A quadruple mass Coriolis vibratory gyroscope operating in the mode-matched condition has been redesigned with the singular focus of minimizing nonlinear transduction mechanisms, thereby allowing for angle random walk (ARW) noise reduction when operating at amplitudes higher than 2 mu m. This is achieved through the following steps: (i) redesigning the Coriolis mass folded flexures and shuttle springs, (ii) linearizing the antiphase coupler spring rate while maintaining parasitic modal separation, (iii) replacing parallel plate transducers with linear combs, (iv) implementing dedicated force-balanced electrostatic frequency tuners, and (v) microTorr vacuum packaging enabling operation at the thermoelastic dissipation limit of silicon. Additionally, cross-axis stiffness is reduced through folded-flexure moment balancing to further reduce ARW. By the balancing of positive and negative Duffing frequency contributions, net frequency nonlinearity was further reduced to -20 ppm. The gyroscope presented in this study has achieved an ARW of 0.0005 deg/root hr, with an uncompensated bias instability of 0.08 deg/hr. These advancements hold promise for enhancing the performance of precision vibratory gyroscopes for navigation and North-finding applications. [2023-0144]

We discuss recent research and development efforts towards low cost, size, weight, and power gyroscopes based on piezoelectric MEMS technology. The potential advantages of piezoelectric and ferroelectric material integration into high performance inertial sensors include the following: significantly increased drive amplitudes for Coriolis Vibratory Gyroscopes relative to electrostatic actuators, dynamically equalized and stabilized Quality Factor mismatch (>>10×) in mode-match gyroscopes, and greatly improved drive amplitude (through 3D, sidewall piezoelectric integration) of mode-split gyroscopes. Piezoelectric thin films with large electromechanical coupling coefficients such as lead zirconate titanate (PbZr x Th 1-x O 3 , PZT) can help to enable these performance benefits. Specifically, we will discuss efforts to optimize PZT thin film deposition using sputtering and new efforts to deposit 3D, conformal PZT using Atomic Layer Deposition (ALD). ALD is a well-established thin film growth technique that may enable conformal deposition of thin films on high aspect-ratio features. ALD of piezoelectric films on high aspect-ratio features, such as arrayed actuator elements, may improve the areal piezoelectric energy density (the total maximum piezoelectric energy projected onto the area of a planar substrate) by up to 200x or more, yielding proportionally larger drive amplitudes for CVGs compared to planar piezoelectric drive elements. However, ALD processes for piezoelectric films such as PZT or AlN are not widely reported. Recent laboratory demonstrations of ALD processes for PZT and a structural isomorph lead hafnate titanate (PbHf x Th 1- x O 3 , PHT) have been successful, yielding piezoelectric perovskite films following a post-deposition anneal. Here, we present a modified process for ALD PHT which has yielded ferroelectric remanent polarizations (2P r ) of 68 μC/cm 2 , apply the new process to ‘ALL ALD’ PHT film stacks on 3D-MEMS comb structures, and present initial results on the integration of ALD PHT into ‘planar’ MEMS QMG. We will also discuss recent efforts to grow AlN by ALD, which have yielded c-axis oriented polycrystalline films with high dielectric breakdown voltage > 10 MV/cm and e 31,f of −0.53 C/m 2 on platinized substrates. This paper will also present results of applying piezo- and ferroelectric materials to gyroscopes to improve performance including 50% Q-tuning resulting in a>>10x improved quality factor mismatch.

