Application of near-field scanning microwave microprobe to electrical current density mapping

Abstract

A near-field scanning microwave microprobe (NSMM) has been integrated with electrical current-voltage (I–V) characterization for mapping electrical current density (J) in conducting films at room temperature (RT). In this technique, the focused microwave emitted at the tip of the NSMM was used to alter the local resistance of the sample via heating which results in a voltage response ΔV that depends linearly on the local J and the applied microwave power. In addition to the ΔV map generated during the NSMM scan over a sample, a microwave response map can be recorded simultaneously using the NSMM, providing complementary information of sample morphology and surface impedance. On silver microbridges with predefined patterns, a 10-μm spatial resolution has been demonstrated and better resolution may be achieved with further optimization. Hence, this technique provides a simple and nondestructive method for identification of current-limiting defects in conducting films and may be scaled for reel-to-reel quality control of the high-Tc superconductor coated conductors at RT.

Detection of low-level dissipation and thermal instability in Y Ba2Cu3O7 − δmicrobridges using low temperature near-field scanning microwave microscopy

“…Thus, for a 75-80 mm long NSMM probe, an operating frequency between 1.875 and 2.0 GHz is expected. The tapered Cu tip was fabricated via a rudimentary chemical etching method [9] that typically yielded φ ∼ 20 μm in tip diameter. As a scanning probe in the near-field, the spatial resolution of the NSMM is determined by the larger of the probe's tip diameter or the tip-to-sample distance.…”

“…Early detection of the hot spots is hence important but requires approaches of high sensitivity to the low-level dissipation and high spatial resolution to a microscopic hot spot. Near-field scanning microwave microscopy [6][7][8][9][10][11] (NSMM) is a promising technique for this purpose. The unique advantages of NSMM include noncontact and non-destructive detection of low-level dissipation and thermal instability.…”

Combining Near-Field Scanning Microwave Microscopy With Transport Measurement for Imaging Current-Obstructing Defects in HTS Films

“…For an operating frequency of 2.0 GHz, a resonator length of 3.75 cm is required. For better imaging resolution, the center conductor of the coaxial probe can also be replaced with a small brass tube that has an inner diameter to snugly fit a 200-diameter copper wire that can be tapered at the other end to a fine tip of tip diameter as small as subusing a simple and controlled chemical etching technique [5] When a sample is placed close to the probe tip, the interaction between sample and tip can be modeled as an additional capacitance to the lumped LCR circuit as shown in Fig. 1(c).…”

“…Preliminary work on the application of this technique on conducting silver thin films has been done previously [5] and supporting numerical simulations have also been carried out to gain a better understanding of the mechanism of heat absorption in films by microwave irradiation [6]. In this paper, we present results on applying this technique for imaging current-obstructing defects in YBCO thin films.…”