Working principle of organic field-effect transistor

Organic field-effect transistors (OFETs) have received great attention from researchers due to their outstanding characteristics, including wide material sources, compatibility with flexible substrates, low-temperature processing, suitability for mass production, and low cost. It has a wide range of applications, including fully organic active displays, large-scale and ultra large scale integrated circuits, memory components, sensors, organic lasers, complementary logic circuits, and superconducting material preparation.

Working principle of organic field-effect transistor

Organic field-effect transistors consist of three electrodes: source drain, gate, organic semiconductor layer, and gate insulation layer. According to the structure of the device, organic field-effect transistors can be divided into four categories: bottom gate bottom contact, top gate top contact, top gate bottom contact, and bottom gate I-page contact (Figure 1). The bottom gate and top gate are divided according to the position of the gate. The bottom gate is the gate deposited below the gate insulation layer, while the top gate is the gate deposited above the organic semiconductor and insulation layer; The top contact and bottom contact are divided according to the position of the organic semiconductor and the source drain electrode. The top contact is where the organic semiconductor grows on the gate insulation layer and then deposits the source drain electrode, while the bottom contact is where the organic semiconductor substrate consists of the source drain electrode and the gate insulation layer. Different device structures can lead to different carrier injection methods and device performance. For example, in the bottom gate bottom contact, carriers can be directly injected into the conductive channel from the electrode edge, while in the bottom gate top contact, the organic semiconductor separates the source and drain electrodes from the conductive channel. Carriers injected from the electrode into the conductive channel must pass through the organic semiconductor layer to reach the conductive channel. This is likely to increase the contact resistance and reduce the injection efficiency of carriers. However, in devices with this structure, due to the relatively large contact area between the electrode and the organic semiconductor, the contact resistance becomes very small when the organic semiconductor layer is thin. In addition, since the contact is made by depositing organic semiconductor material directly on the insulating layer, the film quality is also relatively high. The sentence is:, Therefore, the performance of the device is better than that of the bottom contact. However, from the perspective of the manufacturing process of the device, the top contact is formed by depositing the source and drain electrodes on the organic semiconductor thin film, which may cause some negative effects on the organic semiconductor, such as damaging the structure of the organic semiconductor. On the other hand, the size and integration of the top contact device cannot be smaller or higher than that of the bottom contact. Therefore, the top contact is not suitable for large-scale production, which to some extent limits its practical application.

Organic field-effect transistors are structurally similar to capacitors, with the source and drain electrodes and the conductive channel of the organic semiconductor film acting as one electrode plate, and the gate acting as the other electrode plate. When a negative voltage is applied between the gate and source from VGS, positively charged holes will be induced in the semiconductor layer near the insulation layer, and negatively charged electrons will accumulate at the gate. At this point, adding a negative voltage VDS between the source and drain electrodes will generate a current IDS between them. By adjusting VGS and Vns, the electric field strength in the insulation layer can be adjusted, and the density of induced charges varies with the strength of the electric field. Therefore, the width of the conductive channel between the source and drain is different, and the current between the source and drain will also change. Thus, by adjusting the electric field strength in the insulation layer, the purpose of regulating the current between the source and drain can be achieved. Keeping VDS unchanged, when VGS is small, IDS is very small, which is called the "off" state; When VGS is large, IDS reaches a saturation value, which is called the "on" state.