Semiconductor device
A semiconductor device is described, which includes a first transistor, a second transistor, and a capacitor. The second transistor and the capacitor are provided over the first transistor so as to overlap with a gate of the first transistor. A semiconductor layer of the second transistor and a dielectric layer of the capacitor are directly connected to the gate of the first transistor. The second transistor is a vertical transistor, where its channel direction is perpendicular to an upper surface of a semiconductor layer of the first transistor.
1. A semiconductor device, comprising:
a plurality of memory cells stacked over a layer comprising a driving circuit,
wherein each of the memory cells comprises:
a first transistor;
a second transistor; and
a capacitor;
wherein a gate electrode of the first transistor is electrically connected to one of electrodes of the capacitor and to one of a source electrode and a drain electrode of the second transistor,
wherein, in a plane view, a semiconductor layer of the second transistor and a dielectric of the capacitor do not protrude from the gate electrode of the first transistor, and
a channel formation region of the second transistor comprises an oxide semiconductor.
2. The semiconductor device according to claim 1 , wherein the dielectric of the capacitor comprises the same material as the semiconductor layer of the second transistor.
3. The semiconductor device according to claim 1 ,
wherein the oxide semiconductor is an In—Ga—Zn-based oxide.
4. The semiconductor device according to claim 1 ,
wherein each of the first transistor and the second transistor is electrically connected to the driving circuit through a connection electrode layer.
5. The semiconductor device according to claim 1 , further comprising an insulating layer over a first memory cell of the plurality of the memory cells, and a second memory cell of the plurality of the memory cells over the insulating layer.
6. The semiconductor device according to claim 5 ,
wherein the insulating layer comprises a low-dielectric insulating material.
7. The semiconductor device according to claim 1 ,
wherein the semiconductor layer of the second transistor has cylindrical shape.
8. The semiconductor device according to claim 1 ,
wherein the dielectric of the capacitor has cylindrical shape.
9. The semiconductor device according to claim 1 ,
wherein a channel direction of the first transistor is perpendicular to a channel direction of the second transistor.