Research Bits: March 1

Large-scale phased array
Researchers at Princeton University developed a large-scale high-frequency antenna array using thin-film materials.

“To achieve these large dimensions, people have tried discrete integration of hundreds of little microchips. But that’s not practical — it’s not low-cost, it’s not reliable, it’s not scalable on a wireless systems level,” said senior study author Naveen Verma, a professor of electrical and computer engineering at Princeton. “What you want is a technology that can natively scale to these big dimensions. Well, we have a technology like that — it’s the one that we use for our displays” such as computer monitors and liquid-crystal display (LCD) televisions.

The researchers used zinc-oxide thin-film transistors to create a 1-foot-long row of three antennas, in a phased array setup. Phased antenna arrays can transmit narrow-beam signals that can be digitally programmed to achieve desired frequencies and directions. Each antenna in the array emits a signal with a specified time delay from its neighbors, and the constructive and destructive interference between these signals add up to a focused electromagnetic beam.

Phased array systems are used in long-distance communication systems such as radar systems, satellites, and cellular networks, and the researchers said the thin-film antennas could enable them to operate at a different range or radio frequencies.

“A phased array can electrically scan the beam to different directions, so you can do point-to-point wireless communication,” said Can Wu, a postdoctoral researcher at Stanford University. “Large-area electronics is a thin film technology, so we can build circuits on a flexible substrate over a span of meters, and we can monolithically integrate all the components into a sheet that has the form factor of a piece of paper.”

The team fabricated the transistors and other components on a glass substrate but note that a similar process could be used for flexible plastic substrates.

Some of the applications the researchers propose include applying it to walls, where it could enable communication with distributed IoT devices, and to boost communication with aircraft. “With an airplane, because its distance is so far, you lose a lot of the signal power, and you want to be able to communicate with high sensitivity. The wings are a fairly large area, so if you have a single point receiver on that wing it doesn’t help too much, but if you can expand the amount of area that’s capturing the signal by a factor of a hundred or a thousand, you can reduce your signal power and increase the sensitivity of your radio,” said Verma.

3D printed NEMS resonators
Researchers from the Politecnico di Torino and the Hebrew University of Jerusalem used 3D printing to create nano-electro-mechanical system resonators (NEMS, the smaller version of MEMS) with quality, stability, mass sensitivity, and strength comparable to those of silicon resonators.

The team built three of the most common resonator designs (membranes, cantilever, and bridges) with lengths ranging from 20 to 50 µm, width from 2 to 5 µm, and thickness between 250 and 2000 nm, using two-photon polymerization on new liquid compositions. This was followed by a thermal process that removes the organic content, leaving a ceramic structure with high rigidity and low internal dissipation.

“The NEMS that we have fabricated and characterized have mechanical performances in line with current silicon devices, but they are obtained through a simpler, faster, and more versatile process, thanks to which it is also possible to add new chemical-physical functionalities. For example, the material used in the article is Nd:YAG [neodymium-doped yttrium aluminum garnet], normally used as a solid-state laser source in the infrared range,” said Stefano Stassi of the Department of Applied Science and Technology at Politecnico di Torino.

The researchers said that the 3D-printed NEMS create highly sensitive mass and force sensors.

“The ability to fabricate complex and miniature devices that have performance similar to silicon ones by a quick and simple 3D printing process, brings new horizons to the field of additive manufacturing and rapid manufacturing,” added Shlomo Magdassi of the Hebrew University of Jerusalem.