Growth, structural and electrical properties of spin coated LaNiO3 conducting oxide

Homogenous growth, structural and electrical properties of LaNiO3 (LNO) perovskite thin film nanostructures using spin coating technique on quartz substrate has been studied. LNO has been widely used as a conducting bottom electrode for many perovskite oxide based device, such as, ferroelectric memory and micro sensor devices [1]. The advantages of perovskite materials over the simple Pt-based metal bottom electrodes are that, it has improved polarization fatigue, low leakage currents, aging characteristics and crystallographic compatibility with oxides based ferroelectric and recently reported perovskite resistive random-access memory (RRAM) materials [2,3]. Furthermore, oxide based bottom electrodes offers improved non-volatile memory characteristics such as endurance, low voltage consumption, retention cycle [4] etc. Sol gel spin coating technique was used due to its low cost with no requirement of high vacuum chamber, precision and control in the material composition. Commonly, perovskite LNO has been synthesised using organic solvents such as 2-mithoxyethanol with ethanolamine [5,6], acetic acid with deionized water [7] etc. However, LNO synthesized at higher annealing temperatures helps in attaining phase purity and these solvents showcases limitations such as porous film morphology, large pinhole density, higher surface roughness, etc. [1]. Hence, a modified method is employed in chemical deposition process for growth of LNO on quartz substrates. Poly-vinyl alcohol (PVA) being water soluble has excellent adhesion and thus, PVA has been used in the synthesis process. It also helps in the formation of uniform surface films along with the reduction of cracking density while drying [8]. Furthermore, PVA decomposes at 250 and hence there’s no possibility of any remnants left in the final product, as the samples have been annealed at a much higher temperature. The nanostructured growth of LaNiO3 studied using X-ray diffraction confirmed its standard structural property of phase pure cubic perovskite symmetry. Surface morphological measurements were carried out at different spots to understand the uniformity of the sample, along with monodispersed grain distribution by using atomic force microscope (AFM). The RMS roughness of LNO was found to be 7.08 nm as shown in table 1, which incorporates that it can act as an excellent conducting bottom electrode providing brilliant seeding or buffer layer with enhanced nucleation sites [9]. This low surface roughness is an essential quality for the device formation as it influences smooth and crack free texture for the interface between the active layer and the electrode [1]. The presence of poly-vinyl alcohol used as stabilizing agent in the precursor solution may have influenced in the homogenous, smooth and crack free surface morphology of the film. As shown in fig.1, I-V characteristics of LNO demonstrates a small shift in current with the application of low perpendicular magnetic field of 0.58T. Voltage bias in the sequence of 0V → +Vmax → 0V → -Vmax → 0V was applied for the range of -5Vmax to +5Vmax. The variation in the resistance with the application of external magnetic field gives rise to magnetoresistance (MR) in the sample, which was found to be 48.26%. Henceforth, LNO may assist in forming the succeeding ferroelectric or ferromagnetic multilayer cascade, to enhance the I-V curve and further form a device heterostructure.