Organic FET vs. Organic TFT: Key Differences Explained

This article compares Organic Field Effect Transistors (OFETs) and Organic Thin Film Transistors (OTFTs), highlighting their key differences. Both are types of transistors, but they utilize organic materials in their construction.

Organic FET (Organic Field Effect Transistor)

Figure 1 illustrates the structure of an Organic FET. As you can see, the architecture is quite similar to that of a TFT. The key components include:

• Gate Insulator: Typically, silicon dioxide ($SiO_2$) is used as the gate insulator.
• Active Layer: The active FET layer is formed on the substrate using various techniques such as:
  • Thermal evaporation
  • Electro-static lamination
  • Coating from an organic solution

The carrier mobility is a crucial parameter that defines the OFET’s carrier transport characteristics.

Organic TFT (Organic Thin Film Transistor)

Figure 2 shows the general structure of an Organic TFT.

• Basic Construction: A standard TFT consists of a gate (G), an insulator, a semiconductor, and source-drain (S-D) contacts.
• Gate Coverage: The gate electrode should cover the entire transistor channel area.
• Channel Dimensions: The channel is defined by its length (L) and width (W), with W extending in the Z-direction.
• Insulator Thickness: The insulator thickness (d) should be significantly smaller than the channel length (L) to avoid short channel effects ($d << L$).
• Ohmic Contacts: The semiconductor material should form good ohmic contacts with the source and drain electrodes.

The performance of polymer semiconductors has advanced to the point where they are comparable to amorphous silicon (a-Si). This means that applications traditionally using a-Si can now potentially be realized using polymers. Examples include:

• Smartcards
• Simple displays
• Electronic paper

Figure 3 depicts different structural configurations of Organic TFTs. While the performance of these different configurations should ideally be the same, variations can arise due to factors like:

• Interfaces between materials
• The morphology (structure) of the organic film