Edward Wasige

A peeling algorithm for extraction of the HBT small-signal equivalent circuit

Direct extraction is the most accurate method for the determination of equivalent-circuits of heterojunction bipolar transistors (HBTs). The method is based on first determining the parasitic elements and then the intrinsic elements analytically. The accuracy and robustness of the whole algorithm therefore is determined by the quality of the extraction of the extrinsic elements. This paper focuses on a new extraction method for the extrinsic capacitances which have proven to be the main source of uncertainty compared to the other extrinsic parameters. Concerning the intrinsic parameters, all the elements are extracted using exact closed-form equations, including exact expressions for the base-collector capacitances, which model the distributed nature of the base. The expressions for the base-collector capacitances are valid for both the hybrid-/spl pi/ and the physics-based T-topology equivalent circuits. Extraction results for InP HBT devices on measured S-parameters up to 100 GHz demonstrate good modeling accuracy.

A LiÉnard Oscillator Resonant Tunnelling Diode-Laser Diode Hybrid Integrated Circuit: Model and Experiment

We report on a hybrid optoelectronic integrated circuit based on a resonant tunnelling diode driving an optical communications laser diode. This circuit can act as a voltage controlled oscillator with optical and electrical outputs. We show that the oscillator operation can be described by Lienards equation, a second order nonlinear differential equation, which is a generalization of the Van der Pol equation. This treatment gives considerable insight into the potential of a monolithic version of the circuit for optical communication functions including clock recovery and chaotic source applications.

Nonlinear Dynamics of Resonant Tunneling Optoelectronic Circuits for Wireless/Optical Interfaces

We report on experimental and modeling results on the nonlinear dynamics of a resonant-tunneling-diode-based (RTD) optoelectronic circuits that can be used as the basis of a wireless/optical interface for wireless access networks. The RTD-based circuits are optoelectronic integrated circuits that have negative differential resistance and act as optoelectronic voltage-controlled oscillators. These circuits display many of the features of classic nonlinear dynamics, including chaos and synchronization. These highly nonlinear oscillators behaves as injection-locked oscillators that can be synchronized by a small injection signal of either wireless or optical origin, and thus, can transfer phase encoded information from wireless to the optical domain or the optical to the wireless domain.

A Sub-Critical Barrier Thickness Normally-Off AlGaN/GaN MOS-HEMT

A new high-performance normally-off gallium nitride (GaN)-based metal-oxide-semiconductor high electron mobility transistor that employs an ultrathin subcritical 3 nm thick aluminium gallium nitride (Al0.25Ga0.75N) barrier layer and relies on an induced two-dimensional electron gas for operation is presented. Single finger devices were fabricated using 10 and 20 nm plasma-enhanced chemical vapor-deposited silicon dioxide (SiO2) as the gate dielectric. They demonstrated threshold voltages (Vth) of 3 and 2 V, and very high maximum drain currents (IDSmax) of over 450 and 650 mA/mm, at a gate voltage (VGS) of 6 V, respectively. The proposed device is seen as a building block for future power electronic devices, specifically as the driven device in the cascode configuration that employs GaN-based enhancement-mode and depletion-mode devices.

DC Characterization of Tunnel Diodes Under Stable Non-Oscillatory Circuit Conditions

A common problem in designing with Esaki tunneling diodes in circuits is parasitic oscillations, which occur when these devices are biased in their negative differential resistance (NDR) region. Because of this, the measured current-voltage (I-V) characteristics in the NDR region are usually incorrect, with sudden changes in current with voltage and a plateaulike waveform in this region. Using a full nonlinear analysis of the shunt-resistor-stabilized tunnel diode circuit, we have established the criteria for the range of element values that give stable operation. On this basis, I-V measurement circuits can be designed to be free from both low-frequency bias oscillations and high-frequency oscillations. The design equations lead to a direct I-V measurement setup in which the stabilization resistor in series with a capacitor can be employed. Experimental results validate the approach, and this is confirmed by second-derivative analysis (d2I/dV2) of the measured I-V characteristics.

GaAs FET characterization in a quasi-monolithic Si environment

GaAs FET chips are planar embedded in a high resistivity silicon substrate and characterized up to 40 GHz in a coplanar environment. Hybrid interconnects (bonding wires) are replaced by thin film ones (air bridges). Small signal equivalent circuit extraction results confirm the expected low parasitic inductance values. These are reduced by more than 50% of the typical bonding wire interconnects.

A design procedure for tunnel diode microwave oscillators

Negative differential resistance (NDR) devices such as Esaki tunnel diodes or resonant tunnelling diodes are ideal for the realisation of high frequency oscillators. However, the oscillation frequency cannot usually be predicted precisely and the output power is quite weak. In this paper, a tunnel diode oscillator topology to which the conventional negative resistance oscillator methodology can be employed is shown to yield predictable oscillation frequencies, delivering the maximum possible output power. Methods for DC and RF characterization of NDR devices are also described.

12 GHz coplanar quasi-monolithic oscillator

First results on coplanar quasi-monolithic (QM) circuits with GaAs FETs embedded in a silicon substrate are presented. Typical monolithic integration techniques are used for the fabrication of the passive circuitry and interconnects to the active devices. Measurements on a 12 GHz oscillator demonstrate the viability of the proposed technology.

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.

AlN/GaN MOS-HEMTs With Thermally Grown Al 2 O 3 Passivation

This paper reports on the processing and characterization of AlN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOS-HEMTs). The devices employ thermally grown Al2O3 as a gate dielectric and surface protection and passivation, which is an approach that provides an opportunity to define the ohmic contact areas by wet etching of Al (and optimization of this processing step) prior to the formation of Al2O3 and ohmic metal deposition. The devices also employ a new process technique that significantly suppresses leakage currents on the mesa sidewalls. Fabricated devices exhibited good direct current and radio frequency performance. A high peak current, i.e., ~ 1.5 A/mm, at VGS = +3 V and a current-gain cutoff frequency fT and maximum oscillation frequency fMAX of 50 and 40 GHz, respectively, were obtained for a device with 0.2-μm gate length and 100- μm gate width. Additionally, a robust method for the extraction of the small-signal equivalent circuit suitable for process optimization is described. It relies on intimate process knowledge and device geometry to determine equivalent circuit elements of the fabricated AlN/GaN MOS-HEMTs.