Negative Capacitance Effect in Ag/a-In2Se3/CdS/CdSe/C Dual Band Stop Filters

In the current study, a 1.5 lm thick three channel microwave band filter is designed and characterized. The thin film device which was constructed from the indium selenide, cadmium sulfide and cadmium selenide stacked dielectric materials sandwiched between silver and carbon films is studied by means of x-ray diffraction, energy dispersive x-ray analysis and impedance spectroscopy techniques. It was observed that the Ag thin film substrate induced the formation of the hexagonal a-In2Se3 phase of indium selenide. The x-ray analysis has also shown that the deposition of hexagonal CdS over Ag/a-In2Se3 and that of hexagonal CdSe over a-In2Se3/CdS under vacuum pressure of 108 bar is of a highly strained and mismatched physical nature. The impedance spectroscopy analysis in the frequency domain of 0.10–1.80 GHz has shown that; while the Ag/a-In2Se3/C channel exhibit negative capacitance (NC) effects in the frequency domain of 0.10–1.40 GHz, the Ag/a-In2Se3/CdS/C and the Ag/a-In2Se3/CdS/CdSe/C channels displayed a NC feature in the domains of 1.24–1.40 GHz and 1.10–1.56 GHz, respectively. The fitting of the capacitance spectra in accordance with the modified Ershov model allowed determining the NC and band filtering parameters. It was also observed that, although the Ag/a-In2Se3/C channel behaves as a high frequency low pass filter, the second and third channels displayed band stop filter features with notch frequencies of 1.38 GHz and 1.49 GHz, respectively. The features of the device nominate it for use as a parasitic capacitance canceller and as a three channels microwave filter