Three-Dimensional $\hbox {4F}^{2}$ ReRAM With Vertical BJT Driver by CMOS Logic Compatible Process

A new 3-D vertical bipolar junction transistor (BJT) resistive-switching memory (ReRAM) cell with complimentary metal-oxide-semiconductor-compatible process has been demonstrated and characterized. A new logic-compatible BJT is vertically formed underneath the resistive stacked film of TiN/Ti/HfO₂/TiN as a high-performance current driver and bit-cell selector. Using a shallow and tiny N-type lightly doped drain to be an emitter connects with ReRAM film as the bitline, a very thin and self-aligned P-pocket implant layer to be the wordline, and the N-well is the collector of the cells. As a result, the new 3-D ReRAM cell is very area saving and efficiently operated by the high-gain (β >; 50) BJT at a low voltage of 2 V for reset and 1.5 V for set. By adapting the highly shrinkable 3-D BJT current driver in ReRAM, the ReRAM is fully decoupled with the gate length and oxide thickness of logic metal-oxide-semiconductor field-effect transistors; furthermore, it can easily be scaled down to 4F² under the lithographic limitation of defining ReRAM film with F² area.