Industry experts see great opportunities for organic electronics. One of the promising technologies is organic thin-film transistor (OTFT) technology.
By Gerwin Gelinck, Mieke Van Bavel, Paul Heremans
Over the last 25 years, the field of organic electronics has evolved from early research toward maturity and is now on the verge of a significant breakthrough. Tremendous progress has been made in terms of materials synthesis and device concepts. Various devices such as organic light-emitting diodes (OLEDs), field-effect transistors, biosensors, and photovoltaic devices have come forth. While today only a few companies make products based on organic semiconductors, many predict this number to grow in the future.
Among the promising technologies is organic thin-film transistor (OTFT) technology, implying the deposition of thin films of organic semiconducting active layers, as well as the dielectric layer and metallic contact, on a substrate. These transistors are the fundamental building blocks for a wide range of applications such as flexible displays, intelligent food packaging and low-cost, low-end integrated microelectronics where the high performance of conventional electronics is not necessary. OTFTs today have comparable—or even improved—characteristics, such as amorphous Si thin-film transistors.
But the true advantage of organic transistor technology is the combination of the highly attractive mechanical properties of organics with low-temperature processing (below 150°C) and simple manufacturing techniques. Because many organic materials can be dissolved in organic solvents, organic thin films can be formed easily using a solution or a printing process without using vacuum equipment. This enables a technician to create low-cost, large-area electronics on flexible, lightweight plastic substrates. Besides the development of processing techniques, research today targets increased performance, scaled down feature sizes, and integration with other system elements such as organic light-emitting devices (OLEDs) or Flash memory.
In this article, we evaluate the use of OTFTs in two application areas: flexible optical displays and low-cost, low-end integrated microelectronics. For these applications, OTFT is expected to have a high industrial impact. Besides giving generic insights, most of the results presented in this article have been obtained by Holst Centre, imec, and TNO within their program on organic transistors.
With this program, Holst Centre develops technologies for making OTFTs on plastic foils and helps to promote the industrialization and commercialization of organic electronics. Holst Centre (the Netherlands) is an Open Innovation R&D Centre. A key feature is its partnership model with industry and academia around shared roadmaps and programs. It is this kind of cross-fertilization that enables Holst Centre to tune its scientific strategy to industrial needs.
On a high-resolution electronic display, each pixel typically is switched on and off via one or more transistors. We call this matrix of transistors the backplane. Today’s backplanes are built from Si transistors. But, for tomorrow’s applications, we need a pliable or rollable display that we can carry around, but one that is still large enough to match our fingers sizewise. We want a display that has the readability and flexibility of paper, but with the capability to update information on the page. Processes to fabricate Si-based backplanes on rollable surfaces are very expensive.
A cheaper alternative is to fabricate the backplanes using organic thin-film transistors. An attractive first application is a flexible, re-flective electrophoretic display. A second generation of rollable displays will be light-emitting.
There is a lot of room for improvement, both in energy consumption and quality of display, but seeing as this has not matured yet, we can expect more to come. This is an industry that is worth taking note of!
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