Production of silicon micro- and nanosensors with today’s technologies requires a full-scale clean-room laboratory costing millions of euros – facilities that few organisations can afford. What’s more, integrated-circuit manufacturing technologies used in sensor production are highly standardised processes, optimised for extremely large production volumes of hundreds of millions of devices per year. These sensors, known as Micro Electromechanical Systems (MEMS), are engineered from thin slices of silicon, the same material used to manufacture integrated circuits and other micro-sized electronic devices.
Researchers at KTH Microsystem Technology have demonstrated a manufacturing concept that could pave the way toward simple, inexpensive “printing” of 3D silicon structures
Schematic of the 3D printing process and an image of a manufactured microstructure
Advanced Functional Materials - 3D Free-Form Patterning of Silicon by Ion Implantation, Silicon Deposition, and Selective Silicon Etching
Abstract - A method for additive layer-by-layer fabrication of arbitrarily shaped 3D silicon micro- and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide.
“It could be made very easy, flexible and cheap compared with today’s manufacturing processes. All you’ll need is a 3D printer and someone to draw the structure in a drafting programme on a computer,” says Frank Niklaus, Associate Professor at KTH Microsystem Technology.
The new manufacturing technology consists of a layer-by-layer process for defining 3D patterns in silicon, using focused ion beam writing followed by silicon deposition. The layered 3D silicon structures are defined by repeating these two steps over and over, followed by a final etching step in which the excess silicon material is dissolved away. The researchers note, however, that the system has so far only been tested manually on relatively simple structures, and that more testing lies ahead to definitively prove the concept’s viabilityand that more development lies ahead to implement the concept in a manufacturing tool known as a 3D printer.
“In a future manufacturing process, the structure would first be designed in a 3D drawing programme. The drawing is then sent to a 3D printer that recreates the structure in silicon, layer by layer from the bottom up,” explains Niklaus.
the researchers are working to refine the process on a larger scale, and they plan to develop 3D printer that enables the creation of complex 3D silicon nanostructures. The next step is to commercialise the manufacturing technology in collaboration with partners from industry.
Sensors that detect the orientation and movements of mobile phones or airbag systems in cars are just a few examples of the applications for micro and nano-scale sensors.
“Just imagine all the new applications that people could come up with if they had an easy and cheap way to manufacture nanostructures for sensors and devices. With this tool, we want to enable smaller markets and organisations to advance sensors and other technologies in ways that we can’t even imagine today. I’d compare it to the way affordable computing opened things up for innovation in information technologies over the last 30 years or so.”
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