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Photographs showing processes after the trench formation. (a)(b)(c)after NbN film deposition, (d)(e) after Cu plating, (f)(g)(h) after CMP
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Based on the concept of a novel approach to make a compact SMES unit composed of a stack of Si wafers using MEMS process proposed previously, a complete fabrication of a traversable 3 µam thick NbN film superconducting coil lined with Cu plated layer of 42m in length in a spiral three-storied trench engraved in and extended over a whole Si-wafer of...
Citations
... Ultrathin NbN films and fibers are used in producing logical devices [1], bolometers [2], resonators [3], terahertz radiation receivers [4], voltage standards [5] and other devices widely used in measurement instrumentation. Wide and relatively thick (units of micrometers) niobium nitride films are used in energy storage devices [6]. ...
Using time sweeps of the current through a sample of a superconducting film, the effect of the current sweep rate on the process of heat propagation from current contacts is investigated. The samples used were NbN films with temperatures below and above the temperature of transition to the superconducting state. A method for determining the critical heating of key zones of the sample is proposed. The propagation velocities of the resistive front and normal domain in a superconductor are estimated at different temperatures. Keywords: niobium nitride films, time sweep of the current, resistive front, normal domain.
... На основе ультратонких пленок и нитей NbN изготавливаются логические устройства [1], болометры [2], резонаторы [3], приемные элементы терагерцевого излучения [4], стандарты напряжения [5] и другие устройства, которые часто используются в измерительной технике. Широкие и относительно толстые (единицы микрометров) пленки нитрида ниобия применяются в накопителях энергии [6]. ...
Using time sweeps of the current through a sample of a superconducting film, the effect of the current sweep rate on the process of heat propagation from current contacts is investigated. The samples used were NbN films located below and above the transition temperature to the superconducting state. A method for determining the critical heating of key zones of the sample is proposed. The propagation velocities of the resistive front and normal domain in a superconductor are estimated at different temperatures.
... The measurement of the current-voltage characteristics in cryogenic temperatures together with the measurement of magnetic field by a gauss meter showed an energy storage of 0.01 mJ [20]. Increasing the NbN thickness by mitigating the film stress [23], the stored energy increased up to 0.1 mJ [24]. Here, the experimentally obtained jc of NbN-1100 A/mm 2 -was used [19]. ...
... Here, the experimentally obtained jc of NbN-1100 A/mm 2 -was used [19]. The largest S near the central axis of the coil unit, Smax, estimated from the magnetic flux density B along the central axis of a single-layer solenoid was 0.11 GPa, which was well below σSi/3 [20,24]. ...
A compact superconducting magnetic energy storage system (SMES) produced by Si micro fabrication technologies has been proposed to improve electricity storage volume density, w, in the sub-Wh/L range of conventional SMESs and to produce them at a low cost by mass production. In parallel with the experimental development reported previously, a series of trials was performed to estimate a feasible value of w based on the calculation of the magnetic field generated by the compact SMES by improving the calculation models step by step. In this work, the experimentally obtained magnetic flux density dependence of superconductive critical current density was taken into consideration for the first time in this series of trials, together with the additional improvement of the calculation models. The results of the estimation indicated that a compact SMES produced by the proposed concept can attain a w in the Wh/L range or more, ranking with or surpassing that of presently used capacitors.
... Если образцы первого типа используются обычно в качестве детекторов [1,2], и уменьшение размеров здесь напрямую связано с увеличением чувствительности, то вторая группа часто применяется в сильноточной технике, где и необходимо учитывать нагревание токонесущих элементов. Применение широких и относительно толстых пленок возможно в сверхпроводящих магнитах и накопителях энергии, которые исследуются сейчас в качестве альтернативы аккумуляторам [3][4][5]. ...
The analysis of heat transfer in the contact-film-substrate system under conditions when the heat removal from the sample to the substrate is insufficient to ensure that the sample is not overheated. For low temperatures, a method is proposed for increasing the heat removal from thin-film samples by passing a high-density electric current through them. The property of an anomalously high thermal conductivity of copper at temperatures from 5 to 50 K was used as the main factor in enhancing heat removal. The heat equation for the film-substrate system was numerically solved under the condition of additional heat transfer to potential contacts. It has been shown that beryllium bronze contacts can provide efficient heat removal from samples of superconducting films in a resistive state under conditions of strong Joule heat release.
