Engineers shrink atomic-force microscope to dime-sized device

March 10, 2017

A MEMS-based atomic force microscope developed by engineers at the University of Texas at Dallas that is about 1 square centimeter in size (top center), shown attached here to a small printed circuit board that contains circuitry, sensors and other miniaturized components that control the movement and other aspects of the device. (credit: University of Texas at Dallas)

University of Texas at Dallas researchers have created an atomic force microscope (AFM) on a chip, dramatically shrinking the size — and, hopefully, the price — of a microscope used to characterize material properties down to molecular dimensions.

“A standard atomic force microscope is a large, bulky instrument, with multiple control loops, electronics and amplifiers,” said Dr. Reza Moheimani, professor of mechanical engineering at UT Dallas.  “We have managed to miniaturize all of the electromechanical components down onto a single small chip.”

Moheimani and his colleagues describe their prototype device in this month’s issue of the IEEE Journal of Microelectromechanical Systems.

A conventional AFM consists of a tiny cantilever, or arm, that has a sharp tip attached to one end. As the apparatus scans back and forth across the surface of a sample, or the sample moves under it, the interactive forces between the sample and the tip cause the cantilever to move up and down as the tip follows the contours of the surface. Those movements are then translated into an image. (credit: CC/Opensource Handbook of Nanoscience and Nanotechnology)

An atomic force microscope (AFM) is a scientific tool that is used to create detailed three-dimensional images of the surfaces of materials, down to the nanometer scale — roughly on the scale of individual molecules.

“An AFM is a microscope that ‘sees’ a surface kind of the way a visually impaired person might, by touching. You can get a resolution that is well beyond what an optical microscope can achieve,” explained Moheimani, who holds the James Von Ehr Distinguished Chair in Science and Technology in the Erik Jonsson School of Engineering and Computer Science.

The MEMS version

The UT Dallas team created its prototype on-chip AFM using a microelectromechanical systems (MEMS) approach.

“A classic example of MEMS technology are the accelerometers and gyroscopes found in smartphones,” said Anthony Fowler, PhD, a research scientist in Moheimani’s Laboratory for Dynamics and Control of Nanosystems and one of the article’s co-authors. “These used to be big, expensive, mechanical devices, but using MEMS technology, accelerometers have shrunk down onto a single chip, which can be manufactured for just a few dollars apiece.”

The MEMS-based AFM is about 1 square centimeter in size, or a little smaller than a dime. It is attached to a small printed circuit board that contains circuitry, sensors, and other miniaturized components that control the movement and other aspects of the device.

Conventional AFM (credit: Asylum Research, Inc.)

Because conventional AFMs require lasers and other large components to operate, their use can be limited. They’re also expensive. “An educational version can cost about $30,000 or $40,000, and a laboratory-level AFM can run $500,000 or more,” Moheimani said. “Our MEMS approach to AFM design has the potential to significantly reduce the complexity and cost of the instrument.

“One of the attractive aspects about MEMS is that you can mass-produce them, building hundreds or thousands of them in one shot, so the price of each chip would only be a few dollars. As a result, you might be able to offer the whole miniature AFM system for a few thousand dollars.”

Semiconductor-industry uses

A reduced size and price tag also could expand the AFMs’ utility beyond current scientific applications.

“For example, the semiconductor industry might benefit from these small devices, in particular companies that manufacture the silicon wafers from which computer chips are made,” Moheimani said. “With our technology, you might have an array of AFMs to characterize the wafer’s surface to find micro-faults before the product is shipped out.”

The lab prototype is a first-generation device, Moheimani said, and the group is already working on ways to improve and streamline the fabrication of the device.

Moheimani’s research has been funded by UT Dallas startup funds, the Von Ehr Distinguished Chair, and the Defense Advanced Research Projects Agency.

Abstract of On-Chip Dynamic Mode Atomic Force Microscopy: A Silicon-on-Insulator MEMS Approach

The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm×8μm in closed loop. [2016-0211]