An 0.18-μm CMOS for mixed digital and analog applications with zero-volt-Vth epitaxial-channel MOSFETs

An 0.18-μm CMOS technology with multi-V_ths for mixed high-speed digital and RF-analog applications has been developed. The V _ths of MOSFETs for digital circuits are 0.4 V for NMOS and -0.4 V for PMOS, respectively. In addition, there are n-MOSFET´s with zero-volt-V_th for RF analog circuits. The zero-volt-V_th MOSFETs were made by using undoped epitaxial layer for the channel regions. Though the epitaxial film was grown by reduced pressure chemical vapor deposition (RP-CVD) at 750°C, the film quality is as good as the bulk silicon because high pre-heating temperature (940°C for 30 s) is used in H₂ atmosphere before the epitaxial growth. The epitaxial channel MOSFET shows higher peak g_m and f_T values than those of bulk cases. Furthermore, the g_m and f_T values of the epitaxial channel MOSFET show significantly improved performances under the lower supply voltage compared with those of bulk. This is very important for RF analog application for low supply voltage. The undoped-epitaxial-channel MOSFETs with zero-V_th will become a key to realize high-performance and low-power CMOS devices for mixed digital and RF-analog applications