Power/Performance Bits: Jan. 3

Optical device integration
Researchers from the University of Strathclyde, University of Glasgow, and the Australian National University propose a way to place multiple micron-scale optical devices made from different materials close together on a single silicon chip.

“The development of electronics that are based on silicon transistors has enabled increasingly more powerful and flexible systems on a chip,” said Dimitars Jevtics from the University of Strathclyde. “Optical systems on a chip, however, require integration of different materials on a single chip and, therefore, have not seen the same development in scale as silicon electronics.”

“On-chip optical communications, for example, will require the assembly of optical sources, channels and detectors onto sub-assemblies that can be integrated with silicon chips,” said Jevtics. “Our transfer printing process could be scaled up to integrate thousands of devices made from different materials onto a single wafer. This would enable micron-scale optical devices to be incorporated into future computer chips for high-density communications or into lab-on-a-chip bio-sensing platforms.”

The transfer printing method uses a soft polymer stamp mounted on a robotic motion control stage to pick up an optical device from the substrate on which it was made. The substrate onto which it will be placed is then positioned under the suspended device and accurately aligned using a microscope. Once aligned properly, the two surfaces are brought into contact, which releases the device from the polymer stamp and deposits it onto the target surface. Advances in accurate micro-assembly robotics, nanofabrication techniques and microscopy image processing helped make this approach possible.

“By carefully designing the geometry of the stamp to match the device and controlling the stickiness of the polymer material, we can engineer whether a device will be picked up or released,” said Jevtics. “When optimized, this process does not induce any damage and can be scaled up using automation to be compatible with wafer-scale manufacturing.”

To demonstrate the technique, the researchers integrated aluminum gallium arsenide, diamond, and gallium nitride optical resonators onto a single chip. The also created semiconductor nanowire lasers by placing nanowires onto host surfaces in spatially dense arrangements.

“As a manufacturing technique, this printing approach is not limited to optical devices,” said Jevtics. “We hope that electronics specialists will also see possibilities for how it could be applied in future systems.”

Next, they plan to replicate these results with larger numbers of devices to show that it works at larger scales as well as combine the transfer printing approach with an automated alignment technique.

Magnetic energy harvesting
Bioengineers at University of California Los Angeles propose a wearable energy harvesting device to power wearable and implantable diagnostic sensors.

It relies upon the magnetoelastic effect, which is the change of how much a material is magnetized when tiny magnets are constantly pushed together and pulled apart by mechanical pressure. The researchers found that the effect can exist in a soft and flexible system, not just one that is rigid. The team used microscopic magnets dispersed in a paper-thin silicone matrix to generate a magnetic field that changes in strength as the matrix undulated. As the magnetic field’s strength shifts, electricity is generated.

“Our finding opens up a new avenue for practical energy, sensing and therapeutic technologies that are human-body-centric and can be connected to the Internet of Things,” said Jun Chen, an assistant professor of bioengineering at UCLA Samueli. “What makes this technology unique is that it allows people to stretch and move with comfort when the device is pressed against human skin, and because it relies on magnetism rather than electricity, humidity and our own sweat do not compromise its effectiveness.”

The team built a small, flexible magnetoelastic generator made of a platinum-catalyzed silicone polymer matrix and neodymium-iron-boron nanomagnets. About the size of a U.S. quarter, the device was affixed it to a subject’s elbow with a soft, stretchy silicone band. The magnetoelastic effect they observed was four times greater than similarly sized setups with rigid metal alloys. As a result, the device generated electrical currents of 4.27 milliamperes per square centimeter, which the team said is 10,000 times better than the next best comparable technology.

The flexible magnetoelastic generator is sensitive enough that it could convert human pulse waves into electrical signals and act as a self-powered, waterproof heart-rate monitor. The electricity generated can also be used to sustainably power other wearable devices, such as a sweat sensor or a thermometer.

The researchers said that the device has shown good durability, testing well even after being soaked in artificial perspiration for a week. They have filed for a patent on the technology.