Thin film transistor

A thin film transistor suitable for being disposed on a substrate is provided. The thin film transistor includes a gate electrode, an organic gate dielectric layer, a metal oxide semiconductor layer, a source electrode and a drain electrode. The gate electrode is disposed on the substrate. The organic gate dielectric layer is disposed on the substrate to cover the gate electrode. The source electrode, the drain electrode and the metal oxide semiconductor layer are disposed above the organic gate dielectric layer, and the metal oxide semiconductor layer contacts with the source electrode and the drain electrode. Because the channel layer of the thin film transistor is a layer of metal oxide semiconductor formed at a lower temperature, thus the thin film transistor can be widely applied into various display applications such as flexible display devices.

TECHNICAL FIELD

The present invention relates generally to a semiconductor structure, and more particularly to a thin film transistor.

BACKGROUND

With the progress of fabricating technique, various display applications are developed out. To meet the requirements of lighter, thinner, shorter, smaller, and more portable, the development of display applications of the next generation is focused on the flexibility and portability. Currently, flexible displays and electronic paper displays attract considerable attention and are also well researched and developed.

Nowadays, thin film transistors are widely used in various display devices. Thus, the structure design and the materials of thin film transistors significantly affect the performance of display devices.

Generally, a thin film transistor at least includes a gate electrode, a source electrode, a drain electrode and a channel layer. The conductivity of the channel layer can be controlled by adjusting the potential of the gate electrode such that the source electrode and the drain electrode are electrically conducted (on-state) or isolated (off-state). In known thin film transistors, channel layer usually includes amorphous silicon (a-Si) or poly-silicon (p-Si).

However, a high process temperature is required for thin film transistors having channel layer of either a-Si or p-Si. Furthermore, flexible display devices usually include a flexible substrate such as a plastic substrate. As commonly known, plastic substrate has a low softening temperature. Thus, when thin film transistors with channel layer of either a-Si or p-Si are applied into flexible display devices, the flexible substrate transforms or deteriorates in the fabricating process of thin film transistors. Therefore, the known thin film transistors are not suitable for being applied into flexible display devices.

SUMMARY

The present invention provides a thin film transistor that can be manufactured without high temperature process and thus can be widely applied into various display applications.

In one embodiment, a thin film transistor suitable for being disposed on a substrate is provided. The thin film transistor includes a gate electrode, an organic gate dielectric layer, a metal oxide semiconductor layer, a source electrode and a drain electrode. The gate electrode is disposed on the substrate. The organic gate dielectric layer is disposed on the substrate to cover the gate electrode. The source electrode, the drain electrode and the metal oxide semiconductor layer are disposed above the organic gate dielectric layer, and the metal oxide semiconductor layer contacts with the source electrode and the drain electrode.

In another embodiment, a thin film transistor suitable for being disposed on a substrate is provided. The thin film transistor includes a gate electrode, an organic gate dielectric layer, a metal oxide semiconductor layer, a source electrode and a drain electrode. The source electrode, the drain electrode and the metal oxide semiconductor layer are disposed on the substrate, and the metal oxide semiconductor layer covers the source electrode and the drain electrode. The gate electrode is disposed on the metal oxide semiconductor layer to cover the source electrode and the drain electrode. The gate electrode is disposed on the organic gate dielectric layer.

Because the channel layer of the thin film transistor is metal oxide semiconductor that can be formed without high temperature processes, thus the thin film transistor can be widely applied into various display applications such as flexible display devices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a schematic view of a thin film transistor (TFT)100in accordance with a first embodiment. Referring toFIG. 1, the TFT100is disposed on a substrate101, and includes a gate electrode110, an organic gate dielectric layer120, a metal oxide semiconductor (MOS) layer140, a source electrode132, and a drain electrode134. The substrate101, for example, is a rigid substrate such as a glass substrate101, or a flexible substrate such as a plastic substrate.

It should be noted that if the substrate101is a flexible substrate, the substrate101can be disposed onto a rigid carrier plate (not shown) at first. After the TFT100is finished, the rigid carrier plate can be separated from the substrate101.

Referring again toFIG. 1, the gate electrode110is disposed on the substrate101, and the organic gate dielectric layer120is disposed on the substrate101to cover the gate electrode110. The source electrode132, the drain electrode134, and the MOS layer140are disposed above the organic gate dielectric layer120, and the MOS layer140contacts with the source electrode132and the drain electrode134. The MOS layer140includes indium gallium zinc oxide (IGZO), indium zinc oxide (IZO) or a combination thereof. In the present embodiment, the source electrode132and the drain electrode134are individually dispose on the organic gate dielectric layer120. Then, the MOS layer140is disposed on the organic gate dielectric layer120to cover the source electrode132and the drain electrode134(as shown inFIG. 1). In another embodiment, the MOS layer140can also be disposed on the organic gate dielectric layer120at first, and then the source electrode132and the drain electrode134are disposed on the organic gate dielectric layer120to cover a portion of the MOS layer140(not shown). However, the configuration of the MOS layer140, the source electrode132, and the drain electrode134are not limited to the above examples. Additionally, in the present embodiment, the TFT100further includes a protective layer150disposed on the substrate101and covering the MOS layer140, the source electrode132and the drain electrode134.

