The linearity of the power response of yttrium iron garnet films to a microwave pulse having length shorter than the delay time characteristic of the specimen is investigated. In particular, a threshold is found above which output power increases with respect to standard linear trend. The above novel effect, analyzed in some detail on five epilayers of different thicknesses, cannot be explained in terms of usual nonlinear processes. An interpretation in terms of soliton excitation, accounting for the existence in the system of both intrinsic nonlinearity and dispersion, is proposed. PACS numbers: 75.30.Ds, 76.50.+g, 85.70.Ge Presently, solitons are an active field of interest in both fundamental and applied solid-state physics. The mathematical advances in finding out analytical solutions to a certain number of nonlinear dispersive wave functions 1 have given a powerful tool to their study and characterization.As is well established, a soliton results as a fairly delicate balance between the dispersion (which forces the signal to spread out) and the nonlinearity (which forces the signal to steepen) of the system under investigation. Apart from the interest in basic research, the remarkable applications of soliton propagation in optical fibers, 2 nonlinear transmission lines, 3 and Josephson junctions 4 (just to mention a few of them) seem to justify the search for solitons in media which are inherently both dispersive and nonlinear. Some systems in the field of acoustical 5 and radio-frequency signal transmission are in principle suitable to fit those requirements. Among them, the analysis of possible soliton excitation in a magnetostatic wave (MSW) device such as a dispersive delay line 6 operating at microwave frequency is particularly appealing. From a theoretical standpoint, a dipolar model dealing with the nonlinear properties of nonexchange MSW's propagating in a low-loss magnetic film of yttrium iron garnet (YIG) has been recently developed. 7 To account only for nonlinearities produced by self-action processes, a nonlinear Schrodinger equation describing the evolution of envelope solitons has been derived in the weak nonlinearity approximation. In this way, expected threshold powers for the onset of selfmodulation and self-channeling have been derived.Furthermore, through an analysis of the unique experimental data available in current literature, it turns out that attempts to detect purely magnetostatic solitons in YIG films have been so far unsuccessful. 8 In this framework, some nonlinear phenomena, interpreted in terms of multisoliton excitation as deduced by our analyzing the time envelope of an output pulsed signal, 8,9 have been reported. In order to get that result, the operational frequency had to fall within a few defined regions of the spectrum close to so-called repulsion gaps. 10 According to the theory and experimental findings, 11 resolvable gaps can be observed under specific conditions of spin pinning whenever the dipolar and exchange energy terms are comparable in magnitude. From an ...

The capability of scanning microwave microscopy for calibrated sub-surface and non-contact capacitance imaging of silicon (Si) samples is quantitatively studied at broadband frequencies ranging from 1 to 20 GHz. Calibrated capacitance images of flat Si test samples with varying dopant density (10(15)-10(19) atoms cm(-3)) and covered with dielectric thin films of SiO2 (100-400 nm thickness) are measured to demonstrate the sensitivity of scanning microwave microscopy (SMM) for sub-surface imaging. Using standard SMM imaging conditions the dopant areas could still be sensed under a 400 nm thick oxide layer. Non-contact SMM imaging in lift-mode and constant height mode is quantitatively demonstrated on a 50 nm thick SiO2 test pad. The differences between non-contact and contact mode capacitances are studied with respect to the main parameters influencing the imaging contrast, namely the probe tip diameter and the tip-sample distance. Finite element modelling was used to further analyse the influence of the tip radius and the tip-sample distance on the SMM sensitivity. The understanding of how the two key parameters determine the SMM sensitivity and quantitative capacitances represents an important step towards its routine application for non-contact and sub-surface imaging.

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The charging of the dielectric used for the actuation in microelectromechanical system (MEMS) devices is one of the major failure sources for switches based on this technology. For this reason, a better understanding of such an effect is vital to improve the reliability for both ground and space applications. In this paper, the expected response of MEMS switches to unipolar and bipolar dc actuation voltages has been measured and modeled. Two configurations of MEMS switches, namely, an Ohmic series and a shunt capacitive one designed for microwave applications, have been studied as a test vehicle for charging effects related to the dc actuation pads. The recorded data have been interpreted mainly through the Poole–Frenkel effect due to charge injection when a high voltage is applied to the dielectric layer. Metal-Insulator-Metal (MIM) structures have been also considered as a complementary information for the response of the dielectric material.