Dielectric elements

CVD gaseous reactants (precursors) delivered to a heated substrate in a flow reactor undergo tliennal reaction to deposit solid films at atmospheric or reduced pressure, and volatile side products are pumped away. CVD is used for conductors, insulators and dielectrics, elemental semiconductors and compound semiconductors and is a workliorse in tire silicon microelectronics industry. 

Structural binder A wide range of applications in electronics makes use of the plastics as a structural binder to hold active materials. For example, a plastic such as polyvinylidene fluoride is filled with an electroluminescent phosphor to form the dielectric element in electroluminescent lamps. Plastics are loaded with barium titanate and other high dielectric powders to make slugs for high K capacitors. The cores in high frequency transformers are made using iron and iron oxide powders bonded with a plastic and molded to form the magnetic core. 

Dielectric elements that are based on nanostructures are of recent interest for the scaling-down of DRAMs (dynamic random access memories) [11.2]. The need to reduce capacitance requires materials with larger dielectric permittivity. One method to achieve this is to disperse conductive particles in a dielectric matrix by using nanoparticles, the dissipation factor is kept low. 

In reality, the trapping potential contains terms other than the harmonic one. Higher order even terms (r, z , etc.) in the potential are unavoidable for practically-feasible shapes of the electrodes. Although odd terms are absent in a perfectly-symmetric trap, the symmetry is, in practice, broken by contact potentials [35] due to material deposited on the electrodes, by surrounding conductive or dielectric elements as well as by small misalignments and imperfections of the electrodes. Hence odd terms proportional to z, z etc., can be expected to be present also. 

Available information Elemental, chemical, and dielectric Elemental... 

Capacitors. Aluminum in the form of foil dominates all other metals in the construction of capacitor electrodes. Dry electrolytic and nonelectrolytic c aci-tors are the basic condenser types in extensive commercial use. Dry electrolytic capacitors usually employ parallel coiled or wr )ped aluminum foil ribbons as electrodes. Paper saturated with an operative electrolyte and wrapped into the coil mechanically separates the ribbons, hi designs for intermittent use in alternating circuits, both electrodes are anodized in a hot boric acid electrolyte. The resulting thin anodic films constitute the dielectric element. 

The described approach is suitable for the reconstruction of complicated dielectric profiles of high contrast and demonstrates good stability with respect to the noise in the input data. However, the convergence and the stability of the solution deteriorate if the low-frequency information is lacking. Thus, the method needs to be modified before using in praetiee with real microwave and millimeter wave sourees and antennas, whieh are usually essentially band-limited elements. 

A method has been worked out for eddy current testing of surfaces and surface cracks or corrosion under dielectric or non-magnetic metal layer of up to 10 mm. The method is based on excitation of eddy currents by a coil with U - type core and information reading by a sensitive gradientometric element located on a axis of symmetry of the core (fig. 1). 

The dielectric constant is concerned with the electrical properties of a material. The dielectric constant for a solid is a 3 x 3 matrix with different components according to the Cartesian axes. These elements are given by ... 

In addition to the obvious effect of high dielectric constant glasses on the capacitance of the circuit elements iato which they enter, their dielectric strengths maybe more important. Siace the amount of energy a capacitor can store varies as the first power of the dielectric constant and the second power of the voltage, a glass with twice the dielectric strength is as effective as one with four times the dielectric constant. 

The composition of an optoelectronic memory card (eg. Laser Card of Drexler Technology Corp.) (162) is outlined in Figure 21 (163). Primary elements are polycarbonate foils with thicknesses of 250 to 400 )Tm, respectively, that are employed because of their high operating temperature and their good mechanical, optical, and dielectric characteristics. The OMC can be used as a ROM or a WORM media. Both possibiUties of information deposition can be used separately or in combination. 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

A substrate is a robust element that provides mechanical support for the die. It can be mounted with more than one die such packages are called multichip modules. Because parasitic capacitance effects are directiy proportional to the dielectric constant, substrate material should have a low dielectric constant. 

Interior of capacitive element containing tantalum, tantalum pentoxide (dielectric), manganese dioxide (solid electroyte)... 

Both antimony tribromide and antimony ttiiodide are prepared by reaction of the elements. Their chemistry is similar to that of SbCl in that they readily hydroly2e, form complex haUde ions, and form a wide variety of adducts with ethers, aldehydes, mercaptans, etc. They are soluble in carbon disulfide, acetone, and chloroform. There has been considerable interest in the compounds antimony bromide sulfide [14794-85-5] antimony iodide sulfide [13868-38-1] ISSb, and antimony iodide selenide [15513-79-8] with respect to their soHd-state properties, ferroelectricity, pyroelectricity, photoconduction, and dielectric polarization. 

Overcurrent will also mean an overvoltage across the capacitor units, which would inflict greater dielectric stresses on the capacitor elements. 

The elements thus formed are then inserted into a sheet steel container, vacuum dried and impregnated, with suitable non-PCB dielectric, which may be an oil dielectric or epoxy resin. The capacitor shell is then hermetically sealed, in oil dielectrics, to avoid any leakage of dielectric during operation. 

Until the 1970s the chemical used as the impregnating and dielectric medium for capacitor units was PCB (polychlorinated biphenyl) liquid. It was found to be toxic and unsafe for humans as well as contamination of the environment. For this reason, it is no longer used. The latest trend is to use a non-PCB, non-toxic, phenyl xylyl ethane (PXE-oil), which is a synthetic dielectric liquid of extremely low loss for insulation and impregnation of the capacitor elements or to use mixed polypropylene or allpolypropylene (PP) liquids as the dielectric. A non-oil dielectric, such as epoxy resin, is also used. 

We provide in Table 25.1 a brief comparison of the different types of dielectrics in use for impregnation and insulation while forming capacitor elements. The table will also help make a proper choice of the dielectric and the type of capacitors for a particular application. 

The thickness of the dielectric coating on individual elements is nearly double the above... 

The metallized film capacitors have the characteristic of self-healing. On a small dielectric failure the capacitor element is not rendered completely unserviceable. After clearing the fault, the affected capacitor element returns to the circuit and the capacitor unit functions normally. Only the punctured area is eliminated from the element and causes a negligibly small reduction in its capacitance value. Such a characteristic is termed self-healing and such capacitors are known as the self-healing type. 

The capacitor element in this case is made up of extremely thin metallic films. When a dielectric failure occurs in any of the elements, the current passes through the film. The film, being too thin to sustain the current, fuses only at the point of dielectric puncture clearing the fault quickly. The external fuses remain intact, and so remains the affected element in service. Some manufacturers claim that 10000 such failures and healings may reduce the rating of the element or the unit made up of such elements by barely I %. 

---