A Bipolar Rram Selector With Designable Polarity Dependent On-Voltage Asymmetry

Bipolar RRAM memory cells show different extents of asymmetry in set/reset voltages. Recently, our group has demonstrated a symmetric Si epitaxy based 4F(2) punch-through diode based NPN selector. Here, we demonstrate that a modification of the doping profile of the NPN diode selector produces designable asymmetry in the I-V characteristics. We demonstrate based on a TCAD study that replacing the uniform p region in the symmetric NPN structure by an asymmetric p/p-bilayer could lead to an asymmetry in the turn-on voltage vertical bar Von+vertical bar/vertical bar Von-vertical bar by a factor of similar to 1:2. Our calculations show that the on-current ( few mu A at 20nm technology node or >1MA/cm(2)) and on-voltage asymmetry control is adequate for various promising bipolar RRAM memory elements from literature. Finally, the on-voltage asymmetry control is experimentally demonstrated based on a low temperature (<700 degrees C) Si epitaxy process; the measured asymmetry in the new experimental devices is about vertical bar Von+vertical bar/vertical bar V-on-vertical bar =1:2.1 compared to the a vertical bar Von+vertical bar/vertical bar Von-vertical bar=1:1.2 in the symmetric devices.