Challenges and opportunities for transient thermal imaging of microelectronic devices

In the development of electronic devices, transient thermal information is necessary to validate whether the entire device or a specific part of the device is operating properly. This becomes even more important for higher frequency operation of such devices. Sometimes, this is more important for the circuit designers, process engineers, or chip architects, rather than the thermal or package engineers who mostly need just a few points or locations of time-averaged temperature data during the design phase. For the time domain, recent developments in thermoreflectance imaging allow us to achieve a wide range of time scales from 50 nanoseconds up to milliseconds. This study provides an example of transient thermal imaging on a test chip along with the thermoreflectance imaging technique. The discussion covers the relationship of spatial resolution and time resolution considering the `time constant' component of the chip. Spatial resolution for thermoreflectance is limited by the diffraction of the illuminating light, time resolution is limited by the high speed electrical signal management, and temperature resolution is limited by the signal-to-noise ratio. Time averaging, therefore, plays an important role in determining temperature resolution. The scientific inter-relationship between these factors adds to the complexity. The modeling work described above provides a guideline for the `scope' and `probe' depending on the dimensional scale of interest.