The gate electrode110, for example, includes molybdenum. The organic gate dielectric layer120and the protective layer140, for example, include flexible organic materials such as organic polymers (i.e., resin or other polymers). The source electrode132, and the drain electrode134, for example, is a composite layer of titanium/aluminum/titanium.

In another embodiment, as shown inFIG. 2, a TFT200may further include a barrier layer160interposed between the organic gate dielectric layer120and the MOS layer140. The barrier layer160, for example, includes silicon oxide, and the barrier layer160is configured for isolating the organic gate dielectric layer120from the MOS layer140such as to avoid the organic gate dielectric layer120changing the performance of conductivity of the MOS layer140.

In addition, the source electrode132and the drain electrode134inFIG. 1are disposed on a portion of the organic gate dielectric layer120, and the MOS layer140is disposed on the source electrode132, the drain electrode134and a portion of the organic gate dielectric layer120that is not covered by the source electrode132and the drain electrode134. However, the film stack structure of the TFT100is not limited to the illustrated one ofFIG. 1. In another embodiment, as shown inFIG. 3, the organic gate dielectric layer120only covers gate electrode110such that portions of the source electrode132, the drain electrode134, and the MOS layer140are located on the organic gate dielectric layer120.

Compared with known ones, TFTs100,200including the MOS layer140as channel layer can have higher electron mobility. Thus, TFTs100and200can be applied in back plates of organic light emitting diode or other applications. Furthermore, because the TFT100can be fabricated at a low temperature, thus when the substrate101of the TFT100or200is a flexible substrate such as a plastic substrate, the substrate101doesn't deteriorate or transform during the fabricating process of the TFT100or200. That is, the TFT100or200can be used in flexible display applications such as electronic paper or flexible display devices.

The TFT100or200described above is a bottom gate type. However, the present embodiment is not limited to the bottom gate type and other configuration of the gate structure is further described as follows.

FIG. 4is a schematic view of a TFT in accordance with another embodiment. Referring toFIG. 4, a TFT400is disposed on a substrate401, and the TFT400includes a source electrode412, a drain electrode414, a MOS layer420, an organic gate dielectric layer430and a gate electrode440. The substrate401can be a rigid substrate such as a glass substrate or a flexible substrate such as a plastic substrate.

As described in above embodiments, when the substrate401is a flexible substrate, the substrate401can be disposed onto a rigid carrier plate (not shown) before performing a fabricating process of the TFT400. After the TFT400is finished, the rigid carrier plate can be separated from the substrate401.

Referring again toFIG. 4, the source electrode412and the drain electrode414are disposed on the substrate401. The MOS layer420is disposed above the substrate401to cover the source electrode412and the drain electrode414. The MOS layer420may include an indium gallium zinc oxide (IGZO), indium zinc oxide (IZO) or a combination thereof. The organic gate dielectric layer430is disposed on the MOS layer. The gate electrode440is disposed on the organic gate dielectric layer430. Additionally, in the present embodiment, the TFT400further includes a protective layer450disposed on the organic gate dielectric layer430to cover the gate electrode440. The TFT400is a top gate type.

The gate electrode440, for example, includes molybdenum. The organic gate dielectric layer430and the protective layer450, for example, consist of flexible organic materials such as organic polymers (i.e., resin or other polymers). The source electrode412, and the drain electrode414, for example, is a composite layer of titanium/aluminum/titanium.

To avoid the negative influence of the organic gate dielectric layer430to the MOS layer420, in another embodiment, as shown inFIG. 5, a TFT500further includes a barrier layer460disposed between the organic gate dielectric layer430and the MOS layer420.

Similar to the reasons of the TFTs100,200, the TFTs400,500also have improved electron mobility compared with those know TFTs.

In summary, the embodiment or the embodiments may have at least one of the following advantages. TFTs of the embodiments utilize a MOS layer as the channel layer. Thus, the electron mobility of the channel layer is improved. In addition, because the MOS layer doesn't require a high temperature fabricating process, and the organic gate dielectric layer can be a flexible organic material, therefore the TFT of the embodiments can be applied into flexible display devices, thereby improving the flexibility of TFT applications.