We report GeTe-based phase change material RF switches with on-state resistance of 0.07 ohm*mm and off-state capacitance of 20 fF/mm. The RF switch figure-of-merit, R<sub>on</sub>*C<sub>off</sub> is comparable to RF MEMS ohmic switches. The PCM RF shunt and series switches were fabricated for the first time in a lateral FET configuration to reduce parasitics, different from the vertical via switches. In a shunt switch configuration, isolation of 30 dB was achieved up to 67 GHz with return loss of 15 dB. RF power handling was tested with ~10 W for series and 3 W for shunt configurations. Harmonic powers were suppressed more than 100 dBc at fundamental power of 1 W, for future tunable and reconfigurable RF technology.
Antennas collect radio waves and channel them into radio frequency (RF) transmission lines which direct the signals to circuits from which information can be demodulated and decoded. Glass, the most common portal between outside and inside environments, is clear at the visible part of the electromagnetic spectrum, and it is also relatively transparent to a large portion of the electromagnetic spectrum useful for radio wave communications. Since glass as a building material is used everywhere, it could be a readily accessible substrate upon which to mount or fabricate the antennas and RF electronics, but only if these circuit components are also transparent. In this paper, we present our development to date of glass RF circuits along two tracks: 1) transparent antennas and 2) graphene based active and passive circuit elements. Along the first track we have demonstrated antennas made from nanowire films capable of an optical transparency of 72% and sheet resistance of 4-5Ω/sq. Along the second track, we have in so far demonstrated graphene on glass field effect transistors with an fmax of 7 GHz, varactors with 1.4:1 tuning range, resistors with 3-70 kΩ, and capacitors from 13-860 pF. This is just the start; our plans are to increase the frequency and tuning ranges of the active and passive devices. Since graphene is inherently transparent at visible wavelengths, we ultimately would like to merge these two tracks to integrate active and passive RF circuitry with the antenna either directly on glass or as an applique put on glass, circuits which we’ve termed RF Glass®.
We are developing micro chemical sensor nodes that can be used for real time, remote detection and early warning of
chemical agent threats. The chemical sensors in our sensor nodes utilize GaN HEMTs (High Electron Mobility
Transistors) fabricated with catalytically active transition metal gate electrodes. The GaN HEMT chemical sensors
exhibit high sensitivity and selectivity toward chemical agent simulants such as DECNP (Diethyl cyano phosphonate),
and this is the first time that chemical agent simulants have been detected with GaN micro sensors. Response time of the
GaN HEMT sensor to a chemical species is within a second, and the maximum electronic response speed of the sensor is
~3 GHz. A prototype micro chemical sensor node has been constructed with the GaN sensor, a micro controller, and an
RF link. The RF sensor node is operated with a single 3V Li battery, dissipating 15 mW during the RF transmission with
5 dBm output power. The microcontroller allows the operation of the RF sensor nodes with a duty cycle down to 1 %,
extending lifetime of the RF sensor nodes over 47 days. Designed to transmit RF signals only at the exposures to
chemical agents and produce collective responses to a chemical agent via a sensorweb, the GaN micro chemical sensor
nodes seem to be promising for chemical agent beacons.
We present a prototype photodetector in which the built-in "tunneling structure" serves as an internal gain
mechanism for photon detection. Initial feasibility studies demonstrated that the new photon detector offers an optical
responsivity as high as 3000 A/W peaked at λ=1.3 μm at less than 1 V bias applied. The measurements were carried out
using a photospectrometer setup in a continuous mode at room-temperature. Very strong (> 1000) responsivity is also
measured from visible to SWIR even with a simple optical coupling scheme that utilizes very thin absorber layers in the
prototype devices. The dark current density is ~ 5×10<sup>-10</sup> A/μm<sup>2</sup> at the operating bias. Room-temperature NEP was calculated based on a shot noise measurement, yielding NEP of 4~ 5×10<sup>-15</sup> W/Hz<sup>1/2</sup> and D* of 2~3×10<sup>12</sup> cmHz<sup>1/2</sup>/W,
peaked at a bias of 0.3 V at a fixed wavelength of λ=1.3 μm.