 6-fold stacked Si-QDs with 2nm-thick SiO2 interlayers, whose areal dot density and average dot size were 5.7×1011cm-2 in each dot layer and -5nm in height, and studied progress on electron distribution in 6-fold stacked Si-QDs with 2nm-thick SiO2 interlayers from the measurements of temporal changes in the surface potential after electron charging and discharging locally at room temperature using an AFM/Kelvin probe technique in clean room air. First, by scanning an area of 2×2μm2 with the AFM tip biased at +3V with respect to the substrate in a tapping mode, the area was negatively charged due to electron injection from the substrate to the dot through the bottom tunnel oxide and subsequently, the central part of 100×100nm2 in the pre-charged area was scanned with the tip biased at -3V to emit the electrons from the Si-QDs to the substrate. As a result, the negative charging level was markedly reduced in the central part in comparison to its peripheral region. And then, the surface potential of the negatively-charged peripheral region was decay monotonously with time as a result of progressive electron tunneling to the substrate. In contrast to this, the temporal change in the surface potential of the central part shows that the electron charging proceeds with time until the surface potential becomes almost the same as that in the peripheral region. This result can be interpreted in terms of lateral spreading of electrons stored in the Si-QDs layer due to the potential difference between the central part and its peripheral region more negatively charged.

Artificial Modulation of Ferroelectric Thin Films into Antiferroelectric through H+ Implantation for High-Density Charge Storage

Hydrogen ions are implanted into Pb(Zr0.3Ti0.7)O3 thin films at the energy of 40 keV with a flux of 5 × 1014 ions/cm2. Pseudo-antiferroelectric behaviour in the implanted thin films is observed, as confirmed by the measurements of polarization versus electric hysteresis loops and capacitance versus voltage curves. X-ray diffraction patterns show the film structures before and after H+ implantation both to be perovskite of a tetragonal symmetry. These findings indicate that hydrogen ions exist as stable dopants within the films. It is believed that the dopants change domain-switching behaviour via the boundary charge compensation. Meanwhile, time dependence of leakage current density after time longer than 10s indicates the enhancement of the leakage current nearly in one order for the implanted film, but the current at time shorter than 1 s is mostly the same as that of the original film without the ionic implantation. The artificial tailoring of the antiferroelectric behaviour through H+ implantation in ferroelectric thin films is finally proven to be achievable for the device application of high-density charge storage.

Low Voltage Operation of High-κ HfO2/TiO2/Al2O3 Single Quantum Well for Nanoscale Flash Memory Device Applications

Memory characteristics of the high-κ HfO2/TiO2/Al2O3 single quantum well in a p-Si/Al2O3/HfO2/TiO2/Al2O3/platinum capacitor structure have been investigated. All high-κ films have been deposited by atomic layer deposition. A significant memory window of ∼1.6 V at a low gate voltage operation of 2 V, a high charge storage density of ∼3.6×1012/cm2, a moderate leakage current density of 1×10-6/cm2 at a gate voltage of -2 V, and a negligible charge loss of <5% up to 104 s of retention for the high-κ HfO2/TiO2/Al2O3 single quantum well memory capacitor have been observed as compared with those of pure HfO2, pure TiO2, and pure Al2O3 charge trapping layers. Excellent memory characteristics of the high-κ HfO2/TiO2/Al2O3 single quantum well device are obtained due to charge storage in the quantum well. The high-κ HfO2/TiO2/Al2O3 quantum well device with a low gate voltage operation of <2 V can be used in future nanoscale flash memory device applications.

Barium Strontium Titanate Capacitors for Embedded Dram

AbstractLong recognized as the best potential solution to the continued scaling of the onetransistor/one-capacitor standalone dynamic random access memory (DRAM) beyond a gigabit, barium strontium titanate (BST) and other high permittivity dielectrics are fast becoming enablers to embedding large amounts of memory into a high performance logic process. System requirements such as granularity, bandwidth, fill frequency, and power pose major challenges to the use of high density standalone DRAM, leading to the current push for embedded solutions where very wide buses are possible. As a result, projected embedded memory sizes are rapidly approaching that of the standalone products, and with the high wafer cost of the combined logic plus memory process, bit cell scaling is critical. The BST memory cell, with its low thermal budget processing, very high charge storage density, and high conductivity metal electrodes has the potential to be efficiently embedded with traditional logic flows if the materials and integration challenges of the required three dimensional (3D) bit cell capacitors can be solved. BST materials properties such as dielectric relaxation, interface capacitance, and resistance degradation and their impact on capacitor scaling will be reviewed along with the electrode materials issues associated with certain 3D capacitor designs. The scaling limits of BST bit cells in the deep sub-micron regime will be discussed.

