Towards ultrasonic through-silicon vias (UTSV)

3D interconnects between stacked silicon chips in 3D integrated circuits (3DICs) have been realized with through-silicon vias (TSVs). These call for special processing microfabriation techniques requiring through wafer etching and metal filling, which add to the cost and can lead to lower chip reliability due to thermal expansion mismatch related strain fields. In this paper, we present a novel interconnect for 3DICs - an ultrasonic TSV implemented with piezoelectric aluminum nitride (AlN) thin film transducers on silicon. Whereas TSVs require a physical via through the entire thickness of a wafer, the ultrasonic TSV works by propagating signals from one aluminum nitride (AlN) transducer to another with bulk acoustic waves through the silicon wafer. This technology has the potential to simplify processing in 3DIC manufacturing and integration and increase TSV density.