Integration of a Piezoelectric Layer on Si FinFETs for Tunable Strained Device Applications

Earlier theoretical reports predicted that the usage of a piezoelectric stressor layer around the FinFET, i.e., the PiezoFET, offers a great potential for steep subthreshold slope devices. For the first time, we analyzed the practical realization of such PiezoFETs comprising a piezoelectric stressor layer, lead-zirconate-titanate (PZT), and aluminum-nitride (AlN) deposited on n-type silicon FinFETs. A high-piezoelectric response in the range of 100 pm/V has been obtained for the PZT PiezoFET evidencing the converse piezoelectric effect in the device. The piezoelectric response for the AlN device was much less (13 pm/V) as expected. Underlying device properties, such as subthreshold swing (SS) and low-field electron mobility have been significantly affected by the presence of the PZT stressor. A 20%-50% change in the mobility and a change in the SS (about 5 mV/decade) have been observed. The change can be attributed to the strain induced reduction of the interface trap density at the Si/SiO2 interface. This strain is partly formed by the bias over the piezoelectric layer, which indicates the converse piezoelectric effect related tunable strain in both the silicon channel and gate oxide.