The impact of drift region length on total ionizing dose effects on LDMOSFET

The adjustment of drift region length increases the design flexibility of laterally diffused metal oxide semiconductor field effect transistor (LDMOSFET) characteristics, such as breakdown voltage and on-resistance. However, its impact on the total ionizing dose (TID) effects on the device cannot be ignored. The changes in threshold voltage ($V_{\mathrm{th}}$), transconductance (g_m), drain current ($I_d$), and on-resistance (R_on) of N-channel LDMOSFET (NLDMOSFET) with two different drift region lengths after TID irradiation were studied in this article. We found that the shift of $V_{\mathrm{th}}$ and g_m after irradiation was almost identical for both devices, whereas there was a noticeable difference in the shift of $I_d$ and R_on. The influences of traps and interface states in gate oxide and field oxide on device characteristics were discussed through technology computer-aided design (TCAD). Ultimately, we discovered that the degradation of $V_{\mathrm{th}}$ after irradiation was primarily related to the gate oxide, while the degradation of drain current in linear region ($I_{\mathrm{dlin}}$) after irradiation was mainly related to the drift region. The degradation of g_m and R_on were related to the degradation of $V_{\mathrm{th}}$ and $I_d$. Although the long drift region is beneficial to the breakdown and power characteristics of LDMOS devices, it causes a significant deterioration in the TID effect, which is worth considering in the design of devices and circuits applied in radiation environment.