Dependence of the Noise Parameters of the GaAs Mesfet on Technology, Parasitic Components and Bias Conditions in the Frequency Range Up to 12 GHz

A procedure is described, which permits the theoretical determination of the influence of bias conditions, technological parameters and parasitic components on noise behaviour of microwave GaAs-MESFETs in the GHz-range and experimental verification of the results. For calculation of the internal dc-parameters a saturated channel region has been considered, which extends over the drain end of the gate contact. The noise temperature of the active epi-layers strongly depends on fabrication process and must be measured in the GHz-region on ungated MESFETs. The use of a buffer layer, 1.5¿m thick, suppresses the noise temperature of the active layers and prevents the breakdown of the back diode space charge and the substrate current Isub caused by avalanche multiplication effects. Calculations of noise parameters as a function of dc-bias and frequency are in good agreement with experimental results. A computer program, on the basis of correlation matrices, premits the analytical calculation of the influence of all parasitic and feedback elements. We found that the greatest influence on optimum noise figure results from parasitic resistances while equivalent noise resistance Rn depends strongly on lead inductances.