Organic transistor 'limitation' improves stability

What many engineers once saw as a flaw in organic electronics could actually make these devices more stable and reliable, according to new research from the University of Surrey.

The paper, published in Joanneum Research Materials, 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.

“For years, engineers have tried to remove contact energy barriers, and with good reason: more often than not, they hold back performance. Our research turns that idea on its head. We found that small, well-controlled barriers actually make the transistor’s operation far more stable,” said Dr Radu Sporea, Associate Professor in Semiconductor Devices.

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 suitable 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 aging 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.

Image credit: University of Surrey