Capacitorless Dynamic Random Access Memory with 2D Transistors by One-Step Transfer of van der Waals Dielectrics and Electrodes

Abstract

Dynamic random access memory (DRAM) has been a cornerstone of modern computing, but it faces challenges as technology scales down, particularly due to the mismatch between reduced storage capacitance and increasing OFF current. The capacitorless 2T0C DRAM architecture is recognized for its potential to offer superior area efficiency and reduced refresh rate requirements by eliminating the traditional capacitor. The exploration of two-dimensional (2D) materials further enhances scaling possibilities, though the absence of dangling bonds complicates the deposition of high-quality dielectrics. Here, we present a hexagonal boron nitride (h-BN)-assisted process for one-step transfer of van der Waals dielectrics and electrodes in 2D transistors with clean interfaces. The transferred aluminum oxide (Al₂O₃), formed by oxidizing aluminum (Al), exhibits exceptional flatness and uniformity, preserving the intrinsic properties of the 2D semiconductors without introducing doping effects. The MoS₂ transistor exhibits an extremely low interface trap density of about 3 × 10¹¹ cm^–2 eV^–1 and a leakage current density down to 10^–7 A cm^–2, which enables effective charge storage at the gate stack. This method allows for the simultaneous fabrication of two damage-free MoS₂ transistors to form a capacitorless 2T0C DRAM cell, enhancing compatibility with 2D materials. The ultralow leakage current optimizes data retention and power efficiency. The fabricated 2T0C DRAM exhibits a rapid write speed of 20 ns, long data retention exceeding 1,000 s, and low energy consumption of approximately 0.2 fJ per write operation. Additionally, it demonstrates 3-bit storage capability and exceptional stability across numerous write/erase cycles.