The effect of stoichiometry on the microstructure and properties of lead lanthanum titanate thin films

Thin films of Lead Lanthanum Titanate (PLT) corresponding to 28 at. % of La were prepared by the metal-organic decomposition (MOD) process. The films were fabricated from two solutions of different composition. The composition of the first solution was determined, assuming that the incorporation of La3+ in the PbTiO3 structure gives rise to A-site or Pb vacancies, whereas for the composition of the other solution the creation of B-site or Ti vacancies was assumed. The effect of excess lead on the microstructure and the optical and electrical properties was studied for 0% to 20% excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with a lattice constant of 3.92 Å. Optical and electrical measurements showed the films made assuming B-site vacancies had better properties. In general, excess PbO was found to improve the optical transmittance as well as the electrical properties of films. However, in films assuming the formation of B-site vacancies, PLT showed improved electrical properties only up to 5–10% excess PbO, while higher PbO additions had a deleterious effect. The films had a high resistivity, good relative permittivity, low loss, very low leakage current density, and high charge storage density. A type-B film with 10% excess Pb had a relative permittivity of 1340 at 100 kHz and a charge storage density of around 16.1 μC/cm2 at a field of 200 kV/cm at room temperature.

Preparation of (Pb0.88La0.12)TiO3 thin films for dynamic random access memory by low pressure-metalorganic chemical vapor deposition

La-modified lead titanate (PLT) thin films were prepared by hot-wall type low pressure-metalorganic chemical vapor deposition method. Pb(dpm)2, La(dpm)3, and titanium tetraisopropoxide were used as source materials. The films were deposited at 500°C under the low pressure of 1000 mTorr and then annealed at 650°C for 10 min in oxygen ambient. Sputter-deposited platinum electrodes and 180 nm thick PLT thin films were employed to form MIM capacitors with the best combination of high charge storage density (26.7 μC/cm2 at 3V) and low leakage current density (1.5 × 10-7 A/cm2 at 3V). The measured dielectric constant and dielectric loss were 1000∼1200 and 0.06∼0.07 at zero bias and 100 kHz, respectively.

The effect of deposition temperature on the material and electrical properties of PZT thin films for ULSI DRAM applications

Abstract The effects of deposition temperature on the properties of thin films of sputtered lead-zirconate-titanate (PZT) have been studied for ULSI DRAM storage capacitor dielectric applications. The films were deposited by reactive dc magnetron sputtering from a multi-component target. The grain size for the films deposited at 400°C was found to be less than 1000 A, while it was ∼ 10–30 μm for films deposited at 200°C. Small grain-sized material is desirable since it leads to better cell-to-cell uniformity in terms of charge storage capacity and other electrical and reliability properties. The optimum lead compensation was found to increase as the deposition temperature (T dep) increased. Leakage current density stays fairly constant as T dep is varied. As-deposited films, with a deposition temperature of 500°C, were rich in the perovskite phase and showed a high charge storage density of 11.2 μC/cm2 and a low leakage current density of 5.1 × 10−7 A/cm2 (both at 1.5 V). This implies the possibility of e...

Charge Storage on Thin SrTiO3 Film by Contact Electrification

Charge storage on thin SrTiO3 (STO) film was investigated by contact electrification. An atomic force microscope (AFM) biased by the voltage was used to deposit the charges by contact electrification and to detect electrostatic force change induced by contact electrified charges. As a result, writing, reading and erasing were demonstrated successfully with a small pattern, small letters and small dot arrays. Besides, two adjacent positive charge dots were discriminated with separation as small as ∼63 nm. These results revealed the potential capability of the present system, i.e., contact electrification on STO film with a biased AFM, for high-density charge storage.

Sputtered ferroelectric thin films for dynamic random access memory applications

Abstract A low thermal budget (with 550°C annealing) process with Ti-compensation for sputtered ferroelectric PZT thin films has been developed. PZT films with a composition near the morphotrophic phase boundary (Zr/Ti = 53/47) annealed at 550°C for 1 hr in a N2 ambient exhibits high charge storage density and low leakage current density, which are the important requirements of dielectric materials for ULSI DRAM cells. It was also found that Ti compensated films show good fatigue endurance in comparison with non-Ti compensated films.