ed by Chang-Beom Eom, a UW-Madison professor of materials science and engineering and physics, the researchers study the advanced piezoelectric material lead magnesium niobate-lead titanate, or PMN-PT. Such materials exhibit a “giant” piezoelectric response that can deliver much greater mechanical displacement with the same amount of electric field as traditional piezoelectric materials. They also can act as both actuators and sensors. For example, they use electricity to deliver an ultrasound wave that penetrates deeply into the body and returns data capable of displaying a high-quality 3-D image.
Currently, a major limitation of these advanced materials is that to incorporate them into very small-scale devices, researchers start with a bulk material and grind, cut, and polish it to the size they desire. It’s an imprecise, error-prone process that’s intrinsically ill-suited for nanoelectromechanical systems (NEMS) or microelectromechanical systems (MEMS).
Until now, the complexity of PMN-PT has thwarted researchers’ efforts to develop simple, reproducible microscale fabrication techniques. Applying microscale fabrication techniques such as those used in computer electronics, Eom’s team has overcome that barrier, integrating PMN-PT seamlessly onto silicon. Because of potential chemical reactions among the components, they layered materials and carefully planned the locations of individual atoms.
Onto a silicon “platform,” they add a very thin layer of strontium titanate, which acts as a template and mimics the structure of silicon. Next comes a layer of strontium ruthenate, an electrode Eom developed some years ago, and finally, the single-crystal piezoelectric material PMN-PT.
His team calls devices fabricated from this giant piezoelectric material “hyperactive MEMS” for their potential to offer researchers a high level of active control. Using the material, his team also developed a process for fabricating piezoelectric MEMS.
Applied in signal processing, communications, medical imaging and nanopositioning actuators, hyperactive MEMS devices could reduce power consumption and increase actuator speed and sensor sensitivity. Additionally, through a process called energy harvesting, hyperactive MEMS devices could convert energy from sources such as mechanical vibrations into electricity that powers other small devices; for example, for wireless communication.