Semiconductor device including memory cell which includes transistor and capacitor
An object of the present invention is to provide a semiconductor device in which stored data can be held even when power is not supplied for a certain time. Another object is to increase the degree of integration of a semiconductor device and to increase the storage capacity per unit area. A semiconductor device is formed with a material capable of sufficiently reducing off-state current of a transistor, such as an oxide semiconductor material that is a wide-bandgap semiconductor. With the use of a semiconductor material capable of sufficiently reducing off-state current of a transistor, the semiconductor device can hold data for a long time. Furthermore, a wiring layer provided under a transistor, a high-resistance region in an oxide semiconductor film, and a source electrode are used to form a capacitor, thereby reducing the area occupied by the transistor and the capacitor.
1. A semiconductor device comprising a memory cell, the memory cell comprising a transistor and a capacitor,
wherein the transistor comprises:
an oxide semiconductor film;
a first electrode layer and a second electrode layer over the oxide semiconductor film;
a gate insulating film over the oxide semiconductor film; and
a gate electrode layer over the gate insulating film,
wherein the capacitor comprises:
part of the oxide semiconductor film;
an insulating film over the part of the oxide semiconductor film; and
the second electrode layer over the insulating film,
wherein the part of the oxide semiconductor film, the insulating film of the capacitor, and the second electrode layer of the capacitor overlap with each other, and
wherein the gate insulating film of the transistor is separated from the insulating film of the capacitor.
2. The semiconductor device according to claim 1 ,
wherein the oxide semiconductor film comprises a channel formation region, a pair of first regions with the channel formation region therebetween, and a pair of second regions with the channel formation region therebetween,
wherein one of the pair of first regions and one of the pair of second regions are stacked, and
wherein the other of the pair of first regions and the other of the pair of second regions are stacked.
3. The semiconductor device according to claim 1 ,
wherein the oxide semiconductor film comprises a channel formation region, a pair of first regions with the channel formation region therebetween, and a pair of second regions with the channel formation region therebetween,
wherein one of the pair of first regions and one of the pair of second regions are stacked,
wherein the other of the pair of first regions and the other of the pair of second regions are stacked, and
wherein a resistance value of the pair of first regions is higher than a resistance value of the pair of second regions.
4. The semiconductor device according to claim 1 , wherein the oxide semiconductor film comprises indium and zinc.
5. The semiconductor device according to claim 1 , wherein the oxide semiconductor film comprises a carrier concentration being less than or equal to 1×10 12 /cm 3 .
6. The semiconductor device according to claim 1 , wherein the part of the oxide semiconductor film of the capacitor and the insulating film of the capacitor function as a dielectric of the capacitor.
7. The semiconductor device according to claim 1 , wherein the capacitor further comprises a third electrode layer below a bottom surface of the part of the oxide semiconductor film of the capacitor.