| RESEARCH HIGHLIGHTS |
scanning electron microscopy analysis of the solidified emulsion revealed that the drugs and polymer spheres had integrated into a porous, scaffold-like structure. After mechanically grinding the freeze-
dried emulsion into drug nanostructures, the researchers found their open framework made it simple to dissolve them into
water. Furthermore, the drugs could be transformed into nanoparticles with yields of 100 per cent using surprisingly low levels of PEG-PNIPAM spheres. “The polymer structure and level of
branching directly affect drug nanoparticle stabilization. This method gives us a way to investigate it systematically,” says Jackson.
He notes that this method is synthetically straightforward and could be applied to a wide range of pharmaceuticals.
1. Wais, U., Jackson, A. W., Zuo, Y., Xiang, Y., He, T. & Zhang, H. Drug nanoparticles by emulsion-freeze- drying via the employment of branched block copolymer nanoparticles. Journal of Controlled Release 222, 141–150 (2016).
Electronics:
DIAMONDS MAKE A DEVICE COOLER
A LAYER OF DIAMOND CAN PREVENT HIGH-POWER ELECTRONIC DEVICES FROM OVERHEATING
Powerful electronic components can get very hot. When many components are combined into a single semiconductor chip, heating can become a real problem. An overheating electronic component wastes energy and is
at risk of behaving unpredictably or failing altogether. Consequently, thermal manage- ment is a vital design consideration. This becomes particularly important in devices made from gallium nitride. “Gallium
nitride is capable of handling high voltages, and can enable higher power capability and very large bandwidth,” says Yong Han from the A*STAR Institute of Microelectronics. “But in a gallium nitride transistor chip, the heat concentrates on tiny areas, forming several hotspots.” This exacerbates the heating problem. Han and co-workers demonstrate both
experimentally and numerically that a layer of diamond can spread heat and improve the thermal performance of gallium nitride devices. The researchers created a thermal test
chip that contained eight tiny hotspots, each 0.45 by 0.3 millimeters in size, to generate the heat created in actual devices. They bonded this chip to a layer of high-quality diamond fabricated using a technique called chemical vapor deposition. The diamond heat spreader and test chip were connected using a thermal compression bonding process. This was then connected to a microcooler, a device con- sisting of a series of micrometer-wide channels and a microjet impingement array. Water impinges on the heat source wall, and then passes through the microchannels to remove the heat and keep the structure cool. Han and the team tried their device by
A test sample comprised of a thermal chip, a heat spreader and a microcooler demonstrates the efficiency of diamond for removing heat from hotspots in semiconductor electronics.
generating 10–120 watts of heating power in test chips of 100 and 200-micrometer thickness. To dissipate the heating power, the diamond heat spreading layer and microcooler helped maintain the structure at a tempera- ture below 160 degrees Celsius. In fact, the maximum chip temperature was 27.3 per cent lower than another device using copper as the heat spreading layer, and over 40 per cent lower than in a device with no spreading layer. The experimental results were further
confirmed by thermal simulations. The sim- ulations also indicated that the performance
www.astar-research.com A*STAR RESEARCH 17
© 2016 A*STAR Institute of Microelectronics
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