Abstract
We report the design, fabrication, and characterization of miniaturized, flush-mounted Langmuir probe arrays for RF diagnosis of plasmas in the HF to microwave range of frequencies. We developed probes of radii ≥125 μm by electroless nickel metallization of ultrasonically drilled through-substrate vias. Planar arrays with as many as 25 probes spaced 1.6 mm apart (39 probes/cm2) in Pyrex, silicon carbide, and alumina substrates were produced. The sensor system was built to have a frequency response between 2 MHz and 3 GHz, and a probe impedance greater than or within close range of the plasma sheath impedance for plasma densities ≥1016 m -3 . We characterized a self-biasing nickel probe part of a 2×2 array with alumina substrate using a high-density magnetized helicon plasma source; we found that the measurement of the plasma potential from the MEMS probe compares well with independent measurements using a hot emissive probe and an ion sensitive probe. The sensor technology can be used to monitor plasma-based manufacturing systems, plasma-based energy generation systems, and as on-board plasma diagnostics in spacecraft including nanosatellites.
Highlights
L ANGMUIR probes (LPs) are used to estimate the electron temperature, electron density, and electric potential of a plasma
Microfabrication, and characterization of batch-fabricated flush-mounted MEMS Langmuir probe arrays (LPAs) for high-density plasma diagnostics, within HF to S bandwidth
Our apparatus is composed of the MEMS LPA chip, a network of the probe electronics, signal transmission lines, feedthrough shaft, shielding box for the electronics, SMA connectors, flanges for vacuum seal, and electrical feedthroughs; our apparatus is capable of measuring plasma events at frequencies as high as 3 GHz
Summary
L ANGMUIR probes (LPs) are used to estimate the electron temperature, electron density, and electric potential of a plasma. Due to their simplicity and low cost, LPs have been extensively used in characterizing a wide range of plasmas. Macro versions of flush-mounted Langmuir probe arrays have been reported to diagnose high-density plasmas [6]. Miniaturized flush-mountable Langmuir probe arrays (LPAs) can be used as ‘sensorial skin’ on spacecraft, tokamaks, or microfabrication plasma reactors to measure the plasma with high spatial resolution; these sensors can be used as a scientific payload in a nanosatellite. Microfabrication, and characterization of batch-fabricated flush-mounted MEMS LPAs for high-density plasma diagnostics, within HF to S bandwidth.
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