Study of electrical performance and stability of solution-processed n-channel organic field-effect transistors
TL;DR: In this paper, a solution processed n-channel organic field effect transistors based on [6,6]-phenyl C61 butyric acid methyl ester with high mobility and low contact resistance are reported.
Abstract: Solution processed n-channel organic field-effect transistors based on [6,6]-phenyl C61 butyric acid methyl ester with high mobility and low contact resistance are reported. Ca, Au, or Ca capped with Au (Ca/Au) was used as the top source/drain electrodes. The devices with Ca electrodes exhibit excellent n-channel behavior with electron mobility values of 0.12 cm2/V s, low threshold voltages (∼2.2 V), high current on/off ratios (105–106) and subthreshold slopes of 0.7 V/decade. By varying the channel lengths (25–200 μm) in devices with different metal/semiconductor interfaces, the effect of channel length scaling on mobility is studied and the contact resistance is extracted. The width-normalized contact resistance (RCW) for Au (12 kΩ cm) is high in comparison to Ca (7.2 kΩ cm) or Ca/Au (7.5 kΩ cm) electrodes at low gate voltage (VGS=10 V). However, in the strong accumulation regime at high gate voltage (VGS=30 V), its value is nearly independent of the choice of metal electrodes and in a range of 2.2–2.6 kΩ cm. These devices show stable electrical behavior under multiple scans and low threshold voltage instability under electrical bias stress (VDS=VGS=30 V, 1 h) in N2 atmosphere.
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TL;DR: Recently unprecedented values of μ ∼ 10 cm(2) /Vs have been achieved with solution-processed polymer based OFETs, a value competing with mobilities reported in organic single-crystals and exceeding the performances enabled by amorphous silicon.
Abstract: For at least the past ten years printed electronics has promised to revolutionize our daily life by making cost-effective electronic circuits and sensors available through mass production techniques, for their ubiquitous applications in wearable components, rollable and conformable devices, and point-of-care applications. While passive components, such as conductors, resistors and capacitors, had already been fabricated by printing techniques at industrial scale, printing processes have been struggling to meet the requirements for mass-produced electronics and optoelectronics applications despite their great potential. In the case of logic integrated circuits (ICs), which constitute the focus of this Progress Report, the main limitations have been represented by the need of suitable functional inks, mainly high-mobility printable semiconductors and low sintering temperature conducting inks, and evoluted printing tools capable of higher resolution, registration and uniformity than needed in the conventional graphic arts printing sector. Solution-processable polymeric semiconductors are the best candidates to fulfill the requirements for printed logic ICs on flexible substrates, due to their superior processability, ease of tuning of their rheology parameters, and mechanical properties. One of the strongest limitations has been mainly represented by the low charge carrier mobility (μ) achievable with polymeric, organic field-effect transistors (OFETs). However, recently unprecedented values of μ ∼ 10 cm(2) /Vs have been achieved with solution-processed polymer based OFETs, a value competing with mobilities reported in organic single-crystals and exceeding the performances enabled by amorphous silicon (a-Si). Interestingly these values were achieved thanks to the design and synthesis of donor-acceptor copolymers, showing limited degree of order when processed in thin films and therefore fostering further studies on the reason leading to such improved charge transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary "CMOS-like" logic for the design of digital ICs, easing the scaling down of critical geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, we review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-volume micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices in order to achieve the operation frequencies needed for applications, such as flexible radio-frequency identification (RFID) tags, near-field communication (NFC) devices, ambient electronics, and portable flexible displays.
476 citations
TL;DR: A comprehensive overview on the subject of current injection in organic thin film transistors is offered: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices.
