This work presents a survey of the mechanisms of the polarization in ferroelectric thin films which are relevant for application in non-volatile ferroelectric memories (FeRAM). Since the integration of these materials in new memory generations requires small structures and therefore a maximum utilization of the switchable polarization, the distinction between the several polarization mechanisms is of specific interest. Standard characterization methods, such as hysteresis loops, C-V measurements and fast pulse switching tests are evaluated and used to distinguish between the reversible and irreversible contributions to the total polarization. The respective contributions are described qualitatively and demonstrated at spin-coated SrBiTa2O9 thin films and compared with Pb(Zr,Ti)O3 films. Additionally, a method is described to obtain the static hysteresis curve, a precise characterization of the polarization which does not depend on the measuring frequency. These data are compared with C-V measurements. It is shown that the standard dynamic hysteresis curve reveals misleading statements about the remanent polarization and the coercive voltage.

An optimized process of Pb(Zr,Ti)O3(PZT) ferroelectric capacitor has been investigated in order to develop a highly scaleable 1T/1C ferroelectric random access memory. The PZT ferroelectric capacitor, Pt/PZT/Pt stack, was formed on the TiO2/SiO2/Si substrate. The PZT thin films were prepared by conventional sol-gel multi-coating method. Physical and electrical properties of the PZT ferroelectric capacitors were characterized by XRD, SEM, TEM and RT6000S, respectively.

It was revealed that the microstructure of PZT thin film is strongly influenced by sol-gel coating process, especially depending on coating methods of the first PZT layer. The second phase was observed in the PZT thin films, which is found to be pyrochlore phase. The size and density of pyrochlore phase were significantly reduced by modifying the coating methods of first PZT layer. Microstructure of PZT thin film capacitors was evaluated in detail along with electrical properties such as remnant polarization, coercive electric field, and dielectric leakage. The sensing Pr window was also introduced for proper sensing margin in IT/1C ferroelectric random access memory. This concept is well verified by 64Kb 1T/1C ferroelectric random access memory.

The fabrication of high yielding ferroelectric capacitors on CMOS wafers is difficult due to the negative impact of post-capacitor process steps, especially the interlayer dielectric and the metal interconnect sinter. Proper selection of the process for each layer of the capacitor structure is necessary to minimize hysteresis damage to the ferroelectric capacitors during their construction. The authors fabricated integrated PZT capacitors on blank silicon wafers using lift off processes for the bottom and top electrodes and a combination titanium dioxide/silicon dioxide dielectric between the ferroelectric capacitors and the metal interconnect layer. A 15 minute nitrogen anneal at 450 degrees centigrade after the metal interconnect patterning did not damage the capacitor hysteresis loops. Statistical testing of over 700 capacitors for shorts indicated a defect rate of 127 defects per square centimeter. This is sufficiently low enough to generate 50% yield in a production 64Kbit double-sided-sense nonvolatile memory. At 3.5V, the capacitors generated 14.0 microcoulombs per square centimeter with a standard deviation of 2.3 microcoulombs per square centimeter. The authors have set a target for future lots of 20 defects per square centimeter with 32 microcoulombs per square centimeter at 2.0V with a standard deviation of 1.6 microcoulombs per square centimeter.

Using scanning probe microscopy, we have written nonvolatile electronic nanofeatures in the metallic perovskite oxide SrRuO3. The structures were written in epitaxial thin film Pb(Zr0.52Ti0.48)O3 (PZT) / SrRuO3 heterostructures by locally switching the polarization field of the ferroelectric PZT layer with an atomic force microscope (AFM). The resulting field effect changes the sheet resistance of the SrRuO3 layer by up to 300 ohms per square. Using the AFM as an electric field microscope, it is also possible to visualize the charge distribution of the written areas on the PZT surface. Large areas of up to 100 μm2 have been polarized and imaged with submicrometer resolution, with the smallest features having linewidths of 170 nm. This approach to local electronic doping is reversible and allows one to write nonvolatile submicron electronic features in two dimensions without lithographic steps or permanent electrical contacts required.

