3.3 Contactless 3-D ICs 53 bonding is required. A variety of solutions can be used to detach the handle wafer. The time required to accomplish this step also depends on the size of the wafer [86]. 3.3 CONTACTLESS 3-D ICs Although the majority of the processes that have been developed for 3-D ICs utilize vertical interconnects with some conductive material, other techniques that provide communication among circuits located on different planes through the coupling of electric or magnetic fields have been demonstrated. Capacitively coupled circuits are presented in subsection 3.3.1. Inductive vertical interconnects are discussed in subsection 3.3.2. 3.3.1 Capacitively Coupled 3-D ICs In capacitively coupled signaling, the interplane vias are replaced