L-shaped Tunnel Field-Effect Transistors (L-shaped TFETs) with High Current Drivability and Low Subthreshold Swing

Abstract

In order to solve power crisis in highly-scaled CMOS technology, a novel tunnel field-effect transistors (TFETs), named L-shaped TFETs, have been proposed and its electrical properties are examined. It features band-to-band tunneling (BTBT) direction parallel to the normal electric field induced by gate electrode. Because carrier injection is occurred perpendicular to the channel direction, cross-sectional area and barrier width of BTBT junction could be defined by structural parameters. Using the commercial TCAD device simulator, its electrical characteristics are examined and optimized. It is expected that the L-shaped TFETs will reveal better performance than conventional ones in terms of subthreshold swing (S), on-current (Ion) and short channel effect. In addition, the performance of L-shaped TFET inverters has been compared with that of conventional TFET ones for its complementary logic application. After the key process techniques are obtained, control and comparison samples are fabricated at Inter-University Semiconductor Research Center (ISRC) of Seoul National University (SNU), Korea. The main process technique is as follow: in-situ doped epitaxial layer growth for constantly doped source region, selective epitaxial layer growth of silicon at low temperature for tunneling region, and guarantee sub-3-nm gate dielectric. From the electrical measurement of transfer and output characteristics, it is verified that 102 mV/dec minimum S in conventional TFET is improve to 7, 34 and 59 mV/dec in L-shaped TFET. In addition, the Ion of L-shaped TFET is more than 10 times larger than that of conventional one. Extracting several parameters such as source/drain resistance, channel resistance, mobility, and tunneling resistance, it is clear that the improved performance comes from the reduction of tunneling resistance. From this study, it is demonstrated that L-shaped TFET will be one of the most promising candidate for a next-generation low-power device.