Ambipolar Thin-film Transistors Research Articles

Bio-inspired synaptic behavior simulation in thin-film transistors based on molybdenum disulfide.

Synaptic behavior simulation in transistors based on MoS2 has been reported. MoS2 was utilized as the active layer to prepare ambipolar thin-film transistors. The excitatory postsynaptic current phenomenon was simulated, observing a gradual voltage decay following the removal of applied pulses, ultimately resulting in a response current slightly higher than the initial current. Subsequently, ±5V voltages were separately applied for ten consecutive pulse voltage tests, revealing short-term potentiation and short-term depression behaviors. After 92 consecutive positive pulses, the device current transitioned from an initial value of 0.14 to 28.3 mA. Similarly, following 88 consecutive negative pulses, the device current changed, indicating long-term potentiation and long-term depression behaviors. We also employed a pair of continuous triangular wave pulses to evaluate paired-pulse facilitation behavior, observing that the response current of the second stimulus pulse was ∼1.2× greater than that of the first stimulus pulse. The advantages and prospects of using MoS2 as a material for thin-film transistors were thoroughly displayed.

SnSe ambipolar thin film transistor arrays with copper-assisted exfoliation

SnSe is a layered metal chalcogenide with potential ambipolar applications. However, the scale of devices is subject to limitation of milli/centi-meter-sized two-dimensinal (2D) flakes. Here, we demonstrate the preparation of wafer-scale SnSe ambipolar thin film transistor (TFT) arrays. The a-axis-oriented SnSe thin films were prepared via atomic layer deposition. The processes of lithography and copper-assisted exfoliation help to peel off unnecessary films to form isolated SnSe flakes. After evaporating nickel as contact electrodes, TFT arrays were successfully fabricated. The on/off current ratios are upgraded from 103 to 104 through annealing at 500 °C to improve the crystalline quality of SnSe, and both hole and electron mobilities increase fivefold to 41.29 and 34.99 cm2 V−1 s−1, respectively. The devices exhibit from symmetric ambipolar to hole-dominated behaviors as SnSe channel thickness increases to 50 nm. The copper-assisted exfoliation method provides an etching technique to make patterned 2D devices.

Demonstration and analysis of ambipolar SnO inverter with high gain

Ambipolar materials offer a unique and simple route toward cost-effective complementary thin film circuits. SnO is one of the few metal oxide semiconductors that demonstrates ambipolar behavior. In this work, we demonstrated an ambipolar SnO inverter with record high inverter gain and corroborated our experimental results with a comprehensive analytical model. First, we developed ambipolar SnO thin film transistors (TFTs) with symmetric p-type and n-type conduction. Using these ambipolar SnO TFTs, we fabricated ambipolar SnO inverters. Our ambipolar SnO inverter shows a record gain of 432 (V/V), which is the highest reported among all ambipolar material systems. To understand our high inverter gain, we developed a comprehensive analytical model to analyze the transition region of an ambipolar inverter. Our analytical model showed an excellent match with our experiment results. Furthermore, our analytical model shows that to achieve a high inverter gain and a voltage transition point in the middle of the supply voltage range, we must minimize channel length modulation and match the p- and n-type behaviors of the ambipolar TFTs. By expanding our understanding of ambipolar inverter behavior, this work highlights the possibilities of ambipolar SnO TFTs for future high performance complementary thin film circuits.

Erratum to “Characterization and Modeling of Reduced-Graphene Oxide Ambipolar Thin-Film Transistors”

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Binary-Synaptic Plasticity in Ambipolar Ni-Silicide Schottky Barrier Poly-Si Thin Film Transistors Using Chitosan Electric Double Layer.

We propose an ambipolar chitosan synaptic transistor that effectively responds to binary neuroplasticity. We fabricated the synaptic transistors by applying a chitosan electric double layer (EDL) to the gate insulator of the excimer laser annealed polycrystalline silicon (poly-Si) thin-film transistor (TFT) with Ni-silicide (NiSi) Schottky-barrier source/drain (S/D) junction. The undoped poly-Si channel and the NiSi S/D contact allowed conduction by electrons and holes, resulting in artificial synaptic behavior in both p-type and n-type regions. A slow polarization reaction by the mobile ions such as anions (CH3COO− and OH−) and cations (H+) in the chitosan EDL induced hysteresis window in the transfer characteristics of the ambipolar TFTs. We demonstrated the excitatory post-synaptic current modulations and stable conductance modulation through repetitive potentiation and depression pulse. We expect the proposed ambipolar chitosan synaptic transistor that responds effectively to both positive and negative stimulation signals to provide more complex information process versatility for bio-inspired neuromorphic computing systems.

