Novel LDMOS Structure for 2 GHz High Power Basestation Application

An LDMOS is described for high power (>70W) 2 GHz basestation application that includes several novel structures. High power gain is achieved by minimizing gate resistance and feedback capacitance. The gate resistance is reduced by using metallized submicron polysilicon gates and the feedback capacitance is lowered by a metal shielding between drain and gate. The source is directly connected to ground thus avoiding common lead inductance and optimizing power gain. In power MOS devices differential mode oscillations can hamper uspcaling of the device to higher output powers. In our LDMOS we prevent this by using a novel, very compact lay-out that we call ´MONOMOS´, since it merely consist of one integral active area. This is made possible by using very long gate fingers that still have low gate resistance because of metallization of the polysilicon. The LDMOS shows high gain (12 dB) at high output powers (70W) at 2 GHz and low intermodulation distortion, which makes it an excellent device for CDMA basestations. Both gain and distortion are substantially better than those of bipolar transistors.