PZT Capacitors Research Articles

Characterization of PZT capacitors with SrRuO3 electrodes

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.

Ferroelectric characteristics of and capacitors in a radiation environment

(PTO/YBCO) and (PZT/ YBCO) structures were fabricated on and substrates by the pulsed excimer laser deposition (PLD) method, respectively. In order to investigate total dose radiation effects on the Au/PTO/YBCO and Au/PZT/YBCO ferroelectric (FE) capacitors, the capacitance-voltage (C-V) and the retained polarization properties of the capacitor were measured before and after -ray irradiation. The results showed that, with the increment of the dose, the retained polarization and the dielectric constant of the FE capacitors decreased; but the absolute value of the negative and positive coercive fields of the PZT capacitor increased while that of the PTO capacitor decreased. The results have been interpreted by radiation-induced positive charges and the defect trap model.

Characterization of Sol-Gel PZT Capacitors with SrRuO<sub>3</sub> and Pt Electrodes

Characterization of Sol-Gel PZT Capacitors with SrRuO<sub>3</sub> and Pt Electrodes

Fabrication Technology of Ferroelectric Memories

Two types of ferroelectric memories have been proposed. One is a 1 transistor and 1 capacitor (1T1C) type and another is an FET (field effect transistor) type. The fabrication technique for fabrication ferroelectric capacitors on polycrystalline Si (poly-Si) was very effective for high density 1T1C ferroelectric memory and metal-ferroelectric-metal-insulator-semiconductor (MFMIS) FET with stable properties. MFMIS FET is one type of FET ferroelectric memory which we proposed. To obtain good ferroelectric capacitors on poly-Si, we used Ir based materials as electrodes of the capacitors. By using Ir based electrodes, the characteristics of Pb(Zi,Ti)O3 (PZT) capacitors on poly-Si were equivalent to those on SiO2. Moreover, the PZT capacitors with Ir based electrodes showed dramatic improvement in fatigue and imprint properties.

Growth, Microstructural and Ferroelectric Properties of PZT Films Prepared by Pulsed Laser Deposition Method

AbstractPb(ZrxTi1−xO3 (lead zirconate titanate or PZT) ferroelectric thin film capacitors are of considerable interest for the realization of memory devices such as nonvolatile random access memories (NVRAMs). The PZT capacitors were prepared on platinized silicon Pt/(100)Si using conducting oxide LaxSrl.xCOO (lanthanum strontium cobalt oxide or LSCO) as electrodes. The PZT and LSCO thin films were deposited by the KrF excimer laser ablation technique. The optimum preparation conditions such as oxygen pressure, laser energy influence and substrate temperature were investigated. The PZT and LSCO films grown on Pt/(100)Si are polycrystalline. The crystallographic properties of the films were determined using X-ray diffractometer (XRD) method. The cross-sectional transmission electron microscope showed very smooth interface among different layers of films. The electrical characterizations of the films including hysteresis loop, fatigue, and retention properties were determined by the RT66A Standardized Ferroelectric Test System.

Synthesis and Characterization of Ferroelectric Thin Films by KrF Excimer Laser Ablation for Memory Applications

AbstractPb(ZrxTi1-x)O3 (lead zirconate titanate or PZT) ferroelectric thin film capacitors are of considerable interest for the realization of memory devices such as nonvolatile random access memories (NVRAMs). The PZT capacitors were prepared on platinized silicon Pt/(100)Si using conducting oxide LaxSr1-xCoO3 (lanthanum strontium cobalt oxide or LSCO) as electrodes. The PZT and LSCO thin films were deposited by the KrF excimer laser ablation technique. The optimum preparation conditions such as oxygen pressure, laser energy influence and substrate temperature were investigated. The PZT and LSCO films grown on Pt/(100)Si are polycrystalline. The crystallographic properties of the films were determined using X-ray diffractometer (XRD) method. The electrical characterizations of the films including hysteresis loop, fatigue, and retention properties were determined by the RT66A Standardized Ferroelectric Test System.

