IR microscopy technology
Probe propels IR thermal microscopy to a new level
Adding a tiny probe to an IR microscope improves its temperature measurement capability, in turn giving new insights into the local heating profile of HEMTs and LEDs, according to a UK team comprising Chris Oxley, Richard Hopper, Dominic Prime, Mark Leaper and Gwynne Evans from De Montfort University and Andrew Levick from the National Physical Laboratory.
D
evices are being driven at higher and higher power densities. Cranking up the current in
LEDs increases their brightness, making them suitable for deployment in car headlights, projectors and general illumination. Meanwhile, the emergence of RF transistors made from GaN rather than GaAs has increased the W/mm2 figure by an order of magnitude.
Creating these new chips - which can extract far more performance from the same-sized footprint - is helping to drive the compound semiconductor industry forward. Customers incorporating these chips into their products are able to buy fewer of them, making whatever they build
not only cheaper to produce, but also simpler, smaller, lighter and potentially more reliable.
It is very rare to enjoy gains without paying a penalty somewhere, and in this case it is the issues relating to a hotter device. Temperatures tend to vary across the chip, creating localised hot spots that are seen as a common cause of device failure. Exposing their location and recording the local temperature offers an important first step on the road to improving the thermal management of the chip and ultimately increasing its reliability. Raman thermography offers one well-developed approach to uncovering local temperatures on a chip. This technique
Figure 1: The Quantum Focus IR microscope has a 256 x 256 pixel InSb detector array cooled to 77 K to detect radiation in the 2-5 µm wavelength band. Using a 25x objective the spatial resolution is around 3 µm over a field of view 230 µm x 230 µm. The temperature sensitivity is 0.1 °C and it has a temperature range of 300 °C. The instrument has been provided with the capability of DC and RF probing, enabling electrical bias and electrical measurements to be made during thermal characterisation of the device
January / February 2011
www.compoundsemiconductor.net 33
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