Dual-gate Organic Transistors Research Articles

Single and dual-gate organic field-effect transistors based on diketopyrrolopyrrole-diethienothiophene polymers: performance modulation via dielectric interfaces

Low-power, flexible, and properly encapsulated integrated circuits are the basic requirements of the solution-processed printed and wearable electronic prototypes for various emerging applications including display circuits, sensors, and radio-frequency identification tags. The organic field-effect transistor is one of the important types of devices used in such prototypes and its industrial applicability is essential for the printed electronics technology. The performance deterioration upon encapsulated through the thick layer of air-stable dielectric material such as amorphous fluoropolymer [CYTOP] - must be compensated by device engineering. In this work, we used furan and thiophene flanked diketopyrrolopyrrole donor-acceptor conjugated polymers namely PDPPF-DTT and PDPPT-DTT, and its comparative study was performed using Cytop as a dielectric material. The work advances interface engineering towards the single-gate and dual-gate organic transistors. Dual-gate transistors performance modulation using Cytop dielectric opens new research avenues towards stability enhancement of such transistors for real-world applications.

Enhanced Functionality of Dual-Gate Organic Transistors Based on Semiconducting/Insulating Polyblend-Induced Asymmetric Charge Modulation Layers.

Dual-gate organic thin-film transistors (DG-OTFTs) with enhanced functionality, including large current enhancement behavior, highly efficient threshold voltage controllability, and self-contained dual-mode logic gate features, are reported. These DG-OTFTs are based on a semiconducting/insulating polyblend-based active layer with asymmetric top and bottom charge modulation layers (atb-CMLs). The atb-CMLs are automatically generated through the preparation of multilayer stacks of phase-separated semiconducting poly(3-hexylthiophene) (P3HT):insulating poly(methylmethacrylate) (PMMA) polyblend layer, poly(vinylidene fluoride) (PVDF) layer, and cross-linked-poly(4-vinylphenol) (cPVP) layer. They consist of a thin PMMA bottom layer and an uneven-shaped PMMA:PVDF miscible mixture-based top layer. The presence of the polarizable insulating PMMA, PVDF, and PMMA:PVDF mixture regions causes the bottom and top CMLs to experience electrical polarization, which induces the dipole field to achieve efficient charge modulation functions in DG-OTFTs. Owing to the presence of atb-CMLs, the DG-OTFTs exhibit unprecedented electrical characteristics, such as the easy depletion of the bottom channel by the top gate potential. However, the top channel can work properly only when given a bottom gate potential (either positive or negative). Given these unusual electrical features, the design of the fundamental dual-mode logic gates (e.g., AND and OR gates) can be achieved with just one DG transistor. This finding opens an interesting direction for the preparation of DG-OTFTs with diverse operating modes and increasing functionality, thereby widening the application potential of such transistors.

Low-Voltage, Dual-Gate Organic Transistors with High Sensitivity and Stability toward Electrostatic Biosensing.

High levels of performance and stability have been demonstrated for conjugated polymer thin-film transistors in recent years, making them promising materials for flexible electronic circuits and displays. For sensing applications, however, most research efforts have been focusing on electrochemical sensing devices. Here we demonstrate a highly stable biosensing platform using polymer transistors based on the dual-gate mechanism. In this architecture a sensing signal is transduced and amplified by the capacitive coupling between a low-k bottom dielectric and a high-k ionic elastomer top dielectric that is in contact with an analyte solution. The new design exhibits a high signal amplification, high stability under bias stress in various aqueous environments, and low signal drift. Our platform, furthermore, while responding expectedly to charged analytes such as the protein bovine serum albumin, is insensitive to changes of salt concentration of the analyte solution. These features make this platform a potentially suitable tool for a variety of biosensing applications.

Three-dimensional monolithic integration in flexible printed organic transistors

Direct printing of thin-film transistors has enormous potential for ubiquitous and lightweight wearable electronic applications. However, advances in printed integrated circuits remain very rare. Here we present a three-dimensional (3D) integration approach to achieve technology scaling in printed transistor density, analogous to Moore’s law driven by lithography, as well as enhancing device performance. To provide a proof of principle for the approach, we demonstrate the scalable 3D integration of dual-gate organic transistors on plastic foil by printing with high yield, uniformity, and year-long stability. In addition, the 3D stacking of three complementary transistors enables us to propose a programmable 3D logic array as a new route to design printed flexible digital circuitry essential for the emerging applications. The 3D monolithic integration strategy demonstrated here is applicable to other emerging printable materials, such as carbon nanotubes, oxide semiconductors and 2D semiconducting materials.

