V-shaped-gate GaAs m.e.s.f.e.t. for improved high-frequency performance

The idea of gate shaping in f.e.t.s was implemented into the GaAs-m.e.s.f.e.t. structure. A m.e.s.f.e.t. with 2 ?m gate length was fabricated, the measured m.a.g. data of which allow an extrapolation to an fmax of about 45 GHz.     

Tungsten/gold gate GaAs microwave f.e.t.

Preliminary results on the performance of a W/Au gate GaAs f.e.t. having T-type gate cross-section are reported. The Au overhang on the W gate can be used to self-align the source and the drain with respect to the gate, which can be used to achieve submicrometre gate dimensions rather easily. An f.e.t. with 0.7 ?m gate length and 140 ?m gate periphery exhibited a measured maximum available gain (m.a.g.) of 14 dB at 8 GHz, Experiments on the W Schottky diodes indicate that the leakage current, instead of degrading, is actually reduced by annealing at high temperature in a H2 atmosphere for 10 min.     

U.H.F. low-noise GaAs m.e.s.f.e.t. amplifier for colour t.v. broadcasting translator

Low-noise amplifiers for u.h.f. colour t.v. broadcasting translator use have been successfully developed by using 1 ?m gate GaAs m.e.s.f.e.t.s. The obtained performances revealed that a GaAs m.e.s.f.e.t. has low-noise and low intermodulation distortion characteristics, even in the 500?800 MHz frequency range, compared with a Si bipolar transistor.     

High-speed 1 ?m GaAs m.e.s.f.e.t.

By minimising parasitic series resistances, a GaAs m.e.s.f.e.t. with 1 ?m gate length was fabricated, possessing the highest known r.f. power gain, measured up to 18 GHz, for GaAs m.e.s.f.e.t.s.     

New estimate of the minimum noise figure of a m.e.s.f.e.t.

New estimates of the drain and gate noise multiplication parameters, the correlation coefficient and the minimum noise figure for a m.e.s.f.e.t. are advanced. For an uncooled GaAs m.e.s.f.e.t. having a 1 ?m gate length, a minimum possible noise figure of 1 dB at 10 GHz is predicted. InP is only marginally better.     

X and Ku band GaAs m.e.s.f.e.t.

A GaAs Schottky-barrier f.e.t. (m.e.s.f.e.t.) with a 1 ?m gate has been built, which is suitable for X band and Ku band applications. The unilateral power gain over the X band is above 9 dB and the noise figure is only 5 dB at 10 GHz.     

High-yield self-alignment method for submicrometre GaAs m.e.s.f.e.t.s

A high-yield self-alignment technique for submicrometer GaAs m.e.s.f.e.t.s is described. This method allows the production of submicrometre gate lengths and source-drain spacings by means of standard contact photolithography without requiring a particularly fine geometry on the masks. A 0.5 ?m long gate and a source-drain spacing of 2 ?m were obtained.     

GaAs power f.e.t.s with electron-beam-defined gates

The fabrication of GaAs power f.e.t.s having 1 ?m electron-beam-defined gates with 4800 ?m total gatewidth is described. The microwave performance at X-band is compared with that of conventionally defined devices having 2 ?m gate lengths.     

Computer study of submicrometre f.e.t.s

The electrical properties of f.e.t.s with submicrometre gates are investigated by means of a 2-dimensional computer model. It is found that the gain-bandwidth product increases with decreasing gate length and reaches a value of 70 GHz for 0.1 ?m gates. This improvement is, however, at the expense of open-circuit voltage gain. A practical limit of the gate length for useful devices is found to be about 0.1 ?m.     

Planar GaAs normally-off j.f.e.t. for high speed logic circuits

Planar GaAs j.f.e.t.s in the normally-off mode were fabricated by direct selective ion implantation into a semi-insulating Cr-doped substrate for n-type active regions and selective Zn diffusion for p-type gate areas. The p-n junction gate, typically 2 ?m in length and 20 ?m in width, was formed without appreciable anomalous lateral diffusion. A 15-stage ring oscillator formed with resistor-f.e.t. logic gates exhibited a propagation delay time of 73 ps per stage with a power-delay product of 320 fJ. The minimum power-delay product was 5.6 fJ with delay time of 163 ps.     

Large signal GaAs m.e.s.f.e.t. model and distortion analysis

A simple large signal model, derived from small signal measurements over a range of bias points, is presented for a 2 ?m gate length GaAs m.e.s.f.e.t. Its accuracy is verified by comparing model-predicted second harmonic distortion via time domain and Volterra analyses, with measurements to input frequencies of 4.5 GHz.     

