Preparation of Devices

In the experiment, the four-layer structure device was fabricated. The preparation flow of device is shown in Fig. 2-2.

2.3.1 Preparation of Sputter Targets

Because the LNO and SZO thin films are deposited by the sputter system, it needs two kinds of disk-shaped sputter targets, including the LNO and the doped SZO powder targets.

I. Synthesis of the LaNiO³ Powder Target

The LNO and SZO targets are prepared by the conventional solid-state powder-mixing method. There are six steps in the synthesis processes. First, two kinds of the oxide powders, La2O3 and NiO, were mixed by the rule of stoichiometry. It should be especially careful of the equivalent mol because

1 mol of the LNO is composed of 0.5 mol of the La2O3 and 1 mol of the NiO. Second, the mixed powder was put into a jar with anhydrous alcohol and rolling glass balls, and then was mixed adequately by a grinder. Third, the mixture was dried by an 85^oC oven. The fourth step was the sintering step. It was the most critical process, because the sintering temperature and the heating time would affect on the LNO qualities including the resistance and orientation of the LNO sputtered films. The dried mixture was put into a furnace to execute a sequence of sintering, 600^oC for 2 hours and 1300^oC for 10 hours. In the fifth step, the mixed powder was put in the beaker and baked it in the oven at 150^oC for 2 hours. Finally, the mixed powder put in the disk-shaped target was squeezed by a high pressure of 2000 pounds for 60 seconds such that a compact target was produced for sputtering work.

The preparation flow of the LNO target was showed in Fig. 2-5.

II. Synthesis of the SrZrO³ Powder Target

The SZO powder was synthesized from two kinds of oxide powder, SrCO3 and ZrO2. In order to substitute Zr atom, it was considered the suitable ionicradius compared with Zr atom. Considering all the conditions, transition metaloxide V2O5 was added to form the doped SZO powder.

Because V has freakyoxidation number, it could show more effect on the electric properties of our memory thin films. For example, when it is expected to synthesize 0.2 mol% V-dopedSZO powder, it should use 1 mol of SrCO3, 0.997 mol of ZrO2, and 0.00075mol of V2O5. After mixing above elements of the doped SZO powder, the same steps were followed as synthesis of LNO powder. The mixed powder was put into a furnace of a sequence of sintering process. In the last step, a disk-shaped target was

made by a high pressure of 2000 pounds for 1 min.The manufacturing process was showed in Fig. 2-5. In this study, we prepared pure (undoped), 0.1%, 0.2%, 0.3% and 0.4% V-doped SZO powder.

2.3.2 Thin Film Depositions

The LNO bottom electrode and the doped SZO films were deposited by RF magnetron sputter sequentially. To meet our demands for different process recipe, several parameters were controlled to deposit the films based on the plasma theorem and the models of the thin film growth. There were many parameters including the chamber pressure, the RF power, the working temperature, the ambient conditions, and the deposition time. In general, chamber pressure affected the mean free path (MFP) of plasma which is relative to the deposition rate. The lower pressure was choice to create the larger MFP in the chamber, which leads to the higher deposition rate. Moreover, the deposition rate is dependent on the RF power as well. In the experiment, while depositing both the LNO and doped SZO films, the RF power was set 100 or 150W and the chamber pressure at 10 mTorr. In addition, the temperature and the ambient condition could have influence on the density of the defects, the crystallization, the conductivity, the stoichiometry, and the dielectric constant of thin films.

For the accuracy of the atmosphere, it needs the base pressure about 3×10^-5 Torr before sputtering. Next, to maintain the ambient condition, the flow rate of Ar and O2 by MFC was controlled, and the working pressure was kept by the valves among low pressure where the plasma was generated.

2.3.3 Heat Treatment after Thin Film Depositions

There were two purposes for the experiment using the RTA systems. One is in order to get stronger crystallization orientation or better conductivity of the LNO buffer layer. The other is to control the properties of our sample by changing the heating profile of RTA temperature. The RTA model was FE-004A made by JETFIRST.

2.3.4 Deposition of the Top Electrode

Before the Al top electrodes were deposited on the doped SZO films, the sample had been adhered to a metal mask. The metal mask had different hole with three kinds of diameters that are 150, 250, and 350µm. So the different areas are defined for the top electrodes, which are 1.767×10^-4, 4.908×10^-4, and 9.612×10^-4 cm².

Al used as the top electrode was deposition by a thermal evaporation coater (EBX-6D) manufactured by ULVAC. The samples were loaded with metal masks on the spinning holder, which made the deposition rate more uniform.

Then, the rough pump and the turbo pump would work in term in order that the base pressure before deposition reached 5×10^-6 Torr.