Liquid-Solid Dual-Gate Organic Transistors with Tunable Threshold Voltage for Cell Sensing.

Liquid electrolyte-gated organic field effect transistors and organic electrochemical transistors have recently emerged as powerful technology platforms for sensing and simulation of living cells and organisms. For such applications, the transistors are operated at a gate voltage around or below 0.3 V because prolonged application of a higher voltage bias can lead to membrane rupturing and cell death. This constraint often prevents the operation of the transistors at their maximum transconductance or most sensitive regime. Here, we exploit a solid-liquid dual-gate organic transistor structure, where the threshold voltage of the liquid-gated conduction channel is controlled by an additional gate that is separated from the channel by a metal-oxide gate dielectric. With this design, the threshold voltage of the "sensing channel" can be linearly tuned in a voltage window exceeding 0.4 V. We have demonstrated that the dual-gate structure enables a much better sensor response to the detachment of human mesenchymal stem cells. In general, the capability of tuning the optimal sensing bias will not only improve the device performance but also broaden the material selection for cell-based organic bioelectronics.

Optically controllable dual-gate organic transistor produced via phase separation between polymer semiconductor and photochromic spiropyran molecules.

We produced an optically controllable dual-gate organic field-effect transistor by a simple one-step spin-coating of a mixed solution of photochromic spiropyran (SP) and poly(3-hexylthiophene) (P3HT). Postannealing enhanced polymer chain ordering of P3HT to induce phase separation into an SP-rich lower layer and an SP-free upper layer. These layers worked independently as transistor channels with distinct optical responsivity. The top channel was optically inactive, but the bottom channel was optically active, because of the photoisomerization of SP. These results demonstrate the potential of our technique to produce a multifunctional photoactive organic transistor by a simple process.

Single and dual gate OTFT based robust organic digital design

This paper analyzes and compares the performance of the single gate (SG) and dual gate (DG) organic thin film transistors (OTFTs) based inverter circuits. The DG-OTFT device performs better than SG-OTFT mainly in terms of mobility, on–off current ratio and sub-threshold slope. The mobility of DG device is almost five times higher than the SG, while, an increase of 74% in on–off current ratio and a decrease of 41% in sub-threshold slope are observed. Two different configurations of inverter circuits i.e. diode-load logic (DLL) and zero-Vgs-load logic (ZVLL) are studied. The static and dynamic behaviors of the p-type DLL and ZVLL inverters using SG and DG organic transistors are observed. The DG-OTFT improves gain and noise margins for both DLL and ZVLL inverter circuits. Using DG device, propagation delay reduces by 59% for DLL and 42% for ZVLL as compared to SG OTFT based configurations. Moreover, fixed back gate bias technique further enhances the noise margin and gain by 8% and 18% for DLL and 19% and 26% for ZVLL configurations, respectively. Finally, bootstrapping technique is also applied to the dual gate inverters that further boosts the noise margin and gain for DLL and ZVLL configurations.

Unipolar Organic Transistor Circuits Made Robust by Dual-Gate Technology

Dual-gate organic transistor technology is used to increase the robustness of digital circuits as illustrated by higher inverter gains and noise margins. The additional gate in the technology functions as a VT-control gate. Both zero-VGS-load and diode-load logic are investigated. The noise margin of zero- VGS-load inverter increases from 1.15 V (single gate) to 2.8 V (dual gate) at 20 V supply voltage. Diode-load logic inverters show an improvement in noise margin from ~0 V to 0.7 V for single gate and dual gate inverters, respectively. These values can be increased significantly by optimizing the inverter topologies. As a result of this optimization, noise margins larger than 6 V for zero- VGS-load logic and 1.4 V for diode-load logic are obtained. Functional 99-stage ring oscillators with 2.27 μs stage delays and 64 bit organic RFID transponder chips, operating at a data rate of 4.3 kb/s, have been manufactured.