Time and frequency domain CCD-based thermoreflectance techniques for high-resolution transient thermal imaging

Thermoreflectance microscopy is a well established method for the thermal imaging of (opto)electronic components and ICs. The technique combines submicron spatial resolution with excellent temperature resolution (10mK can be achieved). The dynamic thermal behavior can be studied using either a transient pulsed boxcar or frequency domain approach, the latter including homodyne and heterodyne lock-in systems. Temporal scales in the nanosecond range can be resolved. The basic principles of the various methods are reviewed, and their associated advantages and drawbacks are compared. We also propose a novel heterodyne technique as an alternative to the ´four bucket´ method that has been used so far. Our approach greatly reduces the timing complexity while eliminating a major source of systematic error. Illustrative case studies present the transient and AC heat diffusion in integrated gold heaters, and separate imaging of Joule and Peltier effects in a 20×20μm² thermoelectric microcooler.