Effects of hydrogen plasma treatment on the physical and chemical properties of tin oxide thin films for ambipolar thin-film transistor applications

In this study, we investigated the physical and chemical properties of H 2 plasma-treated tin oxide (SnO X ) thin films, followed by their applications in ambipolar thin-film transistors (TFTs). Finely controlled H 2 implantation was carried out using a reactive-ion-etching system at a radio frequency power of 30 W and under various exposure times. H 2 plasma treatments induced changes in the chemical structures and surface morphologies of the SnO X thin films, including a partial phase transformation of Sn and SnO to SnO 2 . The defects originating from oxygen vacancies (O Vac s) in the SnO X thin films were passivated by H via the formation of Sn–H bonds, which decreased the density of subgap states in the SnO X thin films. The H 2 plasma-treated SnO X TFTs showed considerably improved ambipolarity and electrical performance. Complementary metal–oxide–semiconductor (CMOS) logic inverters comprising H 2 -plasma-treated ambipolar SnO X TFTs exhibited a maximum gain of 34.5 V/V at a supply voltage of 10 V. The results of this study present the meaningful investigation of H 2 plasma-treated ambipolar SnO X TFTs that can be used to fabricate CMOS circuits for various applications.

High hysteresis and distinctive optoelectronic memory effect for ambipolar thin-film transistors using a conjugated polymer having donor–acceptor heterojunction

π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units are alternatively bonded to generate ambipolar copolymer (i.e. P(BDBT-co-N2200)) for achieving donor-acceptor (D-A) heterojunction. From the laser confocal microscope photoluminescence (PL) spectra of the P(BDBT-co-N2200) copolymer, PL characteristic peaks of PBDB-T and N2200 are simultaneously observed at 695, 760, and 860 nm. The thin-film transistors (TFTs) using P(BDBT-co-N2200) copolymer show ambipolar transistor characteristics originating from the coexistence of p-type and n-type semiconducting macromolecular units. Interestingly, a high hysteresis is observed in the transfer and output characteristics of the TFTs because of the interface traps and near-interface bulk traps. Under light irradiation, distinctive photocurrents and hysteresis are observed, suggesting the optically mediated charge release and photogating effects caused by trap states. Charge trapping with a high hysteresis and photoconduction with the photogating effect of the P(BDBT-co-N2200)-based ambipolar TFTs induce stable and repeatable writing, reading, and erasing operations. The optoelectronic memory devices using the P(BDBT-co-N2200)-based ambipolar TFTs are realized with the merit of a long charge storage time of 40 s. The π-conjugated copolymer, P(BDBT-co-N2200) exhibiting D–A heterojunction, can be applied to multifunctional devices, such as photoresponsive ambipolar transistors and optoelectronic memory devices, for image sensing and data storage. Optoelectronic memory devices using the ambipolar thin-film transistors of π-conjugated P(BDBT-co-N2200) copolymer having donor-acceptor heterojunction are realized with the merit of a long charge storage time. • π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units were alternatively bonded to generate ambipolar copolymer with donor-acceptor (D-A) heterojunction. • The P(BDBT-co-N2200)-based TFT showed photoresponsive ambipolar transistor characteristics. • The P(BDBT-co-N2200)-based ambipolar TFTs were successfully operated as optoelectronic memory devices with repeatable writing, reading, and erasing processes. • Readout current charges were constant regardless of the variation in waiting times and linearly increased with increasing light exposure time.

Characterization and Modeling of Reduced-Graphene Oxide Ambipolar Thin-Film Transistors

The rise of graphene as an innovative electronic material promoted the study and development of new 2-D materials. Among them, reduced graphene oxide (rGO) appears like an easy and cost-effective solution for the fabrication of thin-film transistors (TFTs). To understand the limits and possible application fields of rGO-based TFTs, a proper estimation of the device parameters is of extreme importance. In this work, liquid-gated ambipolar rGO-TFTs are characterized and a description of their working principle is given. Particular attention is paid toward the importance of the transistors’ OFF-state conductivity that was modeled as a resistance connected in parallel with the TFT. Thanks to this model, the main transistor parameters were extrapolated from rGO-TFTs with different levels of electrochemical reduction. The extracted parameters allowed understanding that rGO-TFTs have similar holes and electrons mobilities, and the more pronounced p-type behavior of the devices is due to a positive shift in the p-type and n-type threshold voltages.

