Planar Circuits for Non-contact Near-Field Microwave Probing

This paper presents a planar microwave probe circuit for non-contact near-field probing of quasi-planar structures which can be made of metal, dielectric or semiconductor. The probe circuit demonstrated here consists of a high-Q resonator in the range between 900 MHz and 5GHz hybridly integrated with a microstrip circuit and field-concentrating micro-meter size probe tip which determines the spatial resolution of the detection process. The design of the probe circuit and measurement system are presented, along with measurements of a GaAs test circuit and a Si CMOS chip. By scanning the probe above a quasi-planar sample, two-dimensional data sets of complex S-parameters are obtained and appropriate processing is applied to extract information about the sample.