Active matrix substrate and method for producing active matrix substrate

An active matrix substrate having a displaying region that includes a plurality of pixel regions and a non-displaying region excluding the displaying region, the active matrix substrate comprising:

• a substrate;
• a plurality of source bus lines extending along the first direction and a plurality of gate bus lines extending along a second direction which intersects the first direction, the source bus lines and the gate bus lines being supported on the substrate;
• and
• a thin film transistor disposed in each of the plurality of pixel regions, wherein,
• each thin film transistor includes a gate electrode, an oxide semiconductor layer disposed on the gate electrode via a gate insulating layer, and a source electrode and a drain electrode being disposed on the oxide semiconductor layer and electrically connected to the oxide semiconductor layer;
• the plurality of gate bus lines and the gate electrode are made of a first electrically conductive film;
• at least part of each of the plurality of source bus lines, the source electrode, and the drain electrode have a multilayer structure including a lower layer that is made of a second electrically conductive film and an upper layer that is made of a first transparent electrically conductive film;
• the active matrix substrate
• further includes a pixel electrode disposed in each of the plurality of pixel regions and a common electrode disposed on the pixel electrode via an interlevel insulating layer, the pixel electrode being made of the first transparent electrically conductive film and the common electrode being made of a second transparent electrically conductive film;
• or further includes, in each of the plurality of pixel regions, a pixel electrode disposed on the thin film transistor via an interlevel insulating layer, the pixel electrode being made of a second transparent electrically conductive film;
• and
• a plurality of first oxide strips are disposed between the plurality of source bus lines and the gate insulating layer, the plurality of first oxide strips being made of a same oxide semiconductor film as the oxide semiconductor layer and extending along the first direction, and in each of the plurality of source bus lines, the lower layer is located on an upper face of one corresponding first oxide strip among the plurality of first oxide strips, and the upper layer covers an upper face and a side face of the lower layer and a side face of the one corresponding first oxide strip and is in contact with the gate insulating layer.

A method of producing an active matrix substrate having a displaying region that includes a plurality of pixel regions and a non-displaying region excluding the displaying region, the active matrix substrate including:

• a plurality of source bus lines and a plurality of gate bus lines;
• a thin film transistor and a pixel electrode disposed in each of the plurality of pixel regions;
• and a common electrode, the method comprising:
• (a) a step of forming, on the substrate, a first electrically conductive film, and thereafter patterning the first electrically conductive film to form a gate metal layer that includes the plurality of gate bus lines and a gate electrode of each thin film transistor, and forming a gate insulating layer covering the gate metal layer;
• (b) a step of forming an oxide semiconductor film and a second electrically conductive film in this order on the gate insulating layer, and thereafter patterning the second electrically conductive film and the oxide semiconductor film, where,
• in a transistor formation region in which to form the each thin film transistor, an electrode layer to become a source/drain of the thin film transistor is formed from the second electrically conductive film, and an oxide semiconductor layer to become an active layer of the thin film transistor is formed from the oxide semiconductor film, and,
• in a source bus line formation region in which to form the plurality of source bus lines, a plurality of preliminary source bus lines having a first width are formed from the second electrically conductive film, and a plurality of first oxide strips having the first width are formed from the oxide semiconductor film;
• (c) a step of forming a first transparent electrically conductive film that covers the plurality of preliminary source bus lines and the electrode layer, and thereafter patterning the first transparent electrically conductive film, the plurality of preliminary source bus lines, and the electrode layer, and forming a source electrode and a drain electrode of the each thin film transistor to obtain the each thin film transistor and to obtain the pixel electrode and the plurality of source bus lines, wherein at least part of each of the plurality of source bus lines, the source electrode, and the drain electrode have a multilayer structure including a lower layer and an upper layer,
• the pixel electrode is formed from the first transparent electrically conductive film,
• in the transistor formation region, the upper layer of the source electrode and the upper layer of the drain electrode are formed from the first transparent electrically conductive film, and the lower layer of the source electrode and the lower layer of the drain electrode are formed from the electrode layer,
• in the source bus line formation region, the upper layer of the plurality of source bus lines is formed from the first transparent electrically conductive film, the lower layer of the plurality of source bus lines is formed from the plurality of preliminary source bus lines, the lower layer of each of the plurality of source bus lines having a second width which is smaller than the first width;
• (d) a step of forming an interlevel insulating layer that covers the thin film transistor and the plurality of source bus lines;
• and
• (e) a step of forming a second transparent electrically conductive film on the interlevel insulating layer, and patterning the second transparent electrically conductive film to form the common electrode.