Lead-free piezoelectric boost for medical sensors
Researchers at EPFL in Switzerland have developed a lead-free piezoelectric material that could boost the performance of micromachined medical sensors.
The gadolinium-doped cerium oxide promises to be 100 times more effective that today’s materials and bio-compatible for medical applications.
By manipulating atomic defects in a lead-free material that is normally not piezoelectric, it is possible to induce a large piezoelectric effect.
“Piezoelectric materials convert electrical energy into mechanical energy and vice-versa,” said Dr. Dae-Sung Park, a postdoc at EPFL’s research group for ferroelectrics and functional oxides, headed by Prof. Dragan Damjanovic. “They are practical and versatile and can be used as force sensors, actuators for moving objects or high-frequency resonators for imaging and electronic filters.”
Micro-electro-mechanical systems (MEMS) hold great promise for biomedical applications, such as for diagnostics, prognostics and therapeutics, but the lead metal that the best of them contain is toxic to the human body and environment. Researchers are therefore working to create lead-free alternatives to the piezoelectric materials currently employed in MEMS.
The research done by Dr. Park and Prof. Damjanovic was carried out under the BioWings project, a Horizon 2020 project to develop lead-free MEMS that can be used as actuators in various types of biomedical applications.
“The main objective of BioWings is to develop systems that are based on a property called electrostriction, rather than piezoelectricity,” says Damjanovic.
Electrostriction, like piezoelectricity, entails converting electrical into mechanical energy. It occurs to some extent in all materials, but the effect is usually very small. “The main difference between piezoelectricity and electrostriction is that piezoelectric materials either expand or contract depending on the electrical field that’s applied,” says Damjanovic. “Electrostrictive materials deform the same way regardless of the orientation of the electric field.”
The EPFL researchers found a way to break this symmetrical electrostrictive effect by applying a constant electric field in addition to an alternating field . This essentially turned the electrostrictive property of gadolinium-doped cerium oxide into a piezoelectric one.
“The addition of gadolinium in ceria creates a large concentration of atomic defects (oxygen vacancies) that are mobile in the presence of an electric field. That means that a strong piezoelectric effect in gadolinium-doped cerium oxide can be induced by controlling the defects,” says Park. “By manipulating the mobile defects, we can increase piezoelectric susceptibility by a factor of 100 relative to even the most powerful lead-containing piezoelectric materials.” Damjanovic adds: “Our goal is not to eliminate or replace these materials, but rather to provide alternatives to those containing lead.”
“Ours is a major scientific discovery for the fields of ionic, piezoelectric and ferroelectric materials,” said Park.
The project has received funding from the European Union under the Horizon 2020 framework, as part of the Future Emerging Technologies (FET) Open programme. The project partners include research centers in Denmark, Israel, Sweden and Switzerland.
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