Modelling the m.e.s.f.e.t. output nonlinearity

Conditions governing the modelling of transductance and drain-conductance nonlinearities from measured data are investigated. A simple representation for regions close to pinch-off, corresponding to mixer operation, is obtained. Results of the modelling are compared to measurements on a typical 1 ?m gate length m.e.s.f.e.t.     

GaAs heterojunction f.e.t. with epitaxial Ge gate

A Ge heterojunction-gate GaAs f.e.t. has been developed using p-type epitaxial Ge gates deposited by vacuum evaporation on heated n-type GaAs substrates. Boron-ion implantation of the gate and an aluminium overlay was used to lower the gate resistance. A typical 8 ?m gate-length device exhibited a noise figure of 5.2 dB with 4.5 dB associated gain at 1.8 GHz.     

Fabrication of a m.o.s.f.e.t. with `spoxide? as the gate dielectric having low interface state density

Spin-on oxide (Spoxide), which forms part of the class of deposited oxides, has been found to produce a good electrical interface with silicon after HCl annealing, and surface-state densities of the order of 4 × 1010 eV?1 cm?2 are easily achievable. An n-channel depletion-type m.o.s.f.e.t. has been fabricated with Spoxide as the gate dielectric.     

GaAs m.e.s.f.e.t. prepared by organometallic chemical vapour deposition

GaAs m.e.s.f.e.t.s with gate dimensions of 1.5 ?m × 300 ?m were fabricated in the epitaxial layers grown by organometallic chemical vapour deposition (o.m.c.v.d.) technique. The average saturation velocity in the channel was deduced to be 1.3 × 107 cm/s and is equal to that of epitaxial layers grown by AsCl3 chemical vapour deposition (c.v.d.). The velocity degraded region was confined to within about 350 ? of the interface. A gain of 10 dB and a noise figure of 3 dB with an associated gain of 5.5 dB at 8 GHz were measured.     

14-GHz band 1 watt GaAs f.e.t. amplifier

A 14.0?14.5 GHz 1 W amplifier using 0.5 ?m gate length power GaAs f.e.t.s has been developed. The amplifier, consisting of a cascade of three single-ended stages, realises 13 dB small-signal gain, 1.1 W output-power saturation and 39 dBm third-order intermodulation intercept. The circuit design and the microwave performance of the amplifier are discussed.     

Enhancement-mode GaAs m.o.s.f.e.t. on semi-insulating substrate using a self-aligned gate technique

A self-aligned gate notched channel GaAs m.o.s.f.e.t. structure on semi-insulating substrate is presented. Device operation is mainly in enhancement mode. The transconductance is comparable to enhancement-mode m.e.s.f.e.t.s, j.f.e.t.s and s.i.g.f.e.t.s; however, the output-current capability is essentially increased.     

Microwave InxGa1?xAsyP1?y/InP f.e.t

Microwave performance of InxGa1?xAsyP1?y quaternary alloy metal-semiconductor field effect transistors (m.e.s.f.e.t.s) is reported. Liquid-phase epitaxy (l.p.e.) using a step cooling technique has been employed to grow submicrometre quaternary layers having room-temperature bandgaps of 0.9, 1.0, 1.05, 1.15 and 1.2eV. F.E.T.s having gate dimensions of 1×200 ?m and a channel length of 5 ?m have been fabricated using 1.15 and 1.2 eV quaternary alloys. A maximum d.c. transconductance of about 10 mS and a maximum available gain of about 7 dB at 10 GHz have been obtained.     

Modelling the 3rd-order intermodulation-distortion properties of a GaAs f.e.t.

A simple analytical model of the 3rd-order intermodulation-distortion properties of a GaAs field-effect transistor is proposed. The model takes into account the distortion-producing nonlinearities of the Schottky-bairier junction, the trans-conductance and the drain conductance. Parameters of the model are presented for a GaAs f.e.t. of 0.5 ?m gate length, and the model-predicted distortion characteristics are compared with measured data.     

GaAs f.e.t. mixer operation with high intermediate frequencies

GaAs f.e.t. mixer operation is investigated at 6 GHz when the intermediate frequency is around 1 GHz. A 3 dB improvement in noise figure is measured, compared with 30 MHz i.f. operation. Other characteristics, such as conversion gain and dynamic range, are similar. Broadband operation is also investigated. With 0.5 ?m gate device, on s.s.b. noise figure of 5.6 dB is achieved with a conversion gain of 10 dB.