Threshold Switch Assisted Memristive Memory with Enhanced Read Distinguishability

We present a technique to improve the distinguishability of the stored memory states in a memristive (resistive) random-access memory (ReRAM) cell, utilizing controlled phase transitions in an augmented threshold switch (TS). Oxide memristors exhibit significant device-to-device and cycle-to-cycle variations between the low and high resistive states. This leads to degraded distinguishability during the read operation and makes it challenging to design sense amplifiers. To circumvent this major issue, here we propose to augment volatile threshold switches with the ReRAM cell and trigger selective phase transitions to enhance the overall cell resistance ratio. We first analyze the biasing constraints to successfully implement our technique in a memristive memory cell. We keep the TS in the metallic state during write operations. Whereas for read operations, we ensure that the TS remains in the insulating (metallic) state when the memristor in the ReRAM is in high (low) resistance state. With proper co-design, our technique can improve the read current ratio and sense margin of conventional ReRAM cells by up to
$\sim 10\mathbf{X}$
and
$\sim 5\mathbf{X}$
(respectively), with iso-cell area. Our approach has negligible impact on the write performance, contingent upon the appropriate choice of TS and memristor pair.