In this study, bilayer thin films with different layers' order, Ni/Ti/Si (100) and Ti/Ni/Si (100), are prepared by magnetron sputtering at room temperature followed by the thermal annealing in a vacuum in the temperature range from 400°C to 600°C for 1 h. The combination of XRD and SIMS techniques is used to investigate the effect of the layers' inverse arrangement on the crystalline structure, phase formation and elemental composition upon thermal treatment. As revealed, the annealing of the Ni/Ti bilayer leads to the diffusion of Ti atoms through the Ni grain boundaries towards the outer surface. For the case of Ti/Ni bilayer, interdiffusion between Ni and Ti is not detected upon heat treatment, whereas the thermally induced diffusion between Ni and substrate resulted in the formation of NiSi silicides is revealed. The likely structural and thermodynamic reasons for such behaviour are discussed.
A modified macromodel of operational transconductance amplifier is proposed for application in design of high-frequency bandpass active filters based on film bulk acoustic resonators. The presented solution is an optimal tradeoff according to the criteria of completeness of simulated characteristics, its accuracy and calculation time. Nonlinear amplification behavior of the macromodel is modelled by minimax Chebyshev approximation which allows the use of highorder polynomials and solves the convergence challenge. At the same time, bias-dependent noise model accounts for JohnsonNyquist and flicker noise sources enabling the evaluation of active filter's signal-to-noise ratio, noise figure and output dynamic range. Finally, the differential active filter circuit was analyzed to validate the macromodel's capabilities, simulation ranges and filter characteristics.
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