The defects of reported TID reinforced structures and the improved structure

Abstract

We find that the previously reported P-edge N-Metal-Oxide-Semiconductor Field-Effect Transistor (NMOSFET) and dummy gate-assisted (DGA) NMOSFET, to resist the total ionizing dose (TID) effect, have a fatal drawback in that they can only work under a very low drain voltage (Vdd). This paper proposes and demonstrates an improved structure, called P+ edge source NMOS (PES-NMOS), in which the heavily P+ doped belts are only formed on both sides of the source region close to the shallow trench isolation (STI). Both the TCAD software simulations and radiation experiments show that the turn-off current (Ioff) of the PES-NMOS device under 1.8 V Vdd is about 4 to 5 orders of magnitude smaller than that of the control group without reinforcement structure at 300 krad(Si) TID. This result proves that the PES-NMOS can well resist the TID effect and solve the fatal drawback of the reported structures. With the continuous progress of the CMOS process, the thickness of gate oxide becomes very thin, while STI is relatively thick, so the total dose effect on STI is still significant. Therefore, the importance of using the PES-NMOS to suppress the parasitic channel of STI and overcome the shortcomings of the ELT is increasing. Index termsP+ edge source NMOS, total ionizing dose(TID) effect, radiation experiments, radiation hardening by design(RHBD).