Data retention may be affected by depolarization, domain stabilization (ageing or imprint), and fuzzy electric field among neighboring bits in relation to microstructures of ferroelectric media. In this paper, the smearing effect due to electric field between two adjacent bits was demonstrated. In order to minimize the smearing effect, ferroelectric media with the top electrode is proposed by which fuzzy electric field can be screened by bound charges in the electrode. Bit on electrode (BOE) technique was suggested for “Write” (local polarization) and “Read” on ferroelectric media with the top electrode (ferroelectric capacitor). It is noticed that a highly sensitive device such as single electron transistor is indispensable for measuring potential variation in the top electrode of the ferroelectric capacitor media.

A novel method for lowering processing temperature of ferroelectric Pb(Zr1−xTix)O3 (PZT) thin films was developed utilizing a laser-assisted two-step process. In the first step, perovskite phase was initiated in the PZT films by subjecting the films to a fornace anneal at low temperatures in the range of 470 °C to 550 °C depending on the Zr/Ti ratio. Later, the films were laser-annealed (using krF excimer laser) at room temperature to grow the perovskite phase, and to improve microstructure and ferroelectric properties. It was found that this two-step process was very effective in producing excellent quality ferroelectric PZT films at low temperatures. It should be noted that although laser annealing of amorphous and/or pyrochlore films directly (one-step process) produces perovskite phase, the ferroelectric properties of these films, irrespective of the composition, were rather unattractive. Some possible reasons for the ineffectiveness of the one-step process were discussed.

Polarization and polarization fatigue of PZT and other ferroelectric thin films have been studied via the frequency spectra of D-E hysteresis. The coercive field (Ec) of PZT thin films has been found strongly dependent on the measuring frequency, while a relatively flat frequency response is observed with SrBi2Nb2O9 thin films. The different fatigue behavior can be attributed to such a difference in the frequency response. Physical models have been suggested to for domain wall movement in PZT and SrBi2Nb2O9 thin films. Based on these observations, a methodology has been proposed to evaluate the high frequency and fatigue properties of ferroelectric thin films.

The paraelectric cubic to ferroelectric tetragonal phase transformation of thin Pb(Zr,Ti)O3/MgO(001) films was studied in synchrotron x-ray scattering experiments. As the thickness of the film decreases, the transition temperature and the amount of the tetragonal distortion were decreased continuously. The thinnest 250 Å thick film was purely composed of the c-type domains in the ferroelectric tetragonal phase. Based on this, we propose a model for the domain structure of the tetragonal PZT/MgO(001) film that is different from the ones suggested in literature. We attribute the suppression of the transition to the substrate effect that prefers the c-type domains near the interface, and reduces the tetragonal distortion to minimize the film-substrate lattice mismatch.

Epitaxial PbTiO3(PTO) thin films were grown on (001) LaAlO3 (LAO) substrates by a two-step process from a mixed Pb-Ti double-alkoxide solution precursor. Scanning electron microscopy, x-ray diffraction, atomic force microscopy, and transmission electron microscopy were performed to characterize the microstructure of films and to evaluate the epitaxial phenomena. In the first step, very thin PTO films were deposited and then heat treated at 800 °C for lh. The films were broken up into isolated islands that have epitaxial relationship of [100](001)PTO∥[100](001)LAO. In the second step, another PTO thin films were deposited and then annealed at temperatures between 380 °C and 800 °C for 1h. In this seeded process, epitaxial PTO thin films, unobtainable when PTO thin films were deposited on the unseeded LAO substrates, could be grown. The islands formed in the first step act as seeds for the growth of epitaxial thin film in the second step.