Abstract: A high-mobility organic semiconductor employed as the active material in a field-effect transistor does not guarantee per se that expectations of high performance are fulfilled. This is even truer if a downscaled, short channel is adopted. Only if contacts are able to provide the device with as much charge as it needs, with a negligible voltage drop across them, then high expectations can turn into high performances. It is a fact that this is not always the case in the field of organic electronics. In this review, we aim to offer a comprehensive overview on the subject of current injection in organic thin film transistors: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices. Finally, a survey of the most recent accomplishments in the field is given. Principles are described in general, but the technologies and survey emphasis is on solution processed transistors, because it is our opinion that scalable, roll-to-roll printing processing is one, if not the brightest, possible scenario for the future of organic electronics. With the exception of electrolyte-gated organic transistors, where impressively low width normalized resistances were reported (in the range of 10 Ω·cm), to date the lowest values reported for devices where the semiconductor is solution-processed and where the most common architectures are adopted, are ∼10 kΩ·cm for transistors with a field effect mobility in the 0.1-1 cm(2)/Vs range. Although these values represent the best case, they still pose a severe limitation for downscaling the channel lengths below a few micrometers, necessary for increasing the device switching speed. Moreover, techniques to lower contact resistances have been often developed on a case-by-case basis, depending on the materials, architecture and processing techniques. The lack of a standard strategy has hampered the progress of the field for a long time. Only recently, as the understanding of the rather complex physical processes at the metal/semiconductor interfaces has improved, more general approaches, with a validity that extends to several materials, are being proposed and successfully tested in the literature. Only a combined scientific and technological effort, on the one side to fully understand contact phenomena and on the other to completely master the tailoring of interfaces, will enable the development of advanced organic electronics applications and their widespread adoption in low-cost, large-area printed circuits.
386 citations
TL;DR: In this article, the authors present a deep insight into different organic/inorganic materials used for the dielectric layer, electrodes and substrate for thin film transistors (TFTs).
Abstract: This paper reviews recent advancements in the field of organic electronics. Performance of p- and n-type conducting polymers and small molecule organic semiconductors is presented primarily in terms of mobility and current on/off ratio. Moreover, it presents a deep insight into different organic/inorganic materials used for the dielectric layer, electrodes and substrate for thin film transistors (TFTs). The electrical characteristics and performance parameters of single and dual gate structures are compared. In addition, performance dependence of organic TFT (OTFT) is discussed on the basis of contact resistance, channel length and thickness of the active layer. The paper thoroughly discusses several important applications of OTFTs including inverter, organic static random access memory, radio frequency identification tag and DNA sensors. It also includes several limitations and future prospects of organic electronics technology.
125 citations
TL;DR: In this article, 2,2′-bithiazole was synthesized in one step and copolymerized with dithienyldiketopyrrolopyrrole to afford poly(dithienymylldiketsopyrylopyrdrug-biomethane)-bithiaide, PDBTz, which exhibited electron mobility reaching 0.3 cm2 V 1 s−1 in organic field effect transistor (OFET) configuration.
Abstract: The electron deficiency and trans-planar conformation of bithiazole is potentially beneficial for the electron-transport performance of organic semiconductors. However, the incorporation of bithiazole into polymers through a facile synthetic strategy remains a challenge. Herein, 2,2′-bithiazole was synthesized in one step and copolymerized with dithienyldiketopyrrolopyrrole to afford poly(dithienyldiketopyrrolopyrrole-bithiazole), PDBTz. PDBTz exhibited electron mobility reaching 0.3 cm2 V–1 s–1 in organic field-effect transistor (OFET) configuration; this contrasts with a recently discussed isoelectronic conjugated polymer comprising an electron-rich bithiophene and dithienyldiketopyrrolopyrrole, which displays merely hole-transport characteristics. This inversion of charge-carrier transport characteristics confirms the significant potential for bithiazole in the development of electron-transport semiconducting materials. Branched 5-decylheptacyl side chains were incorporated into PDBTz to enhance polyme...
79 citations
TL;DR: In this article, the authors demonstrate efficient electron injection from a high work function metal in staggered transistors based on the high mobility poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis (dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}.
Abstract: We demonstrate efficient electron injection from a high work function metal in staggered transistors based on the high mobility poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}. Channel length scaling shows that the linear mobility for electrons remains higher than 0.1 cm2/V s when reducing the channel length to a few micrometers. Field-enhanced injection favors downscaling at a fixed lateral voltage and reduces the contact resistance to 11 kΩ cm at high gate voltages for channels of only a few micrometers. The contacts are asymmetric, with the source contribution dominating the overall resistance, consistent with an injection limited regime rather than bulk-limited as generally found in staggered transistors.
