Pt/Ti/SiO2/Si substrates

Pt/Ti/SiO2/Si structures have been studied to investigate the structural, chemical, and microstructural changes that occur during annealing. Grain growth of the as-deposited Pt columns was observed after annealing at 650 °C, and extensive changes in the Pt microstructure were apparent following a 750 °C anneal for 20 min. In addition, two types of defects were identified on the surfaces of annealed substrates. Defect formation was retarded when the surface was covered with a ferroelectric film. Concurrent with the annealing-induced Pt microstructure changes, Ti from the adhesion layer between the Pt and the SiO2 migrated into the Pt layer and oxidized. It was shown with spectroscopic ellipsometry and Auger electron spectroscopy that for long annealing times, the titanium oxide layer can reach the Pt surface. Consequently, at the processing temperatures utilized in preparing many ferroelectric thin films, the substrate is not completely inert or immobile. The changes associated with Ti migration could be especially problematic in techniques that require the substrate to be heated prior to film depositio

Microstructure Evolution of In Situ Pulsed-Laser Crystallized Pb(Zr0.52Ti0.48)O3 Thin Films

Integration of lead zirconate titanate (PZT) films with temperature-sensitive substrates (CMOS, polymers) would benefit from growth at substrate temperatures below 400°C. In this work, in situ pulsed-laser annealing [Rajashekhar et al. (2013) Appl. Phys. Lett., 103 [3] 032908] was used to grow crystalline lead zirconate titanate (PbZr0.52Ti0.48O3) thin films at a substrate temperature of ~370°C on PbZr0.30Ti0.70O3-buffered platinized silicon substrates. Transmission electron microscopy analysis indicated that the films were well crystallized into columnar grains, but with pores segregated at the grain boundaries. Lateral densification of the grain columns was significantly improved by reducing the partial pressure of oxygen from 120 to 50 mTorr, presumably due to enhanced adatom mobility at the surface accompanying increased bombardment. It was found that varying the fractional annealing duration with respect to the deposition duration produced little effect on lateral grain growth. However, increasing the fractional annealing duration led to shift of 111 PZT X-ray diffraction peaks to higher 2θ values, suggesting residual in-plane tensile stresses in the films. Thermal simulations were used to understand the annealing process. Evolution of the film microstructure is described in terms of transient heating from the pulsed laser determining the nucleation events, while the energy of the arriving species dictates grain growth/coarsening

Piezoelectric amplifiers with integrated actuation and sensing capabilities

We report in this work on unprecedented levels of parametric amplification in microelectromechanical systems (MEMS) resonators with integrated piezoelectric actuation and sensing capabilities operated in air. The method presented here relies on accurate analytical modeling taking into account the geometrical nonlinearities inherent to the bridge-like configuration of the resonators used. The model provides, for the first time, precise analytical formula of the quality factor (Q) enhancement depending on the resonant mode examined. Experimental validations were conducted for resonant modes exhibiting, respectively, hard and soft-spring effects when driven in the nonlinear regime; Q amplification by a factor up to 14 has been obtained in air

Coherent Growth of a-Fe2O3 in Ti and Nd Co-doped BiFeO3 Thin Films

Coherent dendritic α-Fe2O3 precipitates were observed to form at the surface of epitaxial films of (Bi0.75Nd0.25)(Fe0.97Ti0.03)O3 (BNFO) grown by pulsed laser deposition. The Fe2O3 dendrites are assemblages of nanosized particles with an approximate length of 500 nm. Through the use of atomic resolution scanning transmission electron microscopy, a transition zone at the BNFO/α- Fe2O3 interface, ∼ 2 unit-cells wide, was observed to be Fe2O3-rich with the perovskite structure. It is proposed that the formation of the Fe2O3-rich perovskite structure encourages epitaxial growth of the α-Fe2O3 rather than the formation of the incoherent Fe2O3 particulate second phase frequently reported in BiFeO3-based thin films

Pyroelectric response of lead zirconate titanate thin films on silicon: Effect of thermal stresses

Ferroelectric lead zirconate titanate [Pb(ZrxTi1-xO)(3), (PZT x:1-x)] has received considerable interest for applications related to uncooled infrared devices due to its large pyroelectric figures of merit near room temperature, and the fact that such devices are inherently ac coupled, allowing for simplified image post processing. For ferroelectric films made by industry-standard deposition techniques, stresses develop in the PZT layer upon cooling from the processing/growth temperature due to thermal mismatch between the film and the substrate. In this study, we use a non-linear thermodynamic model to investigate the pyroelectric properties of polycrystalline PZT thin films for five different compositions (PZT 40:60, PZT 30:70, PZT 20:80, PZT 10:90, PZT 0:100) on silicon as a function of processing temperature (25-800 degrees C). It is shown that the in-plane thermal stresses in PZT thin films alter the out-of-plane polarization and the ferroelectric phase transformation temperature, with profound effect on the pyroelectric properties. PZT 30:70 is found to have the largest pyroelectric coefficient (0.042 mu C cm(-2)degrees C-1, comparable to bulk values) at a growth temperature of 550 degrees C; typical to what is currently used for many deposition processes. Our results indicate that it is possible to optimize the pyroelectric response of PZT thin films by adjusting the Ti composition and the processing temperature, thereby, enabling the tailoring of material properties for optimization relative to a specific deposition process. (C) 2013 AIP Publishing LLC

OPTIMIZED DESIGN, FABRICATION AND CHARACTERIZATION OF PZT UNIMORPH MICROACTUATORS FOR DEFORMABLE MIRRORS

ABSTRACT This paper describes an optimization of PZT unimorph membrane microactuators in view of their application to deformable mirrors (DMs). PZT unimorph actuators of various electrode designs, silicon membrane thickness, and membrane sizes were fabricated and characterized. A mathematical model was developed to further assist the optimization of membrane thickness and electrode sizes, and excellent agreement with experiment was obtained. For a 2.5rnm diameter actuator with 2#m thick PZT and 15#m thick silicon membrane, the measured vertical stroke was 5.4#m at 50V. The measured resonant frequency of the unimorph actuator was 47kHz, far exceeding the bandwidth requirement of most DMs (-lkHz)