Whenever the electric field in a device varies sufficiently rapidly with distance and/or time, significant deviations of the electron drift velocity from the static velocity-field characteristic occur. These relaxation effects manifest themselves not only in the high-frequency properties, but also in the static device properties of devices such as transferred-electron devices and field-effect transistors. Important quasi-static effects are drift velocity overshoot in FET's and relaxation effects in the bistable switching in TE devices. The ultimate speed limitations of TE devices are governed by relaxation effects. Transit-time modes are superior to the LSA mode, barrier-type contacts to n + -on- n contacts, and InP to GaAs.

Hot-electron relaxation effects in devices☆

Digital electronics at gigabit-per-second data rates is emerging as a new branch of science and engineering. A particular field of application opens up in advanced radar and sensing systems where large amounts of data have to be dealt with in real time. Analog-to-digital (A/D) converters with microwave sampling rates and multipliers for high-data-yield processing are specifically required subcircuits. In communications, special 1 to 2 Gbit/s systems have been developed, but a further commercial need develops in domestic satellite links and in fiber-optical communications with its potential high bandwidth capabilities. Corresponding gigabit measuring and test instrumentation is required and being implemented. Gigabit circuitry has so far mainly been realized in hybrid-integrated technology. However, the full use of modern technological tools now allows for the fabrication of gigabit monolithic integrated circuits (IC's), with circuits up to 4 Gbit/s implemented. In circuit design, specific problems must be solved which are due to the involved wide bandwidths at microwave spectral frequencies. High packing density is required for low interconnection delay, but power dissipation leads to limitations. Gigabit electronics is based on devices with switching speeds in the range of a few hundred picoseconds and lower. Besides pin diodes and Schottky diodes, transistors are investigated at first. While the Si bi-polar has been improved, it is the GaAs MESFET and the GaAs junction FET which excel in speed, with LSI capabilities. Very recently, a considerable speed improvement was reported for Si n-MOSFET's. Unique properties for gigabit logic are shown by transferred-electron devices. However, the lead with regard to high speed and low power have Josephson junctions of the in-line junction and of the interferometer types. The present phase of rapid gigabit IC development, with expected LSI circuits in the 2 to 5 Gbit/s range and MSI circuits up to 15 Gbit/s, will stimulate further applications.

Gigabit electronics&#8212;A review

A new minimax network optimization algorithm not requiring derivatives has been developed. It is based on successive linear approximations to the nonlinear functions defining the problem. Adequate modeling of distributed parameter circuits for optimization purposes often involves parasitic, etc., which makes the gradient computation by the adjoint network method or related methods rather complicated, and often numerical errors are introduced in the gradients. Consequently, the algorithm is found to be of particular relevance in optimum design of practical microwave networks. The relative advantages of the proposed algorithm are established by comparison with known gradient and nongradient algorithms based on optimization of cascaded transmission-line transformers. The relevance to microwave filter design is demonstrated by an example which represents an improvement of analytical filter design results. Finally, optimum broad-band design of a practical coaxial transferred-electron reflection-type amplilier is carried out by means of the proposed method. The results are supported by experimental verification.

/pdf/efficient-minimax-design-of-networks-without-using-21bk51705l.pdf

Efficient Minimax Design of Networks without Using Derivatives

A circuit technique is described whereby the electronic tuning range obtained by varactor tuning solid-state oscillators, such as Gunn oscillators, can be improved. The principle of the technique has been demonstrated by doubling the tuning range obtained from a coaxial X-band Gunn oscillator using distributed circuit elements. An analytical expression for the improved tuning range is presented and predictions for the improvement in an existing microstrip X-band oscillator using chip devices given.

A circuit technique for broadbanding the electronic tuning range of Gunn oscillators

The trapping conditions of a high-field domain at the anode are studied by varying doping density, applied bias voltage, and doping notch depth and width near the cathode. It is shown that the frequency band of negative conductance of the trapped-domain mode depends significantly on the doping density, and a diode having the doping density of 3 × 1015/cm3exhibits the negative conductance over the wide range from 4 GHz to 42 GHz. The upper frequency limit of the negative conductance is due to the series resistance in the low-field region and the lower limit is determined by carrier transit-time effects in high-field region. The operation mode of a trapped-domain diode will change into a traveling dipole or accumulation mode from a trapped-domain mode depending on the doping density and the operation frequency for a large-signal operation.

An analysis of wide-band transferred electron devices

A current drop of 41.5 percent and a switching time of 110 ps is reported for a 10-µm supercritically doped n+-n-n+GaAs transferred electron device operated as a bistable switch into a 25-Ω resistive load. An investigation to check that no microwave oscillations occur is presented.

http://ieeexplore.ieee.org/iel5/5/31183/01451507.pdf

A high current drop GaAs bistable switch

Bistable switching in supercritically doped n+-n-n+GaAs transferred electron devices (TED's) is investigated experimentally and interpreted in computer simulations, for which details of the computer program are given. Three switching modes all leading to stable anode domains are discussed, namely: 1) cathode-triggered traveling domain; 2) cathode-triggered accumulation layer; 3) anode-triggered domain. Relative current drops up to 40 percent, and switching times down to 60 ps are obtained in low-duty-cycle pulsed experiments with threshold currents around 400 mA. Optimum device parameters are shown to be as follows: 1) doping in the 3-4 × 1015cm-3range; 2) length around 6 µm; 3) doping gradients below 20 percent; 4) high-quality interfaces.

/pdf/bistable-switching-in-supercritical-n-n-n-gaas-transferred-4qz8j843gp.pdf

Bistable switching in supercritical n + -n-n + GaAs transferred electron devices

Small-signal negative conductances from 5 to 17 GHz in both voltage polarities are reported for CW-operated 10-µm supercritically doped n+nn+GaAs transferred electron devices. The conceptually different behavior in the two polarities for the frequency dependence of the negative conductance is interpreated by means of computer simulations, and the stabilizing mechanisms involved are discussed.

A broad-band negative conductance GaAs TED

/pdf/on-the-design-of-transferred-electron-oscillators-and-op71mg5dqq.pdf

On the Design of Transferred Electron Oscillators and Amplifiers

Bistable switching with current drops of 40% and switching times of 100 ps are obtained in pulsed operation of 10?m supercritically doped n+ nn+ GaAs Transferred Electron Devices (TEDs). When CW-operated the same devices exhibit a 5-17 GHz bandwidth for the stable negative resistance.

/pdf/stable-amplification-and-high-current-drop-bistable-3fhv01v6zj.pdf

Stable Amplification and High Current Drop Bistable Switching in Supercritical GaAs Tills

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