The aim of this paper is to determine the percolation threshold of electrical conductivity of zinc oxide (ZnO). Percolation threshold is the name for the minimum thickness of the layer deposited on the substrate that the conductive material must have in order to achieve the path by which electrons can pass from one end of the substrate to the other. We will deposit the ZnO layers with an ALD (Atomic Layer Deposition) device. ALD is a device that deposits ZnO layer by layer on the substrate. We will have three substrates: glass, glass covered with a layer of Al2O3 and silicon covered with a layer of Al2O3. Prior to the synthesis of Al2O3 and ZnO, the substrates will be purified in water and isopropanol. Also, we will observe how the electrical conductivity depends on the roughness of the substrate. Substrate roughness will be measured before ZnO deposition. After ZnO synthesis and determination of the percolation threshold of electrical conductivity for different substrates, the samples will be recorded with a Scanning Electron Microscope SEM. Finally, we will give a certain surface characterization of the synthesized layers.