ABSTRACT
Electrical impedance is one of the most important and frequently referred to properties of a material. The quantity is a complex number with strong frequency dependence. One of the major challenges of combinatorial materials science is reliable, rapid, nondestructive, and quantitative screening of electrical properties of materials chips. No existing tool with these capabilities was available at the time of our initial effort in combinatorial materials science. Most inspection tools in the semiconductor industry employ light as a probing signal. However, a material’s index of refraction (i.e., the electrical impedance) at light frequencies (1016/ s) has almost no direct correlation with the electrical impedance at working frequencies (109/s) of microelectronics. For electronic applications, lower-range microwave frequencies (i.e., 1-10 GHz) are most relevant and best suited to characterize electrical impedance. However, the wavelengths of propagating microwaves in this frequency range are very long (order of centimeters), which limit the spatial resolution of the measurements. Rapid development in both the microelectronics industry and materials science has also raised the demand for nondestructive and spatially resolved quantitative characterization of electrical impedance. During our endeavor in combinatorial materials sciences, a scanning evanescent microwave probe with capability of satisfying these demands has been invented and developed. In this chapter we will discuss its development.
