The plasma transistor: A microcavity plasma device coupled with a low voltage, controllable electron emitter

A microplasma transistor has been realized by injecting electrons into the sheath of a rare gas plasma with a low voltage ( Vb <25 V), controllable electron emitter. Integrating a solid state emitter with a 500 μm diam. cylindrical microcavity plasma yields a three terminal current-controlled device capable of modulating the conduction current and light intensity generated by the microplasma. For an emitter voltage of Vb =-10 V, the rms charge carried by the conduction current of a Ne microplasma is tripled relative to the value measured for no current injection. Similarly, the wavelength-integrated visible emission is increased by 2.7 and 4 dB for Vb=-5 and -25 V, respectively. From the continuity equation for charged particle flux in the sheath, the electron density at the edge of the sheath is determined to be ns = (3±1) × 1012 cm-3 for an electron temperature in the 1-5 eV range. Energizing the electron emitter is estimated to reduce the ratio of the ion to electron number densities at the cathode surface from 25 to 14. A parameter Βp, defined as the microplasma transistor conductance normalized to that for the conventional plasma device (i.e., Vb =0), is introduced and found to be ∼40 for this unoptimized device when Vb =5 V.