LOGIC CIRCUIT, LIGHT EMITTING DEVICE, SEMICONDUCTOR DEVICE, AND ELECTRONIC DEVICE
First Claim
1. A logic circuit comprising:
- a depletion-type transistor in which a high power supply potential is applied to one of a source and a drain and a gate is connected to the other of the source and the drain; and
an enhancement-type transistor in which one of a source and a drain is connected to the gate of the depletion-type transistor and a low power supply potential is applied to the other of the source and the drain,wherein the depletion-type transistor and the enhancement-type transistor each comprise;
a gate electrode;
a gate insulating film over the gate electrode;
an oxide semiconductor layer over the gate insulating film;
a source electrode and a drain electrode which edge portions of the gate electrode overlap and which are in contact with the oxide semiconductor layer; and
an oxide insulating film in contact with the oxide semiconductor layer and over a channel formation region,wherein a thickness of the oxide semiconductor layer of the depletion-type transistor is larger than a thickness of the oxide semiconductor layer of the enhancement-type transistor,wherein a first signal is input to the gate electrode of the enhancement-type transistor, andwherein a potential of a portion where the enhancement-type transistor and the depletion-type transistor are connected to each other is output as a second signal.
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Accused Products
Abstract
An object is to obtain a desired threshold voltage of a thin film transistor using an oxide semiconductor. Another object is to suppress a change of the threshold voltage over time. Specifically, an object is to apply the thin film transistor to a logic circuit formed using a transistor having a desired threshold voltage. In order to achieve the above object, thin film transistors including oxide semiconductor layers with different thicknesses may be formed over the same substrate, and the thin film transistors whose threshold voltages are controlled by the thicknesses of the oxide semiconductor layers may be used to form a logic circuit. In addition, by using an oxide semiconductor film in contact with an oxide insulating film formed after dehydration or dehydrogenation treatment, a change in threshold voltage over time is suppressed and the reliability of a logic circuit can be improved.
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Citations
10 Claims
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1. A logic circuit comprising:
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a depletion-type transistor in which a high power supply potential is applied to one of a source and a drain and a gate is connected to the other of the source and the drain; and an enhancement-type transistor in which one of a source and a drain is connected to the gate of the depletion-type transistor and a low power supply potential is applied to the other of the source and the drain, wherein the depletion-type transistor and the enhancement-type transistor each comprise; a gate electrode; a gate insulating film over the gate electrode; an oxide semiconductor layer over the gate insulating film; a source electrode and a drain electrode which edge portions of the gate electrode overlap and which are in contact with the oxide semiconductor layer; and an oxide insulating film in contact with the oxide semiconductor layer and over a channel formation region, wherein a thickness of the oxide semiconductor layer of the depletion-type transistor is larger than a thickness of the oxide semiconductor layer of the enhancement-type transistor, wherein a first signal is input to the gate electrode of the enhancement-type transistor, and wherein a potential of a portion where the enhancement-type transistor and the depletion-type transistor are connected to each other is output as a second signal. - View Dependent Claims (2, 3, 7, 8, 9, 10)
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4. A logic circuit comprising:
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a depletion-type transistor in which a high power supply potential is applied to one of a source and a drain and a gate is connected to the other of the source and the drain; and an enhancement-type transistor in which one of a source and a drain is connected to the gate of the depletion-type transistor and a low power supply potential is applied to the other of the source and the drain, wherein the depletion-type transistor and the enhancement-type transistor each comprise; a gate electrode; a gate insulating film over the gate electrode; and a source electrode and a drain electrode which edge portions of the gate electrode overlap and which are provided over the gate insulating film, an oxide semiconductor layer over the gate electrode and covering the edge portion of the source electrode and the drain electrode; and an oxide insulating film in contact with the oxide semiconductor layer and over a channel formation region, wherein a thickness of the oxide semiconductor layer of the depletion-type transistor is larger than a thickness of the oxide semiconductor layer of the enhancement-type transistor, wherein a first signal is input to the gate electrode of the enhancement-type transistor, and wherein a potential of a portion where the enhancement-type transistor and the depletion-type transistor are connected to each other is output as a second signal. - View Dependent Claims (5, 6)
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Specification