20 Years of reconfigurable field-effect transistors: From concepts to future applications

The reconfigurable field-effect transistor (RFET), is an electronic device whose conduction mechanism can be reversibly reconfigured between n-type and p-type operation modes. To enable this functionality, those devices do not rely on chemical doping caused by impurities but rather on electrostatic doping, i.e. the generation of mobile carriers via an external potential. This functionality has been first concieved in the early 2000s to reduce the source-drain leakage in ambipolar thin film transistors. Over the years many different concepts have been developed employing different conduction mechanisms as well as channel materials, such as silicon nanowires, carbon nanotubes or two-dimensional layered materials. In addition the focus the research shifted more and more towards the circuit level, bringing the unique device characteristics to fruitation. In this work, we will give an historic overview of the main development phases including thier key-achievements starting from the earlier years reaching untill today. Further, we discuss the most interesting circuit properties arising from the device functionality and summarize the broad range of their potential future applications.

Selenophene-containing semiconducting polymers for high-performance ambipolar thin film transistor application

The development of high-performance and well-balanced ambipolar conjugated polymers are critical to next generation optoelectronic devices. Herein, we report the synthesis and characterization of two APBDOPV polymers containing alternative bis-thiophene, and bis-selenophene as comonomers. The relationship between the structure and opto-electrical property, thin film morphology, molecular packing and solution processing thin film transistors have been investigated systemically. Our results showed that by increasing the size of the chalcogen atom, a stronger red-shifted absorption spectrum, higher IP and a reduced optical band gap are observed for selenophene-containing polymers. The enhanced EA and the planar backbone make both polymers as ambipolar charge transport behaviors under ambient conditions. Particularly, selenophene-containing polymer exhibits much higher and well-balanced hole/electron mobilities up to 0.11/0.15 cm2 V−1 s−1 under ambient conditions with a BGTC device configuration. After further optimization of the TGBC configuration, higher hole/electron mobility of 0.19/0.76 cm2 V−1 s−1 are achieved. Our results also demonstrate that introducing the chalcogen atom into the conjugated backbone is an effective approach to tune the property of the semiconducting polymers.

ZnO/graphene ambipolar transistor with low sub-threshold swing

We reported on enhanced device performance of ambipolar thin-film transistors (TFTs) with hybrid channel of Zinc oxide (ZnO) and multi-layer graphene (MLG), especially in reduced sub-threshold swing characteristics and increased carrier mobilities for the ambipolar conduction. The Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) showed that the single-layer graphene could be damaged by oxidation during the ZnO growth process. In MLG, we observed that the graphene layers distant from the interface of ZnO/graphene could be protected, leading to enhanced electrical properties in ZnO/graphene hybrid TFTs. These results showed that the ZnO/MLG hybrid structure is a suitable building block to realize advanced TFTs with low power consumption and high switching speed.

Dielectric/Semiconductor Interfacial p‐Doping: A New Technique to Fabricate Solution‐Processed High‐Performance 1 V Ambipolar Oxide Transistors

Herein, dielectric/semiconductor interfacial p‐doping is used to develop a high‐carrier‐mobility and balanced ambipolar tin oxide (SnO2) thin‐film transistor (TFT). To introduce this interfacial doping, TFTs are fabricated by using two different ion‐conducting oxide dielectrics containing trivalent atoms. These ion‐conducting dielectrics are LiInO2 and LiGaO2 containing a mobile Li+ ion that reduces the operating voltage of these TFTs to ≤2.0 V. During SnO2 thin film deposition, the interfacial SnO2 layer is p‐doped by an In or Ga atom of the gate dielectric and therefore, hole conduction is facilitated in the channel of the TFT. To realize this interfacial doping phenomenon, a reference TFT is fabricated with a Li2ZnO2 dielectric that contains a divalent zinc atom. Comparative electrical data indicate that TFTs with LiInO2 and LiGaO2 dielectrics are ambipolar in nature, whereas the TFT with a Li2ZnO2 dielectric is a unipolar n‐channel transistor, corroborating the interfacial doping of SnO2. Most interestingly, using a LiInO2 dielectric, a 1.0 V balanced ambipolar TFT with high electron and hole mobility values of 7 and 8 cm2 V−1 s−1, respectively, can be fabricated, with an on/off ratio &gt; 102 for both operations. The TFT with a LiInO2 dielectric is utilized successfully to fabricate a low‐voltage complementary metal–oxide–semiconductor (CMOS) inverter.

