1 Mb 0.41 µm² 2T-2R Cell Nonvolatile TCAM With Two-Bit Encoding and Clocked Self-Referenced Sensing

This work demonstrates the first fabricated 1 Mb nonvolatile TCAM using 2-transistor/2-resistive-storage (2T-2R) cells to achieve >10× smaller cell size than SRAM-based TCAMs at the same technology node. The test chip was designed and fabricated in IBM 90 nm CMOS technology and mushroom phase-change memory (PCM) technology. The primary challenge for enabling reliable array operation with such aggressive cell is presented, namely, severely degraded sensing margin due to significantly lower ON/OFF ratio of resistive memories (~102 for PCM) than that of traditional MOSFETs (>105 ). To address this challenge, two enabling techniques were developed and implemented in hardware: 1) two-bit encoding and 2) a clocked self-referenced sensing scheme (CSRSS). In addition, the two-bit encoding can also improve algorithmic mapping by effectively compressing TCAM entries. The 1 Mb chip demonstrates reliable low voltage search operation (VDDmin ~750 mV) and a match delay of 1.9 ns under nominal operating conditions.