Dielectric materials history

Also, dielectric materials, especially, during the exposure to the atmosphere, absorb water and OH leads to detrimental interface reactions and water absorption and interface reactivity of yttrium oxide gate dielectrics on silicon was investigated. From the infrared absorption analysis, water vapor was significantly absorbed in the atmosphere. Similar oxidation are expected other high-K materials while the rate of OH absorption is expected to depend on the deposition process and their thermal history [29]. 

Copper- Clad Dielectric Materials. Due to relative ease of implementation, copper-clad dielectrics are used on a iarger scale than unclad dielectrics. Copper-clad dielectrics provide a method that requires the ieast number of changes in manufacturing flow because they typically use the same dielectric and reinforcements found in standard PWBs. Copper-clad-based materials have a longer history in making blind vias than any other method. This makes many designers, OEMs, and PWB fabricators more comfortable with copper-clad-based materials. 

Electrets are dielectric materials capable of quasi-permanently storing electric charges at their surface or in their bulk. This chapter presents a brief history of electret research, followed by a classification and introduction of the most important electret materials. The chapter also discusses ferroelectrets and recent developments in charge stability. 

The characterization of solid polymeric material often includes the need to characterize the variety of molecular motions present as well as the molecular and morphological structure. NMR relaxation measurements have a long history of application to molecular motion studies of polymers where NMR data often complements mechanical and dielectric measurements with a more complete identification of the mobile, or immobile, entities. 

Bisphenol-A carbonate has been widely studied by dielectric [8-26], dynamic mechanical [27 31] and thermally stimulated depolarization (TSD) [10- 13 32 35] techniques. However, differences in the compositions of the materials studied, and in their thermal history and pretreatment, have led to apparently conflicting results being reported in the literature, as discussed in detail in a recent paper [6]. In the present study contour maps of complex relative permittivity for both basic and u.v.-resistant grades of LEXAN have been obtained over an extended range of experimental conditions using a single apparatus, with each grade of material subject to the same thermal history. 

Around I960, Harrick [63] and Fahrenfort [64] demonstrated that ATR can be used for absorption measurements of thin films (the history of the method was well documented by Mirabella [65]). Since this time, the method has been extensively developed to study film on substrates with various optical properties (dielectrics, semiconductors, and metals) and shapes on bulk samples and on powders. The theory of ATR for thin layers is considered by Harrick [66] and Hansen [67] and has been reviewed in detail [68-72]. In this section, the experimental conditions necessary for the measurement of ATR in ultrathin films will be discussed in particular the effects of the materials for the IRE substrate as well as of the angle of incidence will be considered. This will allow the capabilities of the ATR method for a particular system to be estimated and, to a certain... 

Conductive-system dispersive response may be associated with a distribution of relaxation times (DRT) at the complex resistivity level, as in the work of Moynihan, Boesch, and Laberge [1973] based on the assumption of stretched-exponential response in the time domain (Eq. (118), Section 2.1.2.7), work that led to the widely used original modulus formalism (OMF) for data fitting and analysis, hi contrast, dielectric dispersive response may be characterized by a distribution of dielectric relaxation times defined at the complex dielectric constant or permittivity level (Macdonald [1995]). Its history, summarized in the monograph of Bbttcher and Bordewijk [1978], began more than a hundred years ago. Until relatively recently, however, these two types of dispersive response were not usually distinguished, and conductive-system dispersive response was often analyzed as if it were of dielectric character, even when this was not the case. In this section, material parameters will be expressed in specific form appropriate to the level concerned. 

Flow and cure of an aerospace adhesive. The rheological changes in a material during complex thermal histories can provide valuable information about processing, chemical structure, and end-use performance. Dielectric analysers can characterise dramatic and rapid changes in a polymer s physical state, even into the final stages of cure, which can significantly influence the physical and chemical properties of the finished product. 

Through off-line product development, the scientist or engineer can use dielectric properties to optimise the processing thermal history of products, and predict material processibility and end-use product performance. 

Influence of thermal history on Nylon 6,6. Dielectric analysis is an effective tool for characterising the influence of thermal history on the molecular structure of a material and, in turn, on molecular relaxation. 

One of the most extensively studied pdymers of medium crystallinity is poly-(vinylidene fluoride). The interest in this polymer results from its use as a piezoelectrical and pyro-electrical material (Nakamura and Wada, 1971 Hiqrakawa and Wada, 1973 Murayama, 1975 Murayama and co-workers, 1975 Muiayama and Hashizume, 1976 Mopsik and Broadhurst, 1975). Many dielectric studies have been made and recent work includes that of Koizumi and co-workers (1969), Sasabe and co-workers (1969), Yano (1970), Kakutani (1970), Osaki and cowoikers(1971), Nakagawa and Ishida (1973), Uemura (1974), Osaki and Iriiida (1974), Yano and co-workers (1974) and Brereton and co-workers (1977). It is evid it from these and eadier studies that the dielectric behaviour of this polymer is one of the most complex of the linear polymer systems. Studies have been made of samples of different (i) ciystal forms, (ii) orientations, (iii) crystallinity, (iv) thermal and electrical histories. At least four relaxation regions are observed, being labelled here as a, Oc,... 

Apart from nonlinearities in their D(E) characteristics, the dielectric displacement D of ferroelectric materials also depends on the electric field history, a phenomenon known as ferroelectric hysteresis. The common approach to measure D(E) or P(E) hysteresis curves utilizes the Sawyer-Tower circuit (Sawyer and Tower 1930) (cf Fig. 9a) that operates in the voltage-voltage mode. 

A solid or liquid dielectric inserted between two electrodes can support only a limited voltage. Several physical mechanisms can lead to a current instability and to breakdown, e.g., thermal instabilities in materials with thermally activated conductivities, transitions from trap-controlled transport to band transport, impact ionization, etc. (Zeller, 1987). Which one of the different mechanisms ultimately determines the dielectric strength depends on materials parameters, geometry, voltage pulse forms (including history), temperature, etc. (O Dwyer, 1973). 

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