Machine Design

Scanning for Ideas: Thin-Film Device Keeps Chips and Lasers Cool

Laser diodes used to illuminate telecom fiberoptic cables keep getting smaller and smaller. But they still generate heat that needs to be removed.

For example, a low-power laser diode might generate only 0.09 W of power. But the diode measures 300 200 μm, so it puts out about 150 Wcm2. To keep these and similarly small devices cool and operational, engineers at Nextreme Thermal Solutions Inc., Durham, N.C. (nextreme.com), developed the UPF OptoCooler, a thin-film thermoelectric cooling device for flip-chip packages. It can remove up to 420 mW at 25°C ambient and has an active footprint of 0.55 m2. Thin-film device keeps chips and lasers cool This lets it pump 78 Wcm2 or cool to 45°C. The device also lets engineers tackle thermal problems at the source rather than just try to cool an entire enclosure, an inefficient approach..

The device contains thermal bumps, in effect a series of copper pillars with a thin film of thermal material (either an n or p-type semiconductor) that converts pillars into solid-state heat pumps. The bumps cool on one side and heat on the other as current passes through them. Heat moves in the direction of the current. This is known as the Peltier Effect. (Conversely, applying a temperature gradient to the properly doped bumps would create current, thus generating electricity from heat, i.e., the Seebeck Effect.)

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