UOTFT

Universal Organic TFT SPICE Model

A Robust SPICE Model for Simulating a Wide Range of Organic TFT Technologies

The UOTFT model combines in a unique way the robust concepts of the universal charge based field effect transistor modeling with specific organic TFT (OTFT) channel charge, mobility and contact resistance bias and temperature dependences. This approach maximizes UOTFT generic modeling capabilities and makes it suitable for a large variety of the OTFT device architectures, material specifications and fabrication technologies.

Model Features

• The universal interpolation of the drain current between linear and saturation operation regimes
• Unified charge based description of the mobility, drain-source current and gated-drain and gate-source capacitances
• The universal mobility law based on variable range hopping (VRH) theory and OTFT operation in the channel accumulation mode
• A physical temperature scaling of the model parameters based on exponential distribution of traps and the percolation theory for the conductance in disordered materials
• A trap distribution based charge and capacitance model
• The source and drain access series resistances including diode-like nonlinear contact resistances
• The thermal RC network for the modeling of self-heating effects
• The gate RC network for the modeling of frequency dispersion effects
• The extrinsic overlap capacitances
• The noise model
• The geometrical scalability

The equivalent circuit of the UOTFT model.

The bottom-gate bottom-contact OTFT architecture.

Simucad Implementation

• The UOTFT is implemented into Simucad’s independently compiled model library (ModelLib). It can be accessed within SmartSpice as TFT model LEVEL=37
• The equivalent circuit and the extrinsic model components are compatible with the existing a-Si and poly-Si RPI TFT models (LEVEL=35 and 36)
• User friendly parameter clipping, advanced internal model diagnostics, and extensive set of output variables
• Improved simulation speed based on VZERO and BYPASS SmartSpice options

Benefits From Using UOTFT

• A dedicated organic TFT model suitable for analog, digital and RF circuit design
• With the model scalability, UOTFT requires only a single global parameter set for different device geometries and temperatures
• The physical meaning of the model parameters provides an easy direct or optimization based parameter extraction

Comparison between simulated (lines) and measured (circles) output characteristics of the organic TFT for Vg=-10V, -20V, -30V and -40V.

Comparison between simulated (lines) and measured (circles) transfer characteristics of the organic TFT in the linear operation region with Vds=-3V (blue line and circles) and saturation operation region with Vds=-30V (red line and circles).

Comparison between simulated (lines) and measured (circles) input characteristics of the organic TFT in saturation region at different temperatures: T=270K (dark blue), T=280K (light blue), T=300K (green), T=310K (pink) and T=330K (red).

References

1. A. Fjeldly, T. Ytterdal, M. Shur, Introduction to Device Modeling and Circuit Simulation, John Wiley & Sons, Inc., New York, 1998.
2. B. Iniguez, R. Picos, D. Veksler, A. Koudymov, M.S. Shur, T. Ytterdal, W. Jackson, “Universal Compact Model for Long- and Short-Channel Thin-Film Transistors”, Solid-State Electronics, 52 (2008), p. 400.
3. M. Fadlallah, W. Benzarti, G. Billiot, W. Eccleston, D. Barclay, “Modeling and Characterization of Organic Thin Film Transistors for Circuit Design”, J. Applied Physics, 99 (2006), p. 104504-1.
4. M.C.J.M. Vissenberg, M. Matters, “Theory of the Field-Effect Mobility in Amorphous Organic Transistors”, Physical Review B, 57 (1998), p. 12964.
5. UK Technology Strategy Board project TP/J2519J: Physical modeling of Organic Semiconductors (PMOS), Project Partners: Cambridge Display Technology Ltd and Silvaco Data Systems (Europe) Ltd, Cambridge, 2007.
   

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