Thin-film capacitors

Wound foil capacitors Thin film and ceramic... 

Use Thin coatings of high purity and uniformity on almost any substrate that will resist a high vacuum, as paper, fabric, polyethylene and polystyrene film, ceramics, metals, many solid chemicals electronic miniaturization systems capacitors thin film circuits. 

The main commercial use of solid SiO is as a vapor-deposition material for the production of SiOx thin films for optical or electronic applications (antireflective coatings, interference filters, beam-splitters, decorative coatings, dielectric layers, isolation layers, electrodes, thin-film capacitors, thin-film transistors, etc.), for diffusion barrier layers on polymer foils or for surface protection layers.Other uses for SiO have been proposed, such as the substitution of elemental silicon in the Muller-Rochow process for the production of organosilicon halides, because solid SiO can be produced at lower temperatures than elemental silicon. 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures. 

There is also growing iaterest ia thin-film dielectric capacitors. For example, through the use of processiag techniques such as sol—gel solution deposition, thin (--- 0.25 fim) ceramic layers having dielectric constants ranging from 500 to 2000 ia the PZT, Pb(Zr,Ti)03, and PMN—PT, Pb(Mn2 3Nb2 3)03-PbTi03, compositional families respectively, have been prepared (3). 

Numerous uses for PZT/PLZT thin films are under investigation. The device that, as of this writing, is closest to commercialization is a nonvolatile memory. This device, which utilizes a ferroelectric thin-film capacitor integrated onto siUcon circuitry, provides memory retention when the power is off because of the polarization retention of the ferroelectric capacitor. One and zero memory states arise from the two polarization states, — and +F, of the ferroelectric. Because PZT is radiation-hard, the devices are also of interest for military and space appHcations. 

Applications Although a wide range of metals can be sputtered, the method is often commercially restricted by the low rate of deposition. Applications include the coating of insulating surfaces, e.g. of crystal vibrators, to render them electrically conducting, and the manufacture of some selenium rectifiers. The micro-electronics industry now makes considerable use of sputtering in the production of thin-film resistors and capacitors . ... 

Capacitor There are several applications for plastics in electrical devices that use the intrinsic characteristics of the plastics for the effect on the electrical circuit. The most obvious of these is the use of plastics particularly in the form of thin films as the dielectric in capacitors. TP polyester films such as Mylar are especially useful for this type of application because of the high dielectric strength in conjunction with a good dielectric constant. 

Historically, the first capacitors using an electrocfiemical system were the electrolytic capacitors. Built like film capacitors, they have electrodes made of aluminum foil on which by electrochemical oxidation a thin film of aluminum oxide (i.e., 10 to lOOnm thick) is grown to serve as the dielectric. Solutions are used as the electrolyte which aid self-repair of the oxide film on aluminum after accidental damage. Such electrolytes are solutions of salts of a number of orgaiuc acids (trifluoroacetic, salicylic, and some others). Because of the small thickness of the oxide layer, electrolytic capacitors have a markedly higher capacity than film capacitors. They can thus be used in the microfarad range. 

Hence, Tct is seen to increase with pore density and pore radius. However, a problem appears at a porous substrate when thin films are to be deposited during metallization to form interconnections, thin-film capacitors, etc.335 Sputtered material falls deep into the pores, which affects the planarity of the deposited layer and the electrical resistivity of the oxide layer underneath.335 To cope with this effect, the porous oxide should be padded by inorganic (A1203 and Si02) or organic (polyimide, negative photoresist) layers. 

Aluminum metallization in combination with tantalum thin films is used for manufacturing thin-film capacitors built into the metallization pattern.340... 

There are three major classes of palladium-based hydrogen sensors [4], The most popular class of palladium-based sensors is based on palladium resistors. A thin film of palladium deposited between two metal contacts shows a change in conductivity on exposure to hydrogen due to the phase transition in palladium. The palladium field-effect transistors (FETs) or capacitors constitute the second class, wherein the sensor architecture is in a transistor mode or capacitor configuration. The third class of palladium sensors includes optical sensors consisting of a layer of palladium coated on an optically active material that transforms the hydrogen concentration to an optical signal. 

Sometimes molecules are used as layers in other devices. For example, molecules can act as capacitors, and this relatively new field is promising for applications in energy storage as well as providing typical capacitance behavior in thin film devices [121, 122]. 

The measurement of changes of the surface potential Vo at the interface between an insulator and a solution is made possible by incorporating a thin film of that insulator in an electrolyte/insulator/silicon (EIS) structure. The surface potential of the silicon can be determined either by measuring the capacitance of the structure, or by fabricating a field effect transistor to measure the lateral current flow. In the latter case, the device is called an ion-sensitive field effect transistor (ISFET). Figure 1 shows a schematic representation of an ISFET structure. The first authors to suggest the application of ISFETs or EIS capacitors as a measurement tool to determine the surface potential of insulators were Schenck (15) and Cichos and Geidel (16). 

Deposition of thin films is used to change the surface properties of the base material, the substrate. For example, optical properties such as transmission or reflection of lenses and other glass products, can be adjusted by applying suitable coating layer systems. Metal coatings on plastic web produce conductive coatings for film capacitors. Polymer layers on metals enhance the corrosion resistance of the substrate. 

The success of CD CdS in photovoltaic cells has driven related research with potential applications in other semiconductor devices. Since the CD process seems to play a role in the favorable properties of the CdS windows by decreasing interface recombination, studies of its passivation properties on other interfaces and surfaces have been carried out, with considerable success. For example, when a very thin film (ca. 6 nm) was deposited between InP and SiOi, the resulting reduction of the interface state density led to improved electrical properties of metal-insulator-semiconductor capacitors and field effect transistors (FETs)... 

As shown in Fig. 12.4, aluminum electrolytic capacitors usually consist of an aluminum foil with a thin film of anodically-formed aluminum oxide (dielectric), an aluminum foil, an electrolyte solution, and a separator. The whole sandwich is compactly rolled and packed in a container. The electrolytic capacitors are in wide use, because of their small sizes, high capacitances, and low prices. However, the characteristics of electrolytic capacitors are apt to deteriorate with time. Recently,... 

It is of interest primarily for very uniform ultra-thin films and coatings (0.002-5 mils) in applications such as electrical resistors, thermistors, thermocouples, stator cores, connectors, fast-sensing probes, photo cells, memory units, dropwise steam condensers for recovery of sea water, pellicles for beam splitters in optical instruments, windows for nuclear radiation counters, panels for micrometeorite detection, dielectric supports for planar capacitors, encapsulation of reactive powders, and supports in x-ray and optical work. Any significant growth would depend upon a major breakthrough in process techniques and a consequent lowering in price. 

Aluminum Oxide Moisture Sensor. This type of sensor is a capacitor, formed by depositing a layer of porous aluminum oxide onto a conductive substrate, and then coaling the oxide with a thin film of gold The conductive base and the gold layer become the capacitor s electrodes. Water vapor penetrates the gold layer and is absorbed by the porous oxidation layer The number of water molecules absorbed determines the electrical impedance of the capacity, which is. m turn, a measure of water vapor pressure. 

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