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 universal charge-based field-effect transistor modeling with organic TFT (OTFT) specific charge, mobility and contact resistance bias and temperature dependencies. 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

  • Accurate implementation of a Unified Charge Control Model (UCCM) for OTFTs having exponentially distributed density of states in the organic semiconductor and operating in the channel accumulation mode in the presence of interface traps
  • A new universal carrier mobility law valid in all operation regions
  • A new unified description of the drain-source current in linear and saturation operation regimes including the effects of the channel length modulation and diffusion carrier transport
  • Implicit non-linear gate bias dependent parasitic resistance model
  • Drain-source leakage current model
  • Physical temperature scaling of mobility model parameters based on percolation theory
  • Temperature scaling of parasitic resistances
  • Unified Meyer capacitance model, or Leroux’s charge model, for the description of the channel charge dynamics
  • The extrinsic gate RC network for the modeling of frequency dispersion effects
  • Extrinsic overlap capacitances
  • Thermal RC network for the modeling of self-heating effects
  • Noise model
  • Geometrical scalability
The equivalent circuit of the UOTFT model.

(a)
(b)
Two different OTFT architectures: (a) bottom-gate bottom-contact (BGBC) and (b) top-gate bottom-contact (TGBC). The UOTFT model performance is demonstrated here for OTFTs from both architectures having also different organic semiconductor (OSC) materials.

 

Silvaco Implementation

  • The UOTFT model can be accessed within SmartSpice when TFT model LEVEL=37 syntax is used.
  • Equivalent circuit and the extrinsic model components are compatible with the existing a-Si and poly-Si RPI TFT models (LEVEL=35 and 36)
  • The Silvaco implementation also includes user friendly parameter clipping, advanced internal model diagnostics, and extensive set of output variables
  • Simulation speed based on VZERO and BYPASS SmartSpice options has been improved

Benefits Of Using UOTFT

  • UOTFT is suitable for analog, digital, and RF organic circuit design with OTFTs based on different device architectures, materials, and process technology
  • Being temperature and geometry scalable, the UOTFT model requires only a single global parameter set for organic circuit design with different OTFTs geometries and operation temperatures
  • The physical meaning of the model parameters provides an easy direct or optimization based parameter extraction procedure
  • In the strong accumulation region, the UOTFT model is compatible with the simple threshold voltage based models widely used in organic TFT literature
Comparison between simulated (lines) and measured (circles) transfer characteristics of the BGBC OTFT 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) output characteristics of the BGBC OTFT for Vg=-10V, -20V, -30V and -40V
Comparison between simulated (lines) and measured (circles) transfer characteristics of the BGBC OTFT in saturation region at different temperatures: T=270K (dark blue), T=280K (light blue), T=300K (green), T=310K (pink) and T=330K (red)

Comparison between simulated (lines) and measured (circles) transfer characteristics of the TGBC OTFT in the forward and reverse operation region with Vds=-30V Comparison between simulated (lines) and measured (circles) output characteristics of the TGBC OTFT for Vg=-10V (blue), -20V (red), -30V (pink) and -40V (black)


(a)

(b)
Comparison between simulated (lines) and measured (circles) transfer characteristics in the logarithmic (a) and linear (b) scales of the TGBC OTFT for Vds=-30V at different temperatures: T=300K (blue) and T=353K (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.C.J.M. Vissenberg, M. Matters, “Theory of the Field-Effect Mobility in Amorphous Organic Transistors”, Physical Review B, 57 (1998), p. 12964.
  4. S. Mijalkovic, D. Green, A. Nejim, A. Rankov, E. Smith, T. Kugler, C. Newsome, J. Halls, “UOTFT: Universal Organic TFT Model for Circuit Design”, Digest of the 6th International Conference on Organic Electronics, Liverpool, June, 2009.
  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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