72 citations
References
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TL;DR: In this paper, solution-processed n-type organic field effect transistors (OFETs) based on the fullerene derivative {6}-1-(3-(2- thienylethoxycarbonyl)-propyl)propyl)-{5}-l-phenyl-[5,6]-C61 (TEPP) and phenyl-C61-butyric acid methyl ester (PCBM) in a multiring source/drain structure are reported.
Abstract: Solution-processed n-type organic field-effect transistors (OFETs) based on the fullerene derivative {6}-1-(3-(2- thienylethoxycarbonyl)-propyl)-{5}-l-phenyl-[5,6]-C61 (TEPP) and phenyl-C61-butyric acid methyl ester (PCBM) in a multiring source/drain structure are reported. Devices with TEPP show high electron mobility up to 7.8 x 10-2 cm2/Vs in the saturation regime for bottom-contact OFETs with Au S/D electrodes with a solution-processed fullerene derivative. The ON/OFF ratios reported in this letter, which are in the range of 105 -106, are among the highest values reported for such devices. This mobility is always higher compared to PCBM devices prepared in identical conditions. The mobility of TEPP and PCBM increased with increasing temperatures in the range of 100-300 K with activation energy of 78 and 113 meV, respectively, which suggests that the thermally activated hopping of electrons is dominant in TEPP.
48 citations
TL;DR: In this article, the authors have studied the time-dependent degradation of ON current of amorphous silicon thin-film transistors (a-Si:H TFTs), which is a function of stress duration, stress temperature, and stress bias.
Abstract: We have studied the time-dependence degradation of ON current of amorphous silicon thin-film transistors (a-Si:H TFTs), which is a function of stress duration, stress temperature, and stress bias. A simple method with stretched-exponential equation and current-voltage function is used to characterize and predict the TFT performance. Bias-temperature stress at different stress voltages has been performed on a-Si:H TFTs. A new method using ON current degradation to analyze TFT device performance is presented, which is different from the conventional threshold-voltage shift method. We have also observed that the beta value in the ON current degradation method compared to the threshold-voltage shift method, with a stretched-exponential stress time, is related to beta~beta0-TST/T0. Finally, we have also used the new equation to evaluate the performance of the gate-driver-on-array circuit in our products. If the limitation of the current for the pull-down device is 1times10-6 A, then the operation time of the pull-down device can be estimated to about 1219 h when key pulled-down TFT is operating at 60degC.
24 citations
TL;DR: In this paper, the source and drain parasitic resistances of amorphous silicon based thin film transistors (aSi:H TFT) are investigated using a very simple TFT model including a parameter extraction method.
Abstract: The source and drain parasitic resistances of amorphous silicon based thin film transistors (aSi:H TFT) are investigated using a very simple TFT model including a parameter extraction method. We show that this method provides an accurate measurement of these resistances and clearly explains their influence on the apparent field effect mobility µ a of the TFTs. We compare the parasitic resistances of TFTs for the top nitride (TN) and bottom nitride (BN) configurations and we show that the usual different performances observed on the two configurations can be mainly attributed to the differences in the parasitic resistances.
16 citations
TL;DR: In this paper, the authors investigate charge injection into a methanofullerene and investigate the temperature and electric field dependent source-drain currents from contact limited [6,6]-phenyl C61-butyric acid methyl ester (PCBM) thin film transistors.
Abstract: In this study we investigate charge injection into a methanofullerene. The temperature and electric field dependent source-drain currents from contact limited [6,6]-phenyl C61-butyric acid methyl ester (PCBM) thin film transistors (TFTs) were analyzed. A form for the temperature and field dependent behavior of the parasitic contact resistances between metal and semiconductor was proposed based on a diffusion limited thermionic emission (DLTE) injection current and accounting for the disorder in the system. The temperature dependent current-voltage characteristics were initially modeled with a model for field effect behavior in amorphous organic semiconductors from the literature to determine material parameters. The initial fit resulted in discrepancies between the experimental data and the data predicted by the model. Modifying the model to account for the effects of contact resistances led to much better agreement between the experimental and predicted data. Based on these results, the DLTE injection current describes the injection process in PCBM TFTs well.
12 citations