Ambipolar FETs Research Articles

Two-component heterojunction-based ambipolar field effect transistors for improved sensitivity of ammonia sensor

To improve the sensing response of ammonia (NH3) sensors, a two-dimensional configuration molecule 5,11-di-naphthalen-2-yl-6,12-dihydro-indolocarbazole (ICZ-NA) was designed and synthesized as the p-channel organic semiconductor material. Bilayer organic field-effect transistor (OFET) was constructed with ICZ-NA and N,N’-bis(n-octyl)-2,6-dicyanonaphthalene-1,4,5,8-bis(dicarboximide (NDI-8CN2) as p-type and n-type active semiconductor materials respectively, and the two-component devices exhibits excellent ambipolar FET performance. The thin film transistors based on single-component and two-component were further used as sensors for ammonia detection. Compared with the sensors based on NDI-8CN2, the sensitivity and selectivity of ammonia detection based on two-component sensors have been greatly improved, and the ratio of current change can still be maintained over 3.65 %, when the gas concentration lower to 10 ppb level. The higher sensing response and low limit of detection demonstrate that the two-component ambipolar configuration is a highly effective method for improving sensing response capability.

A review of crosstalk polymorphic circuits and their scalability

Using a control variable, the functionality of Polymorphic circuits can be modified, making them adaptable and useful for reconfiguring circuit behavior — all the way from gate level to system level. State-of-the art polymorphic circuits are based on custom non-linear circuit design or emerging devices such as ambipolar FET, configurable magnetic devices etc. While some of these approaches are inefficient in performance, others involve exotic devices. The Crosstalk computing based polymorphic circuits offer a fresh perspective. In Crosstalk, the interconnect interference between nanoscale metal lines is intentionally engineered to exhibit the programmable Boolean logic behavior. This approach relies on the coupling between metal lines and not on the transistors for computing, resulting in better scalability, security by obscurity, and fault tolerance by reconfiguration. Our novel approach is backed by the mathematical formulation that conveys the rationale to generalize and achieve a wide variety of polymorphic circuits. Our experiments, including design, simulation, and Power Performance Area (PPA) characterization results indicate that crosstalk circuits provide significant improvement in transistor count (about 3x), switching energy (2x), and speed (1.5x) for polymorphic logic circuits. In the best-case scenario, the transistor count reduction is 5x. This paper presents Crosstalk computing’s fundamentals, polymorphism and the scalability aspects to compete/co-exist with CMOS for digital logic implementations below 10 nm. Our scalability study uses Open Source 7 nm PDK, considers all process variation aspects and accommodates worst-case scenarios. The study results for various benchmark circuits show that the Crosstalk technology is a viable alternative to CMOS for digital logic implementations below 10 nm, having 48% density, 57% power, and 10% performance gains over equivalent CMOS counterparts. Finally, we compare Crosstalk Polymorphic Circuit design technique with similar approaches described in related works and discuss its features and constraints.

High-performance ambipolar field-effect transistors with a Ph-BTBT-10/PMMA/ZnO structure

Ambipolar FETs were designed and fabricated based on the Ph-BTBT-10/PMMA/ZnO structure by a solution process.

Crosstalk-Computing-Based Gate-Level Reconfigurable Circuits

The functionality of polymorphic circuits can be altered using a control variable. Owing to the multifunctional embodiment in polymorphic circuits, they are helpful to reconfigure circuit behavior from the gate level to the system level, either on the fly or off-line. The polymorphic circuit approaches available in the literature are either based on custom nonlinear circuit designs or special emerging devices, such as ambipolar FET and configurable magnetic devices. While some of these approaches are inefficient in performance, the other approaches involve exotic devices. We have proposed a novel polymorphic circuit design approach based on crosstalk (CT) computing, where we leverage deterministic signal interference between nanometal lines for logic computation and reconfiguration. In this article, we elaborate upon the polymorphic circuit design in CT computing through mathematical formulation, which conveys the rationale to generalize and achieve a wide variety of polymorphic circuits, and then demonstrate a comprehensive list of polymorphic circuit designs. In addition, all circuits are characterized and benchmarked against CMOS circuit implementations to gauge the benefits. Finally, we compare the CT polymorphic circuit approach with other approaches in the literature and highlight its unique features and limitations. The ability to design a wide range of polymorphic logic circuits (basic and complex logics) compact in design and minimal in transistor count is unique to CT computing, which leads to benefits in the circuit power, performance, and area (PPA). Our circuit designs, simulation, and PPA characterization results show that the polymorphic CT circuits provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> improvement in transistor count, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> improvement in switching energy, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times $ </tex-math></inline-formula> improvement in speed for polymorphic logic circuits. In the best-case, the transistor count reduction is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times $ </tex-math></inline-formula> .

