Disordered wall arrays by photo-assisted electrochemical etching in n-type silicon

The fabrication of ordered, high aspect-ratio microstructures in silicon by use of photo-assisted electrochemical etching is an important technology, where voltage and current density are significant factors. In this paper, disordered walls appear in 5-inch n-type silicon wafers when a large current density is used. Based on the theory of space charge region, these disordered walls are caused by the contradiction between the protection from dissolution by a high applied voltage and the dissolution by a high current density. To verify this point, wall arrays were fabricated at different applied voltages and current densities. Moreover, the critical voltage was kept constant and different current densities were applied to obtain conditions for avoiding disordered walls and achieving uniform wall arrays. Finally, a wall array with a period of 5.6 μm and a depth of 55 μm was achieved at an applied voltage of 3 V and a monotonically increasing current density ranging from 22.9 to 24.5 mA/cm^2.

Effect of pretreatment on electrochemical etching behavior of Al foil in HCl-H_2SO_4

The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H3PO4 or 0.125 mol/L NaOH solution at 40 ℃ for different time and then DC electro-etched in 1 mol/L HC1＋2.5 mol/L H2SO4 electrolyte at 80 ℃. The pitting potential and self corrosion potential of A1 foil were measured with polarization curves （PC）. The potentiostatic current--time curve was recorded and the surface and cross section images of etched A1 foil were observed with SEM. The electrochemical impedance spectroscopy （EIS） of etched A1 foil and potential transient curves （PTC） during initial etching stage were measured. The results show the chemical pretreatments can activate A1 foil surface, facilitate the absorption, diffusion and migration of C1- onto the A1 foil during etching, and improve the initiation rate of meta-stable pits and density of stable pits and tunnels, leading to much increase in the real surface area and special capacitance of etched A1 foil.

Preparation of Electrode Array by Electrochemical Etching Based on FEM

Process technology of multiple cylindrical micro-pins by wire-electrical discharge machining （wire-EDM） and electrochemical etching was presented. A row of rectangular micro-columns were machined by wire-EDM and then machined into cylindrical shape by electrochemical etching. However, the shape of the multiple electrodes and the consistent sizes of the electrodes row are not easy to be controlled. In the electrochemical process, the shape of the cathode electrode determines the current density distribution on the anode and so the forming of multiple electrodes. This paper proposes a finite element method （FEM） to accurately optimize the electrode profile. The microelectrodes row with uniformity diameters with size from hundreds micrometers to several decades could be fabricated, and mathematical model controlling the shape and diameter of multiple microelectrodes was provided. Furthermore, a good agreement between experimental and theoretical results was confirmed.

GaN hexagonal pyramids formed by a photo-assisted chemical etching method

A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed anal- ysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.

Selective electrochemical etching of cantilever-type SOI-MEMS devices

It is possible to achieve selective electrochemical etching between different materials,such as p-and n-type silicon.However,achieving selective electrochemical etching on two different regions of the same p-type silicon material is a problem that has rarely been considered.Herein,a novel selective electrochemical etching technique for cantilever-type silicon-on-insulator(SOI)wafer-based microswitches is proposed.In this study,a p-type handle layer was selectively etched,and a p-type device layer was passivated.This was achieved using a circuit with two voltage sources:voltages of−1.2 and 0 V were applied to the handle and device layers,respectively.It was found that the proposed etching process can effectively prevent the in-use sticking of a cantilever-type switch.This is accomplished by increasing the gap between the device layer and its underlying handle layer and increasing the roughness of these layers.The technique is applicable to the fabrication of various cantilever-type SOI microelectromechanical systems,irrespective of the resistivity of the SOI wafer.

Green and scalable electrochemical routes for cost‐effective mass production of MXenes for supercapacitor electrodes

One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.

Effect of chemical plating Zn on DC-etching behavior of Al foil in HCl-H_2SO_4

The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0%NaOH solution containing trace amount of Zn2＋and Zn was chemically plated on its surface through an immersion-reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl-H 2 SO 4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve （PC） and electrochemical impedance spectroscopy （EIS）. The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn-Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2＋concentration.

