Growth of high-density Ir nanocrystals by atomic layer deposition for nonvolatile nanocrystal memory applications

Abstract

A careful investigation is made of the growth of Ir nanocrystals (NCs) on Al2O3 by atomic layer deposition (ALD), and a charge trapping memory device using ALD-grown Ir NCs as the charge trapping layer and ALD-grown Al2O3/HfO2 as the tunneling/blocking layers is fabricated. It is found that the ex situ nucleation of Ir NCs on ALD-grown Al2O3 is difficult, though in situ growth can produce pure metallic Ir NCs with a face-centered cubic crystalline phase directly on ALD-grown Al2O3 at the initial growth stage, which follows the nucleation incubation model. The growth of these metallic Ir NCs is attributed to the presence of a uniform coverage of reactive groups (hydroxyl or dimethylaluminum) on the as-deposited fresh ALD-grown Al2O3 surface, which greatly promotes the uniform nucleation of Ir. Electrical measurements of p-Si/Al2O3/Ir NCs/HfO2 memory cells exhibit a large memory window of 4.2 V at the sweeping gate voltage of ±10 V, and a ∼76% retention property after 104 s at 75 °C. Also, a stable memory window of ∼2 V is achieved during the first 105 program/erase cycles under a ±10 V/10 ms program/erase operation. In situ ALD-grown Ir NCs with the highest density of 0.6 × 1012/cm2 provide a potential approach to fabricate large-area high-density NCs for future ultrahigh-density nonvolatile NC memory applications.