High-Performance Bidirectional Chemical Sensor Platform Using Double-Gate Ion-Sensitive Field-Effect Transistor with Microwave-Assisted Ni-Silicide Schottky-Barrier Source/Drain

This study proposes a bidirectional chemical sensor platform using ambipolar double-gate ion-sensitive field-effect transistors (ISFET) with microwave-assisted Ni-silicide Schottky-barrier (SB) source and drain (S/D) on a fully depleted silicon-on-insulator (FDSOI) substrate. The microwave-assisted Ni-silicide SB S/D offer bidirectional turn-on characteristics for both p- and n-type channel operations. The p- and n-type operations are characterized by high noise resistance as well as improved mobility and excellent drift performance, respectively. These features enable sensing regardless of the gate voltage polarity, thus contributing to the use of detection channels based on various target substances, such as cells, antigen-antibodies, DNA, and RNA. Additionally, the capacitive coupling effect existing between the top and bottom gates help achieve self-amplified pH sensitivity exceeding the Nernst limit of 59.14 mV/pH without any additional amplification circuitry. The ambipolar FET sensor performance was evaluated for bidirectional electrical characteristics, pH detection in the single-gate and double-gate modes, and reliability in continuous and repetitive operations. Considering the excellent characteristics confirmed through evaluation, the proposed ambipolar chemical sensor platform is expected to be applicable to various fields including biosensors. And through linkage with subsequent studies, various medical applications and precision detector operations for specific markers will be possible.

ZrS2 symmetrical-ambipolar FETs with near-midgap TiN film for both top-gate electrode and Schottky-barrier contact

ZrS2 amibipolar MISFETs are obtained in operations with both electrons and holes. A layered polycrystalline ZrS2 thin film was formed by sputtering and sulfur-vapor annealing on a whole surface of a 2.4 cm × 2.4 cm SiO2/Si substrate. The ZrS2 FETs have Al2O3 gate insulator and TiN film for both the top-gate electrode and Schottky-barrier contact, which show symmetrical I d–V gs curves with a V off of 0.4 V contributed by the TiN film with midgap work function to the sputtered ZrS2 film. Notably, ambipolar FET operations because of both electrons and holes were successfully observed with an on/off current ratio of 250. This is an important step to realize n/p-type unipolar ZrS2 FETs.

Compact I-V Model for Ambipolar Field-Effect Transistors With 2D Transition Metal Dichalcogenide as Semiconductor

In this work, a compact current-voltage (I-V) model is proposed for 2-dimensional transition metal dichalcogenides (TMDs) ambipolar field-effect transistors (ambipolar FETs). Charge control method was used to derive the I-V model. Impurity dopant, interface traps and dependence of carrier mobility on gate voltage are considered in the model. The compact I-V model is based on semiconductor device physics. I-V characteristics of TMD ambipolar FETs predicted by the compact model agree well with those obtained by 2-dimensional numeric simulator and no fitting parameter is needed. In addition, I-V characteristics and carrier area density calculated by the compact model are compared with experimental data published elsewhere. And the result derived from the compact model is consistent with the experimental data published. The compact I-V model provides a tool to evaluate the performance of TMD ambipolar FETs and integrated circuits based on these devices.

