Scientists find that a ‘design limitation’ in transistors actually improves performance

The paper, which will be presented at the IEEE International Electron Devices Meeting (IEDM) 2025, describes how embracing small energy barriers at the metal/semiconductor interface of organic thin-film transistors (OTFTs) can help them perform more consistently and operate more reliably over time.  

Organic thin-film transistors (OTFTs) are a key component of what are thought to be the next generation of flexible and wearable electronics. They are lightweight, low-cost and printable on large areas, but their long-term stability has been a persistent challenge. 

Working with collaborators in Austria and industry partners at Silvaco Europe, the team fabricated flexible transistors using a silver contact material, common in printed electronics, and demonstrated improved current uniformity between devices. Even at very low operating voltages (≤ -4 V), the transistors maintained stable performance, making them ideal for low-power and wearable applications. 

The key to understanding the improved stability in the devices was enabled by exploring the novel ‘multimodal transistor’ (MMT) design with two gate electrodes, allowing separate control of current injection and flow. This separation makes the MMT an ideal test structure for confirming the physics behind contact-controlled operation.  

Using advanced computer simulations, the researchers confirmed that when the contact barrier is kept low but significant, the transistor operates in a contact-controlled mode, where current flow is primarily governed by the semiconductor/contact interface rather than the channel. This makes the devices more resistant to voltage shifts caused by trapped charges and other ageing effects that typically affect devices that rely on the channel for operation by eliminating energy barriers at the contacts. 

In future, the use of MMTs and their robust operation could simplify the pixel circuits used in next-generation OLED or microLED displays, reducing manufacturing complexity and improving energy efficiency. 

Access to the equipment and expertise at JOANNEUM RESEARCH MATERIALS was facilitated through the “EMERGE” Project of the European Union’s Horizon 2020 research and innovation programme.