A coaxially packaged MADT for microwave applications

The techniques needed to bring the potentiality of transistors to the microwave regions are certainly becoming progressively better understood, but the ways and means of actually using them at these frequencies are not yet generally known. The purpose of this paper is to describe the fabrication of the Coaxial MADT with both package design and high-frequency transistor design in mind, and to present some of the advantages that the coaxial package presents from a standpoint of circuits. The transistor design involved scaling-down of electrode diameters to approximately 50% of the smallest previous MADT electrode diameters. The emitter electrode is 2.5 mils in diameter, and the collector electrode is 4.5 mils in diameter. This change effected a substantial decrease in both emitter and collector barrier capacitance. Using standard Philco electro-chemical etching and plating techniques and disused n-type germanium, it is possible to place the emitter electrode onto that resistivity material which will provide a compromise between low Rb¹and high ftoptimizing for fmax. By this same method, it is possible to place the collector accurately on that resistivity material which will effect a compromise between low Cc, and high ft.