Leakage Current Behavior in CaZrO 3 Thin Films for High- k Applications
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Leakage Current Behavior in CaZrO3 Thin Films for High-k Applications Ting Yu, Weiguang Zhu, Xiaofeng Chen, Yuekang Lu Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 ABSTRACT
Electrical properties and leakage current mechanisms of perovskite CaZrO3 dielectric thin films have been studied in this paper. CaZrO3 thin films were deposited on Pt/SiO2/n-Si substrate by the sol-gel wet chemical technology, and then annealed at temperatures ranging from 550 to 700 ºC for 1h in O2. The films with platinum (Pt) top and bottom electrodes were characterized with respect to the leakage current as a function of temperature and applied voltage. The CaZrO3 film annealed at 600 °C was amorphous and showed good electrical properties with a dielectric constant of about 15 and leakage current density of 10-8 A/cm2 at high applied electrical field of 2.5 MV/cm. The data can be interpreted via a Schottky barrier model. The conduction mechanism at low electric fields is due to Ohmic conduction. On the other hand Schottky mechanism dominates at the intermediate fields. The high dielectric constant, low leakage current density and high breakdown strength suggest that the CaZrO3 thin film is a promising candidate for high-k applications.
INTRODUCTION
With the rapid reduction in the dielectric thickness, numerous difficulties have been faced in CMOS technology regarding their growth, integration and the reliability. One of the most fundamental restrictions to scaling of CMOS structures is the gate leakage current. As silicon dioxide becomes thinner, the gate leakage current through the film increases exponentially. For silicon dioxide at a gate bias of ~1V, the leakage current density changes from 1×10-12 A/cm2 at ~35 Å to 1×10 A/cm2 at ~15 Å: thirteen orders of magnitude change in current for a thickness change of little more than a factor of 2 [1]. The material properties of alternative higher-k dielectrics have therefore attracted increasing attention. Metal-oxides with high dielectric constants have the potential to extend scaling of transistor gate capacitance beyond that of silicon dioxide. Many materials such as Al2O3 [2], ZrO2 [3], HfO2 [4] and SrTiO3 [5] etc have been investigated to replace silicon dioxide as possible gate dielectrics. Perovskite oxides have received great attention recently as high-temperature proton conductors [6, 7]. Alkaline-earth zirconates (such as CaZrO3 and SrZrO3) are in general chemically stable and have high dielectric constant. Their perovskite structure, high-temperature properties and high dielectric constant make them promising candidates to serve as a gate material. In this article, the leakage current behaviors in Pt/CaZrO3/Pt capacitors prepared by
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using the sol-gel technology are reported. We will examine both the field and temperature dependence of the leakage of CaZrO3 films, and the mechanisms on leakage current are therefore discussed.
EXPERIMENTAL DETAILS
CaZrO3 thin films were deposited on
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