Engineers unveil centimetre-sized AFM

Editorial

Rebecca Pool

Thursday, February 16, 2017 - 15:15
Image: MEMS-based AFM attached to a small printed circuit board. [University of Texas at Dallas]
 
Researchers at The University of Texas at Dallas have created an atomic force microscope on a chip, dramatically reducing the complexity and price compared to the macroscale system.
 
As Professor Reza Moheimani from Mechanical Engineering at UT Dallas says: "A standard atomic force microscope... has multiple control loops, electronics and amplifiers. We have managed to miniaturize all of the electromechanical components down onto a single small chip."
 
Moheimani  and his team created the prototype on-chip AFM using a microelectromechanical systems (MEMS) approach.
 
"Classic examples of MEMS technology are the accelerometers and gyroscopes found in smartphones," explains Dr Anthony Fowler, a research scientist in Moheimani's Laboratory for Dynamics and Control of Nanosystems.
 
"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," he adds.
 
The MEMS-based AFM is about 1 cm2 and is attached to a small printed circuit board, about half the size of a credit card.
 
The PCB contains circuitry, sensors and other miniaturised components that control the movement and other aspects of the device.
 
According to Moheimani: "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 MEMS-based AFM operates in tapping mode, and as the probe moves back and forth across a sample, a feedback loop maintains the height of that oscillation, ultimately creating an image.
 
"A 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," says Moheimani.
 
"An educational AFM can cost about $30,000 or $40,000, and a laboratory-level AFM can run to $500,000 or more," he adds. "But you can mass produce MEMS... 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."
 
The researcher believes the semiconductor industry would benefit from their on-chip dynamic mode AFM. 
 
"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," he highlights.
 
The lab prototype is a first-generation device, and the group is working on ways to improve and streamline the fabrication of the device.
 
 
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