Preparation and characterization of SnO films via reactive sputtering for ambipolar thin-film transistor applications

SnO films are prepared by reactive magnetron sputtering under various O2 partial pressures along with post-annealing in air. The results indicate that the O2 partial pressure during reactive sputtering process not only influences the composition of the SnO film but also its texture. For the SnO film deposited under 10% O2 partial pressure, its direct bandgap increases from 2.49 to 2.64 eV with elevating the post-annealing temperature from 250 °C to 400 °C. The above SnO-based channel thin-film transistors (TFTs) exhibit a typical ambipolar feature after post-annealing at ≥250 °C in air. For the TFTs annealed at 300 °C for 30 min, the extracted hole and electron field-effect mobility is 1.48 cm2V−1s−1 and 0.21 cm2V−1s−1, respectively. The performance of both p- and n-type TFTs could be further improved by optimizing fabrication process and post-annealing conditions because of a trade-off between hole and electron mobility.

Symmetric Ambipolar Thin-Film Transistors and High-Gain CMOS-like Inverters Using Environmentally Friendly Copper Nitride.

Oxide semiconductor thin-film transistors (TFTs) are currently used as the fundamental building blocks in commercial flat-panel displays because of the excellent performance of n-channel TFTs. However, except for a few materials, their p-channel performances have not been acceptable. Although some p-type oxide semiconductors exhibit superior hole transport properties, their TFT performances are greatly deteriorated, which is a major obstacle in the development of complementary metal-oxide-semiconductor (CMOS) circuits. Herein, an ionic nitride semiconductor, copper nitride (Cu3N), composed of environmentally benign elements is shown to exhibit highly symmetric hole and electron transport, indicating its suitability for application in CMOS circuits. We performed a two-step investigation. The first step was to examine the ultimate potential of Cu3N using an electric-double-layer transistor structure with epitaxial Cu3N channels measured at 220 K, which exhibited ambipolar operation with hole and electron mobilities of ∼5 and ∼10 cm2 V-1 s-1, respectively, and a high on/off ratio of ∼105. The second step is to demonstrate the feasibility of TFT circuits with a polycrystalline channel on non-single-crystal (SiO2/Si) substrates. CMOS-like inverters composed of two polycrystalline Cu3N ambipolar TFTs on a SiO2/Si substrate exhibited a high voltage gain of ∼100.

Ambipolar thin-film transistors based on organic semiconductor blend

Abstract Ambipolar thin-film transistors are fabricated employing p-channel (2-decyl-7-phenylbenzo[b]benzo [4,5]thieno[2,3-d]thiophene; Ph-BTBT-C10) and n-channel (N,N'-di-n-octyl-3,4,9,10-perylenetetracarboxylic diimide; PTCDI-C8) semiconductors in bilayer and bulk heterojunction architecture. Bilayer organic semiconductors with small thickness of the first layer exhibit ambipolar device characteristics with relatively poor electrical performance. On the other hand, bulk heterojunction organic thin-film transistors (OTFTs) with optimized blend ratio exhibited higher ambipolar charge transport properties with carrier mobility as high as 0.22 and 0.038 cm2 V−1s−1 for hole and electron, respectively. Complementary-like inverters fabricated based on optimized bulk heterojunction OTFTs show high transfer gain of 96.

Solution-Processed Hybrid Ambipolar Thin-Film Transistors Fabricated at Low Temperature

We demonstrate solution-processed hybrid ambipolar thin-film transistors (TFTs) employing a stack structure composed of indium–gallium–zinc-oxide (IGZO) and single-wall carbon nanotube (SWCNT) as an active channel fabricated at low temperature. With an optimized deep-ultraviolet (DUV) photo annealing process for sol–gel based IGZO thin film on SWCNT random networks, the ambipolar transport of both electrons and holes with good electrical characteristics was realized. We also investigate the effect of DUV photo annealing on the material characteristics of solution-processed hybrid stack films and on the device performance of solution-processed hybrid ambipolar TFTs compared to those of samples thermally annealed at 500 °C, which is required for solution-processed high-quality IGZO thin films. The Raman spectra show that DUV photo annealing ensures hole transport in SWCNT random networks of a hybrid stack film, where the intensity of the 2D peak to the G peak was not changed compared to that of pristine SWCNT random networks. We believe that these analytical investigations reveal that DUV photo annealing is a promising method by which to realize hybrid ambipolar SWCNT/IGZO TFTs fabricated at low temperature.

