Design of Au/Cdbr₂/Au as Negative Capacitance Devices and as Band Filters Suitable for 4G Technologies

Herein, cadmium bromide thin film devices are designed for possible use in communication technology. The 1.0 $\mu m$ thin layer of CdBr₂ is sandwiched between two Au (1.0 $\mu m$ thick) layers using the thermal evaporation technique under a vacuum pressure of 10^-5 mbar. The Au/CdBr₂/Au devices are structurally morphologically and electrically characterized. It is observed that the hexagonal cadmium bromide exhibits large lattice mismatches with cubic Au substrates. The randomly distributed nano- rod like grains is accompanied with average surface roughness of ~26 nm. When an ac signal of low amplitude is imposed between the terminals of the Au/CdBr₂/Au devices, a negative capacitance effect in the frequency domain of 10-1800 MHz is observed. In addition, analysis of the impedance spectra in the same domain has shown that the device behaves as band pass/stop filters suitable for 4G technology. The microwave based standard analysis of the Au/CdBr₂/Au band filters have shown that it displays a notch ($f_{co}$) frequency of 2.0 GHz. The cutoff frequency at $f_{co}$ reaches 7.86 GHz. The features of the Au/CdBr₂/Au devices nominate it for use as microwave resonators and as negative capacitance devices suitable for; 4G technology, noise reduction and for parasitic capacitance cancellation.

Keywords:
CdBr₂; 4G band filter; negative capacitance; microwave resonators