NTW: In simple terms, how does your actuator work?
Tat Joo Teo: The actuator is realized by the marriage of an electromagnetic (EM) driving scheme and a flexure-based linear bearing. The EM driving scheme, which is similar to that in a voice-coil actuator, consists of stationary permanent magnets and a moving air-core coil. A dual-magnet configuration has been devised to increase the flux density between the air gaps, while the moving coil is supported by the linear flexure bearing without friction. When the coil is energized by a current source, the Lorentz force generated will drive the air-core coil to give a linear motion. Currently, our prototype actuator provides a large thrust force of 60 NA–1 with a positioning accuracy of 10 nm throughout 4 mm of displacement.

How will the device improve the performance of NIL equipment?
One of the big advantages can be seen when you look at the de-molding process that takes place in soft-NIL. This procedure requires a few millimetres of travel to remove the template from the substrate. In existing NIL machines, the imprinting head uses a coarse-fine motion control system. A servo-motor in conjunction with a lead screw is employed to achieve millimetres of travel, while an additional piezo-actuator with nano-resolution and a range of a few hundred micrometres is integrated to realize the fine positioning of the template.

Using our actuator design, the NIL imprinting head can be more compact and less complex, as our single unit provides nanometre resolution over a stroke length of several millimetres.

Why was it important to model the behaviour of the actuator?
During the imprinting processes, transition between the fine positioning and direct-force control is crucial. Modelling the behaviour of our actuator allows the development of a sophisticated solution to realize a smooth transition between both control schemes. Such a smooth transition is essential as it can protect the silicon template from damage by preventing a sudden approach to the substrate during the imprinting process. It also helps to preserve the imprinted features on the substrate by preventing sudden extrusion during the de-molding process.

What are the next steps for you and your colleagues?
We are now working on a three degrees-of-freedom imprinting head with active tilting alignment capability for use with multilayer step and flash NIL. We will engage industrial partners to commercialize the technology once the research prototype has been successfully developed.

The researchers presented their work in Nanotechnology.