Effect of Ohmic Contacts on Polysilicon Memory Effect

Abstract

AbstractPolysilicon memory switching is demonstrated in vertical n-i-p diodes with TiN contacts and feature size 150 nm. An increase of more than three orders of magnitude forward current at +2 V is achieved after the application of a +8 V programming pulse. The programming pulse electro thermally melts the polysilicon through Joule heating, and the quenched diodes have higher forward current. By changing one of the contacts from TiN to TiSi2, polysilicon memory switching is eliminated, with high forward current in the diode before and after a programming pulse. The TiSi2 contact seeds the crystallization of polysilicon with fewer defects during fabrication, compared to crystallization with TiN-only contacts, as shown by transmission electron microscopy. The mechanisms for increased forward current induced by either programming the TiN-only contacted diodes or making one contact TiSi2 are discussed.