DEPOSITION OF VANADIUM DIOXIDE THIN FILM BY USING THERMAL ATOMIC LAYER DEPOSITION WITH WATER REACTANT

Abstract

Due to its fast switching speed, fine endurance, and low power consumption, resistance random access memory (ReRAM) has positive prospect for next generation non-volatile memory. Moreover, as small as ideal 4F2 (where F is the minimum realizable cell size) memory cell size is possible when ReRAM device has cross-point array-type. However, cross-point array-type ReRAM device has sneak-path current which is undesired leakage current entering the circuit. In case of bipolar ReRAM device, in contrast with unipolar ReRAM device, there is no proper solution to solve the leakage current. It is need to find out appropriate selection device for cross-point array-type bipolar ReRAM device because it has fine memory properties. Pr0.7Ca0.3MnO3, Cr-doped SrZrO3, and TiO2 is candidates of transition metal oxide switching materials. Among these candidates, vanadium dioxide (VO2) shows first-order metal insulator transition (MIT) at 68℃. Below 68 ℃, crystal structure of VO2 is distorted rutile (monoclinic) structure. It encounters phase change from distorted rutile to undistorted rutile structure (tetragonal) when VO2 receives energy such as heat or light. This MIT characteristic has many advantages such as high ON/OFF ratio, stable switching operation, and high current density. There are some of the methods of depositing VO2 thin film such as sputtering, sol-gel method, and chemical vapor deposition (CVD). However, it is hard to deposit the film uniformly in 3D device, and make complex structure. Thus, atomic layer deposition (ALD) gets an interest to deposit DRAM and other non-volatile memories. Furthermore, ALD can control the thickness of the thin film to the atomic level accurately. However, it is difficult to establish the ALD process to make monoclinic VO2 phase because the deposition temperature of ALD is lower than that of CVD. Vanadium oxide film deposited by ALD usually has V2O5 structure because the phase of V2O5 is shown at low temperature. VO2 is appeared when deposited at high temperature. ALD makes oxygen rich vanadium oxide thin film. At the complex V-O system, diverse vanadium oxide phases with different crystal structures like V2O5 and tetragonal VO2 phases exist. In this paper, we demonstrate the deposition of a nanoscale VO2 thin film using ALD with H2O reactant. First of all, we investigate X-ray diffraction peak of thin film to show stoichiometric monoclinic VO2. We use scanning electron microscope to figure out the thickness and uniformity of VO2 thin film. Also, using X-ray photoelectron spectroscopy, we investigate binding energy of VO2. Lastly, we probe electrical properties of VO2 using current voltage analysis.