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Organic Permeable Base Transistors (OPBTs) reach a very high transit frequency and large on-state currents. However, for a later commercial application of this technology, a high operational stability is essential as well. Here, the stability of OPBTs during continuous cycling and during base bias stress is discussed. It is observed that the threshold voltage of these transistors shifts toward more positive base voltages if stressed by applying a constant potential to the base electrode for prolonged times. With the help of a 2D device simulation, it is proposed that the observed instabilities are due to charges that are trapped on top of an oxide layer formed around the base electrode. These charges are thermally released after removing the stress, and the device reaches its initial performance after around 24–48 h. 

Doping organic semiconductors has become a key technology to increase the performance of organic light-emitting diodes, solar cells, or field-effect transistors (OFETs). However, doping can be used not only to optimize these devices but also to enable new design principles as well. Here, a novel type of OFET is reported—the vertical organic tunnel field-effect transistor. Based on heterogeneously doped drain and source contacts, charge carriers are injected from an n-doped source electrode into the channel by Zener tunneling and are transported toward a p-doped drain electrode. The working mechanism of these transistors is discussed with the help of a tunnel model that takes energetic broadening of transport states in organic semiconductors and roughness of organic layers into account. The proposed device principle opens new ways to optimize OFETs. It is shown that the Zener junction included between the source and drain of the vertical organic tunnel field-effect transistors suppresses short channel effects and improves the saturation of vertical OFETs. 

Research in Organic Permeable Base Transistors (OPBTs) has led to a significant increase in their performance. However, despite this progress, understanding of the working mechanism of OPBTs is still limited. Although first numerical models of OPBTs are able to describe the switching mechanism of OPBTs correctly, they neglect currents injected at the base electrode, which leads to unrealistically low off-currents and high ON/OFF ratios. Here, a tunneling model is developed that is capable of describing injection of charges through a thin oxide layer formed around the base electrode of OPBTs. With the help of this injection model, the performance of the base-collector diode of OPBTs is discussed. In particular, the model is used to explain the reduction in backward currents due to an exposure to ambient air by an increase in the thickness of the oxide layer. Furthermore, the tunnel model is used to show that the reduction in backward currents of the base-collector diode leads to a decrease in off-currents of complete OPBTs, which in turn leads to an increase in their ON/OFF ratio. 

Abstract Organic permeable‐base transistors (OPBTs) show potential for high‐speed, flexible electronics. Scaling laws of OPBTs are discussed and it is shown that OPBT performance can be increased by reducing their effective device area. Comparing the performance of optimized OPBTs with state‐of‐the‐art organic field‐effect transistors (OFETs), it is shown that OPBTs have a higher potential for an increased transit frequency. Not only do OPBTs reach higher transconductance values without the need for sophisticated structuring techniques, but they are also less sensitive to parasitic contact resistances. With the help of a 2D numerical model, the reduced contact resistances of OPBTs are explained by a homogeneous injection of current across the entire emitter electrode, compared to injection in a small area along the edge of the source of OFETs.