Karina Jeronimo

The addition of piezoelectric zinc oxide (ZnO) fillers into a flexible polymer matrix has emerged as potential piezocomposite materials that can be used for applications such as energy harvesters and pressure sensors. A simple approach for the fabrication of PDMS-ZnO piezoelectric nanocomposites based on two ZnO fillers: nanoparticles (NP) and nanoflowers (NF) is presented in this paper. The effect of the ZnO fillers’ geometry and size on the thermal, mechanical and piezoelectric properties is discussed. The sensors were fabricated in a sandwich-like structure using aluminium (Al) thin films as top and bottom electrodes. Piezocomposites at a concentration of 10% w/w showed good flexibility, generating a piezoelectric response under compression force. The NF piezocomposites showed the highest piezoelectric response compared to the NP piezocomposites due to their geometric connectivity. The piezoelectric compound NF generated 4.2 V while the NP generated 1.86 V under around 36 kPa pressure. The data also show that the generated voltage increases with increasing applied force regardless of the type of filler.

A novel patterning method for the selective growth of ZnO nanorods has been developed, which can avoid any etching steps and longtime lift-off processes. In the simplified process, the deposition of a titanium buffer layer is omitted, and a 50 nm ZnO thin-film seed layer is deposited by e-beam evaporation directly onto the silicon patterned with the photoresist. The omitted titanium buffer layer has been observed to result in the absence of the ZnO seed layer on the photoresist. Then, the ZnO nanorods with diameters ranging from 50 to 500 nm have been found to grow hydrothermally only on the regions without the photoresist. The photoresist remains on the substrate after the hydrothermal growth, which can protect areas from the polluted solution and unwanted nanorods. After all processes, the photoresist can be removed easily by the solvent without any unwanted damage of nanorods. With this simplified method, ZnO nanorods can be synthesized and patterned with only one step of lithography, which can be used for novel ZnO based devices.