D.L. Edgar

Fabrication of 30 nm T gates using SiNx as a supporting and definition layer

A new process has been developed to fabricate 30 nm T gates for high performance metal–semiconductor field effect transistors and high electron mobility transistors. The fabrication of short gate length T gates becomes increasingly difficult as the footwidth of the gate is made smaller and this is particularly true when the footwidth is less than 50 nm. In this process a thin SiNx layer is deposited on the substrate prior to the application of a bilayer of poly(methylmethacrylate)/Shipley UVIII resist. After resist patterning by electron beam lithography the nitride layer is etched at a low bias voltage that causes negligible substrate damage. This process step helps to define the gate footwidth and improves mechanical stability of the gate. The measured gate resistance was 375 Ω/mm.

CPW Interconnects for MMIC Applications on Low Resistivity CMOS Grade Silicon Using Micromachined SU8 Negative Resist

In this work we present measured and modelled RF behaviour of a coplanar waveguide (CPW) fabricated on CMOS grade low resistivity Silicon 2¿-cm using a novel micromachined SU8 negative resist interface layer. CPW lines were designed and fabricated on the SU8 interface layer of different thickness from 25 ¿m to 125 ¿m. An attenuation of less than 0.6dB/mm at 60GHz was achieved. Physical line modelling and E-M simulations were performed to support the experimental results and to determine the SU8 dielectric parameters. Micromachining of CPW structures were also investigated where a reduction in loss by more than 30% was achieved.

Substrate Modes in Double-Layered Coplanar Waveguides

Leakage of energy from Coplanar Waveguides (CPW) at high frequencies has been repeatedly observed. By using basic electromagnetic theory, mathematical models have been derived to predict the critical frequencies at which a conductor-backed double-layered CPW starts to leak. Matching with the experimental results, these models can successfully explain the leakage phenomena in CPWs, and can confirm to which substrate modes, TE or TM, a standard CPW is most likely to leak to. The results of this investigation can also be used as a quantitative guideline in the selection of CPW substrate and in the calculation of the cut-off substrate thickness approximately at millimetre wave frequencies.

First demonstration of InAlAs/InGaAs HEMTs using T-gates fabricated by a bilayer of UVIII and PMMA resists

We report the first lattice matched InP HEMTs fabricated using a T-gate process based on a bilayer of Shipley UVIII DUV resist and PMMA. A DC gate resistance of 220 /spl Omega//mm was achieved, leading to f/sub T/ of 193 GHz and Maximum Available Gain (MAG) values of 13 dB at 94 GHz for 100 /spl mu/m wide devices.

94 and 150 GHz coplanar waveguide MMIC amplifiers realized using InP technology

We report the design, fabrication and measurement of a three stage W-band amplifier with up to 22 dB gain at 94 GHz and a single stage D-band amplifier with 5 dB gain at 150 GHz. Circuits were designed and fabricated in coplanar waveguide technology using a 0.121 /spl mu/m T-gate lattice matched InP HEMT technology.

InP-Based W-band Coplanar Waveguide Couplers

This paper reports on the performance and model extraction of indium phosphide based W-band (67-110 GHz) coplanar waveguide ratrace couplers, branchline couplers and Wilkinson power dividers. The extracted models consist of lumped and distributed circuit elements available in most microwave CAD packages. The accuracy of these models is verified by comparison with measured S-parameter data from 67 to 110 GHz.

Fabrication of on-wafer MMIC compatible integrated NiCr loads

In this work we report on a novel technique for the fabrication of integrated NiCr resistors on GaAs substrates which are compatible with monolithic millimetre-wave integrated circuits (MMMICs) using e-beam lithography. Integrated NiCr resistors are required extensively for broadband RF on-wafer calibration of a vector network analyser and passive and active microwave components realisation. These loads showed a flat frequency response across an ultra-broadband range from DC to 110 GHz. In order to demonstrate the validity of using these NiCr loads on GaAs for on-wafer calibration, active devices were measured after LRRM calibration using the GaAs NiCr loads and compared with measured data of the same devices after LRL calibration.

150GHz Coplanar Waveguide MMIC Amplifier

We report the design, fabrication and measurement of a single stage D-Band amplifier with 3-4dB gain at 150GHz. In addition a three stage D-Band amplifier with 7.5dB gain at 153GHz is reported. Circuits were designed and fabricated in coplanar Waveguide technology using a 0.12¿m T-gate lattice matched InP HEMT technology.

W-Band Performance of Coplanar Waveguide on Thinned Substrates

We report on the measured mmwave (67-110GHz) performance of Coplanar Waveguide components on GaAs substrates as a function of substrate thickness, for calibration and circuit applications in W-band and D-band. W-band measurements show improved mmwave performance of transmission lines and short circuit elements on thinner substrates.

Millimetre wave high efficiency photonic crystal antennas

For a considerable time, the efficiency of planar antennas at high frequency has failed to reach its full potential. Since the planar antenna is an important element in an MMIC transceiver system, this poses a major problem. Due to the nature of the electromagnetic environment the antenna operates in, a large amount of the propagating radiation is coupled into the substrate meaning that only around forty percent efficiency is achieved, especially at millimetre wave frequencies. To improve this situation, methods to control the propagation of electromagnetic radiation from planar antennas is being sought. One method is to use a periodic dielectric structure positioned beneath the radiating antenna to act as a reflector. In this work, the periodic dielectric is a woodpile three-dimensional photonic crystal, fabricated using high resistivity silicon. The photonic crystal has a stop-band in which the resonant frequency of the antenna is contained, thus allowing no signal to pass and thereby reflecting the radiation to enhance the radiation pattern. This paper gives a detailed explanation of the problem, through to the practical results obtained to date from fabrication and measurement.For a considerable time, the efficiency of planar antennas at high frequency has failed to reach its full potential. Since the planar antenna is an important element in an MMIC transceiver system, this poses a major problem. Due to the nature of the electromagnetic environment the antenna operates in, a large amount of the propagating radiation is coupled into the substrate meaning that only around forty percent efficiency is achieved, especially at millimetre wave frequencies. To improve this situation, methods to control the propagation of electromagnetic radiation from planar antennas is being sought. One method is to use a periodic dielectric structure positioned beneath the radiating antenna to act as a reflector. In this work, the periodic dielectric is a woodpile three-dimensional photonic crystal, fabricated using high resistivity silicon. The photonic crystal has a stop-band in which the resonant frequency of the antenna is contained, thus allowing no signal to pass and thereby reflecting the radiation to enhance the radiation pattern. This paper is intended to give a detailed explanation of the problem, through to the practical results obtained to date from fabrication and measurement.