Nonlinear J.F.E.T. model for computer-aided circuit analysis

A simplified circuit model is proposed to represent the nonlinear d.c. and low-frequency small-signal operation of j.f.e.t.s. This model is particularly useful for computer-aided circuit analysis programs, such as the iterative nodal analysis program BIAS-3. Operation in the off, resistance, and pinch-off regions of the j.f.e.t. is included.     

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.     

Direct observation of the depletion layer in a multichannel vertical j.f.e.t. (m.j.f.e.t.)

The letter reports direct observations of the spreading behaviour of the depletion layer into the channel region of the m.j.f.e.t. by scanning electron microscopy. The results are discussed in connection with electrical characteristics. A mechanism for the triode-like operation is also clarified by the concept of a potential profile.     

VDS voltage capabilities of a diffused j.f.e.t. with a vertical-channel arrangement

In the letter, it is shown that the VDS voltage limitation in a j.f.e.t. with a vertical-channel arrangement in the off state is due, not to the breakdown voltage of the gate-drain junction, as for a classical j.f.e.t., but to the field-effect lowering of the potential barrier created in the channel by the polarisation of the gate. The analysis is based on the 2-dimensional numerical solution of the general semiconductor equations.     

Bipolar operation of power junction field effect transistors

Bipolar-mode power j.f.e.t. operation is demonstrated to result in a significant improvement in the on resistance, especially for high-voltage devices. Theoretical analysis and experimental data show that the on resistance varies inversely as the square root of the gate current. High-speed switching in this mode has also been achieved.     

Wide-range monolithic bipolar?j.f.e.t. c.c.o.

A new monolithic current-controlled oscillator (c.c.o.) has been realised in a j.f.e.t.-bipolar technology. Its main advantages are a highly-linear seven decade frequency range and easy temperature compensation for frequency and output voltage.     

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.     

Two-dimensional analysis of j.f.e.t. structures containing a low-conductivity substrate

It is shown that j.f.e.t. structures containing a semiconductor substrate can sometimes exhibit a substantially lower saturation resistance than structures containing an ideally insulating substrate. This characteristic is attributed to velocity-limited carrier transport, in conjunction with the spreading of majority carriers into the semiconductor-substrate material.     

Two-dimensional analysis of substrate effects in junction f.e.t.s

This letter describes a numerical analysis of substrate effects in j.f.e.t.s. It is shown that the addition of a high-resistivity substrate increases the output conductance considerably, whereas the transconductance is not much affected. The substrate behaves roughly like a parallel resistor.     

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.     

Microwave capability of 1.5 ?m-gate GaAs m.o.s.f.e.t.

1.5 ?m-gate GaAs m.o.s.f.e.t.s have been fabricated by anodic oxidation, and the microwave capability has been examined. The maximum oscillation frequency fmax is 22 GHz and the noise figure is 6.1 dB at 8 GHz. The results are comparable to those of GaAs m.e.s.f.e.t.s.     

Performance of selenium-ion-implanted GaAs f.e.t.s

Selenium-ion-implanted GaAs f.e.t.s have given minimum noise figures as low as 3·4 dB and maximum available gains of at least 10 dB at 10 GHz. The devices do not appear to suffer from short-term drift problems, and have greater device-characteristic uniformity and reproducibility than epitaxial f.e.t.s.     

Circuit model for the GaAs m.e.s.f.e.t. valid to 12 GHz

A new equivalent circuit is given for the GaAs m.e.s.f.e.t., which includes resistive loss in the feed back elements. The circuit values are given for several 1 ?m-gate GaAs m.e.s.f.e.t.s. A method for fitting s12 to the measured data is described. Finally, the gain and stability factor of several GaAs m.e.s.f.e.t.s. are extrapolated to 24 GHz from the present model.     

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.     

n-channel inversion-mode InP m.i.s.f.e.t.

Capacitance/voltage and m.i.s.f.e.t. inversion-mode f.e.t. data are reported for p-type InP. It is shown that the surface of this material appears to be inverted at zero gate bias and that good inversion-mode (normally-off) device behaviour is possible.     

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.     

Performance of self-oscillating GaAs m.e.s.f.e.t. mixers at X-band

A new mode of m.e.s.f.e.t. operation, the self-oscillating mixer is reported. Conversion gains of up to 2 dB at 10 GHz and noise figures as good as 15 dB have been demonstrated by using a simple circuit.     

Calculation of intermodulation distortion levels in f.e.t. mixers and modulators

The intermodulation spectrum produced by a junction gate f.e.t. mixer or modulator may be predicted in `class-A? operation by suitably combining recently reported analytical procedures. Extension to discontinuous operation under high-level drive has been found to give satisfactory accuracy.     

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.     

Modelling of an f.e.t. mixer

A theoretical analysis of the mixer operation of an f.e.t. is presented. The model is based on a nonlinear equivalent circuit deduced from small signal S-parameter measurements. A Volterra series analysis enables the conversion gain to be calculated for different circuit conditions.