Ta-Ta2O5-电解液导电体系界面特性的实验研究

分析了阀金属钽氧化膜的形成过程,伏安特性测试结果表明Ta-Ta2O5-电解液体系具有单向导电性.电场作用下,电解液中O2-跃过氧化膜/电解液界面,在氧化膜中形成定向迁移,同时引发膜内二次电子场助发射是该体系的主要导电机理.实验表明,大量二次电子导致介质膜雪崩式击穿是该体系闪火的主要原因,在电解液中添加适量有机物,可以屏蔽O2-使电解液的闪火电压提高30V以上,从而提高液体钽电解电容器的性能.     

Electrical conduction phenomena in thin tetracene films

Thin film aluminium oxide capacitors using anodic Al₂O₃ as the dielectric are described. The dependence of oxide thickness and dielectric loss on anodization voltage was studied. Variation of capacitance with temperature and frequency was also investigated. The capacitors were used in conjunction with tantalum resistors to fabricate an astable multivibrator circuit and the waveforms were recorded. The combination of aluminium oxide capacitors and tantalum resistors has some advantages over all-tantalum RC networks.     

Use of anodic tantalum pentoxide for high-density capacitor fabrication

In this work we report on very thin (10 to 100 nm) tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide to be used as the dielectric of high density MIM and MIS capacitors. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Several counter and bottom electrodes have been used and compared. The effects of the different processing conditions (top-electrode metals, annealing conditions, bottom electrode stoichiometry) on the capacitor performances are extensively discussed throughout this work. The nitrogen content of tantalum nitride films seems to have an important influence on the insulator quality. Leakage currents in the insulator have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. The electrical behaviour of the resulting high-density MIM capacitors has been extensively characterized. Finally, we describe a new method to fabricate MIS diodes with anodic tantalum oxide as insulator.     

改善有机片式固体钽电解电容器性能工艺研究

研究了在被膜过程中表面活性处理及掺杂对聚合物片式钽电容器容量、耐压、等效串联电阻(ESR)等特性的影响。研究结果表明表面活性处理后可以有效改善Ta2O5/PEDOT界面间的匹配,提高电容器容量引出效率;通过添加中间阻隔层(硅烷偶联剂)可以有效地阻挡杂质氧化性离子进入介质膜Ta2O5层,降低聚合物片式钽电容器的漏电流,提高耐压特性;实验结果表明在掺杂剂溶液的浓度为3%,补形成电压为赋能电压的70%时,能有效降低电容器ESR及漏电流。     

电容器用钽阳极失效分析与研究

利用扫描电镜进行电容器用钽阳极失效原因分析,造成单支阳极块漏电流异常偏大甚至被击穿的主要原因为:局部存在的夹杂物质引起氧化膜生长异常导致颗粒表面局部钽氧化物薄膜不连续,大量的电子通过造成漏流偏大甚至击穿。阳极块中出现的异物为原料钽锭中存在的钽的碳化物夹杂,由于其高熔点、耐酸蚀的特点使得钽粉后续处理过程中无法去除而保留在了钽粉中。背散射电子成像可应用于钽样品检测。     

电容器级钽粉关键技术与开发研究

引述了Ta电容器与Al电容器、多层陶瓷电容器相比突出的性能与应用特征，分析了Ta电容器片式化、小型化促进电容器级Ta粉高比容化发展的新趋势，叙述了航空、航天和军工领域对高压电容器高可靠性能的需求，以及对中高压Ta粉向更高电压、更低SER方向发展的引领，回顾了电容器用高比容Ta粉、中高压Ta粉发展应用进程，介绍了经典氟钽酸钾（K2TaF7）金属Na还原法、电子束熔炼法、球磨片式化法生产的高比容Ta粉、高压Ta粉、中压（片状）Ta粉的性能、产品品级及关键技术，分析了30～80kμFV／gTa粉耐压性能影响因素，介绍了Ta粉高比容化、高压化新技术、装置、产品形貌、性能及优缺点，在此基础上提出了电容器级Ta粉高比容化、高压化创新进步的思路。     

Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications

This paper reviews the present knowledge on tantalum pentoxide (Ta₂O₅) thin films and their applications in the field of microelectronics and integrated microtechnologies. Different methods used to produce tantalum oxide layers are described, emphazing elaboration mechanisms and key parameters for each technique. We also review recent advances in the deposition of Ta₂O₅ in the particular field of microelectronics where high quality layers are required from the structural and electrical points of view. The physical, structural, optical, chemical and electrical properties of tantalum oxide thin films on semiconductors are then presented and essential film parameters, such as optical index, film density or dielectric permittivity, are discussed. After a reminder of the basic mechanisms that control the bulk electrical conduction in insulating films, we carefully examine the origin of leakage currents in Ta₂O₅ and present the state-of-the-art concerning the insulating behaviour of tantalum oxide layers. Finally, applications of tantalum oxide thin films are presented in the last part of this paper. We show how Ta₂O₅ has been employed as an antireflection coating, insulating layer, gate oxide, corrosion resistant material, and sensitive layer in a wide variety of components, circuits and sensors.     

Nitrogen-doped tantalum thin film capacitors with improved temperature stability

The changes in capacitance, temperature coefficient of capacitance (t.c.c.) and dissipation factor (tan δ) of tantalum thin film capacitors subjected to heat treatment depend significantly on the nitrogen content of the Ta and the Ta₂O₅. If tantalum films deposited by reactive sputtering contain between 5 and 15 at.% nitrogen, the tan δ and t.c.c. of the finished capacitors can be reduced to constant values of 1.5 × 10^-3 and 135 ppm K^-1 respectively (test frequency 1 kHz) by heat treatment at temperatures between 250° and 350°C. However, if the nitrogen content is smaller or greater, or if β-Ta is used, both the t.c.c. and tan δ increase sharply with rising temperature and prolonged heat treatment.     

Experimental evidence of damaged zones in thin Ta2O5 anodic layers on polycrystalline tantalum foils

The challenge recently demanded of electrolytic tantalum capacitors is to be able to operate above the frequency of 1 MHz which can be carried out insofar as their equivalent series resistance (ESR) is sufficiently small. Now, the mechanical quality of the oxide layers plays a determining part in the value of the ESR and the purpose of the present work is to detect in the oxide layer the areas most likely to be damaged but not yet cracked. It is shown that weaker zones exist in the oxide layer. These zones are revealed by chemical etching. The relative damaged area of one sample relative to another is correlated with the grain size ratio, by means of XPS, SEM and liquid capacitance measurements. It is established that the amorphous oxide is preferentially etched just above the grain boundaries of the tantalum substrate. These results lead to the conclusion that annealing at the greatest possible temperature has the best effect on the mechanical quality of the oxide layer.     

热处理对MIM薄膜二极管Ta2O5绝缘膜微结构及其I-U特性的影响

制备了一种用于有源矩阵液晶显示、具有对称结构的MIM薄膜二极管 ,其中Ta2 O5膜采用溅射 /阳极氧化两步法工艺制成。对绝缘膜进行真空热处理 (一步热处理 )和经真空热处理后再进行大气热处理 (真空 /大气两步热处理 )。用原子力显微镜和透射电子显微镜分析了Ta2 O5膜的微结构 ,测试了MIM薄膜二极管的I U特性曲线。讨论了热处理对Ta2 O5绝缘膜微结构和MIM薄膜二极管I U特性的影响 ,并指出了MIM薄膜二极管I U特性和绝缘膜微结构之间的关系     

DLTS and conductance transient investigation on defects in anodic tantalum pentoxide thin films

In this work we report on deep level transient spectroscopy (DLTS) and conductance transient measurements (G-t) carried out on films of tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide with thickness ranging from 10 to 450 nm. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Leakage currents in the insulator under thermal stress have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. We have found noticeable differences in the dominant conduction mechanisms for thin and thick anodic tantalum pentoxide films. These differences are explained in terms of the thickness dependence of the insulator layer structure. We have characterized the physical nature of the conduction mechanisms in the dielectric films. The Poole–Frenkel effect and the modified Poole–Frenkel effect are suggested. No DLTS signals have been obtained, because transients do not change for temperatures ranging from 77 to 300 K. Conductance transients have important dependencies on voltage bias pulse amplitude and frequency that seem to be closely related to the physical nature of the anodic tantalum pentoxide.     

