Investigation of RF Sputtered Calcium Copper Titanate Thin Films and Nanorods for Gate Dielectric and Memory Applications

Abstract

Oxide thin films, exhibiting high dielectric constant, have drawn great deal of attention for the replacement of SiO2. In view of miniaturization, the monolithic integration of one-transistor one-resistor (1T-1R) design paves a way for the fabrication of robust electronic devices for signal processing and data storage. Calcium copper titanate (CCTO), a cubic perovskite oxide material have drawn a great deal of interest due to its interesting dielectric behavior. It shows an enormous dielectric constant of 104 at 1 MHz frequency with negligible temperature dependence in the range of 100 K to 600 K. Due to the excellent material properties, CCTO is considered as the potential dielectric material for super capacitors, gas sensors, resonators, varistors and memory devices. However, the fabrication of futuristic portable devices demands the use of advanced materials in the form of thin films and nanostructures on silicon substrate. Therefore, a systematic investigation on the processing of CCTO thin films is required as the deposition techniques, deposition parameters and the post deposition treatments strongly affects the morphological and electrical properties of thin films.
CCTO thin films were deposited by RF sputtering method. A 2 inch diameter sputtering target has been fabricated by adopting solid state route, prior to the film deposition. The effect of sputtering parameters such as RF power and deposition pressure on the structural,morphological and electrical properties were investigated. The effect of three different types of post-deposition annealing techniques namely; conventional, rapid thermal and sequential annealing on the properties of CCTO thin films were studied. For improvement of interface and morphological properties, an additional HfO2 buffer layer was used. The structural, electrical properties were studied with the variation of buffer layer thickness. To improve the dielectric properties, Zn incorporated CCTO multilayers were fabricated with various configuration. Moreover, the combined effect of buffer and intermediate layers was studied using the CCTO/Zn/CCTO/HfO2/Si configuration. The dielectric constant, oxide charge density and interface charge density of all the CCTO thin films were estimated from capacitance-voltage (C-V) measurements. Resistive switching behavior of CCTO thin film with different processing parameters were investigated by fabricating metal insulator metal(MIM) structure. The continuous rise in current was observed during the sweep of bias voltage for conventionally annealed films due to the formation of interfacial carriers. The rapid rise in current during set operation is observed as a result of rapid thermal annealing. The switching behavior of the MIM capacitors was explained by the formation and rupture of conducting filaments. The rapid rise in current during set operation with enhanced current on/off ratio has been observed as a result of insertion of Zn intermediate layer.