Moisture Effect on the Threshold Switching of TOPO-Stabilized Sub-10 nm HfO₂ Nanocrystals in Nanoscale Devices

Abstract

The enduring demand for ever-increasing storage capacities inspires the development of new few nanometer-sized, high-performance memory devices. In this work, tri-n-octylphosphine oxide (TOPO)-stabilized sub-10 nm monoclinic HfO2 nanocrystals (NC) with a rod-like and spherical shape are synthesized and used to build up microscale and nanoscale test devices. The electrical characterization of these devices studied by cyclic current–voltage measurements reveals a redox-like behavior in ambient atmosphere and volatile threshold switching in vacuum. By employing a thorough spectroscopic and surface analysis (FT-IR and NMR spectroscopy and XPS), the origin of this behavior was elucidated. While the redox behavior is enabled by residual moisture present during clean-up of the NC and thin film preparation, which leads to a partial desorption of TOPO from the NC surface, threshold switching is obtained for dry TOPO-stabilized HfO2 NC in microchannel as well as in nanoelectrode devices addressing only a few sub-10 nm TOPO-stabilized HfO2 NC. The results show that integration of sub-10 nm HfO2 NC in nanoscale devices is feasible to build up switching elements.

Tailoring of Colloidal HfO2 Nanocrystals with Unique Morphologies and New Self‐Assembly Features

“…[ 14 ] Meanwhile, HfO 2 has also attracted high attention for nonvolatile high‐density memory technologies as well as for neuromorphic devices, which is comprehensively been summarized in a very recent review article by Banerjee et al [ 15 ] Beyond this, Wang et al as well as our group have explored the application of self‐assembling HfO 2 nanocrystals for volatile as well as non‐volatile resistive switching, which may further expand the technological impact of HfO 2 . [ 16,17 ]…”

“…well as non-volatile resistive switching, which may further expand the technological impact of HfO 2 . [16,17] By now, several methods have been applied to chemically synthesize monoclinic or cubic HfO 2 nanocrystals with different sizes. [18][19][20][21][22][23][24][25][26][27][28][29][30] Typical high-boiling solvents in non-aqueous syntheses are benzyl alcohol, benzylamine, and oleylamine.…”

From Gel to Crystal: Mechanism of HfO2 and ZrO2 Nanocrystal Synthesis in Benzyl Alcohol

“…Hafnium oxide nanocrystals are particularly interesting since they are relevant for memory devices, − as X-ray CT contrast agents, − for scintillators, ,, for catalysis, or for radiotherapy . While HfO 2 can be synthesized in benzyl alcohol from HfCl 4 in a pressure bomb (autoclave), the reaction can also be performed in a microwave reactor, considerably shortening the reaction time to 3–4 h .…”

Epitaxial Core/Shell Nanocrystals of (Europium-Doped) zirconia and hafnia

“…1 Colloidal ZrO2 NCs are components for (in)organic composites [2][3][4] while HfO2 NCs find applications in memory devices. 5,6 Due to the high atomic number of hafnium and the high density of hafnia, HfO2 NCs are developed as CT contrast agents, [7][8][9] scintillators, 10 and as radiation therapy enhancers. [11][12][13] Both ZrO2 and HfO2 NCs serve as hosts for optically active lanthanide ions, e.g, europium.…”