The influence of chemical passivation on the PZT/Pt electrode interface

It has been recognized that the interdiffusion of atomic species between a PZT film and the Pt bottom electrode leads to the gradual degradation of a PZT capacitor. In order to prevent this interdiffusion, experimental studies on chemical passivation to the bottom electrode surface were carried out by the sulfurization method. It was observed that a sulfur layer was built up on the Pt substrate with small grains, which resulted in a structural change at the Pt surface. Atomic force microscopy (AFM) showed that the film roughness of the Pt surface was increased by sulfur treatment. Pb(Zr0.5Ti0.5)O3(PZT) thin films were prepared on a Pt/Ti/SiO2Si bottom electrode by spin-coating techniques. The microstructure and the preferred orientation of the PZT films were shown to depend on the sulfur-treated electrode. The PZT capacitor on a clean Pt electrode was confirmed to be ferroelectric with Pr=17.7 μC/cm2 and Ec=65 kV/cm from the P-E hysteresis curves. The fatigue behavior of a PZT film capacitor prepared on a sulfur-treated one was observed to be relaxed, but the absolute value of Pr was paid off.

Effect of Bottom Electrode System on Ferroelectric Properties of Sputter Deposited PZT Capacitors

AbstractRF magnetron sputter deposited PZT films were prepared on various bottom electrode systems such as Pt/Ti/SiO2/Si, IrO2/SiO2/Si, Pt/IrO2/SiO2/Si and Ir/IrO2/SiO2/Si substrates using the ceramic PZT target with Pb1.1(Zr0.52Ti0.48)O3 composition. In order to obtain single perovskite phase, PZT films were sputter-deposited at room temperature under Ar only plasma condition followed by high temperature annealing under oxygen ambient. Regardless of the bottom electrode system, reasonable ferroelectric properties such as 2Pp, Vc could be obtained by 650°C post annealing. Their values were over 20μ C/cm2 and below ± 1.OV when drive voltage was ± 3V, respectively. Hybrid electrode system, namely, thick Pt or Ir and thin IrO2 shows good leakage current characteristics, of ∼ 10−8A/cm2. Fatigue properties of PZT capacitor depend on the test condition. However, retention after 3×104sec showed a degradation of 15% when writing voltage was −5V irrespective of bottom electrode system. Imprint characteristics also showed good results within ± 1 as a figure of merit (FOM).

Interconnect-Related Degradation of PZT Capacitor for FeRAM

AbstractFerroelectric properties of a Pb(Zr,Ti)O3 (PZT) thin film capacitor with a conventional Al/TiN/Ti interconnect are seriously degraded by annealing at around 400°C. The degradation of the PZT capacitor is reduced as the interconnects are narrowed while the total area of the interconnects on the capacitor is fixed. This result cannot be understood by supposing that Ti diffusion into PZT degrades the ferroelectric properties. A possible cause for the degradation is stress placed on the PZT film during the 400°C annealing.

Electrical Properties of PZT Thin Film Capacitors with Novel Pt-Ir Based Electrode Barriers for Nonvolatile Memories

AbstractA new electrode barrier structure based on noble metals Pt and Ir alloys and their oxides was proposed for the integration of PZT capacitors into high density nonvolatile memories. The proposed PtIrOx/PtIr/PtIrOx structure with Pt rich compositions (∼90%) is an excellent conducting electrode for the ferroelectric capacitor and a very good diffusion barrier for species like oxygen and Si. These structures are thermally stable up to the PZT processing temperatures of 650°C. PZT deposited on these electrodes crystallized predominantly in pervoskite phase. The test capacitors showed well saturated hysteresis loops with Pr and Ec of 21.3 µC/cm2 and 43 kV/cm, respectively. An extremely low polarization fatigue of 3% after 1× 1011 repetitions and leakage currents close to those on Pt were observed.

