New layout design methodology for monolithically integrated 3D CMOS logic circuits based on parasitics engineering

We propose a new layout design methodology for monolithically integrated 3D CMOS logic circuits based on parasitics engineering. In order to understand the impact of parasitics in monolithic 3D-stacked CMOS circuits, careful analysis of intra- and inter- layer parasitic capacitances were performed by using physics-based RC extractor for realistic 3D structure. As a result, we found that separation of power-supply (Vdd) and ground-line (GND) layer from logic elements is a key to reduce the parasitic capacitance thanks to be suppressed electrical coupling between stacked layers. By comparative evaluation among possible 3D layer configurations, we revealed that the best configuration is Vdd and GND layer sandwiched between nFET and pFET logic layers. Performance benchmarking by energy consumption-switching delay demonstrated that a 40% improvement of energy-delay product at Vdd = 0.5 V can be achieved by using a proposed layout methodology.