Spice model to accelerate organic TFT design

Universal model is suitable for a large variety of OTFT device architectures, material specifications and fabrication technologies.

Cambridge Display Technology and Silvaco Data Systems have collaborated to develop a new universal organic thin film transistor (UOTFT) Spice model.

Circuit designers can now design and simulate circuits using OTFT (organic thin film transistor) technology.

This is an important step forward in promoting the future use of OTFT technology.

The rapid development of organic electronics is mainly driven by applications that require low cost electronic circuits covering large areas with mechanical flexibility.

Examples are: e-skin, e-paper, e-nose, smart-fabrics, flexible displays, printed electronics or radio frequency identification tags (RFID).

OTFTs form the basis of future organic electronic circuits.

The model is implemented in Simucad SmartSpice, a leading analogue circuit simulator.

The UOTFT Spice model combines universal charge-based field effect transistor modelling with OTFT specific channel charge, mobility bias, temperature dependences, and nonlinear contact resistances.

This combination maximises UOTFT generic modelling capabilities, and makes it suitable for a large variety of OTFT device architectures, material specifications and fabrication technologies.

The design of organic electronics circuits depends on accurate and efficient OTFT compact models in commercial circuit simulation tools.

A range of distinct features in OTFT device properties require special consideration and a different modelling approach compared with their inorganic counterparts.

The most notable differences include a trap-assisted charge distribution and mobility behaviour, unipolar or bipolar charge accumulation operation mode and nonohmic contact resistances.

The existing MOSFET, as well as amorphous and poly-silicon TFT models, are therefore not suitable for the design of OTFT circuits.

According to David Fyfe, CEO of CDT: "This activity will enable CDT to further develop its technology base in these new areas of organic semiconductor technology".

"We are delighted to be working with Silvaco on this project which will speed development and commercialisation of low cost rigid and flexible electronics applications of organic semiconductor technology".

The project is being part-funded by the UK government's Technology Strategy Board and their Technologist for Electrical Systems, Mike Biddle commented: "We are very happy with the excellent progress made by this project, and to see that this new approach will soon be ready for commercial exploitation".

"This is a great example of world class businesses coming together in the UK to research and develop innovative technology that has global market potential".

"We are delighted to be working with a leading organic research company such as CDT, and the UK Government, on such a cutting edge project", said Dr Ivan Pesic, President and CEO of Simucad.

"This new ground-breaking model will enable circuit designers to accurately simulate the next generation of organic circuits".

"We look forward to continuing this partnership on future projects".

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