... A proof of concept has been performed on a single Si wafer using NbN thin films showing energy storage of 0.01 mJ [1]. Increasing NbN thickness by mitigating film stress [2], the stored energy increased up to 0.1 mJ [3]. In a typical favourable design, multiple Si wafers which are engraved with a spiral coil (hereafter, we call it a wafer-coil for simplicity) are stacked to form a cylindrical unit as shown in figure 1(b), and the four units are combined to form a typical favourable minimum system as shown in figure 1(e). ...
Numerical estimations of electricity storage volume density: W for a proposed compact superconducting magnetic energy storage system composed of 4 stacks of 20 to 1800 Si-wafers loaded with superconducting YBa 2 Cu 3 O 7-δ thin film coils in spiral trenches formed by MEMS process were performed in conjunction with estimations of magnetic flux density and electromagnetic hoop stress applied to the coil. Changing the design parameters such as trench depth, trench width, trench wall thickness, number of stacked Si wafers, the inner-radius of the spiral coil under the fixed outer-radius of 47.45 mm, the maximum W was obtained to be 13.6 Wh/l under the constraint of the maximum magnetic flux density applied to the coil: B max < 20 T. The maximum hoop stress applied to the coil was estimated to be much lower than the mechanical strength limit of the Si wafer :4 GPa, indicating that other substrate materials such as typical engineering ceramics can be used in place of Si wafer if microfabrication of spiral trenches is feasible.
The process of heat transfer in NbN film while applying a pulse of current is considered using the 2D inhomogeneous heat equation. The boundary value problem is solved for a longitudinal cross section in the film; the heat transfer problem is solved for a system “contacts-film-substrate-thermostat”. The temperature evolution for the film cross section since the pulse start till the temperature relaxation is visualized. The maximum film heating is evaluated. It was shown that the contact material (beryllium copper BeCu) ensures the effective heat drainage from a superconductive film existing in the resistance mode while passing a heavy current through the film. The developed simulation method and the material for the contacts can be used for other types of metallic or semiconductor films.
The simulation of the process of heat propagation in the NbN film during the passage of a current pulse through it was carried out on the basis of an inhomogeneous two-dimensional equation of heat conduction. The initial-boundary value problem for longitudinal section of the film is solved numerically, and the analysis of heat transport in the system contacts-film-substrate-thermostat is carried out. The temperature evolution of the film cross section from the onset of the pulse to temperature leveling is visualized. It is shown that the contact material (beryllium bronze) provides efficient heat removal from a superconducting film in a resistive state when a high-density current flows through it. The proposed modeling method and contact material can be used to study other metal or semiconductor films.
A 100 m-level spiral trench over 4-inch wafer is fabricated for the coil of the superconducting magnetic energy storage. 3-stepped structure can reduce the disconnection risk caused by the random defects. Si etching scallop is decreased and smoothened by the oxidization and the grown SiO2 etching. This improves the superconducting film quality deposited later. The fabricated coils are 102 m-long single spiral for series coil and 89 m-long 7-parallel spirals for parallel coil.
Mathematical modeling of heat transfer in the film-substrate-thermostat system with a pulsed flow of high-density current through an electrically conductive film has been carried out. On the basis of the simulation, the analysis of the heating of a niobium nitride film with a high resistivity near the critical temperature of the transition to the superconducting state is made. The inhomogeneous heat conduction equation which is solved numerically, simulates heat transfer in the film-substrate-thermostat system for the third on the left and the first on the right initial boundary value problem. Using the symmetry of the problem, the parameter H is determined, which is equal to the ratio of the heat transfer of the film surface to its thermal conductivity; this parameter is necessary for effective heat removal. It is shown that effective heat removal from films can be provided by current-carrying and potential clamping contacts made, for example, of beryllium bronze. This makes possible to study the current-voltage characteristics of superconductors near the critical transition temperature to the superconducting state with high-density currents (104−105A/cm2) without significant heating of the samples.
