Afesomeh Ofiare

High Performance Resonant Tunneling Diode Oscillators for THz Applications

This paper presents monolithic microwave integrated circuit (MMIC) resonant tunneling diode (RTD) oscillator with high performance: high power at high frequencies. The circuit topology employs two In0.53Ga0.47As/AlAs RTDs in parallel and each device is biased individually. These oscillators operate at 125GHz, 156GHz and 166 GHz with output power 0.34 mW, 0.24 mW and 0.17 mW respectively. These are highest power reported for RTD oscillators in D-band (110 GHz-170 GHz) frequency range. The phase noise of the RTD oscillators was characterized and is reported. This work demonstrates the circuit-based RTD oscillator design approach to increase the output power of RTD oscillators at millimeter-waves.

Novel tunnel diode oscillator power combining circuit topology based on synchronisation

Devices with negative differential resistance (NDR) regions in their current-voltage (I-V) characteristics such as tunnel diodes (TD) and resonant tunneling diodes (RTDs) have been used for realizing high frequency oscillators. In this paper, a new power combining technique is presented which combines output power through synchronisation of two coupled tunnel diode oscillators. The measured output power of the two synchronised tunnel diode oscillators realized in microstrip hybrid technology was -6.72 dBm at 716.2 MHz, while that of single tunnel diode oscillator was -9.09 dBm at 575.7 MHz. The circuit topology proposed in this paper can be utilized to realize high power and high frequency RTD terahertz sources.

G-Band MMIC resonant tunneling diode oscillators

This paper presents a G-band (140 -220 GHz) monolithic microwave/ (millimeter-wave) integrated circuit (MMIC) resonant tunneling diode (RTD) oscillator operating at 205.8 GHz with -14.6 dBm output power. The circuit topology employs two InGaAs/AlAs RTDs in parallel. A new RTD epi-layer material design which will greatly benefit micrometer-sized RTD devices for high output power of millimeterwave oscillators is also presented. It is expected that the oscillator output power will reach several mW for RTD oscillators operating in the G-band. This work shows the promising potential of RTD oscillators as terahertz (THz) sources for a variety of applications including high speed wireless communication.

MMIC resonant tunneling diode oscillators for THz applications

This paper presents a monolithic microwave integrated circuit (MMIC) that combines two InGaAs/AlAs resonant tunneling diodes (RTDs) in parallel. By employing appropriate circuitry the oscillators generate an output power of about 1 mW (-0.1 dBm) at 39.6 GHz and (-0.2 dBm) at 75.2 GHz which are the highest power reported for RTD-based oscillators in the relative frequency range. This work demonstrates that circuit-based power combining technique can be used to solve the bottle-neck of RTD oscillators, i.e. low output power at millimeter-wave or even higher frequencies. The techniques show the potential to be implemented at terahertz (THz) frequencies.

Resonant tunneling diode as high speed optical/electronic transmitter

We report both electronic and opto-electronic resonant tunneling diode (RTD) oscillators with relatively high output power. Electronic RTD oscillators working at 125/156/308 GHz with around one half milliwatt output power and optoelectronic oscillators in the 30–105 GHz range with about 1 mW output power at 44 GHz have been developed. First wireless transmission experiments with a 300 GHz oscillator are also reported.

Pulsed I-V and small signal characterisation and modelling of resonant tunneling diodes

This paper describes the use of dc pulses for current voltage (I-V) characterisation of resonant tunnelling diodes (RTDs). The results show that accurate (parasitic) oscillation-free measurements of the negative differential resistance (NDR) region can be done. The proposed technique allows for the monitoring of possible onset of parasitic oscillations during measurements, and so allows for specific measurement windows (when the device is stable) to be identified and so enable accurate measurements. Pulsed I-V experimental results of resonant tunnelling diodes are presented along with modelled I-V curves. In addition, the extraction of a small-signal equivalent circuit model for the RTD from the measured S-parameters (S11) is described.

Bow-tie antenna for terahertz resonant tunnelling diode based oscillators on high dielectric constant substrate

In this paper, a broadband bow-tie slot antenna is presented. The coplanar waveguide (CPW) fed antenna is fabricated on an InP substrate for same chip integration with the promising resonant tunnelling diode (RTD) terahertz (THz) oscillator which has the capability of room temperature operation and with relative high power. The antenna exhibits a very wide bandwidth (return loss S11 <;-10 dB) around the design frequency (300 GHz). However, the radiation pattern is degraded because of the large dielectric constant of the InP substrate. A technique to overcome this problem employing a reflector ground plane underneath a thin substrate of low dielectric constant is presented. Initial simulation results of this technique are reported and experimental validation at lower frequency (17 GHz) shows the feasibility of the concept.

High-frequency resonant tunnelling diode oscillator with high-output power

In this paper, a prototype G-band (140 GHz-220 GHz) monolithic microwave integrated circuit (MMIC) resonant tunneling diode (RTD) oscillator is reported. The oscillator employs two In0.53Ga0.47As/AlAs RTD devices in the circuit to increase the output power. The measured output power was about 0.34 mW (-4.7 dBm) at 165.7 GHz, which is the highest power reported for RTD oscillator in G-band frequency range. This result demonstrates the validity of the high frequency/high power RTD oscillator design. It indicates that RTD devices, as one of the terahertz (THz) source candidates, have promising future for room-temperature THz applications in such as imaging, wireless communication and spectroscopy analysis, etc. By optimizing RTD oscillator design, it is expected that considerably higher power (>1 mW) at THz frequencies (>300 GHz) will be obtained.