Epitaxial Transition Metal Oxide Nanostructures Fabricated by a Combination of AFM Lithography and Molybdenum Lift‐Off

Abstract

In recent years, transition metal oxide films have attracted much research interest because of their remarkable physical properties such as ferroelectricity, ferromagnetism, high T c superconductivity, and colossal magnetoresistance. These useful characteristics make oxide films potential candidates for novel functional devices. For example, great advances have been made in the application of half-metallic oxide materials in magnetic random access memory (MRAM) [1] with a large tunneling magnetoresistance (TMR) ratio. [2,3] Nanostructures of half-metal magnetic oxides are especially of interest for the current-driven magnetization reversal of TMR devices. Ferroelectric oxides provide another example of a useful oxide material with superior properties for non-volatile data storage (Fe-RAM). Obtaining nanostructures of these materials is of paramount importance for realizing a highly integrated Fe-RAM device. The controlled nanofabrication of metal oxides is also important for the investigation of novel nanoscale properties. For example, Yanagisawa et al. [4] have recently demonstrated that the resistivity of a ca. 500 nm wide perovskite (La, Pr, Ca)MnO 3 channel structure rapidly falls off over three orders of magnitude upon the application of a magnetic field, which is very different from the behavior of a large-area thin film. These authors have suggested that (La, Pr, Ca)MnO 3 with a strongly correlated electron system forms an electrical multidomain structure with a grain size of several hundreds of nanometers; as the width of the oxide nanochannel is reduced to the dimensions of the domain size, a single ferromagnetic metal domain in the channel acts as a gate by transforming itself into a charge-ordered insulator.Further discoveries of such novel properties of transition metal oxides are expected upon scaling them down to nanoscale dimensions. Nevertheless, not much progress has been achieved in this area. One of the reasons for this is that the fine fabrication of oxide films with nanoscale control still remains remarkably challenging. At this moment, the lower limit for the fine fabrication of oxides using photolithography is only ca. 1 lm, notwithstanding the remarkable advances in processing silicon surfaces with better than 100 nm resolution.Recently, there have been several reports in the literature dealing with the nanofabrication of transition metal oxides using top-down approaches such as focused ion beam (FIB) lithography, [5][6][7] atomic force microscopy (AFM) lithography, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and electron-beam (e-beam) lithography. [19,20] These methods have been used to achieve feature sizes less than ca. 100 nm. However, each of these top-down methods suffers from some serious drawback. For example, FIB and AFM lithography are suitable for making holes and grooves in selected regions within an oxide film, but are not as useful for defining isolated oxide islands and lines, because such patterns need to be defined by removing all sections of the film that resid...

Epitaxial Nanodot Arrays of Transition‐Metal Oxides Fabricated by Dry Deposition Combined with a Nanoimprint‐Lithography‐Based Molybdenum Lift‐Off Technique

“…Moreover, various artificial lattices, which cannot be fabricated by the sol-gel method, can be fabricated by dry deposition methods. However, simple combination of a dry deposition method with an organic resist mask patterned by the EB method is not feasible, because dry deposition of epitaxial oxide film is usually performed at temperatures as high as several hundred degrees Celsius, which leads to serious damage of the polymer resists.In the present study, we fabricated a large-area nanodot array of Fe 2.5 Mn 0.5 O 4 (FMO) by a combination of PLD, NIL, and the Mo lift-off technique, [30] which can overcome this difficulty. In our previous report on the Mo lift-off technique, Mo nanomasks were processed by AFM lithography, and the masks were used as the resists for the lift-off process instead of polymer resists.…”

Epitaxial Growth of Oxide Films and Nanostructures

“…The high etch selectivity between Mo and MoO 3 enables a simple, reproducible, and versatile lithography technique that may find wide use in laboratories equipped with an AFM for patterning various materials with w30-nm resolution. A spinel ferrite (Fe,Mn) 3 O 4 film was deposited onto the Mo nano-template at 340 C. The Mo nano-template was stable at that temperature, and about 150-nm (Fe,Mn) 3 O 4 nanolines were successfully made after removing the Mo nano-template [97]. deposition process, and the resulting functional oxide nano-wire structure [96,98].…”

Influence of Gas Ambient on Charge Writing at the LaAlO3/SrTiO3 Heterointerface

“…It has been a long-standing obstacle to realize nanoscale patterning of metal oxides. [24][25][26][27] Etching damage caused by chemical and/or physical attack often severely deteriorates the physical properties of metal oxides. Thus, it is rather difficult to find in-depth studies on size effects and quantum transport in metal oxides.…”