Relaxation Behavior and Breakdown Mechanisms of Nanocrystals Embedded Zr-doped HfO2 High-k Thin Films for Nonvolatile Me
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1071-F02-09
Relaxation Behavior and Breakdown Mechanisms of Nanocrystals Embedded Zr-doped HfO2 High-k Thin Films for Nonvolatile Memories Chia-Han Yang1,2, Yue Kuo1, Chen-Han Lin1, Rui Wan2, and Way Kuo2 1 Texas A&M University, College Station, TX, 77843-3122 2 University of Tennessee, Knoxville, TN, 37996 ABSTRACT Semiconducting or metallic nanocrystals embedded high-k films have been investigated. They showed promising nonvolatile memory characteristics, such as low leakage currents, large charge storage capacities, and long retention times. Reliability of four different kinds of nanocrystals, i.e., nc- Ru, -ITO, -Si and -ZnO, embedded Zr-doped HfO2 high-k dielectrics have been studied. All of them have higher relaxation currents than the non-embedded high-k film has. The decay rate of the relaxation current is in the order of nc-ZnO > nc-ITO > nc-Si > nc-Ru. When the relaxation currents of the nanocrystals embedded samples were fitted to the Curie-von Schweidler law, the n values were between 0.54 and 0.77, which are much lower than that of the non embedded high-k sample. The nanocrystals retain charges in two different states, i.e., deeply and loosely trapped. The ratio of these two types of charges was estimated. The charge storage capacity and holding strength are strongly influenced by the type of material of the embedded nanocrystals. The nc-ZnO embedded film holds trapped charges longer than other embedded films do. The ramp-relax result indicates that the breakdown of the embedded film came from the breakdown of the bulk high-k film. The type of nanocrystal material influences the breakdown strength. INTRODUCTION SiO2 has been used as a gate oxide material in ULSIC for decades. As the minimum device dimension is scaled down from 3.5 nm to 1.5 nm, the leakage current of SiO2 (at a gate bias of 1V) increases drastically from 10-12 A/cm2 to 10 A/cm2 due to quantum-mechanical tunneling [1]. There are many studies on replacing SiO2 with high-permittivity (high-k) materials (e.g., Si3N4, HfSixOy, HfO2, ZrO2) for better device performance and reliability [2]. One of the most promising high-k material applications is the high-density nonvolatile memory [3]. For the conventional poly-Si floating gate memory, any point defect in the tunnel dielectric layer can create a leakage channel to drain the stored charges to the substrate. This kind of defect path can be verified using the stress-induced leakage current experiment [5]. When the continuous poly-Si layer is replaced with nanocrystals, the above problem can be avoided [6]-[8]. In this kind of structure, discrete nanocrystalline nodes, isolated from each other by the surrounding dielectric material, can enhance the electrons or/and holes trapping capacity [3] and [4]. In early studies, nc-Si was used as the charge-storage media. Recently, various nc-metals, -metal oxides, and semiconductors have been popular for many advantages, such as the lower power consumption, better scalability and many choices of work functions [9] and [10]. There are reports of embeddin
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