Transistor having a vertical channel

A semiconductor device, comprising:

• an active pillar extending from a substrate in a first direction and including a source and a drain, wherein the source and the drain are arranged in the first direction;
• a channel region formed in the active pillar and between the source and the drain;
• a lightly doped drain (LDD) region formed in the active pillar and between the drain and the channel region;
• a gate insulating layer formed over a sidewall of the active pillar in a second direction, wherein the second direction is perpendicular to the first direction;
• a first gate electrode formed over the gate insulating layer in the second direction, entirely surrounding the source and the channel region, and having a first work function;
• and
• a second gate electrode formed over the first gate electrode in the second direction and having a second work function that is higher than the first work function,
• wherein the first gate electrode is formed over an outer circumference of the active pillar, and the second gate electrode is formed over an outer circumference of the first gate electrode,
• wherein a total height of the first gate electrode is shorter than a total height of the second gate electrode,
• wherein each of the total height of the first gate electrode and the total height of the second gate electrode is measured only in the first direction, and
• wherein the first gate electrode is positioned between the gate insulating layer, which is formed over the sidewall of the active pillar, and the second gate electrode only in the second direction.