Pyroelectric Effects on 1T-1C Fram and 1Tr Fram

AbstractPyroelectric effect on ferroelectricity was examined for PZT capacitors with diodes in series. It was observed that the magnitude of the polarization reversal increases as heating rate increases. The polarization reversal begins to decrease as heating rate becomes very high, which may stem from the fact that pyroelectric charges flow through the PZT film at high temperature as the film loses its resistance at the elevated temperature. A pure remanent polarization reversal model is suggested for the polarization reversal caused by pyroelectric charges. Based on the above results, a thermal shock test method is proposed for quality control of FRAM products. The thermal shock test reveals that pyroelectric effect can be minimized by controlling process for 1T-1C FRAM. It was also observed, by the thermal shock test, that imprint dominates pyroelectric effect in 1Tr cell with MFIS structure.

Scaling possibility of pzt capacitors for high density and low-voltage nvfram application

Scaling limit of the PZT capacitors for high-density and low-voltage Nonvolatile Ferroelectric RAM (NVFRAM) is described using the memory operation scheme for data read-out. The analysis is performed using the measured switching polarization characteristics of our 3 × 3μm2 PZT capacitors applicable to 1 Mbit NVFRAM. 16Mbit NVFRAM can be realized with simple shrinkage of our planar-type PZT capacitor without having to fabricate a stacked or trench capacitor.

Effects of substrate modification on the growth and characteristics of mocvd PZT

Pb(ZrxTi1-x)O3 thin films(PZT) were deposited on Pt/Ti/SiO2/Si(100) and RuO2/Pt/Ti/SiO2/Si(100) substrates by metal-organic chemical vapor deposition(MOCVD). The surface morphology of the Pt substrate was altered with the deposition temperature and thickness. The variations in the microstructure of PZT films were investigated as a function of substrate morphology. In addition, the effects of RuO2/Pt multilayer electrode on the microstructure and electrical properties of PZT capacitor were also studied. Finally, the PZT capacitors integrated on 4” wafer with multilayer electrode were evaluated.

Characterization of hetero-epitaxial PZT capacitor

A hetero-epitaxial Au/PbZr0.48Ti0.52O3(PZT)/SrRuO3(SRO) capacitor was fabricated on a single crystal SrTiO3 (STO) substrate by pulsed laser deposition. An SRO buffer layer (a nucleation layer) was formed at the SRO/STO interface to ensure the highly epitaxial growth of the PZT and SRO films. An X-ray diffraction measurement revealed that the (00l) planes of the PZT and SRO grew parallel to the substrate surface. A transition layer of ∼ 5 nm thickness was observed at the SRO/STO interface by high-resolution transmission electron microscopy (HR-TEM). This transition layer corresponds to the nucleation layer intentionally grown at the interface. Remanent polarization of the capacitor was 32.1 μC/cm2 due to the good epitaxial growth of the films.

The effects of the catalytic nature of capacitor electrodes on the degradation of ferroelectric Pb(Zr,Ti)O3 thin films during reductive ambient annealing

The disappearance of ferroelectricity in Pb(Zr0.52,Ti0.48)O3 (PZT) thin-film capacitors, which is caused by heat treatment in a reductive ambience, is investigated. Bare PZT films are not damaged by annealing in a hydrogen-containing atmosphere (H2 annealing) up to 400 °C, whereas a PZT capacitor with Pt electrodes loses its ferroelectricity during annealing at less than 300 °C. We have found that the degradation of ferroelectricity depends upon the metal used for the top electrode of the PZT capacitor. The increased degradation in the case of a PZT capacitor with Pt electrodes can be explained by a catalytic reaction on the Pt surface. We have made the ferroelectricity of a Pt/PZT/Pt capacitor retained even after the H2 annealing at 300 °C, or above, simply by oxidizing it before the H2 annealing.

