A fundamental oscillation of up to 831 GHz was observed at room temperature in GaInAs/AlAs resonant tunneling diodes integrated with planar slot antennas. The thickness of the collector spacer layer was increased (20 nm) and the mesa area (<1 µm2) was reduced in order to reduce the resonant tunneling diode capacitance. Reduction in the negative differential conductance in the small mesa area was prevented by increasing the emitter doping concentration (3×1018 cm-3) which resulted in an ultra-high peak current density (18 mA/µm2) with a peak-to-valley current ratio of 2. The dependence of oscillation frequency on the mesa area was also studied. The output power was at least 1 µW.
We demonstrate the operation of resonant tunneling diode (RTD) oscillators with high output power (100–200 µW) at frequencies of 430–460 GHz using an offset-fed slot antenna in which the RTD is placed at a certain distance from the center of the slot. The highest output power obtained in this study was 200 µW at 443 GHz for a single RTD with a peak current density of 18 mA/µm2; the RTD was placed 45 µm from the center of a 100-µm-long antenna. Higher output is expected by optimizing the position and mesa area of the RTD and the antenna length.
Low density polyethylene (LDPE) is widely used as a dielectric insulation of power cable. It has already reported that an incorporation of MgO nano particles in LDPE matrix could provide dielectrics with new and improved properties under dc high field. This paper describes high field dielectric properties of LDPE/MgO nano composite material under ac high voltage application. From the results of dissipation current waveform observations under ac high field, the volume resistivity and the relative permittivity for various contents of MgO nano particles in LDPE were estimated at the applied frequency 50 and 200 Hz. Though, the dependences of MgO content on both volume resistivity and relative permittivity under ac high field at 50 and 200 Hz are recognized, but it seems not to be drastically improved by adding a few percent of nano-size filler like those under dc high field.
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