Thin-film transistor device, utilizing different types of thin film transistors

A thin-film transistor device comprising:

• a first thin-film transistor of n-type of electric conduction having a first channel region, a first low-concentration impurity region and a first gate electrode covering nearly the whole first low-concentration impurity region and the first channel region;
• a second thin-film transistor of n-type of electric conduction having a second channel region, a second low-concentration impurity region and a second gate electrode covering part of the second low-concentration impurity region and the second channel region;
• and
• a third thin-film transistor of p-type of electric conduction having a third channel region and a third gate electrode covering the third channel region,
• wherein:
• the impurities are contained at different concentrations in the first and second channel regions and in the third channel region;
• the first and second gate electrodes and the third gate electrode are formed in different structures or by using different materials;
• the first to third channel regions contain impurities of the p-type only, and the first and second channel regions contain impurities of the p-type at a concentration higher than that in the third channel region;
• and
• the first and second gate electrodes have a laminated layer structure including a first layer formed by using a first electrically conducting material and a second layer formed on the first layer by using a second electrically conducting material different from the first electrically conducting material and having a width larger than that of the first layer, and the third gate electrode has a laminated layer structure including a third layer formed by using the first electrically conducting material and a fourth layer formed on the third layer by using the second electrically conducting material and having a width nearly the same as that of the third layer.