Resistive Switching Behavior and Electrical Properties of TiO 2 :Ho 2 O 3 and HoTiO x Based MIM Capacitors
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Resistive Switching Behavior and Electrical Properties of TiO2:Ho2O3 and HoTiOx Based MIM Capacitors H. García1, H. Castán1, S.Dueñas1, E. Pérez1, L. A. Bailón1, K. Kukli2,3, M. Ritala2 and M. Leskelä2 1 Dpto. Electricidad y Electrónica, E.T.S.I.Telecomunicación, University of Valladolid, 47011 Valladolid, Spain. 2 Department of Chemistry, University of Helsinki, FI-00014 Helsinki, Finland. 3 Institute of Physics, Department of Materials Science, University of Tartu, EE-51014 Tartu, Estonia. ABSTRACT Ho2O3-TiO2 based metal-insulator-metal capacitors were grown by ALD, using Ho(thd)3, Ti(OCH(CH3)2)4 and ozone as precursors. The thicknesses of the films were in the range of 7.7 to 25 nm. Some of the films were post-deposited annealed in order to study the treatment effects. The capacitors were electrically characterized. Leakage current decreases as the amount of holmium increased in the films. Resistive switching behavior was obtained in the samples where the leakage current was low. This effect was also observed in Ho2O3 films, where no titanium was present in the films. INTRODUCTION There is an on-going demand for high speed random access memories with low power consumption and enormous packing density. International Technology Roadmap for Semiconductors (ITRS) [1] summarizes the requirements for future dynamic random access memory (DRAM) capacitors. According to the ITRS 2012 edition, DRAM capacitors for 22 nm and beyond should have an equivalent oxide thickness (EOT) of 0.3 nm or less with a leakage current density < 100 nA/cm2. On the other hand, emerging memory technologies are being studied in order to overcome the limitations of DRAM’s memories, such as high power consumption, write/erase time > 10 ns and being volatile memories. Among more than a dozen of emerging memory technologies based on different concepts, resistive random access memories (RRAMs) are one of the most promising candidates [2,3]. These memories performance is originated from a resistive change rather than a capacitive one. Titanium oxide (TiO2) is one of the candidates for being used as dielectric in metalinsulator-metal (MIM) capacitor for DRAM memories [4]: it has a high permittivity value which can be higher than 100 even in thin films, depending on the crystalline phase. However, the main drawback of this material is its small band gap (≈ 3.2 eV), which makes the suppression of the leakage current difficult. However, when mixing with a higher band gap material, the leakage current can be reduced: Al-doped TiO2 MIM capacitors with an equivalent oxide thickness (EOT) = 0.46 nm and low leakage current have been obtained [5]. TiO2 is also known to present resistive switching phenomena [6]. Holmium oxide (Ho2O3) is a dielectric with a moderate permittivity value (k ≈ 12) and a high band gap (5.3 eV), so it has been studied as gate dielectric of MOSFETs transistors [8,9]. In this work, we study the resistive switching behavior and the electrical characteristics of Ho2O3-TiO2 (HoTiOx) mixtures and Ho2O3-doped TiO2 (TiO2:Ho2O3) based MIM capa
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