Fixed-wing MAV attitude stability in atmospheric turbulence—Part 2: Investigating biologically-inspired sensors

This thesis describes the reliable design of tunnel diode and resonant tunneling diode (RTD) oscillator circuits. The challenges of designing with tunnel diodes and RTDs are explained and new design approaches discussed. The challenges include eliminating DC instability, which often manifests itself as low frequency parasitic oscillations, and increasing the low output power of the oscillator circuits.
To stabilise tunnelling devices, a common but sometimes ineffective approach is the use of a resistor of suitable value connected across the device. It is shown in this thesis that this resistor tunnel diode circuit can be described by the Van der Pol model. Based on this model, design equations have been derived which enable the design of current-voltage (I-V) measurement circuits that are free from both low frequency bias oscillations and high frequency parasitic oscillations. In the conventional setup, the I-V characteristic of the tunnelling device is extracted from the measurement by subtracting from the measured current the current through the stabilising resistance at each bias voltage. In this thesis, also using the Van der Pol model, a circuit for the direct measurement of I-V characteristics is proposed. This circuit utilises a series resistor-capacitor combination in parallel with the tunnelling device for stabilisation. Experimental results show that IV characterisation of tunnel diodes in the negative differential resistance (NDR) region free from oscillations can be made.

A new test set-up suitable for radio frequency (RF) characterisation of tunnel diodes over the entire NDR region was also developed. Initial measurement results on a packaged tunnel diode indicate that accurate characterisation and subsequent small-signal equivalent circuit model extraction for the NDR region can be done.
To address the limitations of low output power of tunnel diode or RTD oscillators, a new multiple device circuit topology, incorporating a novel design methodology for the DC bias decoupling circuit, has been developed. It is based on designing the oscillator specifically for sinusoidal oscillations, and not relaxation oscillations which are also possible in tunnel diode oscillators. The oscillator circuit can also be described by the Van der Pol model which provides theoretical predictions of the maximum inductance, in terms of the tunnel diode device parameters, that is required to resonate with the device capacitance for sinusoidal oscillations. Each of the tunnel diodes in the multiple device oscillator circuit is decoupled from the others at DC and so can be stabilised independently. The oscillator topology uses parallel resonance but with each tunnel diode individually biased and DC decoupled making it possible to employ several tunnel diodes for higher output power. This approach is expected to eliminate parasitic bias oscillations in tunnel diode oscillators whilst increasing the output power of a single oscillator. Simulation and experimental oscillator results were in good agreement, with a two-tunnel diode oscillator exhibiting approximately double the output power as compared to that of a single tunnel diode oscillator, i.e. 3 dB higher.
Another method considered for the realisation of higher output power tunnel diode or RTD oscillators was series integration of the NDR devices. A new method to suppress DC instability of the NDR devices connected in series with all the devices biased in their NDR regions was investigated. It was successfully employed for DC characterisation with integrations of 2 and 5 tunnel diodes. Even though no suitable oscillator circuit topology and/or methodology with series-connected NDR devices could be established for single frequency oscillation, the achieved
results indicated that this approach may be worthy of further investigation.
The final aspect of this project focussed on the monolithic realisation of RTD oscillators. Monolithic oscillators in coplanar waveguide (CPW) technology were successfully fabricated and worked at a fundamental frequency of 17.5 GHz with -21.83 dBm output power. Finally, to assess the potential of RTD oscillators for high frequency signal generation, a theoretical analysis of output power of stabilised RTD oscillators was undertaken. This analysis suggests that it may be possible to realise RTD oscillators with high output power (0 dBm) at millimetre-wave and low terahertz (up to 1 THz) frequencies.

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Reliable design of tunnel diode and resonant tunnelling diode based microwave sources

This paper reports a novel acoustic sensor with a frequency output based on AlAs/InxGa1−xAs/GaAs resonant tunneling diode (RTD). The RTD is incorporated in a 1m thick membrane and the fabrication technology of the membrane is based upon the selective etch of GaAs with AlAs as an etch stop layer. A relaxation oscillator is obtained with the RTD biased in the negative differential resistance (NDR) region. Acoustic pressure applied to the RTD changes the frequency of oscillation due to the shift in current–voltage characteristics. The main feature of this sensor type is the direct frequency output, which is linearly dependent on pressure, and the linear sensitivity can be up to 21 kHz/kPa. © 2006 Elsevier B.V. All rights reserved.

A GaAs acoustic sensor with frequency output based on resonant tunneling diodes

This paper reports a novel GaAs micromachined accelerometer based on the meso-piezoresistive effects of resonant tunneling diodes (RTDs). The sensitive unit of the accelerometer is the RTD which is located at the root of the beams. Based on the meso-piezoresistive effects of RTD, the accelerometer transduces acceleration into electrical signal output. This kind of accelerometer has been fabricated by GaAs IC surface processes and control hole etching technology. The output sensitivity and frequency characteristics of the accelerometer have been tested on the vibrating system. The result indicates that when the RTD is biased in the negative differential resistance region, the sensitivity of the suggested accelerometer is up to 90.51 mV/g, and when biased in the positive resistance region, the sensitivity is 2.39 mV/g. It is obvious that the sensitivity in the negative resistance region is more one order higher than that in the positive resistance region, and the sensitivity of the accelerometer can be adjusted through changing the bias voltage. A frequency range of this structure as high as 1.5 KHz has also been achieved.

Development of a novel GaAs micromachined accelerometer based on resonant tunneling diodes

Time-Domain Analysis of Large-Signal-Based Nonlinear Models for a Resonant Tunneling Diode with an Integrated Antenna

We present a novel bulk semiconductor pressure sensor based on an Al/sub x/Ga/sub 1-x/As/GaAs resonant tunneling diode (RTD) with a frequency output. A relaxation oscillator is obtained with the RTD biased in the negative differential resistance (NDR) region. Pressure applied to the RTD changes the frequency of oscillation due to the shift in current-voltage characteristics. Frequency measurements have been performed on [001]-oriented RTD's with [110]-compressive uniaxial pressure. Sensitivities of up to 0.8 kHz/MPa at 113 kHz have been measured. The main feature of this sensor type is the direct frequency output obtained by using only a maximum of three components including the RTD. Using a simplified differential equation of the oscillator circuit, the pressure-dependent effects of the RTD current-voltage characteristics on the sensor output have been investigated.

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A GaAs pressure sensor with frequency output based on resonant tunneling diodes

The subband of Al/sub x/In/sub 1-x/Sb/InSb quantum-well structure under the effect of interdiffusion were calculated. The model use the 14-band calculation and the effective Hamiltonian approach. The results show that the interband transition energy is relatively small, compared to quantum well constructed by As based. With a particular Al concentration and design, the interband transition energy at around 200-300 meV. This is the range for medium wavelength infrared region. Hence, we suggest in this paper to use Al/sub x/In/sub 1-x/Sb/InSb quantum-well structure for infrared detectors. The effect of interdiffusion shows a shift in interband transitions energy, which is useful for find tunneling the transition energy. When it apply to infrared detector, the absorption wavelength can be tune by interdiffusion to a desire value. In this paper, we propose to use antimonide based interdiffusion quantum well as an infrared detector, and show it wavelength tunability.

K. Mutamba

Papers

A GaAs pressure sensor with frequency output based on resonant tunneling diodes

Medium wavelength infrared detector with diffused AlxIn/sub 1-x/Sb/InSb quantum-well structure