Ferroelectric large dielectric loss

Even though some ferroelectric materials, especially the relaxor ferroelectrics, have an extremely large dielectric constant, which is a very desirable property for the dielectric layer of capacitors in ULSI DRAMS, the usually large dielectric loss prevents the materials from being used in the DRAMS. Furthermore, the quite large number of component cations of the relaxor ferroelectric materials makes it almost impossible to deposit thin films using chemical vapor deposition (CVD) which is believed to be the method of choice for mass production of the devices. 

The phase change in ferroelectric liquid crystals can give rise to the pyroelectric effect [3]. Values of p and p/Er are also respectable. However, all the materials reported to date have a large dielectric loss. In addition, it is not possible to obtain optimum thickness structures, whilst still maintaining acceptable thermal mass and conductivity. 

Timability of perovskites is defined according to the dielectric nonlinearity of as functions of electric field above the Ciuie temperature. Ferroelectries for applications in electrically tunable devices are generally in the paraelectric phase [3,4,7-10,13]. The reason is that most of the ferroelectries in polar phase are also piezoelectric. Piezoelectric transformations cause large losses at relatively low microwave frequencies, and additional losses in polar phase are associated with the domain wall movements. Another reason hindering the applications of a ferroelectric in a polar phase is the hysteresis in field-dependent dielectric characteristics [7]. 

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