3‐Masks‐Processed Sub‐100 nm Amorphous InGaZnO Thin‐Film Transistors for Monolithic 3D Capacitor‐Less Dynamic Random Access Memories

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AbstractThe capacitor–less embedded dynamic random access memory (eDRAM) based on oxide semiconductor (OS) transistors exhibits a promising future and thus has lead to a growing demand for nanoscale OS thin–film transistors (TFTs). In this work, a self–aligned top–gate (SATG) amorphous InGaZnO (a‐IGZO) TFT is demonstrated by using the simplest 3‐masks (3M) process, and the downscaling‐related issues are carefully addressed to strengthen its back–end–of–line (BEOL) compatibility and mass producibility. The gate insulator (GI) and associated interface defects of the TFTs are jointly optimized with 4–nm atomic‐layer‐deposited (ALD) AlOx on the pre‐oxidized a‐IGZO. The defects in a‐IGZO channel are further manipulated with a rapid thermal anneal (RTA) in oxygen. By virtue of the strengthened gate controllability and modified channel properties, the fabricated TFT with 97‐nm gate length (Lg) exhibits decent performance, such as a maximum on–state current (ION) of 32.4 µA µm−1, as well as clear linear and saturation characteristics. Based on such 3M SATG a‐IGZO TFTs with high device performance and inherently minimal parasitic capacitances, the developed capacitor‐less eDRAM bit cell achieves a wide sensing margin and a long retention time of over 500 s. A highly manufacturable oxide TFT technology for high–performance and high–density monolithic–3D (M3D) integration is thus well established.