Self-actuating scanning microwave microscopy probes

Abstract

We present the design and experimental results of a scanning microwave microscopy (SMM) system that does not require the use of a conventional atomic force microscope (AFM). Microfabricated SMM probes are actuated by integrated MEMS scanners in a commercially available multi-user process. This design is unique in the sense that the tip can be scanned over the sample both laterally and vertically, over a 10µm × 10µm scan range. We first validate our approach with a test-bench consisting of a fixed probe and an integrated sample-scanning stage. This device is used to obtain characteristic approach curves of S11 as a function of tip-sample separation. We then investigate the effect of tip-sample separation on the resolution of the instrument. CPW probes with integrated 1-D and 2-D actuation are then presented. These devices can be used to modulate the tip-sample separation to off-chip samples with a periodic (200Hz) signal, improving immunity to long-term system drifts. To increase measurement sensitivity, a single-stub matching network has been used to match high tip to sample impedance to the 50 ohm of a performance network analyzer. Measurement results agree very well with reported SMM measurements in the literature