A comparative study of anodic tantalum pentoxide and high-pressure sputtered titanium oxide

In this work we present a new method to fabricate improved TiO₂ films by using a high-pressure sputtering system. In order to minimize the damage induced in the substrate surface by the ion bombardment, a high chamber pressure of 100 Pa is used, which is very much higher than typical values in conventional systems. We present results obtained by X-ray diffraction and FTIR spectroscopy. Moreover, we will compare the properties of the resulting TiO₂-insulator-metal capacitors with those of anodic Ta₂O₅. Very thin films of TiO₂ have been obtained with a very promising quality for future electron device fabrication.     

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.     

Piezoelectric tantalum pentoxide studied for optical tunable applications

Piezoelectric transparent thin films are of great interest for use in tunable filters. We present experimental results on Ta2O5 single layers coated on fused-silica substrates with an electron-beam deposition process. Above 450 degrees C, coatings change from an amorphous to a polycrystallized structure. When this structure shows a preferred orientation matching the piezoelectric tensor of the Ta2O5 crystal and the external electric field, variation in the piezoelectric layer thickness is expected. We detail experimental results in terms of optical (spectrophotometric and scattering measurements) and nonoptical characterizations (x-ray diffraction and scanning electron microscopy). Then the resultant thickness variation under oscillating applied voltage is measured with an extrinsic Fabry-Perot interferometer setup.     

Nanometer sized tantalum pentoxide fibers prepared by electrospinning

Novel, porous tantalum pentoxide (Ta₂O₅) nanofibers with 150–250 nm diameter were obtained by high temperature calcination of the as-electrospun tantalum pentoxide/poly(vinyl acetate) (PVAc) composite fibers prepared by sol–gel processing and electrospinning technique. Surface analysis, structure and elemental composition of these as-electrospun and as-calcinated Ta₂O₅ nanofibers have been studied by scanning electron microscope (SEM) equipped with an energy dispersive X-ray analysis (EDX), high resolution field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction patterns (XRD) and FT-IR. High-resolution FE-SEM images showed the porous nature of Ta₂O₅ nanofibers. EDX analysis revealed the perfect stoichiometry of the nanofibers as Ta₂O₅. A linear correlation was noted between the calcination temperature and orthorhombic crystalline phase evolution of Ta₂O₅.     

Synthesis and characterization of polyvinylpyrrolidine assisted tantalum pentoxide films

Micron thick tantalum pentoxide (Ta₂O₅) films have been proposed as thermal insulating layers in microchemical systems, but so far it has been difficult to deposit thick enough films over complex substrates. So far sol–gel films cracked upon heating whenever the film thicknesses were above 350 nm. A 350 nm thick film is too thin for effective insulation. Other techniques are not suitable for coating the complex structures associated with microchemical systems. In this paper we report sol–gel synthesis of 1.6 μm thick tantalum pentoxide (Ta₂O₅) films. The films are almost crack free, and adhere to silicon surfaces even upon flashing to 900 °C. The key to the synthesis is the addition of Polyvinylpyrrolidine (PVP) to the sol. Films grown in the absence of PVP all show cracks upon calcination to 900 °C while few cracks are seen with PVP. X-ray diffraction and Fourier transform infra red analysis show that orthorhombic Ta₂O₅ is formed in all cases. X-ray photoelectron spectroscopy shows the O:Ta ratio to be 2.8:1. This shows that sol–gel is a viable process for making the micron thick films of Ta₂O₅ needed as insulators for microchemical systems.     

Internal reflection ellipsometry for real-time monitoring of polyelectrolyte multilayer growth onto tantalum pentoxide

Internal reflection ellipsometry was used for detection of the consecutive coating of two polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), onto a tantalum pentoxide (Ta₂O₅) substrate until the 10th bilayer. The UV patterned PAH-PAA-multilayer was characterized in air via ellipsometry and atomic force microscopy. Suited optical models enabled the determination of the layer thicknesses in wet and dry states. Linear multilayer formation could be proved by Attenuated Total Reflection — Fourier Transformed Infrared Spectroscopy measurements following the increase of the ν(C=O) band depending on the adsorption of the PAA. Streaming potential measurements after each layer deposition step indicated a change in surface charge after each layer deposition due to the consecutive coating of PAH and PAA. In this article the internal reflection ellipsometry is shown to be a convenient possibility to analyze the modification of a thin transparent Ta₂O₅ substrate.     

铌、钽电容器性能分析

钽铌属于同族元素 都是阀金属材料,其介电常数分别为27、41,都可以用来制作电解电容器。本文使用铌和钽2种材料分别制作电解电容器,并通过容量损耗测试仪、漏电流测试仪、电子扫描电镜等分析仪器对其和始性能、偏压性能、温度特性、寿命特性及其电介质层的微观特性进行检测分析。结果表明使用铌材料同样可以得到性能较好的电解电容器。     

Tailored quartz pins for high-density microsensor array fabrication

We report on a quartz pin that can be interfaced easily to existing pin printers. The new pin surface can be reversibly derivatized using silanization chemistry, allowing one to reliably print a wide variety of liquid solutions. Feature sizes as small as 9 microm can be produced with the new pin, allowing one to readily create microarrays with a feature density approaching 10(6) spots/cm2.     

