This paper reports the investigation in the pumping capacitance to the charge pump performance. The work proposed a capacitance optimization technique on cascading charge pump which achieves higher power conversion efficiency (PCE) with a lower capacitance. This paper also reports a cross-couple charge pump (CCCP) with 40% (PCE) at 100mV. It features a dynamic gate-bias technique which can improve forward current drivability and reduce reverse-leakage current. The circuit is simulated in 65-nm CMOS technology.