Manufacturing miniature Langmuir probes by fusing platinum bond wires

Abstract

This paper reports on a novel method for manufacturing microscopic Langmuir probes with spherical tips from platinum bond wires by fusing for plasma characterization in microplasma sources. Here, the resulting endpoints, formed by droplets on the ends of a fused wire, are intended to act as a spherical Langmuir probes. For studying the fusing behavior, bond wires were wedgebonded over a 2 mm wide slit, to emulate the final application, and fused with different voltages and currents. For electrical isolation, a set of wires were coated with a 4 µm thick layer of Parylene before they were fused. After fusing, the gap size, as well as the shape and area of the ends of the remaining stubs were measured. The yield of the process was also investigated, and the fusing event was studied using a high-speed camera for analyzing its dynamics. Four characteristic tip shapes were observed: spherical, folded, serpentine shaped and semi-spherical. The stub length leveled out at ∼400 µm as the fusing power increased. The fusing of the coated wires required a higher power to yield a spherical shape. Finally, a Parylene coated bond wire was integrated into a stripline split-ring resonator (SSRR) microplasma source, and was fused to form two Langmuir probes with spherical endpoints. These probes were used for measuring the I-V characteristics of a plasma generated by the SSRR. In a voltage range between -60 V and 60 V, the fused stubs exhibited the expected behavior of spherical Langmuir probes, and will be considered for further integration.

Spatial distribution of the optogalvanic signal in a microplasma detector for lab-on-a-chip gas analysis

“…The SSRR was identical to the one described in Ref. [20], except that the parylene coating of the probes had been removed by plasma etching in an oxygen plasma. It was manufactured by the method described in Ref.…”

“…The SSRR was identical to the one described in [20], except that the parylene coating of the probes had been removed by plasma etching in an oxygen plasma. It was manufactured by the method described in [22], and had a resonance frequency of 2.65 GHz, a characteristic impedance of 50 Ω, and the gap through the resonator was 3 mm long and 4.7 mm wide, figure 2, giving the ring an inner and outer radius of 4.49 mm and 6.50 mm, respectively.…”

“…By employing a microwave-induced microplasma source based on a stripline split-ring resonator (SSRR) [19], and equipping it with miniature plasma probes made from gold or platinum bond wires [20], we have been able to demonstrate the first ever OG detection in a microplasma [18]. We have also developed theory to describe how the OG signal is generated in such a system [21].…”

Optogalvanic spectroscopy with microplasma sources—current status and development towards a lab on a chip

“…For example, the EMC of the stripline concept has been evaluated by the Wheeler cap method [13], and the dielectric properties of HTCC alumina have been charted at frequencies around 2.6 GHz [14]. Different ways of integrating Langmuir probes in the SSRR have also been investigated [15]. These probes have been made from 25 µm in diameter gold or platinum bond wires and are used to analyze the plasma, and, more importantly, extracting the optogalvanic signal from the detector.…”

Extreme-temperature lab on a chip for optogalvanic spectroscopy of ultra small samples - key components and a first integration attempt

“…For the plasma probes, which are located in the plasma source's gap, the above wire technology is used, but with a carefully tailored step to fuse them to form rounded tips allowing Langmuir-probelike measurement of the plasma potential, which is the key to optogalvanic spectroscopy in this embodiment. Compared with the almost spherical tips made previously [11], the tips obtained in HTCC, figure 8, need further work. …”