A new GaAs power MESFET structure for improved power capabilities

A GaAs microwave power MESFET structure is described that achieves a significant improvement of the gate mode attenuation by incorporating a suitably terminated transmission line parallel to the gate. The reduced attenuation allows a much wider single gate (a factor of 4 is possible) and a corresponding improvement of the total output power. It is shown that this approach leads to higher gain and cutoff frequency. An additional advantage of this MESFET structure is its higher input resistance relative to a device with equal total gate width but more gates in parallel. This results in simpler matching circuits of greater bandwidth. The single-gate structure can be connected in parallel to further increase the total output power. The results of an electrical characterization of the devices are presented, and its advantages and potential application are discussed     

Conduction properties of various reactively evaporated silicon oxide films

Evaporation of SiO was carried out in the pressure range 10^-5–10^-1 Torr for several gas compositions. It is observed that the film structure varies from uniform to crystalline. The composition of the crystalline films seems to be close to SiO₂, as confirmed by the structural features seen with a high resolution scanning electron microscope. In the uniform films conduction is considered to occur by Poole-Frenkel emission. In the crystalline films the conduction properties can be explained in terms of a space-charge-limited current.     

Continuous monitor of dangerous levels of microwave power

High mortality rates have been observed when animals arc exposed for up to 100 min in r.f. radiation having frequencies greater than 10 MHz and power densities of the order of 100 mW/cm2. A safety level of 10 mW/cm2 for frequencies above 10 MHz and exposures of the order of 5 min has therefore been generally adopted. A continuously monitoring small-size instrument for dangerous maximum and average levels of microwave power is required, particularly if it can be carried in the pocket of a person in a similar manner as the well known X ray photographic monitor.     

Harmonics and the fundamental-frequency negative conductance of Gunn diodes

Parametric interactions of X-band Gunn diodes between the frequencies 10 and 20 GHz are studies with the help of a coaxial resonator. A diode is placed at various positions along the central conductor so that different load impedances are applied. Very strong variations in microwave amplitude behaviour of the two frequencies were observed, which indicate pronounced interactive effects. These are studied by measuring the negative-conductance as a function of r.f. diode voltage. So far, only a decrease in fundamental-frequency conductance function has been observed due to the presence of harmonic power.     

Dislocations in GaAs produced by device fabrication

Due to the detrimental nature of dislocations on the properties of single-crystal GaAs the dislocation densities induced in the material during some fabrication processes, especially those encountered in the production of Gunn diodes, are investigated. The fabrication processes considered here are thermocompression bonding, heating, quenching, evaporation of contact material, cutting and handling. The results show that thermocompression bonding induces particularly strong damage. Finally several recommendations for optimum fabrication processes are presented which minimize the induced dislocation density.     

A new GaAs technology for stable FETs at 300°C

A technology for the fabrication of GaAs devices for operation at 300°C is presented. The high reliability of the devices is mainly due to diffusion barrier of WSi₂ in the ohmic contacts and to an optimized Si₃N₄ passivation. It is shown that MESFETs produced with this technology demonstrate a remarkable stability of their characteristics, even after 100 h of storage at 300°C, and only a little degradation after 100 h at 400°C     

Simplified Inelastic Design of Steel Girder Bridges

Inelastic design of steel girder bridges can result in beneficial material and fabrication cost savings and reduce the susceptibility of steel girder bridges to fatigue. The ability to redistribute large negative region moments, coupled with section capacities exceeding the yield moment, results in an efficient structure used to its limit-state capacity. Proposed LRFD inelastic design provisions are presented that allow compact or noncompact pier sections resulting in consistent bridge design across the steel girder bridge inventory. This paper illustrates the simplified inelastic design provisions, presents an example design of a two-span composite bridge comprising noncompact sections at the pier, and summarizes the experimental verification of the example design. The proposed inelastic design procedures are simple to apply, removing the cumbersome continuity and iterative requirements of past inelastic design practice.     

Pressure measurement by GaAs piezoelectric sensors

A new pressure sensor for pressures up to 100 bar and temperatures of about 200 degrees C is presented. It uses the piezoelectric effect of 111 oriented semi-insulating GaAs. This material allows the monolithic integration of sensor and electronic circuit.<>     

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.