| 摘要 |
PURPOSE:To see that the current path by the carrier of the same conductivity type as those of a source region and a drain region is hard to be made and that the leak current during off is small by elevating the concentration of the impurities of a conductivity type opposite to that of the source region and the drain region, on the side opposite to a gate electrode out of a channel region. CONSTITUTION:In a bottom gate type transistor, a gate electrode 17 is lower than the polycrystalline Si film 12 where a channel region 15 is provided. But, the concentration of the n-type impurities in the channel region 15 becomes higher as it goes away from the gate region 17 in the thickness direction of the polycrystalline Si film 12, so positive holes are hard to generate on the side opposite to a gate electrode 17 out of the channel region 15. Accordingly, the current path by these positive holes are hard to be made, and the operation of the accumulation mode is suppressed, and the leak currents between the source and the drain during off are small. What is more, the concentration of the n-type impurities is low on the side of the gate electrode 17 out of channel region 15, so the inversion layer is not hard to be formed, and the threshold voltage becomes large to negative side. |