Unusual ambipolar behavior in zinc nitride thin-film transistors on plastic substrates

In this work, an unusual ambipolar behavior in zinc nitride (Zn3N2) based thin film transistors (TFTs) on plastic substrates is presented. Polyethylene terephthalate is used as flexible substrate. The Zn3N2 thin film is deposited by magnetron radio-frequency sputtering at room temperature, whereas spin-on glass is used as gate insulator. The transfer and output characteristics are the typical reported for ambipolar TFTs. The extracted linear mobility was 1.8 cm2 V−1 s−1 for the n-type region and 0.15 cm2 V−1 s−1 for the p-type region. Using a physically-based simulator, the ambipolar output characteristics are simulated. The results presented are promising to develop novel ambipolar Zn3N2 TFTs.

Solution-processable small molecules for bulk heterojunction ambipolar thin-film transistors and complementary-like inverters

Solution-processable thioalkylated bithiophene derivatives with different lengths of side chains (SBT-n; n = 10, 12, 14, 16, 18) have been synthesized and characterized as p-channel organic semiconductors for thin-film transistors (TFTs). Based on a combination of the highest performing SBT derivative (SBT-14) and quinoidals (DTTRQs) as p- and n-channel materials, solution-processed small-molecular bulk heterojunction (BHJ) ambipolar thin-film transistors were fabricated, and the resulting devices showed air-stable and high ambipolar performance with well-balanced electron and hole mobilities as high as 0.70 cm2 V−1 s−1 and 0.21 cm2 V−1 s−1, respectively. Furthermore, complementary-like inverters comprising two ambipolar thin-film transistors were demonstrated, which exhibited a high voltage gain of up to 81. Our study clearly demonstrated that side chain engineering of small molecular organic semiconductors had a significant influence on the electrical performance of TFTs and BHJ transistors, as well as complementary-like inverters.

Benzothiadiazole-Based Small-Molecule Semiconductors for Organic Thin-Film Transistors and Complementary-like Inverters.

New benzothiadiazole derivatives, 4,7-bis(5-phenylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (PT-BTD) and 4,7-bis[4-(thiophen-2-yl)phenyl]benzo[c][1,2,5]thiadiazole (TP-BTD), were synthesized and characterized as small-molecule organic semiconductors for organic thin-film transistors (OTFTs) and complementary inverters. The thermal, optical, and electrochemical properties of the new compounds were fully characterized. Vacuum-deposition and solution-shearing methods were used to fabricate thin films based on these compounds. Thin films based on PT-BTD exhibited p-channel characteristics with hole mobilities as high as 0.10 cm2 V-1 s-1 and current on/off ratios >107 for top-contact/bottom-gate OTFT devices. With an optimized blending ratio of PT-BTD and the representative n-channel semiconductor N,N'-1H,1H-perfluorobutyl dicyanoperylenediimide, bulk heterojunction ambipolar transistors were fabricated with balanced hole and electron mobilities of 0.10 and 0.07 cm2 V-1 s-1 , respectively. Furthermore, a complementary-like inverter was fabricated using ambipolar thin-film transistors, which showed a high voltage gain of 84.

High-Mobility Ambipolar Organic Thin-Film Transistor Processed From a Nonchlorinated Solvent.

Polymer semiconductor PDPPF-DFT, which combines furan-substituted diketopyrrolopyrrole (DPP) and a 3,4-difluorothiophene base, has been designed and synthesized. PDPPF-DFT polymer semiconductor thin film processed from nonchlorinated hexane is used as an active layer in thin-film transistors. As a result, balanced hole and electron mobilities of 0.26 and 0.12 cm(2)/(V s) are achieved for PDPPF-DFT. This is the first report of using nonchlorinated hexane solvent for fabricating high-performance ambipolar thin-film transistor devices.