A new analytical scalable substrate network model for RF MOSFETs

In this work, the substrate parameter scalability of multi-finger RF MOSFET is analyzed and modeled for a broad range of device periphery from 200 μm up to 6 mm. For the first time, a new analytical substrate network model based on device geometry of 0.4-μm thick-oxide NMOS transistors with ring-shaped substrate contact surrounding the device is proposed. The effect of substrate coupling from the drain and source junctions to the top and bottom substrate contacts has not been considered previously in the conventional MOSFET substrate modeling. It is found that this effect dominates the total substrate resistance as device size increases. The new model approximates the distributed substrate coupling effect into vertical and horizontal directions (from the drain and source junctions to the top and bottom substrate contacts, and to the side substrate contacts), and can accurately predict the substrate parameters for a broad range of device periphery. This approximation simplifies the modeling complexity of the distributed substrate coupling and enables the direct calculation of each substrate component from device geometry with great accuracy. The newly proposed analytical substrate model is essential for developing a scalable MOSFET model for high frequency applications.