Material characteristic properties Dielectric constant

Two parallel plates of conducting material separated by an insulation material, called the dielectric, constitutes an electrical condenser. The two plates may be electrically charged by connecting them to a source of direct current potential. The amount of electrical energy that can be stored in this manner is called the capacitance of the condenser, and is a function of the voltage, area of the plates, thickness of the dielectric, and the characteristic property of the dielectric material called dielectric constant. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

The above are of course only some of the most common characteristics. Individual materials may have special properties such as photoconductivity, very low coefficient of friction to steel, high dielectric constant, high ultraviolet light transmission and so on. 

Additional drawbacks to the use of polyimide insulators for the fabrication of multilevel structures include self- or auto-adhesion. It has been demonstrated that the interfacial strength of polyimide layers sequentially cast and cured depends on the interdiffusion between layers, which in turn depends on the cure time and temperature for both the first layer (Tj) and the combined first and second layers (T2) [3]. In this work, it was shown that unusually high diffusion distances ( 200 nm) were required to achieve bulk strength [3]. For T2 > Tj, the adhesion decreased with increasing T. However, for T2 < Tj and Tj 400 °C, the adhesion between the layers was poor irrespective of T2. Consequently, it is of interest to combine the desirable characteristics of polyimide with other materials in such a way as to produce a low stress, low dielectric constant, self-adhering material with the desirable processabiHty and mechanical properties of polyimide. 

There are numerous properties of materials which can be used as measures of composition, e.g. preferential adsorption of components (as in chromatography), absorption of electromagnetic waves (infra-red, ultra-violet, etc.), refractive index, pH, density, etc. In many cases, however, the property will not give a unique result if there are more than two components, e.g. there may be a number of different compositions of a particular ternary liquid mixture which will have the same refractive index or will exhibit the same infra-red radiation absorption characteristics. Other difficulties can make a particular physical property unsuitable as a measure of composition for a particular system, e.g. the dielectric constant cannot be used if water is present as the dielectric constant of water is very much greater than that of most other liquids. Instruments containing optical systems (e.g. refractometers) and/or electromechanical feedback systems (e.g. some infra-red analysers) can be sensitive to mechanical vibration. In cases where it is not practicable to measure composition directly, then indirect or inferential means of obtaining a measurement which itself is a function of composition may be employed (e.g. the use of boiling temperature in a distillation column as a measure of the liquid composition—see Section 7.3.1). 

Modeling of High-Speed Interconnections. Modeling the electrical behavior of an interconnection involves two steps. First, the transmission line characteristics, such as the characteristic impedance, propagation constant, capacitance, resistance, dielectric conductance, and coupling parameters, must be calculated from the physical dimensions and material properties of the interconnection. In addition, structures, such as wire bonds, vias, and pins, must be represented by lumped resistance (R), inductance (L), and capacitance (C) elements. 

Comparison of the properties of CSD thin films to the analogous bulk material properties has also received great attention because of the need for high dielectric constant materials for DRAM applications.Basceri et ai 134,135 jj yg thoroughly considered the differences between film and bulk properties from a fundamental perspective and have been able to interpret these differences in terms of stresses present in the films, compositional differences, and the impact of these characteristics on the phenomenological behavior of the material as predicted from a Landau-Ginzburg-Devonshire approach. All observed differences between film and bulk properties were explainable using this approach. 

Polyethylene foams are used extensively in buoyancy applications because of their excellent water-resistant properties. These basically closed-cell foams absorb less than 0.5% by voliune of water after being immersed for 24 hours. The low density of the foams also contribute to their buoyancy. The excellent dielectric characteristics of polyethylene are retained when it is expanded into foams. Polyethylene foam is a candidate for many electrical-material uses requiring good properties of dielectric strength, dielectric constant, dissipation factor, and volume resistivity (6). 

The dielectric constant of the substrate is the prime property because the propagation speed of the signal is inversely related to it. At these speeds the system has to be designed as a transmission line which must match the impedance of the devices used. Impedance mismatch can lead to reflected signals, and hence to signal distortion. The characteristic impedance of the line is also dependent on the dielectric constant, and for the devices now being used higher impedances are required and, therefore, low dielectric constant substrates. In addition, it is also important to have low-loss materials to prevent distortion of the pulses. 

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