A voltage controlled oscillator (VCO) with its center frequency at 20 GHz is designed and fabricated in TSMC65nm CMOS technology. Several design optimizations are performed including noise of tail current source, dimensions of cross-couples transistors, inductor selection and tuning range. The measurement results show that tuning range is 17.78 to 22.13 GHz and the phase noise is -100dBc @ 1MHz.The total power dissipation under 1V supply voltage is 5.1mW.