An official website of the United States government
Abstract High‐power piezoelectric applications are predicted to share approximately one‐third of the lead‐free piezoelectric ceramic market in 2024 with alkaline niobates as the primary competitor. To suppress self‐heating in high‐power devices due to mechanical loss when driven by large electric fields, piezoelectric hardening to restrict domain wall motion is required. In the present work, highly effective piezoelectric hardening via coherent plate‐like precipitates in a model system of the (Li,Na)NbO3(LNN) solid solution delivers a reduction in losses, quantified as an electromechanical quality factor, by a factor of ten. Various thermal aging schemes are demonstrated to control the average size, number density, and location of the precipitates. The established properties are correlated with a detailed determination of short‐ and long‐range atomic structure by X‐ray diffraction and pair distribution function analysis, respectively, as well as microstructure determined by transmission electron microscopy. The impact of microstructure with precipitates on both small‐ and large‐field properties is also established. These results pave the way to implement precipitate hardening in piezoelectric materials, analogous to precipitate hardening in metals, broadening their use cases in applications.
more »
« less
Heat generation in PZT MEMS actuator arrays
Piezoelectric microelectromechanical systems (piezoMEMS) enable dense arrays of actuators which are often driven to higher electrical fields than their bulk piezoelectric counterparts. In bulk ceramics, high field driving causes internal heating of the piezoelectric, largely due to field-induced domain wall motion. Self-heating is then tracked as a function of vibration velocity to determine the upper bound for the drive levels. However, the literature is limited concerning self-heating in thin film piezoMEMS. In this work, it is shown that self-heating in piezoMEMS transducer arrays occurs due to domain wall motion and Ohmic losses. This was demonstrated via a systematic study of drive waveform dependence of self-heating in piezoMEMS arrays. In particular, the magnitude of self-heating was quantified as a function of different waveform parameters (e.g., amplitude, DC offset, and frequency). Thermal modeling of the self-heating of piezoMEMS using the measured hysteresis loss from electrical characterization as the heat source was found to be in excellent agreement with the experimental data. The self-heating model allows improved thermal design of piezoMEMS and can, furthermore, be utilized for functional heating, especially for device level poling.
more »
« less
- PAR ID:
- 10384184
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 121
- Issue:
- 16
- ISSN:
- 0003-6951
- Page Range / eLocation ID:
- 162906
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.more » « less
-
null (Ed.)Understanding the failure mechanisms of piezoelectric thin films is critical for the commercialization of piezoelectric microelectromechanical systems. This paper describes the failure of 0.6 mu m lead zirconate titanate (PZT) thin films on Si wafers with different in-plane stresses under large electric fields. The films failed by a combination of cracking and thermal breakdown events. It was found that the crack initiation and propagation behavior varied with the stress state of the films. The total stress required for crack initiation was estimated to be near 500 MPa. As expected, cracks propagated perpendicular to the maximum tensile stress direction. Thermal breakdown events and cracks were correlated, suggesting coupling between electrical and mechanical failure. It was also found that films that were released from the underlying substrates were less susceptible to failure by cracking. It was proposed that during electric field loading the released film stacks were able to bow and alleviate some of the stress. Released films may also experience enhanced domain wall motion that increases their fracture toughness. The results indicate that both applied stress and clamping conditions play important roles in the electromechancial failure of piezoelectric thin films.more » « less
-
In this work with a model system (Ba,Ca)TiO3, we analyze the morphologies of CaTiO3-rich precipitates and their impacts on the microstructures in their surrounding BaTiO¬3-rich matrix. Also, the response of ferroelectric domains around CaTiO3-rich precipitates during heating and cooling is observed in-situ with transmission electron microscopy. Domains attached to precipitates are observed remaining unchanged up to the Curie point at which they disappear. During cooling, domains are observed to form in the vicinity of precipitates and being held in place down to room temperature. Both observations corroborate previous findings that precipitates act as domain pinning points, behaving in a similar manner to earlier experiments with electrical field biasing. Dislocations are often seen around precipitates in the matrix grain and are observed interfering with domains during heating cycles. Dislocations may provide an additional mechanism to restrict domain wall motion and offer a greater piezoelectric hardening effect.more » « less
-
Abstract Thin films based on PbZr1−xTixO3and K1−xNaxNbO3are increasingly being commercialized in piezoelectric MEMS due to the comparatively low drive voltages required relative to bulk actuators, as well as the facile approach to making sensor or actuator arrays. As these materials are incorporated into devices, it is critically important that they operate reliably over the lifetime of the system. This paper discusses some of the factors controlling the electrical and electromechanical reliability of lead zirconate titanate (PZT)-based piezoMEMS films. In particular, it will be shown the gradients in the Zr/Ti ratio through the depth of the films are useful in increasing the lifetime of the films under DC electrical stresses.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0114670
