Two-wavelength thermoreflectance in steady-state thermal imaging

Abstract

A methodology of thermoreflectance (TR) imaging using two different optical wavelengths for nonintrusive surface temperature measurement is developed. Compared with the existing single wavelength TR imaging, two-wavelength thermoreflectance (2WTR) imaging collects the required TR signals for temperature measurement solely from the heated target. Therefore, target movement between heated and unheated conditions due to thermal expansion, which is a main obstacle for current single wavelength TR imaging, is properly handled. As a result, a steady state temperature distribution of a heated target can now be determined by the 2WTR imaging method, which is especially useful in determining the operating temperature of microelectronic devices which are sensitive to physical contacts during a measurement. With the 2WTR method, the surface temperature of a microscale gold resistor under different input currents is measured and compared with the results from the corresponding single wavelength TR and heat transfer simulations. The experimental results indicate that 2WTR not only provides temperature measurement with no nonphysical temperature values caused by the target movement, but also has potential for providing a higher signal-to-noise ratio than single wavelength TR when a high bit-depth spatial light modulator and the two optical wavelengths adopted are appropriately selected.