Mitsushi Fujiki

Evaluation of PZT capacitors with Pt/SrRuO3 electrodes for feram

Abstract (Pb, La)(Zr, Ti)O3[PLZT] films were prepared by CSD on sputtered electrodes of Pt/IrO2 on SiO2/Si wafers. Top electrodes consisting of Pt/SrRuO3(SRO) were sputter deposited and the Pt/SRO/PLZT/Pt capacitors were annealed at 600°C. Evaluation of fatigue endurance revealed that more than 6% excess Pb was necessary to produce a fatigue free capacitor. However, the FeCap leakage current increased in proportion to the film excess Pb content. SIMS analysis of the FeCap containing 10% excess Pb revealed that Sr from the 70 nm thick SRO electrode diffused into the PLZT film to the bottom electrode during the anneal resulting in high leakage. FeCap leakage current was greatly reduced by decreasing the PLZT film excess Pb content and SRO film thickness. SRO electrodes with thicknesses of 5 and 15 nm were found to be sufficient to produce a capacitor with high fatigue endurance and little static imprint. These results indicate that the PLZT leakage current was greatly influenced by the Sr interdiffusion and...

Evaluation of (Pb, La)(Zr, Ti)O3 (PLZT) Capacitors of Different Film Thicknesses with Pt/SrRuO3 Top Electrodes

(Pb, La)(Zr, Ti)O3 [PLZT] films with thicknesses of 150, 225 and 300 nm were prepared by chemical solution deposition (CSD) on Pt/IrO2 coated SiO2/Si wafers. Top electrodes of Pt/SRO were sputter deposited and annealed at 600°C to form a capacitor. All three PLZT films were highly (111) oriented and showed high switchable polarization of >40 µCcm-2 at 200 kVcm-1. A coercive field of 40 kVcm-1 was observed for all three films regardless of thickness. Little fatigue degradation was observed up to 1010 cycles. These results indicate that it is possible to combine both oxide and metallic contacts in a high endurance ferroelectric capacitor for low voltage applications.

Characterization of PZT capacitors with SrRuO3 electrodes

Abstract Pb(Zr, Ti)O3 [PZT] capacitors were prepared by CSD on sputtered electrodes of SrRuO3(SRO)/Pt on SiO2/Si wafers. The SRO/Pt bottom electrodes were deposited using two different conditions: (1) at 600°C in-situ (abbreviated HT), and (2) at low temperature followed by a post-deposition anneal at 600°C (abbreviated LTA). The PZT orientation and switching pulse polarization, i.e. HT-SRO (43 μC cm-2) and LTA-SRO (32 μC cm-2) were strongly dependent on the bottom electrodes. Yet neither capacitor showed polarization loss resulting from switching 108 times with ± 5 V pulses. These results indicate that the PZT ferroelectric properties are greatly influenced by the SRO bottom electrode processing conditions.

Microstructure evolution and leakage phenomena of CSD PLZT thin films

Abstract (Pb,La)(Zr,Ti)O3 [PLZT] thin films were deposited by chemical solution deposition (CSD) on sputtered Pt/IrO2 electrodes on SiO2/Si wafers. A relationship between PLZT grain size and leakage was observed with films of 150 nm thick. Large-grained films showed high leakage, whereas fine-grained films showed low leakage. Limited nucleation sites led to pyrochlore at grain boundaries, which may act as an electrical pathway. Thin CSD PLZT film with lower leakage was prepared by shortening the total pyrolysis time. From these results, pyrolysis time was an important parameter used to control film microstructure and leakage.

Degradation of asymmetrical Pt/SRO/PLZT/Pt capacitors: Role of Pt and oxide electrodes

Role of Pt and SRO electrodes in polarization fatigue of PLZT film ferroelectric capacitors is studied. We show that asymmetrical Pt/SRO/PLZT/Pt structure exhibits unusual dependence of the endurance of switching polarization on the driving ac electric field amplitude. Specifically, for high ac electric field amplitude it shows a good switching endurance similar to SRO/PLZT/SRO capacitors, whereas for amplitude lower than 80 kV/cm a pronounced polarization fatigue similar to that of conventional Pt/PLZT/Pt capacitors is observed. Based on the analysis of these results we conclude that the polarization switching endurance under high-amplitude fatiguing cycling is governed only by the top SRO-interface which is not subjected to degradation, whereas the degradation properties of the bottom Pt-interface do not play any role. Comparative analysis of leakage conduction of Pt/PLZT/Pt (i) and Pt/SRO/PLZT/Pt (ii) capacitors in virgin and fatigued states shows that both interfaces of capacitor (i) are subjected to degradation whereas both interfaces of the capacitor (ii) are not degraded. According to our analysis, in asymmetrical Pt/SRO/PLZT/Pt structure the top SRO-interface can protect the bottom Pt interface from degradation if the following conditions are met: 1. Top SRO interface is degradation-free 2. Switching rate at the top electrode is higher than at the bottom one.