Light emitting device and driving method thereof
View Patent ↗According to a driving method of applying a reverse bias voltage, capacitance occurs due to a stacked structure of a conductor, an insulator and a conductor, or due to a structure of a TFT. This capacitance prevents normal operation. The invention provides a pixel configuration including at least a driving transistor for driving a light emitting element and a switching transistor for controlling the driving transistor, wherein the switching transistor is turned on in the case of applying a forward bias voltage after applying a reverse bias voltage. As a result, it is prevented that the potential changes due to unwanted capacitive coupling.
1. A light emitting device comprising:
a light emitting element;
a first transistor for driving the light emitting element;
a second transistor for controlling the first transistor;
a capacitor between the gate electrode and one electrode of the first transistor;
a third transistor for discharging charges of the capacitor;
a fourth transistor between the first transistor and the light emitting element;
a unit for bringing a gate electrode of the first transistor into an electrically non-floating state by controlling the second transistor to be on-state in the case of applying a forward bias voltage to the light emitting element, after applying a reverse bias voltage to the light emitting element; and
a unit for determining a potential of the gate electrode of the first transistor so that the light emitting element emits no light,
wherein a gate electrode of the fourth transistor has a fixed potential.
2. The light emitting device according to claim 1 , further comprising:
an insulating film formed over one electrode of the first transistor,
wherein one electrode of the light emitting element is connected through a contact hole formed in the insulating film.
3. The light emitting device according to claim 1 , wherein one electrode of the light emitting element is formed over one electrode of the first transistor.
4. The light emitting device according to claim 1 , wherein the first transistor and the second transistor have a crystalline semiconductor film.
5. The light emitting device according to claim 1 , wherein the first transistor and the second transistor have an amorphous semiconductor film.
6. The light emitting device according to claim 1 , wherein the first transistor has a gate electrode and a low concentration impurity region overlapping the gate electrode.
7. A driving method of a light emitting device comprising a light emitting element, a first transistor for driving the light emitting element, and a second transistor for controlling the first transistor, comprising the steps of:
bringing a gate electrode of the first transistor into an electrically non-floating state by controlling the second transistor to be on-state in the case of applying a forward bias voltage to the light emitting element after applying a reverse bias voltage to the light emitting element; and
determining a potential of the gate electrode of the first transistor so that the light emitting element emits no light,
wherein a period during which all the scan lines are turned off is provided after a reverse bias voltage is applied to the light emitting element.
8. The driving method of a light emitting device, according to claim 7 , wherein a period during which the reverse bias voltage is applied comprises a period during which all scan lines are turned on before the reverse bias voltage is applied.
9. The driving method of a light emitting device, according to claim 7 , wherein an erasing period is provided before the period during which all the scan lines are turned on.
10. The driving method of a light emitting device, according to claim 7 ,
wherein the period of applying a reverse bias voltage is provided in one frame period;
the one frame period comprises m (m is a natural number of 2 or more) subframe periods SF 1 , SF 2 , . . . , SFm; and
the m subframe periods comprise writing periods Ta 1 , Ta 2 , . . . , Tam and display periods Ts 1 , Ts 2 , . . . , Tsm respectively.