A Compact Physics-Based Surface Potential and Drain Current Model for an S/D Spacer-Based DG-RFET

In this paper, we have developed a physics-based compact model for surface potential and drain current for a dual gate source/drain (S/D) spacer-based silicon nanowire reconfigurable field-effect transistor (RFET). The models are derived by dividing the active region of the device into several portions based on positioning of the gates, spacers, and the metal-silicide Schottky junctions. A charge density expression is first developed and the quasi-fermi potentials for both electron and hole transport are found out by applying the principle of current continuity. Using these and further solving the 2-D Poisson’s equation self consistently for various subregions of the device, the drain current and surface potential are modeled subsequently. The model includes the effects of drain voltage, nanowire radius, temperature and Schottky barrier height. The accuracy of the derived results is tested using 3-D numerical technology computer aided design simulations. The proposed model can be used to study the behavior of ambipolar FETs having S/D spacers for varying device dimensions and also can be utilized for the future design of memory devices and circuits using spacer-based RFETS.

Ambipolar charge distribution in donor–acceptor polymer field-effect transistors

CMS and CMM studies spatially resolved polaronic and electroabsorption features, and the distribution of charge carriers in an ambipolar organic FET.

Sensors: A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers (Adv. Mater. 21/2016).

An ambipolar organic field-effect transistor (OFET) based on poly(diketopyrrolopyrrole-terthiophene) (PDPPHD-T3) is shown by P. Sonar, H. Haick, and co-workers on page 4012 to sensitively detect xylene isomers at low to 40 ppm level in multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, is able to discriminate highly similar xylene structural isomers from each other.

Organic field‐effect transistors fabricated by solution process using TMTSF‐TCNQ complex crystals grown at various temperatures

AbstractField‐effect transistors (FETs) based on crystals of tetramethyltetraselenafulvalene (TMTSF)‐tetracyanoquino‐dimethane (TCNQ) complex were fabricated by solution process. TMTSF‐TCNQ crystals grown at low (2 °C) and high (40 °C) temperatures were different in their shape, color, transparency, and crystal structure. Channel polarity of the fabricated FETs was found to be dependent on the growth temperature of the complex crystals. Namely, the FETs with the high‐ and low‐temperature grown crystals showed p‐ and n‐type characteristics, respectively. Furthermore, ambipolar FET characteristics were obtained when room‐temperature grown crystals were used. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Carbon Nanotube Based Multifunctional Ambipolar Transistors for AC Applications

AbstractField‐effect transistors (FETs) fabricated on large diameter carbon nanotubes (CNTs) present typical ambipolar transfer characteristics owing to the small band‐gap of CNTs. Depending on the DC biasing condition, the ambipolar FET can work in three different regions, and then can be used as the core to realize multifunctional AC circuits. The CNT FET based circuits can work as a high‐efficiency ambipolar frequency doubler in the ambipolar transfer region, and also can function as in‐phase amplifier and inverted amplifier in the linear transfer region. Due to current saturation of the CNT FET, an AC amplifier with a voltage gain of 2 is realized when the device works in the linear transfer region. Achieving an actual amplification and frequency doubling functions indicates that complicated radio frequency circuits or systems can be constructed based on just one kind of device: ambipolar CNT FETs.

Diazaboroles with quinone units: hydrogen bonding network and n-type FETs involving a three-coordinate boron atom

A series of monodiazaborole and bis(diazaborole) derivatives with a quinone moiety have been prepared as stable electron acceptors. They show dark colors in the solid states and reversible reduction potentials in the cyclic voltammograms. X-Ray structure analysis of one derivative revealed a π-stacking structure accompanied with a hydrogen-bonding network. Trifluoromethyl substituted derivatives afforded n-type FET characteristics with an electron mobility of 10−2 cm2 V−1s−1. An ambipolar FET characteristic was also observed in the biphenyl derivative. The planar three-coordinate boron units were used as π-linkers to afford n-type and ambipolar FET characteristics.

Air-stable solution-processed ambipolar organic field-effect transistors based on a dicyanomethylene-substituted terheteroquinoid derivative

Dicyanomethylene-substituted quinoidal mixed oligomer was synthesized as a new soluble organic semiconductor, and OFET devices fabricated with a spin-coated thin film of showed ambipolar FET characteristics with electron and hole mobilities of 1.6 x 10(-2) and 7.0 x 10(-3) cm(2) V(-1) s(-1), respectively.

