Accelerometers in mobile phones, microprocessors in laptops, and gyroscopes that balance drones each rely on microelectromechanical systems, or MEMS for short. Within these small systems are even smaller devices, called actuators and sensors, that perform various physical functions.
One type is a thermal actuator, which transforms energy into motion by the expansion and contraction of materials due to temperature changes. You'll find MEMS thermal actuators inside computer disk drives, scanning probes and microengines.
Currently, these thermal actuators rely on polysilicon, a material that requires high temperatures and consumes a considerable amount of power during the fabrication process. While working on related research, investigators at Carnegie Mellon University's College of Engineering realized they had found an efficient substitute.
Led by Maarten de Boer, professor of mechanical engineering, the team created microelectromechanical thermal actuators with tantalum instead of polysilicon. This lowered both the operating temperature and energy consumption that would be necessary for a given amount of actuation. The results were published in Nature Microsystems & Nanoengineering.
Tantalum is a rare, refractory metal, often used in alloys to increase strength and durability. The researchers theorized that tantalum thermal actuators — due to the metal's large coefficient of thermal expansion compared to the silicon substrate on which it is made — would require less than half the power input for the same force and displacement than those made with polysilicon.
Operating at a lower voltage than other thermal actuators, the tantalum ones are directly compatible with complementary metal oxide semiconductor (CMOS) circuits. The tantalum devices could be processed nearly at room temperature.
"In principle, this work demonstrates the viability of using tantalum not only to fabricate thermoactuators but also many sensors for use in a wide range of integrated nanoelectronics," said de Boer.
