Wide-Range Threshold Voltage Control of Dual-Inner-Gate Gate-All-Around Field-Effect Transistor

Gate-all-around field-effect transistors (GAAFETs) have been known to outperform FinFETs. However, their complex structure poses several process-induced challenges, primarily associated with implementing multiple threshold voltage (Vth) options within a limited voltage range. The "dipolelayer" and inner-outer gate technique have been developed to secure various Vth values for a given voltage range. However, these approaches show high Vth variability or lower on-state drive current (Ion). In this work, we introduce two types of inner gates to secure more diverse Vth values over a wide range while minimizing the degradation of on-state drive current. We have developed an inner–outer gate process compatible with conventional GAAFET and identified and optimized DC and AC performance-affecting parameters. This study demonstrates that dual-inner gate (DIG)-GAAFETs are compatible with the conventional GAAFET process, offering five Vth levels, up to 11.7% shorter RC delay, up to 25.6% higher Ion, and lower Vth variability. These improvements address the issue of limited Vth levels, facilitating versatile applications of GAAFET structures in industry.