A Systematic Material Characterization Method via Near-Field Scanning Microwave Microscopy

Accurate measurement of material dielectric property is essential for engineers to synthesize microwave devices. This article proposes a systematic material characterization method via the coaxial resonator (CR)-based near-field scanning microwave microscopy (NFSMM) with an arbitrary tip shape, from the modeling method to the inversion algorithm. The effective interaction region in the CR-based NFSMM is investigated and determined, which contributes most to the contrast capacitance caused by the tip-sample interaction. Then the Huygens' principle is applied in the forward solver of NFSMM when the samples under test are homogeneous. The relative error of our model is less than 2.1% in numerical validations. Based on the proposed forward solver, a dielectric characterization method via the conjugate gradient (CG) algorithm is proposed and verified with experimental results. The retrieved permittivity of unknown samples matches well with that measured by the transmission line method, and the discrepancy between the two results is less than 3%. The proposed systematic method is promising to provide a new pathway to quantitatively determine the dielectric property of homogeneous samples.