Metal–insulator–metal micro-capacitors for integrated energy storage up to 105 Hz

Metal–insulator–metal (MIM) micro-capacitors for use in integrated energy storage applications are presented. A new, simple and batch Si processing compatible method for the creation of high aspect ratio metallic 3D structures on the surface of a Si substrate is described. The method consists of creating an array of Si nanopillars and then depositing Al at a small angle off the vertical while rotating the sample. Using this method, the effective area of the samples is increased by a factor of 3.8. Various capacitors are created using the described 3D structures as the lower electrode, with anodic alumina and atomic layer deposited HfO2 as the dielectric. Al and Cu top electrodes are also investigated. Large values of capacitance densities as high as 3.2 μF cm−2 are achieved. All capacitors are demonstrated to possess small values of series resistances and stable operation up to a frequency of 105 Hz. These results make the presented MIM capacitors exceed the state-of-the-art while maintaining a simple and integrable fabrication scheme which renders them very interesting for energy storage applications where operational frequencies larger than 1 kHz are required, as is the case in several vibrational energy harvesters.