Nabila Nujhat demonstrates reactive ion etching, part of the fabrication process for the combined magnonic and acoustic devices she is developing.
Dressed in clean-room garb — hairnet, safety glasses, lab coat, and gloves — Nabila Nujhat gets to work on creating a device that she hopes will one day be inside her cellphone.
“We are exploring a very new area, so that’s why I am interested in this research,” said Nujhat, an electrical and computer engineering Ph.D. student in the College of Engineering at Oregon State University.
Her field is magnonics, an emerging technology for advanced electronics. Instead of electric currents, magnonic devices use spin waves, waves of magnetization that travel in magnetic materials, to transmit and process signals.
Nujhat is working to combine spin waves with acoustic wave technology, yet another way of transmitting a signal.
Acoustic wave devices are already in your cellphone. The radio wave that your cell phone receives is converted to an acoustic wave for processing. The acoustic wave devices are part of the filters that make sure you are getting calls and texts for your phone only, and not your neighbor’s phone.
It turns out that acoustic wave devices are pretty good at linear tasks, such as selecting the right frequency, but not so good at more complicated processing tasks, such as shifting frequencies and determining the similarity between two signals. Currently, those tasks are done by electronics, but performance could be improved by replacing them with combined magnonic and acoustic devices.
The advantage, as well as challenge, with spin waves and acoustic waves is that they are much slower than radio waves: A sound wave in a device travels just a few millimeters in the same amount of time that a radio wave could travel half a kilometer. As a consequence, the devices Nujhat is developing need to be tiny. Really tiny.
“At the present moment all the devices we are developing are in the micrometer or nanometer range,” Nujhat said.
So, the advantage is that the devices can be very small — fitting into wearable technology, for example. The challenge is that creating the devices requires state-of-the-art fabrication technology.
The structures Nujhat makes are designed to create, manipulate, and detect acoustic and spin waves. The whole fabrication process, which takes several steps, can take about a week for the devices she is currently working on. The major processes include depositing the material (often aluminum for this application) onto a silicon wafer, using lithography to transfer a pattern onto the material, and then removing the excess material from the pattern (etching).
For devices so small, she needs sophisticated equipment that can do very precise etching to create patterns of one micrometer width. The clean room at Oregon State is fortunate to be equipped with a reactive ion etch, which uses chemically reactive plasma to do the etching. In fact, the presence of well-equipped labs at Oregon State is one of the reasons Nujhat chose to come here.
“There are many steps involved in device fabrication and characterization, but you have the facilities here to do everything,” Nujhat said.
Nujhat is part of the Applied Magnetics Lab, where she works with other graduate students on exploring how the acoustic and spin waves behave and interact, which helps inform the design of new signal processing devices.
“We are at the beginning of a research area that will be very rich to explore for physics, new materials and, naturally, new devices with compactness, power efficiency and functionality we have not seen before,” said Pallavi Dhagat, director of the Applied Magnetics Lab and associate professor of electrical and computer engineering in the College of Engineering.
Note: The purchase of the reactive ion etch was made possible by a grant from M.J. Murdock Charitable Trust.