Anodic oxidation of tantalum in water and biological solutions using current limiting constant voltage method

A reliable method is developed for preparing tantalum pentoxide film targets in natural water and biological fluids (urine, blood plasma and serum) by the anodization of tantalum metal using a current limiting constant voltage method. Tantalum pentoxide film targets are successfully prepared at a current density of 10 mA cm⁻² at an anodic voltage ranging from 20 V to 100 V without any oxide breakdown. The results show that for the same applied voltage, more ionic concentration in biological solutions leads to a higher rate of oxide growth than in water and a darker interference color. The analysis shows that anodic oxidation is more likely to breakdown in a biological environment than in pure water for the same oxidation time and applied voltage. The oxide film capacitance is found to be only slightly dependent on pH and anodic voltage with higher capacitive films in biological solutions than for water.     

Application of electrolytic capacitors in measuring circuits

Conclusions Mass-produced electrolytic, and above all tantalum capacitors approach paper capacitors in many of their characteristics, and are superior to them with respect to their specific charges. In the range of –5 to +50C the electrolytic capacitors' values vary almost linearly with temperature. Moreover, capacitors designed for higher working voltages have a minimum instability. Aluminum capacitors type éM have the maximum instability, amounting approximately to 5–10% per 10C. Capacitors in hermetically-sealed casings types KéG and éGTs, groups OM and PM are 2–3 times more stable than the éM capacitors. Tantalum electrolytic capacitors have a stability 5–10 or more times greater than that of the éM capacitors.The storage of éM capacitors at room temperature for 10,000 h changes their values by 6% towards the end of that time. Aluminum capacitors in hermetically-sealed casings after 2000–4000 h of preliminary storage provide a more stable capacitance, and tantalum capacitors then obtain virtually constant values.It is possible to arrive at the conclusion from the measurement results that electrolytic capacitors, and above all tantalum capacitors, can be used successfully, in many instances, in various measuring circuits. Preliminarytesting and selection of capacitors, as well as the application of thermal compensating elements in measuring circuits with electrolytic capacitors will provide a higher precision of measurements.     

Tantalum anodic oxidation I. Evidence for surface heterogeneity and roughness

A model based on the hypothesis that heterogeneity and roughness play an important role in the anodization of tantalum is proposed. It is shown that the roughness can be described by a well-behaved decreasing function of the oxide thickness, and that the heterogeneity is characterized by the distribution of the prototropic exchange potential. Application to a particular case, the anodization of a β-tantalum film sputtered onto glazed ceramic, shows the interesting result that the surface is formed by two zones, each heterogeneous. The same qualitative behaviour is shown by tantalum nitride films, although for these films the prototropic exchange potential distributions have not been explicitly evaluated.     

锆钛酸铅铁电薄膜电容的研究现状

介绍了Pb(Zr,Ti)O3,(PZT)铁电薄膜电容的研究现状,列举了不同电极和缓冲层所制备出的PZT铁电薄膜电容的结构,并对不同结构进行了分析比较,结果表明由于氧化物电极材料的各种优越性,已被证明可用于替代现有的金属电极材料,从而有效解决了PZT薄膜铁电性能退化的问题,是未来铁电薄膜电容的发展方向.     

镀钽TiNi形状记忆合金表面的XPS分析

采用多弧离子镀的方法在Ti 50.6%(原子分数)Ni形状记忆合金表面沉积了钽镀层。通过X射线光电子能谱(XPS)剖面分析发现TiNi合金表面钽镀层厚度均匀,并且在镀层与基体之间形成一薄层过渡层。将镀钽TiNi合金曝露于空气中后,通过XPS的全谱和高分辨谱图对其表面的成分和价态分析发现,镀钽层表面由于钽在空气中自然氧化形成了一层很薄的钽的氧化膜,最表面为高价钽的氧化物(Ta2O5),次表面为低价钽氧化物的混合物TaO2、TaO和TaOx(x<1)。     

