Degradation analysis in SOI LDMOS transistors with steep retrograde doping profile and source field plate

The benefits of implementing a source field plate in RF ultra-thin SOI power LDMOS transistors with a retrograde doping profile in the entire drift region is evaluated in this paper in terms of hot-carrier degradation (HCD) and capacitance behaviour. The optimisation of the retrograde doping profile allows the current path to be diverted deep inside the active silicon layer in such a way that the surface damage originated by hot carriers is attenuated. However, a slight change in the dose implanted into the drift region can deteriorate the performance in terms of HCD and capacitance. Among the well-known benefits, such as better power efficiency and higher reliability, simulation results show that the source field plate (SFP) leads to an improvement of device stability to implanted dose fluctuations in LDMOS transistors with retrograde doping profiles. Moreover, the retrograde doping profile along with the SFP helps to accelerate the depletion process in the drift region, increasing the variation of the gate-drain capacitance (C_gd) as a function of the drain voltage and thus improving the RF performance.