Effects of hot-carrier stress on the RF performance of 0.18 μm technology NMOSFETs and circuits

The effects of DC hot-carrier stress on DC and RF performance of submicron LDD NMOSFETs are investigated. It is shown that the unity current gain frequency f_T decreases as the transconductance g_m and gate-source capacitance C_gs of the transistor are degraded with stress time. It is observed that the degradation of f_T versus stress time is faster than that of the g_m degradation. This was found to be due to the increase of the C_gs with stress. The threshold voltage V_th and the output conductance g_ds increase and the intrinsic voltage gain of the device A_ν,int decreases by stress. The effect of hot carrier stress on the noise performance of the device is investigated by calculating the minimum noise figure of the device NF_min before and after stress, using the calibrated small signal model of the transistors. The results of the hot carrier experiments on single devices are used to analyze the hot carrier effects on the transistor power gain G_T, input matching Γ_in, noise figure NF and stability factor μ of a low noise amplifier made of these NMOSFETs.