This paper presents, for the first time, an indirect excitation method for three-dimensional fused quartz dual-shell micro-scale Hemispherical Resonator Gyroscope μHRG. The μHRG was fabricated using three wafer bonding and high-temperature micro-glassblowing processes, providing a sensing element (device shell), a self-aligned fixed-fixed anchor for increased immunity to mechanical shocks and vibrations, and a housing (cap shell) for vacuum encapsulation. The novel actuation technique uses piezoelectric actuation to transfer energy from the cap shell to the device shell to excite the resonant element, where the piezoelectric material is deposited and shaped on the outer cap shell. Using the proposed indirect excitation method, the metal coating of the device shell is eliminated, preserving the high quality factor of the pristine fused quartz material. In this paper, we first introduce the mechanism of excitation, supported by Finite Element Analysis (FEA). We then describe the Atomic Layer Deposition (ALD) method of PbHf˟Ti1-˟O3 (PHT) piezoelectric material, followed by the fabrication process of a dual-shell μHRG prototype co-fabricated with an 80 nm layer of ALD PHT actuator. Finally, we experimentally demonstrated the indirect excitation, showing the feasibility of the method as a possible alternative to capacitive or direct piezoelectric actuation. Though early in development, the reported excitation approach may offer a preferable method for excitation of μHRGs, allowing to achieve the ultra-high mechanical quality factor, on the level of the TED-limit of fused quartz.

We demonstrate an N2 plasma-enhanced process for inducing (0001)-oriented ALD-grown AlN on planar substrates. We evaluate the impact of {111}-textured Pt as a growth template, precursor chemistry, dose time, stress-engineered substrates, inductively coupled plasma conditions for film bombardment during growth, and ALD equipment configurations. The thin film transverse piezoelectric coefficient e31,f determined from measurements on microelectromechanical system cantilevers coated by PEALD AlN is reported to be −0.53 ± 0.03 C/m2. An analysis of the Pt-AlN interface properties based primarily on depth-profile x-ray photoemission spectroscopy and transmission electron microscopy-energy dispersive spectra is presented. Other than the c axis wurtzite (0001) diffraction peak, no other AlN peaks were observed above the detection limits for XRD measurements. The XRD rocking-curve full-width half-maximum of the 0001 peaks was 2.9° omega, which was achieved on {111}-textured Pt. The relative dielectric constant was measured to be 8.1 < K < 8.6, and an average dielectric loss of < 0.01 was observed within the applied electric field range of ±3350 kV/cm at 10 kHz. The leakage current of the textured AlN was quite low at 1.5 × 10−6 A/cm2 over the applied field range of ±1820 kV/cm.

The effect of stress gradients introduced by thermal expansion mismatch on the resonant frequency of wafer-level packaged devices using 3D finite element models of clamped-clamped beams is presented. The simulations put bounds on the temperature stability of the resonator and show that the vias can shift the resonant frequency by as much as 3,900 ppm with a 100 C temperature change within the device. It was found that the closer to the anchor point a via is placed, the greater the effect the via has, because the strain generated by the via affects the stiffness of the anchor. The introduction of a more compliant anchor structure can increase the temperature stability of the resonator by up to 10x. Results are compared to measured data from Si MEMS devices

This paper reports the development of piezoelectrically actuated radio frequency (RF) micro-electromechanical systems (MEMS) switches on Si-on-sapphire substrates using a novel greyscale lithography fabrication technique. Lead zirconium titanate (PZT) thin-film actuators are used to close a series ohmic contact single-pole single-throw (SPST) switch implemented in co-planar waveguide (CPW). The switch design on a Si substrate has maximum insertion loss of 2.6 dB from DC – 67 GHz. While over the same frequency span, the switch on a sapphire substrate exhibits insertion loss better than 1.4 dB and isolation better than 15 dB. [2020-0071]

This paper reports on the reliability of RF MEMS switches operating in a cryogenic (< 6 K) environment while monitoring the repeatability of their contact resistance (R-c) over time. Series DC-contact switches were actuated with a bipolar waveform then checked for stiction every 100 thousand contacts, and after every million cycles R-c was measured 100 times. Device lifetimes were limited to under 10 million contacts. The dominant failure mechanism is believed to be charging of the substrate underneath the electrostatic MEMS switch leading to permanent hold down of the device.

