HOT-CARRIER EFFECTS ON THE SCATTERING PARAMETERS OF LIGHTLY DOPED DRAIN N-TYPE METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR

The latest evolution in complementary metal-oxide-semiconductor techno logy has made the metal-oxide-semiconductor field effect transistor (M OSFET) a viable choice for rf applications, especially for frequencies in the low GHz region. However, hot-carrier effects should also be co nsidered carefully when the devices are operating in the GHz regime. H ere, we studied the effects of de hot-carrier stress on lightly doped drain (LDD) n-type MOSFET (NMOSFET) high-frequency performance by meas uring and simulating its s parameters. This is the first time, to the authors' best knowledge, that such experiments are reported. We demons trated clearly the effects of hot-carrier stressing on LDD NMOSFETs by giving representative s-parameter and noise measurement results from a 0.8 mu m long device. We showed that hot-carrier stress can signific antly degrade both s parameters and noise of NMOSFETs, and thus can ha ve considerable consequences for circuit designers. Therefore, these e ffects should be carefully considered when using MOSFETs in high-frequ ency analog circuits. Unfortunately, both MEDICI(R) and SPICE simulati on could not satisfactorily model the LDD MOS structure after hot-carr ier stress. Various results indicated that the current MEDICI platform is not very consistent for ac simulation, although de simulation is v ery good. SPICE simulation showed very promising results when modeling the changes in S12 and S21 due to hot-carrier stress, yet the results for S11 and S22 were not very good. This deficiency implies that a be tter small-signal model for LDD MOS structures would be necessary for SPICE to be useful in modeling hot-carrier effects on MOSFET high-freq uency performance. (C) 1998 American Vacuum Society. [S0734-2101(98)08 402-4].