Electrochemical liftoff of freestanding GaN by a thick highly conductive sacrificial layer grown by HVPE

Separation technology is an indispensable step in the preparation of freestanding GaN substrate. In this paper, a largearea freestanding GaN layer was separated from the substrate by an electrochemical liftoff process on a sandwich structure composed of an Fe-doped GaN substrate, a highly conductive Si-doped sacrificial layer and a top Fe-doped layer grown by hydride vapor phase epitaxy(HVPE). The large difference between the resistivity in the Si-doped layer and Fe-doped layer resulted in a sharp interface between the etched and unetched layer. It was found that the etching rate increased linearly with the applied voltage, while it continuously decreased with the electrochemical etching process as a result of the mass transport limitation. Flaky GaN pieces and nitrogen gas generated from the sacrificial layer by electrochemical etching were recognized as the main factors responsible for the blocking of the etching channel. Hence, a thick Si-doped layer grown by HVPE was used as the sacrificial layer to alleviate this problem. Moreover, high temperature and ultrasonic oscillation were also found to increase the etching rate. Based on the results above, we succeeded in the liftoff of ~ 1.5 inch GaN layer. This work could help reduce the cost of freestanding GaN substrate and identifies a new way for mass production.

Au maskless patterning for vacuum packaging using the electrochemical method

The interconnection of wires is an important issue in vacuum-packaged microelectromechanical systems devices because of the difficulties of hermetical sealing and electrical insulation.This paper presents an approach of Au film selective patterning on highly uneven surfaces for wire interconnections of devices in which silicon-oninsulator(SOI)wafers are anodically bonded to glass.The Au film on the handle layer,functioned as an anode,was selectively removed with electrochemical dissolution in a chloride solution.The choice of etchant solution and etching conditions were optimized to improve the process efficiency,resulting in a high yield of gold portions within the via holes for wire interconnection.The proposed wire interconnection technology was employed to fabricate a vacuum-packaged resonant pressure sensor as a proof-of-concept demonstration.Reliable wire bonding and vacuum package were achieved as well as a Q factor that does not decrease over a year.As a platform technology,this method provides a new approach of wire interconnection for vacuum-packaged devices based on SOI–glass anodic bonding.

激光辅助制备有序孔钽箔及其电容性能研究

目的改善商业钽箔作为钽阳极材料时比容量有限的问题。方法提出了一种利用激光刻蚀技术和电化学腐蚀相结合的工艺在商业钽箔上构筑有序孔用于提升其储电能力的方法,对处理前后钽箔的表面形貌、结构特征以及电容性能发生的变化进行表征。结果利用15 V的电压阳极氧化处理预先在钽箔表面生长一层Ta_(2)O_(5),其具有的厚度更好地适应了1064nm激光的重复扫描。Ta_(2)O_(5)层在激光的作用下被有效去除,电子显微镜的表征结果显示,钽箔表面形成有序分布的阵列型微结构,为钽箔在电化学腐蚀过程中的孔生长提供了范围,这种独特的结构也为钽箔的电化学反应提供了更丰富的活性位点。比电容量的测试结果显示,有序孔钽箔在1mol/L的H2SO4电解质溶液中具有247.4n F/mm^(2)的优异面积比容量,与未处理的商业钽箔21.7nF/mm^(2)的面积比容量相比提升了近11.4倍。结论通过对商业钽箔进行特殊的孔结构设计,可以显著提升其作为电极时的比容量,利用激光刻蚀和电化学腐蚀的双重作用来控制钽箔上孔隙生长的有序性,有望为下一代钽电解电容器阳极材料的研究提供设计思路。

双向脉冲液膜法制备微细工具电极

为实现高效制备微细工具电极,提出一种双向脉冲液膜电化学刻蚀技术,相较于单极性脉冲电源可明显提高加工效率,减小球头直径。实验研究了负脉冲电压、正脉冲电压和脉冲周期对氢气泡、电解产物的运动分布规律以及所制备工具电极形貌的影响。研究发现,负脉冲电压可明显消除扩散层的影响,使电流密度分布更加均匀,并且缩短加工时间;在电解液浓度0.5 mol/L、正电压3 V、负电压-2 V、脉冲周期50μs、占空比40%的条件下,可成功制备出直径约580 nm的球头电极。

