Self-Rectifying Self-Selecting Memory Having Bi-Layer Stacked Dual Functional Material for Logic-in-Memory
Authors: Woo Dae-Seong , Kim Jae-Kyeong , Park Gwang-Ho , Shim Tae-Hun , Park Jinsub , Park Jea-Gun 
Published: December 2024

Recently, a 3D cross-point array (3DXP) consisting of phase-change random-access-memory (PCRAM) and ovonic threshold switching (OTS) selector has been reported as a memory solution for next-generation Compute-Express-Link (CXL) interconnect technology due to nonvolatile characteristics and high scalability1. Neverthless, a 3DXP has been faced limitations in implementing a vertically-stacked high-density memory array due to the high aspect ratio of the serial connection of two devices (i.e., PCRAM and OTS selector) and the thermal disturbance (TDB) problem between adjacent cells by using phase change materials. To oevrcome these limitations, self-selecting memory having polarity-induced threshold voltage (Vth) shift in chalcogenide-based dual functional material (DFM) has been proposed, presenting dual functions of selector and memory2–5. However, several problems should be improved such as the complex composition ratio of DFM, the electroforming process at high voltage, the intrinsic drift phenomenon by atomic rearrangements of pure chalcogenide materials, and the bi-directional current flow in the prograimming process (i.e., set and reset). In addtion, the CPU and GPU overload can be dramatically reduced when combinational logic gates (i.e., 16 Boolean logics) were implemented in the CXL expander via logic-in-memory.
In this study, for the first time, we designed self-rectifying self-selecting memory (SR-SSM) having bi-layer stacked DFM for logic-in-memory. The designed SR-SSM demonstrated abrupt threshold switching at different voltages (i.e., Vth, set of 1.3 V and Vth, reset of 2.0 V) without electroforming-process. The abrupt threshold switching mechanism via the formation of conductive Cu filaments in DFM was proved by measuring the double-sweep DC I-V curves at near-cryogenic temperatures. In addtion, unlike the reported other SSMs, the filamentary switched SR-SSM presented a drift-free property due to the fast rupturing speed of the conductive Cu filaments under 50 ns in DFM. Finally, we implemented all 16 Boolean logic gates via a sequential logic scheme using one or two SR-SSMs. The polarity-induced Vth shift mechanism, electrical perfomance, and logic-in-memory application of the SR-SSM will be presented in detail.

Acknowledgement

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No. RS-2023-00260527) and Institute of Information & communications Technology Planning & Evaluation (IITP) under the artificial intelligence semiconductor support program to nurture the best talents (IITP-(2023)-RS-2023-00253914) grant funded by the Korea government(MSIT).

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