Patent ID: 8298879

Claim:
A thin film transistor formation method, comprising: depositing and patterning a gate electrode over a substrate using a first mask; depositing a gate dielectric layer over the patterned gate electrode; depositing a semiconductive active layer over the gate dielectric layer, the semiconductive active layer comprising: oxygen, zinc, indium and gallium; oxygen, nitrogen, zinc, indium and gallium; or oxygen, nitrogen, tin and zinc; depositing an etch stop layer over the semiconductive active layer; forming a second mask over the etch stop layer; etching the etch stop layer to form a patterned etch stop layer of a device portion of the thin film transistor and remove the etch stop layer from a gate contact portion of the thin film transistor to expose the semiconductive active layer; removing the second mask to expose the patterned etch stop layer; depositing a metal layer over the patterned etch stop layer and the semiconductive active layer; forming a third mask over the metal layer at the device portion of the thin film transistor; etching the metal layer to define a source electrode and a drain electrode at the device portion and remove the metal layer from the gate contact portion; removing the third mask; etching the semiconductive active layer using the source electrode and the drain electrode as a mask to remove the semiconductive active layer from the gate contact portion and expose the gate dielectric layer in the gate contact portion; and etching the gate dielectric layer using a fourth mask to expose a gate contact in the gate contact portion.