Physical Modeling of Amorphous InGaZnO Thin-Film Transistors: The Role of Degenerate Conduction

none3noIn amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs), the electron mobility easily exceeds 10²/Vs and degenerate band conduction is observed. On the other hand, the field-effect mobility is gate voltage-dependent. Here, we propose a physical model for a-IGZO TFTs accounting for both the non-degenerate and degenerate conductions of trapped and free charges. The comparison between the model and the measurements shows that: 1) the shape of the drain current is almost completely defined by the localized density of states and 2) a transition from non-degenerate-to-degenerate conductions is always observed. This explains the measured gate voltage-dependent field-effect mobility and provides a simple and unified physical picture of the charge transport in a-IGZO TFTs.Ghittorelli, Matteo; Torricelli, F.; Kovacs-vajna, Z. M.Ghittorelli, M.; Torricelli, F.; Kovacs-vajna, Z. M

Organic electrochemical transistor immuno-sensor operating at the femto-molar limit of detection

The interfacing of biomaterials to electronic devices is one of the most challenging research fields that has relevance to both fundamental studies and the development of highly performing biosensors. Organic Electrochemical transistors, using an aqueous electrolyte solution, offer a unique set of advantages in the development of biosensor devices. In this paper, we report highly selective organic electrochemical transistor based immune-sensor by modifying the gate electrode with polyclonal anti-human Immunoglobulin G (anti-IgG) antibodies. Extremely low detection of Immunoglobulin G (IgG) at the femto-molar detection limit has been achieved

Operation and modelling of diffusion-driven organic field-effect transistors for high-performance organic electronics

High-gain organic transistors are the key building blocks for the development of high-performance organic electronics, including high-sensitivity sensors, signal amplification in sensing systems and large-scale circuits. In this work, we analyze organic transistors based on the diffusion-driven charge-accumulation architecture. This class of organic field-effect transistors maximizes at the same the transconductance and the output resistance. The analysis is based on both electrical measurements and theoretical analysis. The transistor performances are critically compared with that of conventional organic field-effect transistors. A simple analytical model that accounts for the effect of the control drain on the saturation current is developed. The model is included in a circuit simulator and an active-load voltage amplifier with electrically-tunable gain is designed. The gain and bandwidth of the voltage amplifier are suitable for signal conditioning and amplification in organic smart sensors

Analytical Physical-Based Drain-Current Model of Amorphous InGaZnO TFTs Accounting for Both Non-Degenerate and Degenerate Conduction

In this letter, we propose a physical-based analytical drain current model for amorphous indium–gallium–zinc oxide thin-film transistors (a-IGZO TFTs). As a key feature, the model accounts for both the non-degenerate and the degenerate conduction regimes, including the contributions of trapped and free charges. These two conduction regimes as well as the trapped and free charges are essential to consistently describe a-IGZO TFTs. The model is compared with both exact numerical calculations and measurements. It is continuous, symmetric, simple, and accurate. The model enables to gain physical insight on the material and device properties, and it is a valuable tool for fast process optimization and circuit design

Analytical Physical-Based Drain-Current Model of Amorphous InGaZnO TFTs Accounting for Both Non-Degenerate and Degenerate Conduction

In this letter, we propose a physical-based analytical drain current model for amorphous indium–gallium–zinc oxide thin-film transistors (a-IGZO TFTs). As a key feature, the model accounts for both the non-degenerate and the degenerate conduction regimes, including the contributions of trapped and free charges. These two conduction regimes as well as the trapped and free charges are essential to consistently describe a-IGZO TFTs. The model is compared with both exact numerical calculations and measurements. It is continuous, symmetric, simple, and accurate. The model enables to gain physical insight on the material and device properties, and it is a valuable tool for fast process optimization and circuit design

Unipolar Differential Logic for Large-Scale Integration of Flexible a-IGZO Circuits

A new unipolar differential logic (UDL) for the large-scale integration of amorphous In-Ga-Zn-O (aIGZO) digi- tal circuits is proposed. Only single-threshold, single-gate, aIGZO thin-film transistors are required. The proposed UDL logic gates are very insensitive to the transistor parameters variations (i.e. threshold voltage, mobility, off-current, subthreshold slope) that are inherently due to the large-area low-temperature fabrication processes and to the operating conditions. To assess the UDL effectiveness, a wide range of parameters variations is considered: thanks to the proposed architecture up to 1.5 × 10^7 UDL gates can be integrated with a yield greater than 90%

Electrical Characterization of PEDOT:PSS Strips Deposited by Inkjet Printing on Plastic Foil for Sensor Manufacturing

Inkjet printing is a viable method for rapid and low-cost manufacturing of flexible sensors. In this paper, we study a technique for inkjet printing of poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) strips. A low-cost inkjet desktop printer is used for the fabrication of PEDOT: PSS resistive strips on polyimide substrates. Accounting for several geometries of printed PEDOT: PSS strips, we assess the variability of the fabrication process. Owing to the printing process, we can easily choose the width, length, and thickness. We found that printed strips on polyimide foils show a conductivity equal to 115 S/cm, which linearly increases with the strip thickness. The maximum variability is lower than 13%. The frequency analysis shows a purely resistive impedance in the frequency range investigated (100 Hz-100 kHz). Moreover, the strips folded up to 1000 times shows a resistance variation lower than 6%. The study demonstrates that inkjet printing is a viable method for the simple, fast, reliable, and low-cost fabrication of PEDOT:PSS-based sensors on plastic substrates and circuit interconnections

Accurate Analytical Physical Modeling of Amorphous InGaZnO Thin-Film Transistors Accounting for Trapped and Free Charges

A physical-based and analytical drain current model of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) is proposed. The model considers the combined contribution of both trapped and free charges that move through the a-IGZO film by multiple-trapping-and-release and percolation in conduction band. The model is compared with both measurements of TFTs fabricated on a flexible substrate and numerical simulations. It is accurate in the whole range of a-IGZO TFTs operation. The model requires only physical and geometrical device parameters. The resulting mathematical expressions are suitable for computer-aided design implementation and yield the material physical parameters that are essential for process characterization