Technological developments towards nanometric structures

Millimeter wave device technology requires nm-scale structurization capabilities with optimized surface properties. Results on anodic soft etching and cathodic metallization are reported for nanometrix structures. As a device example, terahertz Schottky diodes were fabricated with good noise performance as mixers operating around 600 GHz.     

A 300 GHz quasioptical schottky frequency doubler

A monolithically integrated frequency multiplier based on a planar antenna providing impedance matching has been realized and measured at 300 GHz. Each of the two circuits comprises a Schottky varactor, slot antenna, MIM-capacitor and microstrip bias feed. The theoretical design aspects, the technological approach and the RF performance are addressed.     

Microelectronics based on compound semiconductors

The compound semiconductor microelectronic applications are reviewed, the relevant material concepts described and some examples presented. These show that the primary interest concerns analogue circuits with increasing complexity, but also that digital capabilities are maturing. The technology and design are now also generally considered in view of high reliability.     

Future developments for Terahertz Schottky barrier mixer diodes

Contents With the steady improvement of whisker contacted GaAs Schottky barrier mixer diodes during the recent years, the frequency range for heterodyne detection has been extended towards frequencies as high as 2.5 THz. However, whisker contacted devices show reliability and handling problems, and space qualification is extremely difficult. Furthermore, whiskered diodes cannot be integrated. This paper shows future planar concepts suitable for THz heterodyne detection in order to overcome the above problems with whisker contacted diodes.

---

Zukünftige Entwicklungen für Terahertz-Schottky-Barrier-Dioden

Übersicht Durch eine fortlaufende Verbesserung von whiskerkontaktierten GaAs-Schottky-Barrier-Mischerdioden konnte der Frequenzbereich für die heterodyne Detektion bis auf 2.5 THz erweitert werden. Neben schwieriger Handhabung zeigen whiskerkontaktierte Bauelemente jedoch Zuverlässigkeits- und Stabilitätsprobleme und sind nicht integrierbar. Als Lösung werden Konzepte für planare Dioden vorgestellt und ihre Eignung für Terahertz-Mischeranwendungen diskutiert.

     

On the interpretation of electrical measurements on the GaAs-MOS system

Detailed evidence is presented which shows that previously published analyses of various investigations regarding the electrical characteristics of the GaAs MOS system lead to incorrect conclusions. Primarily the results were interpreted in terms of models which were developed to fit the Si-SiO₂ interface properties. However, detailed I–V and admittance measurements show that there are basic differences between the two systems, as the one with GaAs exhibits a charge injection phenomenon across the interface barrier, oxide conduction and a complicated (up to now insufficiently understood) interface behaviour. All these effects prevent the determination of interface state densities by conventional methods. The conclusion, that simply because of a high density of interface states neither accumulation nor inversion are possible, is not justified.     

AlGaAs/GaAs/AlGaAs DHBT's for high-temperature stable circuits

High-temperature devices are required for a large number of industrial applications. In order to demonstrate the feasibility of a high temperature operating circuit on GaAs an operational amplifier was designed and fabricated. A corresponding technology for transistors and circuits for operation up to 300°C with AlGaAs/GaAs/AlGaAs DHBT's is presented. For the amplifier circuit an open loop gain of 49.5 dB at room temperature and 35.8 dB at 200°C was measured, which is in good agreement with the circuit simulation. High temperature stability has been proven by a storage test at 400°C over 1000 h for the ohmic contact metallization and 200 h for the transistors     

Long resonator micromachined tunable GaAs-AlAs Fabry-Perot filter

We present novel concepts for tunable optical filters. Long resonant cavities of about 30-/spl mu/m length have been realized with two-chip designs. GaAs technology has been applied to filters that are designed for the use in dense wavelength-division multiplexing (WDM) at wavelengths around 1550 nm. A finesse of 46.7, a full-width at half-maximum (FWHM) of 1.2 nm and electrostatic tuning over a range of 103 nm with an applied voltage of 35 V has been achieved. An alternative tuning concept that allows to tune the resonator length 4 /spl mu/m by heating Ni-Cr resistors placed on the suspending beams of a membrane with an applied voltage of 2.7 V has been realized.     

GaAs enhancement/depletion n-channel MOSFET

The state of the art in the development of GaAs n-channel enhancement/depletion MOSFETs is presented. The static, non-equilibrium and dynamic characteristics are discussed and compared with the behaviour of large-area MOS diodes and a simple theory. It can be concluded, that the device is basically feasible for high speed logic enhancement circuits, pulse recovery purposes and for power applications, although some major oxide/semiconductor interface problems have still to be sorted out.     

Plasma densities and conductivities of semiconductor surfaces

Owing to charge in surface states, a curvature of the energy bands occurs near the surface inside a semiconductor. The shape of the curvature has been calculated, with the approximation that the impurities are fully ionised and the free-carrier distribution is nondegenerate. The results permit the calculation of the plasma-density distribution near the surface and the conductivity variation. It is shown that the conductivity varies to such an extent that bulk values cannot be taken for the computation of the microwave skin depth in semiconductors.