Extremely scaled hetero-junction channel TFT for advanced electronics

In this work, we demonstrate high performance short channel transistor using ultra-thin dual channel layer. The performance of the channel is comparable to emerging two-dimensional materials and superior to that of existing metal oxides. The active channel consists of amorphous Tin-doped Indium oxide and indium-gallium-zinc-oxide (ITO/IGZO) layers. We used sputtering to create the channel layer of combined thickness ~ 4 nm, and Atomic Layer Deposition to deposit high-quality hafnium oxide dielectric at low-temperature (<350°C), making our fabrication approach compatible with low-thermal budget Cu interconnects for back-end-of-line. Our approach results in significant improvement in TFT performance above our earlier published record results for 30 nm IGZO and 10 nm HfO₂. In this study, we have achieved a highest field-effect mobility of 108 cm²V^-1s^-1 for ultra-thin ITO/IGZO channel with thickness of 4 nm. The introduction of a thin-layer ITO significantly suppresses the hysteresis in the device due to compensation of the interfacial/bulk traps. Short channel immunity is observed with significantly low off-state current <1 pA/µm, low subthreshold swing (SS) of <90 mV/decade and high ON/OFF ratio >10⁸, for 50 nm channel length devices. Moreover, unlike Si, there is no significant degradation in long channel transistor performance as the active layer thickness changes from 33 nm to 4 nm. This is achieved by high carrier concentration in thin ITO and controlled electron flow through IGZO.