Occupant protection device
An occupant protection device which can protect an occupant without delay is provided. An image taken by an imaging device is analyzed to judge whether there is an object approaching the subject car. In the case where a collision between the object and the subject car is judged to be inevitable, an airbag device is activated before the collision, whereby the occupant can be protected without delay. By using selenium for a light-receiving element of the imaging device, an accurate image can be obtained even under low illuminance. Imaging in a global shutter system leads to an accurate image with little distortion. This enables more accurate image analysis.
1 . An imaging device comprising:
a pixel portion comprising a plurality of pixels arranged in a matrix; and
a driver circuit,
wherein each of the plurality of pixels comprises a light-receiving element, a first transistor, a second transistor, and a capacitor,
wherein the driver circuit comprises a third transistor,
wherein a cathode of the light-receiving element is electrically connected to a gate of the second transistor through the first transistor,
wherein the capacitor is electrically connected to the gate of the second transistor and an anode of the light-receiving element,
wherein the third transistor is on a different layer from the first transistor, the second transistor, the capacitor, and the light-receiving element,
wherein the first transistor, the second transistor, and the capacitor are overlapped with the anode of the light-receiving element,
wherein the first transistor comprises a first channel formation region, a first conductive layer as a gate, and a source or drain,
wherein the third transistor comprises a second channel formation region and a second conductive layer as a gate,
wherein the anode of the light-receiving element is on a first side of the first channel formation region,
wherein the first conductive layer is on a second side which is on the side opposite to the first side of the first channel formation region,
wherein the anode of the light-receiving element is on a first side of the second channel formation region,
wherein the second conductive layer is on the first side of the second channel formation region,
wherein a first electrode of the capacitor is on the same layer as the first conductive layer, and
wherein a second electrode of the capacitor is on the same layer as a third conductive layer which is electrically connected to the source or drain of the first transistor.
2 . An imaging device comprising:
a pixel portion comprising a plurality of pixels arranged in a matrix; and
a driver circuit,
wherein each of the plurality of pixels comprises a light-receiving element, a first transistor, a second transistor, and a capacitor,
wherein the driver circuit comprises a third transistor,
wherein a cathode of the light-receiving element is electrically connected to a gate of the second transistor through the first transistor,
wherein the capacitor is electrically connected to the gate of the second transistor and an anode of the light-receiving element,
wherein the third transistor is on a different layer from the first transistor, the second transistor, the capacitor, and the light-receiving element,
wherein the first transistor, the second transistor, and the capacitor are overlapped with the anode of the light-receiving element,
wherein the first transistor comprises a first channel formation region, a first conductive layer as a gate, and a source or drain,
wherein the third transistor comprises a second channel formation region and a second conductive layer as a gate,
wherein the anode of the light-receiving element is on a first side of the first channel formation region,
wherein the first conductive layer is on a second side which is on the side opposite to the first side of the first channel formation region,
wherein the anode of the light-receiving element is on a first side of the second channel formation region,
wherein the second conductive layer is on the first side of the second channel formation region,
wherein a first electrode of the capacitor is on the same layer as the first conductive layer,
wherein a second electrode of the capacitor is on the same layer as a third conductive layer which is electrically connected to the source or drain of the first transistor, and
wherein a side surface of the light-receiving element is in contact with an insulating layer.
3 . The imaging device according to claim 1 , wherein the first transistor comprises an oxide semiconductor in the first channel formation region.
4 . The imaging device according to claim 1 , wherein the light-receiving element comprises selenium.
5 . The imaging device according to claim 1 , further comprising a wiring including copper,
wherein the wiring is electrically connected to the first transistor.
6 . The imaging device according to claim 2 , wherein the first transistor comprises an oxide semiconductor in the first channel formation region.
7 . The imaging device according to claim 2 , wherein the light-receiving element comprises selenium.
8 . The imaging device according to claim 2 , further comprising a wiring including copper,
wherein the wiring is electrically connected to the first transistor.