S. Ferguson

Metal gate strained silicon MOSFETs for microwave integrated circuits

In this work a III-V MODFET fabrication process has been adapted to fabricate metal gate silicon based MOSFETs. A range of MOSFETs with gate lengths varying from 1 /spl mu/m to 120 nm were fabricated and all showed good transistor action. The gate metal was Ti/Pd/Au 200 nm thick and both pyramidal and T shaped gates were fabricated. The parasitic gate-source capacitance was reduced by using a spin on dielectric. The strained silicon MOSFETs with rectangular 0.3 /spl mu/m Ti/Pd/Au gates had measured f/sub T/ and f/sub max/, of 11 GHz and 12 GHz respectively. By de-embedding the parasitic pad capacitance the intrinsic f/sub T/ and f/sub max/ are 20 GHz and 21 GHz.

Metallic tunable photonic crystal filter for terahertz frequencies

A tunable metallic photonic crystal filter has been fabricated by deep reactive ion etching of a silicon substrate followed by metallization. The filter plate’s two-layer orthogonal grid structure and integrated mounting lugs were fabricated from a single silicon wafer in two etching steps. A three-step metallization process (evaporation, sputtering, and electroplating) ensured all surfaces were coated with gold to greater than 4.6 times the skin depth at the frequencies of interest. The filter employs a mechanical tuning mechanism, the performance of which was predicted with rigorous full-vector electromagnetic simulations (finite-difference time domain). The prototype has been characterized at frequencies of 70–150 GHz using free-space measurement techniques. Its measured center frequency shifts from 144 to 137 GHz for 300 μm lateral shift of one of the plates, and it has an insertion loss of less than 1 dB.

Selectively dry gate recessed GaAs metal–semiconductor field‐effect transistors, high electron mobility transistors, and monolithic microwave integrated circuits

The application of nanofabrication techniques such as molecular‐beam epitaxy, electron‐beam lithography, and selective reactive ion etching, to metal–semiconductor field‐effect transistor (MESFET), high electron mobility transistor (HEMT), and monolithic microwave integrated circuit (MMIC) fabrication allows precise control of physical device parameters such as layer thickness, doping density, and gate length. Such well characterized, flexible, and accurate technologies allow high performance devices and circuits to be fabricated with predictable yield. The application of nanofabrication techniques to both low noise, 0.2 μm mushroom gate, GaAs/Al0.3Ga0.7As MESFETs and MMICs is demonstrated. The MESFETs have 0.75 dB noise figure and 11 dB associated gain at 12 GHz; while the MMICs have ‘‘right‐first‐time’’ performance with more than 15 dB gain at 44 GHz. It is also shown that these techniques are applicable to pseudomorphic HEMTs and predicted that the use of nanofabrication in general and selective reacti...

Copper-plated 50 nm T-gate fabrication

In this article, the authors report for the first time a route to the realization of scalable sub-100 nm Cu-based T-gates using a fully subtractive, “silicon-compatible” process flow. High resolution electron beam lithography and a low-damage RIE etch process are used to transfer a 50 nm line into ICP-CVD silicon nitride. This pattern forms the T-gate foot. A single blanket metallization is then used to form the Schottky contact, the seed layer for the copper electroplating and a barrier to prevent diffusion of the copper once deposited. A constant potential copper electroplating process has been developed for a Ti/Pt seed layer. Copper films have been deposited with bulk sheet resistance ρsh∼0.1 Ω/◻ (for a 300 nm film) and resistivity ρ=1.8×10−6 Ω cm. The head dimensions of the T-gate are realized by patterning resist on top of the seed prior to electroplating. Heads of width 500 nm were fabricated and shown to have a total gate resistance of Rg=150 Ω mm.

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.