基于电化学液膜法腐蚀制备STM钨探针的研究

高质量的探针是保证扫描隧道显微镜(Scanning Tunneling Microscope,STM)4K分辨率的关键。为得到原子级别的探针,实验基于电化学腐蚀原理,使用垂直液膜法制备钨探针。在制备过程中通过控制变量法,研究了腐蚀电压、液膜下钨丝长度等参数对探针质量的影响,实验发现,当使用2 mol/L的NaOH溶液作为液膜时,最佳腐蚀电压为5 V、最佳液膜下钨丝长度为4 mm。该研究为电化学液膜法腐蚀制备钨探针提供了参考依据。

超薄型高容量刻蚀箔钽阳极电容器的制备

埋入式电容技术在缩小设备体积、降低功耗和提升性能上具有巨大优势。然而,目前商用的电容器的电容密度小、厚度大、成本高或无法与印刷电路板制造相兼容,为了解决这个问题,提出了一种超薄型高容量刻蚀箔钽阳极电容器的制备工艺,以脉冲直流为电流源对钽箔进行电化学刻蚀,大幅提升了钽箔的比表面积,在10V电压下阳极氧化后的比容可达550 nF/mm2。同时,以刻蚀钽箔为基底制备了高质量的钽阳极氧化膜,所形成的化成箔在9 V电压下的漏电流密度仅为24 nA/cm^(2)。固态聚合物阴极由固态钽电容器在PEDOT:PSS的水分散液中浸渍多次而形成,所制备的固态钽电解电容器厚度不足50μm,且表现出优良的频率特性。其等效串联电阻(100 kHz)低至19.2 mΩ,约为日本松下聚合物钽电容器的1/5,在1~100 kHz频率范围内的电容量保持率可达75.5%,与日本松下聚合物钽电容器相比提升55%以上。基于电化学刻蚀的箔式钽电解电容器将进一步推动钽电解电容器的小型化和轻薄化发展,并为埋入式电容技术开辟新的思路。

电解放电复合加工技术现状与展望

电解放电复合加工是实现电加工技术创新和突破的重要途径,可通过耦合放电与电解能场,利用其时/空协同效应实现在可加工性、加工精度及表面质量等方面的提升,故在介绍电解放电复合加工技术概念和原理分类的基础上,着重概述该领域近十年来的关键性研究进展和新技术创新,对除电火花-电解组合加工和电弧复合加工之外的各类电解放电复合加工技术的未来发展方向进行了展望,指出该技术的规模化工程应用仍需在性能突破、精确建模、加工过程智能控制、复合加工装备等方面取得突破性进展。

Two-dimensional TiO_(2)(001)nanosheets as an effective photo-assisted recyclable sensor for the electrochemical detection of bisphenol A

Electrochemical detection is an efficient method for the detection of Bisphenol A(BPA).Herein,a sensitive photo-electrochemical sensor based on two-dimensional(2 D)TiO_(2)(001)nanosheets was fabricated and then used for BPA electrochemical detection.Upon light irradiation,the 2 D TiO_(2)(001)nanosheets electrode provided a lower detection limit of BPA detection compared with an ambient electrochemical determination.The low detection limit is^5.37 nmol/L(S/N=3).Furthermore,profiting from the photoelectric characteristics,the 2 D TiO_(2)(001)nanosheets electrode exhibits a nice regeneration prope rty.After 45 min of light irradiation,the electrochemical signal was regenerated from14.7%to 82.9%of the original signal at the 6th cycle.This is attributed to the non-selective·OH mediation produced by the 2 D TiO_(2)(001)nanosheets mineralizing anodic polymeric products and resuming surface reactive sites.This investigation indicates that photo-assistance is an efficient method to improve the electrochemical sensor for detecting BPA in water environments.

