Research On A Novel Double Doping Polysilicon Gate MOSFET

As a new type of MOS device, double doping poly-silicon gate (DDPG) MOSFET has increased drive current, trans-conductance and cutoff frequency of the device and so on. But after a study, we find that many defects still exist in this device, such as the off-state current and the gate leakage current are much larger than the ordinary single-gate MOS device, the trans-conductance decreasing trend due to the short channel effect is more obvious. So to address these problems, on the basis of DDPG MOSFET structure a novel device DDPGPD MOSFET is presents, the innovation of this device is that a P+ buried layer is added in the channel near the drain side and the D-gate oxide thickness is thickened.First, from the viewpoint of the process started, the process steps to achieve DDPGPD MOSFET are proposed. In particular three main process steps in order to realize the gate structure and add the P+ buried layer and thicken the D-gate oxide layer are given in the detailed process steps and parameters. The detailed fabrication process for this device is designed using process simulation software called TSUPREM and import the resulting file into Medici in order to simulate electrical properties.When comparing the performance of the device must establish a uniform threshold voltage, so the threshold voltage of DDPGPD is analyzed in the first. Since the minimum value of the potential is always kept under the S-gate, thus threshold voltage of the device is increased by increasing the doping concentration of S-gate; D-gate concentration does not affect the device threshold voltage, while increasing the doping concentration of D-gate will increase the drain current. When the doping concentration of P+ buried layer and D-gate oxide thickness in an appropriate range the threshold voltage and the drain current will not be affected. Due to the D-gate of DDPG devices with low work function, the D-gate control is too strong for the channel. Therefore the off-state current and the gate leakage current of DDPG are much larger than ordinary MOS device. But DDPGPD MOSFET can effectively reduce the off-state current and gate leakage current, and it has better inhibition effect on the DIBL effect.DDPGPD transient characteristics are analyzed, including the gate capacitance, the trans-conductance and the cutoff frequency. The components of the gate capacitance are simplified and the equivalent circuit of gate capacitance is given. Compared with DDPG, DDPGPD has a smaller gate capacitance. Compare the different sizes DDPGPD, DDPG and NMOSFET trans-conductance, the DDPGPD device retains the advantages of DDPG trans-conductance which is higher than NMOSFET, further it can suppress the trans-conductance affected by the short channel effect, so that the trans-conductance is further improved. Finally, the cutoff frequency is obtained by calculating the gate capacitance and trans-conductance. The cutoff frequency of DDPGPD has been improved, so as to have a faster response speed.