Side Gate Field Effect Devices on Correlated Oxides by AFM Nanolithography

Charge induction by field effect devices on correlated oxides is of particular interest for smart applications and basic science. Contrary to conventional semiconductors, oxide materials present a broad spectrum of physical properties that are affected by their charge density. Due to the relative high value of charge density of oxides compounds, high polarization dielectric barriers are strictly required for observing detectable modulations. Anyway, thin film dielectric barriers often present low values of the breakdown voltage and of the dielectric constant. The exploitation of high-K oxides, such as SrTiO3 (STO), as substrates and dielectric elements is thus a simple and effective approach to increase dielectric performances. The advantage of the side gate geometry is to combine the best dielectric properties of single crystals substrates with the opportunity to apply very strong electric fields with low voltages (0V - 100 V), being the electric field magnitude approximately equal to the voltage divided by the barrier width. The width of the side gate barriers can be varied from micrometers down to about 100 nm, depending on the patterning technique. Micrometric devices are realized by conventional optical lithography, while submicrometric devices are fabricated by applying Local Anodic Oxidation technique through an Atomic Force Microscope (AFM) [1]. This technique consists in producing localized chemical reactions at nanoscale by simply applying a negative voltage to the tip of the AFM. If operating in air, a nanometer-size water meniscus grows under the tip and acts as a source for oxyanions that activate reactions of chemical decomposition, as evidenced by the formation of mounds at the surface. The overgrown features can be selectively removed by wet etching leaving corresponding grooves down to the substrate, thus allowing the fabrication of submicrometric side gate field effect devices and nanochannels. We present a comparative study of field effect experiments performed on functional oxides by using side gate planar geometries. SrTiO3 [1], (La,Ba/Sr)MnO3 [2] and ZnO [3] epitaxial thin films with different dopants have been deposited by Pulsed Laser Deposition on High-K substrates such as SrTiO3 single crystals. Electrical characterizations at low temperature show that magnetism and transport properties of these oxides can be efficiently modulated by electric fields. [1] L. Pellegrino, I. Pallecchi, D. Marré, E. Bellingeri, and A. S. Siri Appl. Phys. Lett. 81, 3849 (2002) [2] I. Pallecchi, L. Pellegrino, E. Bellingeri, A. S. Siri, and D. Marré Physical Review B 71 014406 (2005) [3] E. Bellingeri, D. Marré, I. Pallecchi, L. Pellegrino, G. Canu and A.S. Siri Thin Solid Films, 486, 186-190 (2005)