![]() For this, the SiO 2 layer is removed from the area from where the base is to be spread. The silicon-di-oxide is an insulating material which does not allow the impurities to enter through it.įor making the wafer, the acceptor type impurities are diffused into the wafer. On the surface of the silicon wafer, Silicon oxide (SiO 2) is grown. The n-type silicon wafer is used for making the collector terminal. The diffusion type silicon transistor is shown in the figure below. In this technique, the alternate p-type and n-type impurities are gaseously diffuse into the wafer of semiconductor material at high temperature for forming the emitter and collector junction. The lead of the emitter and collector deposits on the two sides of the wafer as shown in the figure below. After cooling, the region of p-type germanium is produced, and the alloy of indium and germanium is deposited on the layer. The whole structure is cooled down steadily. The liquid solution of germanium is obtained in indium. The heat should be maintained in such a manner that the temperature should be raised above the melting point of indium but below the melting point of germanium. The indium dots (p-type impurity) are taken on both the side of the wafer and heated. The wafer is lightly doped and taken as a base of the transistor. The very thin layer of germanium crystal wafer is taken. The fabrication technique of making germanium alloy junction PNP transistor is shown in the figure below. The transistor which is built by using an alloy junction technique is capable of handling the maximum rating of current and power. It is the earliest technique of fabrication of transistors. The alloy-junction technique is very less expensive and provides less current gain. These techniques are explained below in details. ![]() ![]() ![]() The avalanche junction and diffused junction are the technique used for the fabrication of the transistor. The entire process of transistor fabrication requires 6 – 8 days. But compound semiconductor is also used for the manufacturing of the transistor. Mostly silicon is used for the fabrication. ![]()
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