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 ID(VDS) are observed at high drain voltage (VDS>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 ID(VGS) characteristics with ultra-abrupt slopes of 5 to 10 mV/dec. Moreover, the hysteresis window DeltaVGS~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.