An advanced oxide MOCVD tool and processes have been developed to deposit large area PbZr1−xTixO3 (PZT) thin films on 6” Si and Pt/Ti/SiO2/Si substrates. The experimental results show the advanced oxide MOCVD tool can achieve the growth of PZT thin films with thickness uniformity of 2% and composition uniformity better that 3% on both 6” Si and Pt/Ti/SiO,/Si wafers at high deposition rates. X-ray patterns showed a single PZT perovskite phase, and AFM showed homogeneous microstructure and low surface roughness. Typically, 300 nm thick PZT films with a grain size about 0.3 μm have Pr greater than 20 - 30 μC/cm2 at 5V, a dielectric constant around 1000, low coercive field (Ec 50 - 70 kV/cm), and fatigue rate (the normalized polarization is about 0.6 after 1010 cycles at 5 V), and leakage current of 2 - 6×lO−7 A/cm2 at 150 kV/cm and room temperature on Pt electrodes. In addition, the effects of reactor design and process conditions on the thickness and composition uniformity, as well as the m i ero structure and properties were also investigated.

Lead zirconate titanate (PZT) thin films have been grown by rf magnetron sputtering on Si substrates from a metallic target of nominal composition Pb1.1(Zr0.4 Ti0.6 in a reactive argon / oxygen gas mixture. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements show clearly a correlation between the evolution of characteristic atomic emission line intensities (Zr - 386.4 nm, Ti - 399.9 nm, Pb - 405.8 nm and O - 777.2 nm) and the thin-film composition determined by a simultaneous use of Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA).

Thin films of SrTiO3 and Ba0.4Sr0.6TiO3 have been pulse laser ablated onto LaAIO3 substrates. Normal metal coplanar capacitor electrodes were patterned on top of these films and the capacitors were incorporated into weakly coupled microstrip resonators. Resonant frequencies and Q's were measured as a function of bias at room temperature and at 77 K. The microwave frequency capacitance and loss is calculated from the resonant properties and compared with the simultaneously measured 1 MHz capacitance and dissipation. Two-tone intermodulation distortion products were measured and the third-order intercept is referenced to the microwave voltage across the capacitors. Commercially available semiconductor varactors were tested in a similar manner. The tuning quality (the ratio of the relative capacitance tuning to dissipation), frequency dispersion, and power handling of these capacitors are compared. Although there appears to be no intrinsic power handling advantage of the paraelectrics over the semiconductor varactors, the paraelectric varactors can offer better tuning quality.

Single phase, (100) oriented Ba0.5Sr0.5TiO3 films have been deposited by pulsed laser deposition onto (100) LaAIO3, SrTiO3, MgO substrates. The dielectric properties of these films were measured using interdigitated capacitors as a function of DC bias and temperature at 1 MHz and as a function of DC bias at 1 to 20 GHz at room temperature. Deposited films were annealed over a temperature range of 900 to 1350 C for 1 to 8 hours to observe its effect on dielectric properties. Chemical analysis on films deposited from stoichiometric targets showed the films to be up to 6% deficient in Ba and Sr under typical PLD deposition conditions. Optimal annealing conditions and target stoichiometries for minimizing dielectric loss and maximizing tuning are discussed.

KTa1−xNbxO3 (KTN) thin films (-6000 Å) were grown on (100) MgO, (100) LaAlO3 (LAO), and (100) SrTiO3(STO) substrates by pulsed laser deposition (PLD). Deposited films were smooth, single phase and exclusively (100) oriented. KTN films deposited on MgO and LAO substrates were easily cracked after deposition or post deposition heat treatment. The film deformation appeared to be caused by strain due to the lattice mismatch between the film and the substrate. A thin buffer layer of ∼100 Å was used to eliminate the cracking problem. The high volatility of K at the film deposition temperature required excess K to be added to the ablation target. Sintering of the target and post-deposition annealing of the films were done in a sealed Pt coated stainless steel container. Rutherford backscattering showed the films to have a 1 to 1 atomic ratio of K to Ta + Nb. On top of the KTN films, Ag interdigitated capacitors were deposited. Room temperature measurements of capacitance and dielectric loss as a function of bias electric field (0 -80 kV/cm) at 1 to 20 GHz were made. Capacitance and dielectric loss measurements were made as a function of temperature and bias electric field at one MHz and as a function of temperature and frequency at 0V DC bias. The results show the strong potential of KTN for use in frequency agile microwave electronics.

