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

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 hat-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 and SPICE simulation could not satisfactorily model the LDD MOS structure after hat-carrier stress. Various results indicated that the current MEDICI platform is not very consistent for ac simulation, although de simulation is very good. SPICE simulation showed very promising results when modeling th e changes in S12 and S21 due to hot-carrier stress, yet the results fo r S11 and S22 were not very good. This deficiency implies that a bette r small-signal model for LDD MOS structures would be necessary for SPI CE to be useful in modeling hot-carrier effects on MOSFET high frequen cy performance. (C) 1998 American Vacuum Society. [S0734-211X(98)06602 -5].