INVESTIGATIONS ON DEPOSITION OF FILMS FOR A THIN-FILM TRANSISTOR

Abstract

The availability of thin-film active devices can provide the micro-circuit designer with an additional degree of freedom. Presumably it will lover costs below those of hybrid circuit and may even increase reliability by eliminating the need to join circuitry prod ed by separate techniques 0 although the deposition techniques for thin ►film passive components -have been well establish- •d, the techniques for the fabrication of aottve elements are still in a developmental stage. Here investigations have been made on the feasibility of fabricating a thin-film transistor in the laboratory. A brie', introduction giving the importanee of the TPT and its appi.io ations, along with the statement of the problem has been given in Chapter 1. A review of the Tfl development and a theoretical background has been given in Chapter 2. Design considerations for the fabrication of the TFT have been d .eouseed in detail in Chapter 3+ The semiconductor material chosen is cadmium eul- phide. It has been Successfully evaporated using a resistance-heated tungsten boat covered with a tungsten wire-mesh obtained from a damaged vacuum tube The experimental details and results have been reported in Chapter 4. For the oxide layer# aluminium oxide has been preferred to the ueuel silicon monoxide, it will yield devices eiith little drift, Two methods have been tried for the formation of aluminium oxide** one by the anodi. ration of aluminium in an aqueous electrolyte and the other by the evaporation of aluminium in an oxidizing atmosphere. These two methods have been discussed in Chapter 5 The formation of the narrow eouroe«»druin gap required to obtain a high gain-bandwidth product is the major problem In the fabrication of a thin-fi .m transistor. A copper wire of diameter 20 a has been used for this purpose. The souxee.«drain contacts have been deposited over the semiconductor using the above wire mask to obtain the required channel gap. Aluminium has been used for the evaporation of source, drain and gate electrodes. To form the narrow gate width required to cover the channel gap, razor blades have been used as maeko i The evaporation technique of aluminium developed for source, drain and ~Oy o1 gate electrode &^ has been dealt in Chapter 6, These layers which have been deposited by using vacuum evaporation technique can be very much useful in the . -Vi,w fabrication of a C43 ooplaner•'eleotrode thin;Etim trans... ietor. The complete fabrication process of thine-fiim~ transistor hap been deecrib+d in Chapter 7. The conc1ud-ing remarks and er geetione for the improvement in the process and the eyotem have been given in Chapter 8. 0 0