This review article presents recent advancements in the design and fabrication of thin‐film (<3 μm) lead zirconate titanate (PZT) microelectromechanical system (MEMS) devices. The article covers techniques for optimizing highly (001)/(100) oriented chemical solution deposited PZT films to achieve improved piezoelectric coefficients. These PZT films combined with surface and bulk micromachining techniques are fabricated into actuators and transducers for radio frequency (RF) switches, nanomechanical logic, resonators, and power transformers for use in communication systems and phased‐array radar. In addition, the large relative displacements generated by PZT thin films have been used to demonstrate mechanical mobility in MEMS devices, including insect‐inspired flight actuators and ultrasonic traveling wave motors. In conjunction with actuation, PZT films are being developed for feedback sensors for the integrated control of insect‐inspired robots.
Shape memory alloys (SMAs) have the potential to be used for a wide variety of microelectromechanical systems (MEMS) applications, providing a unique combination of large deflections and high work output. A major drawback for SMAs in many applications has been the low frequency response, which is typically on the order of 100 Hz or lower, even in microscale SMA actuators. In MEMS applications, the higher surface-to-volume ratios have enabled responses to be improved by an order or magnitude or more. By further shrinking the SMA film/device dimensions, the frequency response may be improved even further. In this paper, we present a new, simplified process for fabricating sputtered, thin film SMA MEMS actuators based on nickel-titanium alloy (NiTi or, aka, NITINOL) that consisted of only one photo step to pattern the actuators using SU8. When heated through its solid–solid phase transition from low-temperature martensite to high-temperature austenite, the NiTi alloy undergoes changes in associated physical properties, such as Young’s modulus, resistivity, and surface roughness, that are critical to controlling MEMS performance. For example, these material property changes allow for the design of active or passive microscale sensors and actuators. In the new process, we are able to fabricate ultrathin films of NiTi with nanoscale thickness, which can be thermally cycled through two stable positions very rapidly, making it an intriguing thermal sensor and actuator material for high frequency applications. Additionally, NiTi can be used as an active thermal switch through resistive (i.e. joule) heating. We demonstrated a greatly improved frequency response of up to 3000 Hz with turn on voltages as low as 0.5 V (corresponding to only 1 mW power consumption) for devices exhibiting microns of cantilever tip deflection over millions of cycles, indicating these new SMA MEMS actuators have potential application for low voltage switching, modulation and tuning.
the underside. At this price point, these processes will enhance the small scale metal fabrication capabilities for a wide range of researchers, educators, and small businesses.
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