The team says thermal management is a struggle for the electronics industry as there is no way to measure temperature accurately at the scale of individual microelectronic devices. The mere introduction of a probe, typically larger than the device itself, affects its temperature and precludes an accurate reading. As a result, device manufacturers often rely on simulations.
"If you just simulated the temperature in a microelectronic device, the next thing you want to do is measure the temperature and see if you're right," said Matthew Mecklenburg, a senior staff scientist at the University of Southern California's Center for Electron Microscopy and Microanalysis (CEMMA). "But a persistent question has been how to make these measurements."
The team realised that, because all materials change volume depending on their temperature, the material being imaged could act as its own thermometer. In the study, aluminium was used because its thermal expansion is relatively large.
To measure the density of aluminium, the team aimed the imaging beam from a transmission electron microscope (TEM) at the aluminum, which caused the charges within the aluminum to oscillate. These charge oscillations, or plasmons, shift depending on a material's density. Using the TEM and electron energy loss spectroscopy (EELS), the team quantified the energy of the aluminum plasmon and determined its temperature with nanometre scale resolution.
"Every semiconductor manufacturer measures the size of their devices using TEMs," said Mecklenburg. "Now, in the same microscope, they can measure temperature gradients in an individual device."
The team plans to translate this technique to other materials, including silicon. By applying the approach – called plasmon energy expansion thermometry, or PEET – to other materials used in microelectronic devices, researchers will be able to map temperatures accurately while they are in operation.