Structural changes of evaporated tantalum during film growth

According to the Sondheimer approximation the resistivity of an infinitely thick film with the same structure as a thin film can be determined from the graph of ?d versus d (where ? is the resistivity and d the film thickness). Since the resistivity is highly sensitive to film structure it is possible to observe structural changes by making in situ measurements during film growth. From these measurements it can be established that tantalum films condense under ultrahigh vacuum at room temperature onto oxide substrates (e.g. Corning 7059 glass, sapphire or BeO) as the β phase. It can be demonstrated that the transition temperature from β-Ta to α-Ta decreases with increasing film thickness. Increasing the substrate temperature (e.g. to 300 °C) causes the tantalum films to nucleate first as the β phase and to be converted into α-Ta during film growth. This effect is influenced by the substrate. The thickness dependence of the structure of tantalum was confirmed by ultrahigh vacuum in situ annealing experiments and electron optical investigations.     

Changes in the phase structure and formation of chemical compounds by ion implantation of tantalum thin films

Evaporated films of tantalum+tantalum oxide, 500 Å thick, were implanted with argon, oxygen and nitrogen ions. The phase structure of the films was determined by transmission electron microscopy and the dose dependence of resistivity and thermal coefficient of resistivity was satisfactorily explained in terms of the precipitation of compounds formed in the film. Argon bombardment had little effect on the structure of a film until sputter etching had reduced the film thickness considerably, when precipitates of TaO₂ in the form of rounded islands were created. Oxygen bombardment resulted in the precipitation of the b.c.c. phase of tantalum, and at higher doses precipitates of TaO₂ were formed. Nitrogen bombardment resulted in a sudden phase change and the precipitation of Ta₄N₅ in the form of hexagonal platelets; the conduction process in these films was highly activated, probably as a result of the presence of an amorphous oxide matrix. The dependence of changes in electrical properties on oxygen content of the film is explained by this phase structure.     

The growth and electrical transport properties of self-organized metal/oxide nanostructures formed by anodizing Ta-Al thin-film bilayers

Anodizing of Ta-Al metal bilayers (Al on Ta) sputter-deposited onto SiO₂ substrates was performed in oxalic acid electrolytes at anode potentials of 53 to 21.5 V in order to form nanoporous alumina layers and sequentially oxidize the tantalum underlayers through the alumina pores. The films formed consist of arrays of tantalum oxide nanohillocks percolating through the residual tantalum layer down to the substrate, so that a self-organized network of tantalum nanowires forms between the substrate and the alumina film. The average width (25–<10 nm), length (70–35 nm), and population density (10⁹–10¹¹ cm^-2) of the nanowires are systematically defined by the initial tantalum thickness (8–22 nm) and the anodizing conditions. The mesh-like, nano-sized morphologies of the tantalum underlayers result in a remarkably wide range of potential-dependent, controlled electrical sheet resistances (10²–10⁷ _Ω/sq). The periodical, tunable, metal/insulator film structure, allowing an increased transition to hopping or tunneling conduction at elevated temperature, leads to negative temperature coefficients of resistance, ranging 300 to 5 ppm/K. Oscillations of the potential-dependent dc conductance registered in the films at room temperature are attributed to the quantum-size effects in the metal/oxide nanostructures. The films are of technological importance for fabrication of thin-film, planar, adjustable resistors with significantly improved performances.     

Current conduction mechanisms in HfO2 and SrHfON thin films prepared by magnetron sputtering

Metal–oxide–semiconductor (MOS) capacitors incorporating HfO₂ and SrHfON gate dielectrics were fabricated by magnetron sputtering. The interface quality, thermal stability, and electrical properties of the MOS capacitors have been investigated. Compared to HfO₂ dielectric film, SrHfON dielectric film has thin interface layer with Si substrate, good thermal stability, and low leakage current densities. The dominant current conduction mechanisms (CCMs) of HfO₂ film are Schottky emission or Poole–Frenkel emission at low and high electric fields. The main CCMs of SrHfON film are Schottky emission or Poole–Frenkel emission at low electric field, whereas, the CCMs are replaced by space charge limited current at high electric field.