New technique to extend the vertical depletion region at SOI-LDMOSFETs

In order to obtain an excellent performance for silicon-on-insulator lateral double-diffused MOSFET (SOI-LDMOSFET) transistors, we introduce a new technique to extend the depletion region along the vertical direction in the drift region. The proposed structure is called vertically depleted LDMOSFET (VD-LDMOSFET). The VD-LDMOSFET structure consists of a buried metal layer in the oxide region. The drift region of the VD-LDMOSFET is vertically depleted, not only from the buried oxide, but also by the incorporated metal layer in the buried oxide. Therefore, a higher drift doping density is achieved by an extension of the depletion region in the drift region and the on-state resistance \(({R}_{\mathrm{ON}})\) reduces without degradation of the breakdown voltage. Also, an additional peak is created in the electric field distribution of the proposed structure and causes a reduction of the electric field peak near the gate and the drift region junction at the top surface of the device. Therefore, the breakdown voltage \(({V}_{\mathrm{BR}})\) of the VD-LDMOSFET structure increases. The simulation results illustrate that by optimizing the doping density of the drift region and the dimensions of the metal layer in the proposed structure, the on-state resistance (28.9%) and the breakdown voltage (36.1%) are improved greatly and a superior tradeoff is achieved compared with a conventional SOI-LDMOSFET (C-LDMOSFET) structure.