Phase tuning by length contraction.

Typical integrated optical phase tuners alter the effective index. In this paper, we explore tuning by geometric deformation. We show that tuning efficiency, Vπ L, improves as the device size shrinks down to the optimal bend radius, contrary to conventional index-shift based approaches where Vπ L remains constant. We demonstrate that this approach is capable of ultra-low power tuning across a full FSR in a low-confinement silicon nitride based ring resonator of 580 µm radius. We demonstrate record performance with VFSR = 16 V, Vπ L = 3.6 V dB, Vπ Lα = 1.1 V dB, tuning current below 10 nA, and unattenuated tuning response up to 1 MHz. We also present optimized designs for high confinement silicon nitride and silicon based platforms with radius down to 80 µm and 45 µm, respectively, with performance well beyond current state-of-the-art. Applications include narrow-linewidth tunable diode lasers for spectroscopy and non-linear optics, optical phased array beamforming networks for RF antennas and LIDAR, and optical filters for WDM telecommunication links.

Large displacement vertical translational actuator based on piezoelectric thin films.

A novel vertical translational microactuator based on thin-film piezoelectric actuation is presented, using a set of four compound bend-up/bend-down unimorphs to produce translational motion of a moving platform or stage. The actuation material is a chemical-solution deposited lead-zirconate-titanate (PZT) thin film. Prototype designs have shown as much as 120 µm of static displacement, with 80-90 µm displacements being typical, using four 920 µm long by 70 µm legs. Analytical models are presented that accurately describe nonlinear behavior in both static and dynamic operation of prototype stages when the dependence of piezoelectric coefficients on voltage is known. Resonance of the system is observed at a frequency of 200 Hz. The large displacement and high bandwidth of the actuators at low-voltage and low-power levels should make them useful to a variety of optical applications, including endoscopic microscopy.

A General Analytical Formulation for the Motional Parameters of Piezoelectric MEMS Resonators.

This paper reports on a general analytical expression for the motional resistance ( ) of an arbitrary mode in a piezoelectric microelectromechanical system resonator with parallel plate electrode geometry. After applying simplifying assumptions and using analytical modes shapes, expressions for the of modes with out-of-plane flexure as the primary displacement are presented. These modes include free-free transverse beam flexure (TBF), unclamped disk flexure resonators (DFRs), and antisymmetric Lamb modes. For verification, is extracted from resonators fabricated in a lead zirconate titanate on silicon process. Predicted of TBF and DFR modes is validated using on-wafer extracted constants, analytical modal properties, and independently measured material properties.

Direct-Write Laser Greyscale Lithography for Multi-Layer Lead Zirconate Titanate Thin Films.

Direct-write laser greyscale lithography has been used to facilitate a single step patterning technique for multi-layer lead zirconate titanate (PZT) thin films. A 2.55 µm thick photoresist was patterned with a direct-write laser. The intensity of the laser was varied to create both tiered and sloped structures that are subsequently transferred into multi-layer PZT(52/48) stacks using a single Ar ion mill etch. Traditional processing requires a separate photolithography step and an ion mill etch for each layer of the substrate, which can be costly and time consuming. The novel process allows access to buried electrode layers in the multi-layer stack in a single photolithography step. The greyscale process was demonstrated on three 150 mm diameter Si substrates configured with a 0.5 µm thick SiO2 elastic layer, a base electrode of Pt/TiO2, and a stack of four PZT(52/48) thin films of either 0.25 µm thickness per layer or 0.50 µm thickness per layer, and using either Pt or IrO2 electrodes above and below each layer. Stacked capacitor structures were patterned and results will be reported on the ferroelectric and electromechanical properties using various wiring configurations and compared to comparable single layer PZT configurations.

Direct-Write Laser Grayscale Lithography for Multilayer Lead Zirconate Titanate Thin Films.

Direct-write laser grayscale lithography has been used to facilitate a single-step patterning technique for multilayer lead zirconate titanate (PZT) thin films. A 2.55- -thick photoresist was patterned with a direct-write laser. The intensity of the laser was varied to create both tiered and sloped structures that are subsequently transferred into multilayer PZT(52/48) stacks using a single Ar ion-mill etch. Traditional processing requires a separate photolithography step and an ion mill etch for each layer of the substrate, which can be costly and time consuming. The novel process allows access to buried electrode layers in the multilayer stack in a single photolithography step. The grayscale process was demonstrated on three 150-mm diameter Si substrates configured with a 0.5- -thick SiO2 elastic layer, a base electrode of Pt/TiO2, and a stack of four PZT(52/48) thin films of either 0.25- thickness per layer or 0.50- thickness per layer, and using either Pt or IrO2 electrodes above and below each layer. Stacked capacitor structures were patterned and results will be reported on the ferroelectric and electromechanical properties using various wiring configurations and compared to comparable single layer PZT configurations.

Rapid Harmonic Analysis of Piezoelectric MEMS Resonators.