Etching Effects on Ferroelectric Capacitors with Multilayered Electrodes

Dry etching of PbZrX Ti1-X O3 (PZT) thin film capacitors with RuOX /Pt multilayered electrodes was studied to examine the etching effects. PZT films were deposited on RuOX /Pt/Ti/SiO2/Si substrates by sol–gel process and Pt films were prepared by DC magnetron sputtering. PZT and Pt thin films were etched with Cl2/C2F6/Ar gas combination in an inductively coupled plasma (ICP) by varying the etching parameters such as coil RF power, dc-bias voltage to wafer susceptor, and gas pressure. Etching effects were investigated in terms of etch rate, etch selectivity, etch profiles, and electrical properties of etched capacitors. Quantitative analysis of the etching damage was obtained by calculating the shift of the coercive field and the switchable polarization in hysteresis loops. Finally, the etching damage mechanism was discussed and the optimization of etching processes for the fabrication of PZT capacitors was attempted to minimize the etching damage to ferroelectric capacitors.

Fabrication and comparison of ferroelectric capacitor structures for memory applications

Ferroelectric capacitors of Pt/PbZrTi1−xTi1−xO3/Pt system were integrated to examine the various capacitor structures. Three test structures of PZT capacitors were chosen for the fabrication and comparison. These were classified by how the capacitor area was defined and whether the sacrificial area of PZT film existed. Process integration includes back-end processing as well as ferroelectric processing. PZT and Pt thin films were prepared by metallo-organic decomposition (MOD) and DC magnetron sputtering, respectively. TiO2 was employed as a reaction barrier layer between PZT and SiO2 interlayer dielectric layer. Process flows for the fabrication of test capacitors have been developed for the device integration. Finally, the test structures of PZT capacitors were evaluated in terms of the electrical properties of the capacitors including hysteresis loop, fatigue, and leakage current as well as process integration.

The use of voltage to accelerate the endurance degradation of PZT capacitors

A voltage vs. endurance model was created to predict the performance of PZT from 3 to 8 volts. Capacitors that are part of the street structure on finished wafer products were cycled from 10 to a total of le 12 cycles. The switched charge was measured over 10 to 12 orders of magnitude in order to develop models to predict performance out to 1e15 cycles. The switched charge was found to degrade as a square function of the log of the number of cycles fatigued. The model was found to fit the data with an r2 greater than .95. Utilizing the minimum allowable charge for a sense amplifier, this model could be used to predict part life over operating voltages.

Etching effects to PZT capacitors with RuOx/Pt electrode by using inductively coupled plasma

The etching damage was studied on lead zirconate titanate (PZT) thin film capacitors with RuOx/Pt multi-layered electrodes. PZT films were deposited on RuOx/Pt/Ti/SiO2/Si substrates by spin coating with the sol-gel solution and etched by an inductively coupled plasma (ICP) etcher. Etching damage was systematically investigated by varying etching parameters such as coil RF power, DC bias to wafer susceptor, and chamber pressure. Quantitative analysis of etching damage was made in terms of the degree of the coercive field shift (Eshift ) in hysteresis loops. In this study, the optimization of etching process for PZT films was attempted to minimize the etching damage to the ferroelectric capacitors.

Full and partial polarization switching characteristics of sol-gel derived Pb(ZrxTi1-x)O3 thin films

In this study, polarization switching characteristics of Pb(Zr x Ti1-x )O3 (PZT) thin films were investigated. Switching times (t s) were found to be decreased as the Zr mol% was increased. But, the switching peak currents (I max) showed the largest value at 50 mol% Zr. As a result of this experiment, t s was found to be depended on the remanent polarization and coercive field and also I max strongly depended on the dielectric constant of PZT thin films. In order to investigate the partial switching kinetics of PZT thin films, short and relatively small voltage pulses were applied to the MFM (metal-ferroelectric-metal) PZT capacitors and polarization switching curves were measured with a variation of the total width of the applied pulses. Also, the switching curves were measured at different applied voltages (4, 8, 10, 12 and 14 V). As the applied voltages increased t s and I max were found to be decreased and increased, respectively. In case of fatigued specimen which we applied ± 10 V square pulse for 1010 cycles, t s and I max were found to be shorter and smaller than those of virgin specimens. This is due to the decrease of the remanent polarization and the increase of the coercive field.