Effects of Back Metal on the DC and RF Characteristics of 3D Stacked InGaAs RF Device for Monolithic 3D RF Applications

In this letter, we demonstrate three-dimensional (3D) stacked InGaAs high-electron-mobility transistors (HEMTs) on Si with back metal for a monolithic 3D RF platform. The devices are fabricated through a wafer bonding technique and the back metal is inserted during the 3D integration process. We investigate the effect of the back metal on the DC and RF performance of 3D stacked InGaAs HEMTs, which are essential to implement the monolithic 3D RF platform. Furthermore, we obtained a current gain cutoff frequency (
${f}_{\text {T}}$
) of 307 GHz and a maximum oscillation frequency (
${f}_{\text {MAX}}$
) of 765 GHz even though it is a 3D stacked device with back metal. The
${f}_{\text {MAX}}$
value is the highest ever reported in 3D stacked RF transistors.