This paper reports on a novel simulation method combining the speed of analytical evaluation with the accuracy of finite-element analysis (FEA). This method is known as the rapid analytical-FEA technique (RAFT). The ability of the RAFT to accurately predict frequency response orders of magnitude faster than conventional simulation methods while providing deeper insights into device design not possible with other types of analysis is detailed. Simulation results from the RAFT across wide bandwidths are compared to measured results of resonators fabricated with various materials, frequencies, and topologies with good agreement. These include resonators targeting beam extension, disk flexure, and Lamé beam modes. An example scaling analysis is presented and other applications enabled are discussed as well. The supplemental material includes example code for implementation in ANSYS, although any commonly employed FEA package may be used.

Phenomenological Model for Defect Interactions in Irradiated Functional Materials.

The ability to tailor the performance of functional materials, such as semiconductors, via careful manipulation of defects has led to extraordinary advances in microelectronics. Functional metal oxides are no exception - protonic-defect-conducting oxides find use in solid oxide fuel cells (SOFCs) and oxygen-deficient high-temperature superconductors are poised for power transmission and magnetic imaging applications. Similarly, the advantageous functional responses in ferroelectric materials that make them attractive for use in microelectromechanical systems (MEMS), logic elements, and environmental energy harvesting, are derived from interactions of defects with other defects (such as domain walls) and with the lattice. Chemical doping has traditionally been employed to study the effects of defects in functional materials, but complications arising from compositional heterogeneity often make interpretation of results difficult. Alternatively, irradiation is a versatile means of evaluating defect interactions while avoiding the complexities of doping. Here, a generalized phenomenological model is developed to quantify defect interactions and compare material performance in functional oxides as a function of radiation dose. The model is demonstrated with historical data from literature on ferroelectrics, and expanded to functional materials for SOFCs, mixed ionic-electronic conductors (MIECs), He-ion implantation, and superconductors. Experimental data is used to study microstructural effects on defect interactions in ferroelectrics.

Total Ionizing Dose Effects on Piezoelectric Thin-Film Cantilevers With Oxide Electrodes.

This paper reports on the ionizing radiation effects in lead-zirconate-titanate (PZT) with varied top electrode material and bias condition during radiation. A technique to characterize the piezoelectric performance of films unclamped from the substrate is described, and used to demonstrate the effects of radiation on the material's electromechanical behavior. Both platinum and iridium oxide top electrodes were examined, and iridium oxide appears to significantly mitigate radiation-induced damage that is observed in platinum top electrode samples. This mitigation of radiation damage is attributed to the reduced number of oxygen vacancies within the PZT films when an iridium oxide top electrode is used. Devices with applied bias during radiation were compared with devices under applied bias only. Applied bias appears to slightly enhance the electromechanical response in the negative bias polarity for irradiated platinum electrode samples suggesting that the bias can cause defects to orient and therefore improve electromechanical response. Ultimately, iridium oxide top electrodes appear to mitigate radiation damage.

Electrode-shaping for the excitation and detection of permitted arbitrary modes in arbitrary geometries in piezoelectric resonators.

This paper reports theoretical analysis and experimental results on a numerical electrode shaping design technique that permits the excitation of arbitrary modes in arbitrary geometries for piezoelectric resonators, for those modes permitted to exist by the nonzero piezoelectric coefficients and electrode configuration. The technique directly determines optimal electrode shapes by assessing the local suitability of excitation and detection electrode placement on two-port resonators without the need for iterative numerical techniques. The technique is demonstrated in 61 different electrode designs in lead zirconate titanate (PZT) thin film on silicon RF micro electro-mechanical system (MEMS) plate, beam, ring, and disc resonators for out-of-plane flexural and various contour modes up to 200 MHz. The average squared effective electromechanical coupling factor for the designs was 0.54%, approximately equivalent to the theoretical maximum value of 0.53% for a fully electroded length-extensional mode beam resonator comprised of the same composite. The average improvement in S(21) for the electrode-shaped designs was 14.6 dB with a maximum improvement of 44.3 dB. Through this piezoelectric electrodeshaping technique, 95% of the designs showed a reduction in insertion loss.

PZT transduction of high-overtone contour-mode resonators.

This paper presents the Butterworth-van Dyke model and quantitative comparison that explore the design space of lead zirconate titanate-only (PZT) and PZT on 3-, 5-, and 10-µm single-crystal silicon (SCS) high-overtone width-extensional mode (WEM) resonators with identical lateral dimensions for incorporation into radio frequency microelectromechanical systems (RF MEMS) filters and oscillators. A novel fabrication technique was developed to fabricate the resonators with and without a silicon carrier layer using the same mask set on the same wafer. The air-bridge metal routings were implemented to carry electrical signals while avoiding large capacitances from the bond-pads. We theoretically derived and experimentally measured the correlation of motional impedance (RX), quality factor (Q), and resonance frequency (f) with the resonators' silicon layer thickness (tSi) up to frequencies of operation above 1 GHz.