Abrupt current switching due to impact ionization effects in Ω-MOSFET on low doped bulk silicon

In this paper, we report very abrupt current switching and hysteresis effects due to saddle point and impact ionization in low doped n-channel Omega-Gate MOSFET (Omega-MOSFET). The Omega-MOSFETs are fabricated on low-doped (8times10¹⁴ cm^-3) bulk silicon by bulk silicon isotropic etching and sacrificial oxidation. A specific abrupt impact ionization and hysteresis of I_D(V_DS) are observed at high drain voltage (V_DS>11 V) on transistors that have short channel effects (L=0.9-10 um). This is explained by the accumulation of a hole pocket under the gate due to the formation of a saddle point region. An outstanding feature is that this effect can be exploited to abruptly switch from low to high current (2 decades of current) states of I_D(V_GS) characteristics with ultra-abrupt slopes of 5 to 10 mV/dec. Moreover, the hysteresis window DeltaV_GS~500 mV is suitable for DRAM memory. Dynamic switching characteristics and a retention time of up to tens of seconds are originally demonstrated. The proposed Omega-MOSFET stands as a very promising alternative to I-MOS devices, being more scalable and integrable on a standard (low cost) bulk-Si Multi-Gate FET platform. Its experimental performances are promising for both small-slope switches and dynamic RAM memories.