A comparison of fully depleted SOI-CMOS transistors in FIPOS and SIMOX substrates

Summary form only given. To maximize the performance of SOI-CMOS transistors, the silicon film under the gate should be depleted, which requires the use of thin-film SOI material. The authors have produced 1-μm thin-film SOI-CMOS transistors in wafers produced by separation by oxygen implantation (SIMOX) and by oxidation of porous silicon (FIPOS) processes. The silicon film thicknesses were approximately 140 nm for the SIMOX wafers and 100 nm for the FIPOS wafers. The basic characteristics of transistors in the two types of material are similar, with high gains and current drives, near-ideal subthreshold slopes, and low junction leakages. In both cases the characteristics are free from the kink seen in partially depleted devices. Both types of n-channel device exhibit slight negative output resistance at high gate voltages. Low-field-inversion mobilities are comparable for the two types of SOI. For SIMOX material the n- and p-channel mobilities are 580 and 220 cm ²/V/s, respectively; for FIPOS the figures are 520 and 235 cm ²/V/s. The back channel mobilities of SIMOX transistors are over 90% of the front channel values; for FIPOS the back channel mobilities are 55-60% of the values for the front channels. The values of ΔL for both front and back channels and for both types of material that show no anomalous lateral diffusion of source/drain dopants has occurred