Sensing device and fabricating method of the same

A sensing device, comprising:

• a substrate;
• a switching element, disposed on the substrate, and comprising a bottom gate electrode, a top gate electrode, a drain electrode, a source electrode, a semiconductor layer located between the bottom gate electrode and the top gate electrode, a first island-shaped gate insulating layer disposed between the bottom gate electrode and the semiconductor layer, and a second island-shaped gate insulating layer disposed between the top gate electrode and the semiconductor layer,
• wherein the source electrode and the drain electrode are arranged along a first direction,
• wherein each of the first island-shaped gate insulating layer and the second island-shaped gate insulating layer has a first side surface and a second side surface opposite to the first side surface, and the first side surface and the second side surface are arranged along a second direction perpendicular to the first direction,
• wherein the top gate electrode has two parts extend downward along a normal direction of the substrate to respectively cover the first side surfaces and the second side surfaces so that two end portions of the top gate electrode respectively physically contact two end portions of the bottom gate electrode to form an annular gate completely surrounding the semiconductor layer, wherein the two end portions of the top gate electrode are arranged along the second direction, and the two end portions of the bottom gate electrode are arranged along the second direction;
• a sensing element, disposed at one side of the switching element, and comprising:
• a lower electrode, electrically connected to the source electrode;
• a photoelectric conversion layer, disposed on the lower electrode;
• and
• an upper electrode, disposed on the photoelectric conversion layer;
• a top insulating layer disposed on the sensing element and the top gate electrode of the switching element, having a first through hole, a second through hole, a third through hole and a fourth through hole, wherein the drain electrode is electrically connected to a drain region of the semiconductor layer through the first through hole, the source electrode is electrically connected to a source region of the semiconductor layer through the second through hole, and the lower electrode is electrically connected to the source electrode through the third through hole;
• and
• a common electrode extending along the second direction, electrically connected to the upper electrode and belonging to a same film layer as the source electrode, wherein the upper electrode is electrically connected to the common electrode through the fourth through hole of the top insulating layer,
• wherein a spacing between the lower electrode and the substrate is less than a spacing between the semiconductor layer and the substrate, with the proviso that the lower electrode is in contact with the photoelectric conversion layer.