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A simple theory of the charging cycle is presented for ovonic switches operating in the relaxation oscillation mode. The theory takes into account the variation of the OFF-state resistance with bias voltage. An analytical expression for the period of oscillation as a function of circuit components and device parameters is obtained showing that a nonlinear increase of the period of oscillation exists with increasing series resistance. The presented theory is in good agreement with experimental results.

Hypersonic attenuation above the structural phase transition temperature r o~1 03°K has been measured from 0.4 to 1 GHz in SrTi0 3 . Studies were made for both polarizations in (100)-and (lll)-oriented single crystals. For temperatures above 150°K, the attenuation of shear waves is temperature-independent, while that of longitudinal waves is monotonically increasing with decreasing temperature. As T -> T a from above, the attenuation of both longitudinal and transverse waves shows a striking increase that continues until Tc^T a , when hypersonic transmission in the medium stops. These observations are explained qualitatively in terms of Akhieser damping of the hypersonic waves by interactions with thermally excited phonons of the acoustic and soft optic modes in SrTi0 3 . It is found that for (T -T a ) >40°K, the temperature dependence of the attenuation of longitudinal waves is given by T/(T -T c ) m with T c =43°K and m ranging from 1 to 1.4. In the interval 10°K< (T-T a )<30 o K, the temperature dependence is well described by (T-T a )~n; the exponent n ranges from 0.9 to 1.2 for longitudinal waves, but it is between 1.9 and 2.2 for transverse waves.