Unipolarization of ambipolar organic field effect transistors toward high-impedance complementary metal-oxide-semiconductor circuits

Ambipolar organic field effect transistors (OFETs), consisting of a composite of polyhexylthiophene (PHT) and [6,6]-phenyl C61-butylic acid methyl ester (PCBM), was converted into a p- or n-type OFET by insertion of a thin tetracyanoquinodimethane (TCNQ) or tetrathiafluvalene (TTF) buffer layer. The interface in the Au/TCNQ/PHT:PCBM composite transports hole but blocks electron, while the transported carrier was switched to electron with insertion of a TTF layer. The selective transport is probably due to vacuum level matching or temporal doping. High impedance in a complementary metal-oxide-semiconductor inverter was demonstrated with unipolarized ambipolar FETs, resulting in a decrease in the through current.

Light illumination effects in ambipolar FETs based on poly(3-hexylthiophene) and fullerene derivative composite films

The effects of light illumination on field effect transistors based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61-butyric methyl ester (PCBM) composite films have been studied. It is found that the light illumination on pure P3HT and PCBM generally resulted in decrease of the threshold voltages and increase of the mobilities by a little. In the composite film at the PCBM contents of x = [P3HT] / ([P3HT] + [PCBM]) = 0.67 ∼ 0.9, an ambipolar field transport appeared. The light illumination effect was observed remarkably in the shift of threshold voltage for the hole generation at x = 0.75. Variations of Hole and electron mobilities and threshold voltage of electron generation upon light illumination were basically similar to those of the pure materials. The results were discussed in terms of the light assisted carrier generation in field effects.

Trap elimination and injection switching at organic field effect transistor by inserting an alkane (C44H90) layer

Recently, it was proposed in the literature that the electron trap on a hydroxyl-containing dielectric interface of an organic field effect transistor (OFET) hinders its n type operation. The authors fabricated pentacene and fullerene OFETs with a hydroxyl-free insulating material, a long-chain alkane, i.e., tetratetracontate (TTC), C44H90 layer coated on the SiO2 dielectric layer. The displacement current measurements clearly demonstrated that the electron trap of the SiO2 surface is suppressed by the TTC layer. For a pentacene FET with an Al electrode and SiO2 dielectric layer, a p type operation was observed, while the operation mode was switched to the n type by the insertion of TTC on the SiO2 interface. By simple patterning of the TTC layer to produce a bipolar injection, the authors fabricated an ambipolar pentacene FET with a single kind of metal electrode. Thus TTC is a good material for the surface modification of a dielectric layer in OFETs.

Transport Phenomena and Conduction Mechanism of Single-Walled Carbon Nanotubes (SWNTs) at Y- and Crossed-Junctions

This letter illustrates the transport phenomena associated with single-walled carbon nanotube (SWNT) junctions of Y- and cross-configurations. Localized gating effect exhibited by Y- and crossed-junctions suggests the resemblance of their electrical characteristics with ambipolar and unipolar p-type FETs, respectively. Temperature dependence of the I-V characteristics reveals that the conduction mechanism in the said SWNT junctions is governed by thermionic emission at temperatures above 100 K and by tunneling at T < 100 K. In-depth analysis of current transport through the crossed- and Y-junction SWNTs is significant in view of their predominant influence on the electrical performance of carbon nanotube networks (CNT-mat).

N-Type and Ambipolar FET Characteristics Using Pyrazinophenanthrolines Linked with Oligothiophenes

Abstract Phenanthroline rings were used to generate n-type FET properties for the first time. A FET device based on a pyrazinophenanthroline with a quinquethiophene unit showed clear ambipolar FET characteristics.

Elementary ambipolar field-effect transistor model

An ambipolar FET can be operated alternatively in n-channel and p-channel modes. A simple conceptual model is proposed. It considers ohmic source and drain contacts, a gradual channel, and the depletion approximation.