Enhanced Photocurrent in Transparent Lead Zirconate-Titanate Thin Film Capacitors Under Sun Light Illumination L. E. Ocola 1 , Hao Li 1 , K. K. Uprety 1,3 and O. Auciello 1,2 1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 3 present address: PPG Industries, Sylmar, CA 91342 ABSTRACT (Pb)(Zr 0.52 Ti 0.48 )O 3 films were fabricated on LaNiO 3 (LNO)/ In 2 O 3 90%SnO 2 10% (ITO) layered transparent electrodes on glass substrates, using chemical solution deposition. The electrical and optical properties of transparent ITO/LNO/PZT/LNO/ITO capacitors fabricated on glass substrates were studied. The remnant polarization (P r ) of the transparent ITO/LNO/PZT/LNO/ITO/glass capacitors was determined from P-E hysteresis loops measurements. Excellent optical transmittance was observed for the whole capacitor structure. The importance of a high performance transparent capacitor is that this structure may enable a new generation of high efficiency transparent electronic devices such as solar energy storage, photovoltaic, and intelligent windows, among others. INTRODUCTION (Pb)(Zr 0.52 Ti 0.48 )O 3 [PZT] is being extensively researched due to its large field of applications in different devices such as non-volatile ferroelectric random access memories (FeRAMs), transducers, sensors and actuators [1-3]. It is also being studied for applications to nanofluidic and photovoltaic devices [4-6]. High performance transparent capacitors may enable a new generation of transparent electronic devices such as high-efficiency solar energy storage and photovoltaic devices, and intelligent windows. Considerable efforts have been undertaken to grow highly transparent PZT films on glass substrates using indium tin oxide (ITO) layers as bottom electrodes [7-9]. ITO has very low electrical resistivity, high infrared reflectivity, and high UV absorption, which makes it an excellent transparent bottom electrode [10]. At room temperature, ITO has a cubic structure with lattice parameter a = 1.022 nm. This is almost two and half times bigger than that of PZT (a ~ 0.404 nm), producing a large lattice mismatch between PZT and ITO [10, 11]. Conductive metallic electrodes such as SrRuO 3 (SRO) and LaNiO 3 (LNO) have been studied for growing PZT films with good crystalline textures and excellent polarization [12, 13]. The oxide electrodes have also been reported to reduce fatigue and reduce leakage current density [13]. LNO, like PZT, has a perovskite pseudo cubic structure with a lattice parameter of 0.386 nm, which is close to that of PZT (0.404 nm) [11]. Studies performed on the LNO vs ITO electrode layer indicate that the thickness of the LNO layer on a glass substrate must exceed 200 nm in order to achieve good electrical conductivity. However, a 200 nm thick LNO layer is non-transparent. On the other hand, ITO layers are highly transparent even when they are relatively thick. PZT films grown directly on ITO layers are highly transparent, but exhibit low crystallinity and preferential orientation, in large extent due to the large lattice miss match between PZT and ITO, resulting in low remnant polarization. The solution is then to use a thin transparent layer of LNO as a buffer layer between PZT and ITO. This paper focuses on a report of the optical and electrical properties of transparent PZT capacitors with layered LNO/ITO electrodes on glass substrates using a chemical solution deposition (CSD) technique. Structural data on these capacitors has been published elsewhere [6]. EXPERIMENTAL The solution for the growth of LNO films was prepared using lanthanum nitrate hexahydrate (Strem 99.999%) and nickel acetate tetrahydrate (Aldric 99.998%) as precursor materials along with 2-methoxyethanol [2MOE] (Aldric 99.9 %) as a solvent. The powders were dissolved in the solvent by heating and stirring in a flask. The solution was then transferred to a container using a 0.2μm filter. Commercially available ITO coated glass from Delta Technologies (1” x 1” with thickness 200 nm) was used as a substrate. Prior to deposition of LNO, the glass substrates were cleaned with acetone and methanol. The LNO layer (40 nm thick) was deposited by spin coating at a speed of 3000 rpm for 30 seconds. The wet film was pyrolized immediately in air at 450 o C for 15 min and final crystallization of the pyrolized film was achieved by annealing in air at 650 o C for 20 min. The PZT solution was prepared using lead (II) acetate trihydrate (Aldric 99%), zirconium (IV) propoxide (Aldrich 97%) and titanium (IV) isopropoxide (Aldric 99.9 %) as precursor materials and 2MOE as a solvent. The molar ratio Zr/Ti was kept at 52/48 and 20% excess Pb was used to compensate for the loss of Pb from the film due to volatile PbO during annealing. The zirconium (IV) propoxide powder was mixed with 2MOE in a flask by stirring. The titanium (IV) isopropoxide was then added to the above solution and stirred. Finally, the lead (II) acetate trihydrate 105 Clean Technology 2008, www.ct-si.org, ISBN 978-1-4200-8502-0