The crystallization of amorphous BST thin films was studied in a synchrotron x-ray scattering experiment. At around 600°C, an intermediate phase, which was suspected to be a metastable pyrochlore phase, was formed. The x-ray reflectivity curves showed that the film-substrate interface became rough as the pyrochlore-like phase was formed. This suggests that the pyrochlore phase was nucleated near the interface area. Upon further annealing to higher temperatures, the film transformed to the crystalline perovskite phase. The crystallization was sensitive to the film thickness. In the thin 550Å thick film, the crystallization occurred at 750 °C with the <001> preferred orientation. On the other hand, the 5500Å thick film became crystalline even at 500°C with random crystalline orientation. The observed thickness dependence of the crystallization suggests that the crystalline perovskite phase was nucleated in the bulk of the film, rather than the near interface area.

Potassium niobate tantalate (KTN) thin films of a range of compositions were grown by pulsed laser deposition onto (100) MgO substrates. Three-segment targets were used including KTaO3, KNbO3, and KNO3. Resulting films were well oriented with the substrates, with the “cubic” (h00) peaks positions shifting with Nb content to that of the (hh0) orthorhombic KNbO3 peak.

Using pulsed laser ablation, we have grown epitaxial bilayers of strontium titanate (STO) and yttrium barium copper oxide (YBCO) on lanthanum aluminate (LAO) and neodymium gallate (NGO) substrates. Using a selective acid etch, we have removed the YBCO from the middle of the bilayer and lifted off the strontium titanate films from their parent substrates. Using coplanar interdigital capacitors patterned on the films' surface, we have measured the dielectric constant and loss as a function of frequency and temperature and have resolved frequency dependent loss peaks which indicate thermally activated behavior. Also, by applying a dc bias to the capacitor, we have seen tuning of the lifted off films' dielectric constants that compares favorably to films attached to substrates.

Nonlinear optical films on GaAs and other III-V (AlGaAs, InGaAs) semiconducting substrates have many potential applications in integrated optics. Until now, the growth of device quality films on GaAs was a major technological challenge. Using Pulsed Laser Deposition (PLD) epitaxial films of prototypical nonlinear KTa0.52Nb0.48O3 (KTN) were successfully deposited on single crystalline GaAs substrates for the first time. In order to alleviate chemical and structural incompatibilities between the GaAs substrate and KTN film at the growth temperature (∼750°C), a novel buffer layer scheme consisting of epitaxial MgO and SrTiO3 buffer layers and a Si3Ni4 encapsulation of the substrate was successfully developed. To obtain films with the required stoichiometry, a segmented target geometry was used consisting of KTN and KNO3 targets. The high crystalline quality of KTN films on GaAs was established by detailed 4-circle x-ray diffraction studies. Rutherford Backscattering studies confirmed the composition of the films. Optical measurements have been carried out on epitaxial KTN films on GaAs. Using an Ar+ laser (457.9 nm) operating in the TEM00 mode, we have observed sharp and distinguishable TE and TM propagating modes in KTN films. The refractive index (n0) of the film at 488 nm is 2.275 which is close to the bulk value of 2.35.

High quality epitaxial PZT optical waveguides have been grown by solid-phase epitaxy based on metal alkoxide solution process. Optical propagation loss was 4 dB/cm in epitaxial PZT thin film optical waveguides grown on SrTiO3 substrates. Epitaxial PZT optical waveguides were grown on Nb doped conductive SrTiO3 substrates, since considerable reduction in drive voltage will be expected when top electrode / optical waveguide / conductive substrate structures are realized. Propagation loss was relatively large, as compared with the structure using non-dope insulative substrates. Preliminary electrooptic deflection devices were fabricated by preparing prism electrodes on the surface of the PZT optical waveguides. Efficient deflection/switching of coupled laser beam in the PZT optical waveguides as large as 26 mrad was observed by applying 70 volts between prism electrode and Nb doped SrTiO3 substrates.

The dielectric and piezoelectric response of sol gel based films and composite coatings is affected by the choice of process, gel composition, thermal cycle, processing atmosphere and poling conditions. Important general factors for thin films are the crystallization kinetics and the effects of residual carbon, while a new dielectric technique allows poling methods to be evaluated.