High performance triangular barrier engineered NIPIN selector for bipolar RRAM

Triangular barrier has been proposed and implemented for the first time in a punch-through diode based selector by dopant profile engineering. Vertical 4F2 diodes have been fabricated on an epitaxial Si stack consists of n+ / i / delta-doped p+ / i / n+ (NIPIN) layers by low temperature (sub-520°C) Si epitaxy. We experimentally demonstrate that while conventional NPN selectors exhibit severe sub-threshold slope degradation at high voltage, NIPIN selectors produce ideal subthreshold slope of ~120mV/decade with negligible degradation. Scaled devices show on-current density of 1-2MA/cm2 below 2V. High on-off current ratio of > 10⁴ is estimated from experiments. The NIPIN shows significant improvements over NPN i.e. sub-2V operation (50% improvement) and non-linearity > 10⁴ (i.e. 2 orders improvement). Perimeter scaling of current due to fringing fields is demonstrated experimentally which improves current density in area scaled devices. Further, the excellent device performance indicates the high quality Si epitaxy grown at sub-520°C that enables low trap density and high in situ dopant activation.