Influence of Fundamental Parameters on the Intrinsic Voltage Gain of Organic Thin Film Transistors

The intrinsic gain is a key metric in analog electronics, it is the highest gain that can be obtained for an amplifier in the transistor configuration. However, there lack the demonstration of the intrinsic gain with different parameters comprehensively, they often focus on one or two features. In this work, we fabricated organic thin film transistors (OTFTs) with two types of semiconducting material to compare the effect of mobility on intrinsic gain and varied structural parameters such as active layer thickness and channel length to explore the impacts of those factors. We found that the intrinsic gain does not have much correlation with the mobility and the contact resistance. In addition, the intrinsic gain decreases as the channel length decreases, the increment of the gate voltage, and the decrease of the thickness of the active layer. The better understanding of different impacts on the intrinsic gain on OTFTs could provide indication for its real application design of organic circuit to obtain higher gain value, which is needed in the future amplifier processing. We fabricated organic thin film transistors (OTFTs) with indacenodithiophene-co-benzothiadiazole (IDTBT) and Poly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine (Poly-TPD) in order to investigate influences of fundamental parameters on intrinsic gain. We varied structural parameters such as active layer thickness and channel length on fabrication of devices. The mobility has extracted and compared with fundamental parameters. Even though devices with Poly-TPD showed lower mobility, but it has higher intrinsic gain. While, IDTBT-based devices showed lower intrinsic gain, even though they have much higher mobility than Poly-TPD-based device. As a result, we confirmed that thick active layer, long channel length, and small gate voltage are favorable to obtaining high intrinsic gain in OTFTs. We suggest that OTFT is a suitable configuration for exploration the intrinsic gain.