ACTIVE MATRIX SUBSTRATE AND ITS PRODUCTION

PURPOSE:To provide an active matrix substrate with which the high-mobility characteristics required for TFTs for display and the low-off current characteristics required for TFTs for driving are compatibly obtd. CONSTITUTION:The TFTs (a), (b) for driving are formed by continuously laminating a semiconductor layer 4a and a gate insulating film 5, then patterning the layer and the film to island shapes. The boundaries between the semiconductor layers 4a and the gate insulating films 5 are good and the insulating films 4a are formed to a large film thickness. The TFTs (c) for display are formed by forming the semiconductor layer 4b to a small film thickness and making the resistance of the TFTs higher to decrease off currents and prevent the degradation in the insulation characteristic in the level difference parts of the gate insulating films 3. Further, side wall insulators are formed on the side walls of the gate electrodes 4b and, therefore, these insulators serve as a mask at the time of forming source regions and drain regions. Parts where these impurity ions are implanted or parts 14, 15 where these impurity ions are not implanted are formed among channel parts 20b and the source regions 12b and the drain regions 13b. The off currents at the time of reverse gate bias are thus decreased.