Toward Single-Atomic-Layer Lithography on Highly Oriented Pyrolytic Graphite Surfaces Using AFM-Based Electrochemical Etching

Atomic force microscopy(AFM)-based electrochemical etching of a highly oriented pyrolytic graphite(HOPG)surface is studied toward the single-atomic-layer lithography of intricate patterns.Electrochemical etching is performed in the water meniscus formed between the AFM tip apex and HOPG surface due to a capillary effect under controlled high relative humid-ity(~75%)at otherwise ambient conditions.The conditions to etch nano-holes,nano-lines,and other intricate patterns are investigated.The clectrochemical reactions of HOPG etching should not generatc debris duc to the conversion of graphite to gaseous CO and CO_(2)based on etching reactions.However,debris is observed on the etched HOPG surface,and incom-plete gasification of carbon occurs during the etching process,resulting in the generation of solid intermediates.Moreover,the applied potential is of critical importance for precise etching,and the precision is also significantly influenced by the AFM tip wear.This study shows that the AFM-based electrochemical etching has the potential to remove the material in a single-atomic-layer precision.This result is likely because the etching process is based on anodic dissolution,resulting in the material removal atom by atom.

The coupling effect of slow-rate mechanical motion on the confined etching process in electrochemical mechanical micromachining

By introducing the mechanical motion into the confined etchant layer technique(CELT), we have developed a promising ultraprecision machining method, termed as electrochemical mechanical micromachining(ECMM), for producing both regular and irregular three dimensional(3 D) microstructures. It was found that there was a dramatic coupling effect between the confined etching process and the slow-rate mechanical motion because of the concentration distribution of electrogenerated etchant caused by the latter. In this article, the coupling effect was investigated systemically by comparing the etchant diffusion, etching depths and profiles in the non-confined and confined machining modes. A two-dimensional(2 D) numerical simulation model was proposed to analyze the diffusion variations during the ECMM process, which is well verified by the machining experiments. The results showed that, in the confined machining mode, both the machining resolution and the perpendicularity tolerance of side faces were improved effectively. Furthermore, the theoretical modeling and numerical simulations were proved valuable to optimize the technical parameters of the ECMM process.

Influence of etching current density on the morphology of macroporous silicon arrays by photo-electrochemical etching

Macroporous silicon arrays（MSA） have attracted much attention for their potential applications in photonic crystals,silicon microchannel plates,MEMS devices and so on.In order to fabricate perfect MSA structure,photo-electrochemical （PEC） etching of MSA and the influence of etching current on the pore morphology were studied in detail.The current-voltage curve of a polished n-type silicon wafer was presented in aqueous HF using back-side illumination.The critical current density J_（PS） was discussed and the basic condition of etching current density for steady MSA growth was proposed.An indirect method was presented to measure the relation of J_（PS） at the pore tip and etching time.MSA growth was realized with the pore diameter constant by changing the etching current density according to the measuring result of J_（PS）.MSA with 295μm of depth and 98 of aspect ratio was obtained.

Influence of voltage on photo-electrochemical etching of n-type macroporous silicon arrays

The influence of voltage on photo-electrochemical etching（PEC） of macroporous silicon arrays（MSA） was researched.According to the theory of the space charge region,I-V scan curves and the reaction mechanism of the n-type silicon anodic oxidation in HF solution under different current densities,the pore morphology influenced by the working voltage were studied and analyzed in detail.The results show that increasing the etching voltage will lead to distortion of the pore morphology,decreasing etching voltage will result in an increase in the blind porosity, and the constant etching voltage for a long time will cause gradual bifurcation.Through the optimization of the process parameters,the perfect MSA structure with a pore depth of 317μm,a pore size of 3μm and an aspect ratio of 105 was obtained.

Hierarchical Porous Patterns of n-type 6H-SiC Crystals via Photoelectrochemical Etching

Hierarchical porous patterns have been fabricated on the C face, Si face, and cross section of n-type 6H-SiC crystal via photo-electrochemical etching using HF/C2H5OH and HF/H2O2 as electrolytes. The porous layer displayed multiple and multiscale microstructures on different faces, including stalactite-like, sponge-like and dendritic porous structures on C face, echinoid micro-patterns on Si face, and columnar and keel-shaped micro-patterns on the cross section. The formation of hierarchical porous pattern is ascribed to the dynamic competition balance between the electrochemical oxidation rate and the oxide removal rate. It was found that increasing the ionic strength of the electrolyte can obviously disturb the surface morphology of the porous SiC during the photo-electrochemical etching. Possible mechanisms for selective etching were further discussed.