Distinguish the effect of Cu additive on complex electrical (dielectric/impedance) behaviors of ZnO thin films

Abstract

The copper element (Cu) substituted ZnO with the common formula ZnO₇₀/Cu_x/ZnO₇₀ (x = 20, 50, and 70 nm) was manufactured using ALD and Dc magnetron sputtering techniques, as a function of the concentration of Cu as interlayer. The effect of the amount of Cu doped in ZnO on the character and dielectric and impedance properties was evaluated. Scanning electron microscopy (SEM) and grazing incident X-ray diffraction (GIXRD) were used to assess the microstructure of the prepared thin films and to obtain grain size measurements. The dielectric properties (ε′, ε″) and the real part of the complex electric modulus (M) were studied as a function of frequency and temperature. A strong dependence and correlation between the dielectric properties and the thickness of the Cu interlayer were investigated. The electrical impedance at different temperatures exhibited a single semicircle, indicating that the response arose from a single capacitive element corresponding to the grains. The conduction of grains and grain boundaries is detected from a complex impedance spectrum by fitting the Nyquist plot with an appropriate electrical circuit. It was revealed that the increase of the thickness of the Cu interlayer of the ZnO/Cu/ZnO system leads to a high dielectric constant and a low value of the real part of the complex electric modulus, which are very good candidates for microwave semiconductor devices and various microelectronic applications.