The Atomic Layer Deposition Technique for the Fabrication of Memristive Devices: Impact of the Precursor on Pre-deposited Stack Materials

Abstract

Atomic layer deposition (ALD) is a standard technique employed to grow thin-filmoxides for a variety of applications. We describe the technique and demonstrate its usefor obtaining memristive devices. The metal/insulator/metal stack is fabricated by meansof ALD-grown HfO2, deposited on top of a highly doped Si substrate with an SiO2 filmand a Ti electrode. Enhanced device capabilities (forming free, self-limiting current,non-crossing hysteretic current-voltage features) are presented and discussed. Carefulanalysis of the stack structure by means of X-ray reflectometry, atomic force microscopy,and secondary ion mass spectroscopy revealed a modification of the device stack fromthe intended sequence, HfO2/Ti/SiO2/Si. Analytical studies unravel an oxidation of the Tilayer which is addressed for the use of the ozone precursor in the HfO2 ALD process. Anew deposition process and the model deduced from impedance measurements supportour hypothesis: the role played by ozone on the previously deposited Ti layer is found todetermine the overall features of the device. Besides, these ALD-tailored multifunctionaldevices exhibit rectification capability and long enough retention time to deserve theiruse as memory cells in a crossbar architecture and multibit approach, envisaging otherpotential applications.