Growth, Characterization and Electrical Properties of PZT thin Film Heterostructures on Silicon by Pulsed Laser Depositi
- PDF / 1,977,741 Bytes
- 6 Pages / 391.5 x 607.5 pts Page_size
- 95 Downloads / 222 Views
the intermediate layers. The growth conditions have been optimized so as to obtain perfect epilayers for each of the compounds. The films have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and were found to possess good electrical properties. EXPERIMENTAL The composition of PZT that has been used is Pb(Zr0. 52Ti0.48)O 3 since the composition near the morphotropic phase boundary has been known to exhibit good ferroelectric properties [11]. The films were grown by PLD. A KrF excimer laser (Lambda Physik) was operated at 248 nm for the purpose of ablation. During all ablation experiments, the laser pulse width was 25 ns and the pulse repetition rate was 10 Hz for all the compounds. The Si substrates were cleaned with acetone and methanol for 15 min each, by ultrasonication and were then dipped in 10% HF for a minute. They were mounted on a heater block parallel to the target at a distance of 5.0 cm. The targets of TiN, MgO, STO, SRO and PZT were 99.9% pure and stoichiometric. The substrate temperature was controlled to within ±5°C with a Eurotherm temperature controller. The laser beam was scanned over the target by mounting it on a stepper motor controlled scanner to prevent local heating. Ablation was carried out in vacuum for TiN and in oxygen partial pressures for the other oxides. An oxygen rich atmosphere was maintained in the chamber (240 mTorr) to obtain proper stoichiometry for the SRO and PZT films and at the end of each run the chamber was flooded with oxygen and then the films were cooled slowly. After the deposition of SRO, the films were covered at the corner with a piece of silicon to expose the bottom electrode. The growth conditions for each of the films were optimized with respect to: (a) substrate temperature, (b) substrate- target distance, (c) oxygen pressure inside the chamber, (d) pulse repetition rate and (e) the laser pulse energy. The crystallinity and the phase purity of the films were checked by a Rigaku X-ray diffractometer. Rocking curves of the (001) reflection of PZT were carried out to estimate the quality of the film. The microstructure of the different epilayers in the film was studied by TEM. Silver electrodes of 200 prm diameter were deposited on top of PZT by electron beam evaporation to serve as the top electrode and SRO was used as the bottom electrode. The thickness of the silver dots was 150 nm. Dielectric hysteresis behavior was studied using a Radiant Technology RT66A loop tracer. The capacitance and the loss tangent of the films were measured at 100 kHz and at a oscillation voltage of 1 volt using a HP 4192A LCZ meter in a standard parallel plate geometry. RESULTS AND DISCUSSIONS Growth and Microstructure Figure 1 shows the XRD pattern of the five layered film deposited on silicon. The film is free from impurity phases that occur due to reactions at the interfaces and shows perfect (001) orientation. XRD pattern was noted for each of the films after the deposition. The optimized growth parameters for each of the epilayers have been
Data Loading...