A linear piezoelectric micromachined ultrasound transducer (PMUT) array was fabricated and integrated into a device for photoacoustic imaging (PAI) of tissue phantoms. The PMUT contained 65 array elements, with each element having 60 diaphragms of 60 mu m diameter and 75 mu m pitch. A lead zirconate titanate (PZT) thin film was used as the piezoelectric layer. The in-air vibration response of the PMUT array elements showed a first mode resonance between 6 and 8 MHz. Hydrophone measurements showed 16.2 kPa average peak ultrasound pressure output at 7.5 mm from one element excited with 5 V-pp input. A receive sensitivity of similar to 0.48 mV/kPa was observed for a PMUT array element with 0 dB gain. The PMUT array was bonded to a custom-printed circuit board to enable compact integration with an optical fiber bundle for PAI. A broad photoacoustic bandwidth of similar to 89% was observed for the photoacoustic response captured from absorbing pencil lead targets. Linear scanning of a single element of a PMUT array was performed on different tissue phantoms embedded with light-absorbing targets to successfully demonstrate B-mode PAI using PMUTs.

Lead zirconate titanate (PZT)-based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized, and tested. The PMUTs had a diaphragm diameter of 60 [Formula: see text], a resonant frequency of ~8 MHz, and an operational bandwidth (BW) of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 Vpp . The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 [Formula: see text] silica beads was shown to be possible with 5 Vpp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move toward diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational BW. Levitation planes were generated above the 30 MHz driving frequency.

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.

Pb(Zr 52 Ti 48 )O 3 (PZT) thin films have been grown by chemical solution deposition on 150 mm Silicon-on-Sapphire (SOS) substrates for RF MEMS applications. Film properties are compared to similar films deposited on typical Si/SiO 2 substrates. PZT films deposited on SOS show improvement in P MAX (37.8 vs. 32.1 μC/cm 2 ) and PREM (22.7 vs. 10.9 μC/cm 2 ) over films deposited on Si. A decrease in maximum εr from 1650 (Si) to 1031 (SOS) is also noted. Crystal structure is examined using x-ray diffraction. Ferroelectric polarization hysteresis curves, dielectric constant tuning, and loss tangent are studied using fabricated capacitors. Piezoelectric coefficients calculated from cantilever LDV measurements are also presented.

This paper documents an architecture approach using extensional mode harmonics to improve the figures of merit (TxFoM) of thin-film piezoelectric MEMS transformers. Modeling of this approach reveals multi-fold improvements in TxFoM as well as the significance and impact of transducer electrical quality factor. Experimental results with PZT-on· $4\mu \mathrm{m}$ Si and AlN transformers verify this architecture approach and show up to 4.3X and 4.4X TxFoM improvements, respectively. These are demonstrated with −63MHz PZT-on-Si and ~69 MHz AlN piezoelectric transformers. Measurement results also reveal the importance of routing resistance and parasitics and their impact on electrical quality factor $Q_{elec}$.

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.

There is continuing interest in radio frequency (RF) microelectromechanical system (MEMS) devices due to their ability to offer exceptional RF performance, high linearity and low power consumption. To date, there is an impressive amount of RF MEMS components such as; switches, resonators, varactors, and tunable inductors that have enabled smaller, cheaper and more efficient RF systems. RF MEMS devices contain micromachined components that have the ability to move so that a change in the mechanical state of a device will result in a change to the device’s RF properties. There are many common modes of actuation, including, but not limited to: electrostatic, magnetostatic, piezoelectric, and electrothermal actuation. Although there are attractive aspects and drawbacks to each of these technologies, this paper will focus on advances in the application of piezoelectric actuation, and in particular the use of lead zirconium titanate (PZT), for RF MEMS.

A Nb superconducting tunable microstrip gap resonator has been designed and fabricated with low stress Au RF MEMS dc-contact switches. The resonator can be tuned in four states from 12-15 GHz. Simulations show that the resonator Q is highly sensitive to the contact resistance of the MEMS when the switches are actuated. Measurements confirm that the Q degrades from 200 to 50. RF performance of the resonator is investigated at cryogenic (4 K) temperatures while the Nb is superconducting.