Energy-Efficient Adiabatic Circuits Using Transistor-Level Monolithic 3D Integration

Charge-recycling adiabatic circuits are recently receiving increased attention due to both high energy-efficiency and higher resistance against side-channel attacks. These characteristics make adiabatic circuits a promising technique for Internet-of-things based applications. One of the important limitations of adiabatic logic is the higher intra-cell interconnect capacitance due to differential outputs and cross-coupled pMOS transistors. Since energy consumption has quadratic dependence on capacitance in adiabatic circuits (unlike conventional static CMOS where dependence is linear), higher interconnect capacitance significantly degrades the overall power savings that can be achieved by adiabatic logic, particularly in nanoscale technologies. In this paper, monolithic 3D integrated adiabatic circuits are introduced where transistor-level monolithic 3D technology is used to implement adiabatic gates. A 45 nm two-tier Mono3D PDK is used to demonstrate the proposed approach. Monolithic inter-tier vias are leveraged to significantly reduce parasitic interconnect capacitance, achieving up to 47% reduction in power-delay product as compared to 2D adiabatic circuits in a 45 nm technology node.