A 4T2R RRAM Bit Cell for Highly Parallel Ternary Content Addressable Memory

In this work, we present a four-transistor-two-resistor (4T2R) ternary content addressable memory (TCAM) bit cell based on the resistive memory (RRAM), comprising the conventional two-transistor-two-resistor (2T2R) cell with two additional comparison transistors. It can effectively amplify the match-line signal ratio (ML-ratio), lower the leakage current of the match cell ( ${I}_{{\mathrm {MATCH}}}$ ), and suppress the read disturbance. The proposed concept is silicon verified using the 180 nm CMOS technology with transition-metal-oxide (TMO) RRAM integrated at the back-end-of-line (BEOL). It achieves a considerable ML-ratio of 1860 and a low ${I}_{{\mathrm {MATCH}}}$ of 11.15 nA on average. In a typical search operation, it shows a negligible ML drop at the match case and a large ML swing range at the mismatch case. The SPICE simulation results further show it can support a long word-length (WDL) of 256 under a clock rate of 100 MHz for search operations, which demonstrates its promise for highly parallel nonvolatile TCAM.