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Dielectric spectroscopy of liquid crystals : electrodes resistivity and connecting wires inductance influence on dielectric measurements

Perkowski P.

Opto-Electronics Review

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2012

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Vol. 20, No. 1

79-86

EN

Dielectric spectroscopy is a very useful experimental method for liquid crystal investigation. Electrodes made from indium tin oxide (ITO) or gold are widely used in measuring cells. During the dielectric spectroscopy measurements performed for smectic liquid crystalline mixture it was found that detection of some important relaxation modes in paraelectric SmA*, ferroelectric SmC* and antiferroelectric SmCA* phases for frequencies higher than 0.2–0.5 MHz is not possible. The measuring setup does not allow us to measure such relaxations due to its own dielectric response covering the dielectric response of liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to non-zero resistivity of electrode material or non-zero inductivity of connecting wires. In this paper, the new model was introduced. Its final equations show how to calculate parameters of relaxations observed in liquid crystals, from dielectric response of the empty and filled measuring cell. The experimental proof of strong influence of measuring setup properties on effective (measured) values of dielectric permittivities was shown.

2

Dielectric spectroscopy of liquid crystals : theoretical model of ITO electrodes influence on dielectric measurements

Perkowski P.

Opto-Electronics Review

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2009

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Vol. 17, No. 2

180-186

EN

Indium tin oxide (ITO) layers are widely used to make electrodes in measuring cells, because these layers are transparent and electrooptical investigations can be performed using such prepared cells. It was found during the dielectric spectroscopy measurements, performed for smectic liquid crystalline mixture, that it is not possible to detect some important relaxation modes in paraelectric SmA*, ferroelectric SmC*, and antiferroelectric SmCA* phases for the frequencies higher than 300 kHz. The measuring cell does not allow to measure relaxations, because its own dielectric behaviour covers the dielectric response of a liquid crystalline medium. One can observe the spurious contribution for high frequency part of the dielectric spectrum, due to the finite resistance of ITO layers. The theoretical model was introduced, which shows how to calculate relaxations related to liquid crystals from dielectric response of the empty and filled measuring cell. The proof of strong influence of cell properties on effective (measuring) values of dielectric permittivities was shown.

3

Process and device requirements for mixed-signal integrated circuits in broadband networking

Iniewski K., Syrzycki M., Voinigescu S.P.

Journal of Telecommunications and Information Technology

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2004

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nr 1

90-98

EN

The paper describes the present status of the broadband wireline infrastructure consisting of the backbone core, metre rings, access network, local and storage area networks. Examples of various mixed-signal integrated circuits are described. Based on these considerations required process and device performance is extrapolated.

4

Modeling SiGe-base HBT using APSYS 2000 - a 2D simulator

Linkowski A., Łukasiak L., Jakubowski A.

Journal of Telecommunications and Information Technology

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2004

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nr 1

36-38

EN

The paper is devoted to optimization of SiGe-base HBT with respect to operation speed by means of numerical simulation. The influence of design parameters on f(T) is studied.