SiGe-Pocket Tunnel FETs for Low Power Logic Applications
Over the last 50 years, conventional scaling (Moore’s law) has provided continuous improvement in semiconductor device/circuit technology and has resulted in unprecedented advancement in electronic systems. However, as transistors scale below 45nm, the non-scalability of subthreshold swing (SS) in conventional MOSFETs has resulted in increased power consumption. Power/thermal issue has become one of the major roadblocks for the scaling of the devices. Therefore, novel devices with steep SS are highly desirable as they offer the same current drive with a reduced supply voltage (VDD) while maintaining a reasonable IOFF. Among all potential device solutions, including negative capacitance FETs (NC-FETs) and NEMS. Tunnel FETs (TFET) have been widely regarded as the most promising candidates, especially for the power-sensitive Internet of things (IoTs) applications.
State-of-the-art TFETs, both group IV and group III-V-based, have been examined to identify the limitations of the previously proposed devices. SiGe-based device solution is identified as the most promising solution because of its FinFET/GAA compatibility, mature synthesis techniques, and tunable bandgap. Compared with III-V-based TFETs, it is more likely to be adopted by future VLSI technologies. TFET with a counter-doped SiGe-pocket is proposed to take the full advantage of the SiGe material system. By adopting the counter-doped SiGe pocket, both tunneling barrier height and width are reduced, which results in significant improvement in ION as well as SS. Vertical p-type TFET with a counter-doped Si0.8Ge0.2 pocket has been experimentally demonstrated. The vertical doping/composition profile was achieved by in-situ doped RPCVD. Improvement in transfer characteristics has been observed when compared with Si TFET and TFET with an intrinsic Si0.8Ge0.2 pocket. It provides a potential device solution for low power logic applications.