阳极氧化铝作为铝电解电容器阳极箔用的研究

采用直流电阳极氧化法在高纯铝箔上制备了多孔阳极氧化铝(AAO)膜,同时采用扫描电子显微镜(SEM)、循环伏安(CV)和电化学阻杭谱(EIS)等技术对AAO膜的表面形貌、厚度和比表面电容性质等进行了表征.结果表明,AAO膜由垂直于膜表面的、孔径在60～80nm之间的平行纳米孔道组成,膜的多孔层厚度约为20μm左右;AAO...     

Effect of thermo-process on anodic capacitor foil manufacturing for AC etching

This investigation studies the anode foil of an aluminum electrolytic capacitor. The electrochemical behavior of high-purity aluminum foils with various thermal treatment parameters was examined. The static capacity increased with the temperature of homogenization treatment and hot rolling. The foil then has fine pits, which are uniformly distributed. Because of stabilizing treatment scattered dislocations and preferred orientation, the stabilized sample had better static capacity than the non-stabilized sample.     

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。     

The optical properties of thin films of tantalum pentoxide and zirconium dioxide

The indices of refraction and absorption of thin films of tantalum pentoxide and zirconium dioxide have been determined in the wavelength range 250–2000 nm. These were obtained from the spectrophotometrically measured reflectance and transmittance of the films at normal incidence, using the method devised by Denton et al. The Ta₂O₅ films were amorphous and had smooth surfaces, and for these films analysis of the dependence of the absorption on photon energy has shown that there are band gaps of 4.15 and 4.51 eV. It is tentatively suggested that the observed absorption is due to direct transitions from a valence band with a spin-orbital splitting of 0.36 eV.

The ZrO₂ films were polycrystalline with rough surfaces and had to be treated as double layer films in order to obtain continuous dispersion curves. They were effectively transparent over the spectral range covered.     

多孔氧化铝膜的制备与形成机理的研究概况

直流恒压条件下,酸性溶液中铝的阳极氧化会形成多孔阳极氧化铝(AAO)。其孔径为纳米级且分布均匀,纵横比大,是合成一维纳米材料的理想模板。本文综述了AAO的结构模型、制备方法、形成机理及其应用热点。     

Reactive D.C. sputtering with the magnetron-plasmatron for tantalum pentoxide and titanium dioxide films

We discuss the approaches to reactive d.c. sputtering and a criterion for the conditions which allow both the sputtering of metal at the target and the oxidation of the growing film on the substrate. Using this criterion stoichiometric deposition of the oxides of titanium and tantalum can be performed in the d.c. mode at maximum rates of 680 and 1050 nm min^-1 respectively. With respect to a given power, up to 55% or 85% of the possible maximum rates in pure argon may thus be converted into oxides. Some properties of the Ta₂O₅ and TiO₂ films produced are given.     

Electron-beam fabrication of high-density amorphous bubble film devices

A low-temperature, all-vacuum process combined with electron-beam lithography suitable for single-level masking devices using 2-μm diameter amorphous bubble films has been developed. A test vehicle which uses 0.75-μm wide chevrons and 1-μm wide T.I bars in an 8,000- bit chip configuration, resulting in an areal density of 1×10⁷bits/in², was used. Important process features are found to be: (1) laminated NiFe films to obtain low Hcand high magneto-resistive effect when deposited at low substrate temperature, (2) maintenance of low surface temperature during metallization to preserve the integrity of exposed and developed electron-beam resist pattern, and (3) proper resist profile for ease of the lift-off process. Excellent bubble device operating characteristics have been obtained as a result of uniformity in materials and structure resulting from careful control of fabrication parameters.     

Composition and density of non-thickness-limited anodic films on aluminium and tantalum

The unusual occurrence of anodic films of unlimited thickness has been recently reported for anodizing of tantalum in certain dehydrated, high-temperature electrolytes with organic solvents. The precise nature of these films is still uncertain. In the present work, non-thickness-limited (NTL) anodic films were formed at 0.1 mA cm⁻² on aluminium and tantalum in glycerol/phosphate electrolyte at 453 K and then examined by Rutherford backscattering spectroscopy (RBS). The results disclosed films composed of alumina and tantala, free of phosphorus species at the resolution of the measurements. Most notably, the densities of the NTL alumina and tantala were about 2.4 and 3.6 g cm⁻³, respectively. These values are less than those of compact anodic films of the type usually grown at high efficiency in aqueous electrolytes by respective factors of about 1.3 and 2.2. This difference in density is attributed primarily to the morphology and structure of NTL film materials, which incorporate significant porosity.     

Powder metallurgical processing and metal purity: A case for capacitor grade sintered tantalum

The paper reviews the role of sintered tantalum as volumetric efficient electrical capacitor. Powder characteristics and sintering aspects are discussed. The role of impurities in influencing the electrical properties has been described. Today’s driving force behind the Ta market is the use of surface mounted versions known as chip types, for applications requiring a wide range of operational temperature, such as automotive electronics.