  The microelectronics industry is pushing the fundamental limit on the
physical size of individual elements to produce faster and more powerful
integrated chips. These chips have nanoscale features that dissipate power
resulting in nanoscale hotspots leading to device failures. To understand the
reliability impact of the hotspots, the device needs to be tested under the
actual operating conditions. Therefore, the development of high-resolution
thermometry techniques is required to understand the heat dissipation processes
during the device operation. Recently, several thermometry techniques have been
proposed,such as radiation thermometry, thermocouple based contact thermometry,
scanning thermal microscopy (SThM), scanning transmission electron microscopy
(STEM) and transition based threshold thermometers. However, most of these
techniques have limitations including the need for extensive calibration,
perturbation of the actual device temperature, low throughput, and the use of
ultra-high vacuum. Here, we present a facile technique, which uses a thin film
contact thermometer based on the phase change material Ge2Sb2Te5, to precisely
map thermal contours from the nanoscale to the microscale. Ge2Sb2Te5 undergoes
a crystalline transition at Tg with large changes in its electric conductivity,
optical reflectivity and density. Using this approach, we map the surface
temperature of a nanowire and an embedded micro-heater on the same chip where
the scales of the temperature contours differ by three orders of magnitude. The
spatial resolution can be as high as 20 nanometers thanks to the continuous
nature of the thin film.
