Stacked pentacene layer organic thin-film transistors with improved characteristics
TL;DR: In this article, photolithographically defined organic thin-film transistors (OTFTs) with improved field-effect mobility and sub-threshold slope were fabricated using two layers of pentacene deposited at different substrate temperatures.
Abstract: Using two layers of pentacene deposited at different substrate temperatures as the active material, we have fabricated photolithographically defined organic thin-film transistors (OTFTs) with improved field-effect mobility and subthreshold slope. These devices use photolithographically defined gold source and drain electrodes and octadecyltrichlorosilane-treated silicon dioxide gate dielectric. The devices have field-effect mobility as large as 1.5 cm/sup 2//V-s, on/off current ratio larger than 10/sup 8/, near zero threshold voltage, and subthreshold slope less than 1.6 V per decade. To our knowledge, this is the largest field-effect mobility and smallest subthreshold slope yet reported for any organic transistor, and the first time both of these important characteristics have been obtained for a single device.
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IBM1
TL;DR: In this article, the authors present new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of organic thin-film transistors (OTFTs) and discuss progress in the growing field of n-type OTFTs.
Abstract: Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.
4,804 citations
TL;DR: The focus of this review will be on the performance analysis of π-conjugated systems in OFETs, a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals that provide an important insight into the charge transport of ρconjugate systems.
Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear
2,942 citations
2,020 citations
TL;DR: In this article, a spin-coated polymer gate dielectric layer was used to obtain a polyvinylphenol-based copolymer-based transistor with a carrier mobility as large as 3 cm2/V's and sub-threshold swing as low as 0.5 V/decade.
Abstract: We have fabricated pentacene organic thin film transistors with spin-coated polymer gate dielectric layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent electrical characteristics, including carrier mobility as large as 3 cm2/V s, subthreshold swing as low as 1.2 V/decade, and on/off current ratio of 105. For comparison, we have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielectric and obtained carrier mobilities as large as 1 cm2/V s and subthreshold swing as low as 0.5 V/decade.
1,225 citations
TL;DR: This paper review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
Abstract: In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
1,192 citations
References
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TL;DR: The thiophene oligomer α-hexathienylene (α-6T) has been successfully used as the active semiconducting material in thin-film transistors and optimized methods of device fabrication have resulted in high field-effect mobilities and on/off current ratios of > 106.
Abstract: The thiophene oligomer α-hexathienylene (α-6T) has been successfully used as the active semiconducting material in thin-film transistors. Field-induced conductivity in thin-film transistors with α-6T active layers occurs only near the interfacial plane, whereas the residual conductivity caused by unintentional doping scales with the thickness of the layer. The two-dimensional nature of the field-induced conductivity is due not to any anisotropy in transport with respect to any molecular axis but to interface effects. Optimized methods of device fabrication have resulted in high field-effect mobilities and on/off current ratios of > 106. The current densities and switching speeds are good enough to allow consideration of these devices in practical large-area electronic circuits.
987 citations
"Stacked pentacene layer organic thi..." refers background in this paper
...less than 10 6, and subthreshold slope greater than 5 V/decade [2], [3]....
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TL;DR: Pentacene-based organic thin-film transistors (TFT's) with field effect mobility as large as 0.7 cm/sup 2/V/spl middot/s and on/off current ratio larger than 10/sup 8/ have been fabricated as mentioned in this paper.
Abstract: Pentacene-based organic thin-film transistors (TFT's) with field-effect mobility as large as 0.7 cm/sup 2//V/spl middot/s and on/off current ratio larger than 10/sup 8/ have been fabricated. Pentacene films deposited by evaporation at elevated temperature at low-to-moderate deposition rates have a high degree of molecular ordering with micrometer-sized and larger dendritic grains. Such films yield TFT's with large mobility. Films deposited at low temperature or by flash evaporation have small grains and poor molecular ordering and yield TFT's with low mobility.
754 citations
"Stacked pentacene layer organic thi..." refers background or methods in this paper
...RECENTLY, organic thin-film transistors (OTFT’s) with field-effect mobility and on/off current ratio comparable to hydrogenated amorphous silicon thin-film transistors (aSi : H TFT’s) have been fabricated using pentacene as the active material [1]....
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...7 cm 2/Vs, and current on/off ratio greater than 10 8 [1]....
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TL;DR: In this article, a maximum field effect mobility of 0.038 cm−2'V−1'1's−1 is reported for devices incorporating pentacene films deposited at room temperature.
Abstract: Pentacene films deposited with molecular beam deposition have been fabricated and characterized with respect to structure and morphology using x‐ray diffraction and scanning electron microscopy. Metal‐insulator semiconductor field‐effect transistor devices based on such films were used to study their transport properties. A maximum field‐effect mobility of 0.038 cm−2 V−1 s−1 is reported for devices incorporating pentacene films deposited at room temperature. The structural characterization revealed the coexistence of two phases: the thermodynamically stable single‐crystal phase and the kinetically favored, metastable thin‐film phase. Such mixed phase films were produced when low deposition rates were used in combination with a substrate temperature of 55 °C. Mixed phase films had transport properties inferior to films consisting solely of one phase, while amorphous films deposited at low surface mobility conditions had extremely low conductivity. Use of prepurified pentacene as source material resulted in...
661 citations
TL;DR: In this paper, the authors show that the large sub-threshold slope typically observed is not an intrinsic property of the organic semiconducting material and that devices with sub-reshold slope similar to amorphous silicon devices are possible.
Abstract: Organic thin-film transistors using the fused-ring polycyclic aromatic hydrocarbon pentacene as the active electronic material have shown mobility as large as 0.7 cm/sup 2//V-s and on/off current ratio larger than 10/sup 8/; both values are comparable to hydrogenated amorphous silicon devices. On the other hand, these and most other organic TFT's have an undesirably large subthreshold slope. We show here that the large subthreshold slope typically observed is not an intrinsic property of the organic semiconducting material and that devices with subthreshold slope similar to amorphous silicon devices are possible.
520 citations
"Stacked pentacene layer organic thi..." refers background in this paper
...We have found that the characteristics of pentacene TFT’s can be improved by using a self-organizing material like octadecyltrichlorosilane (OTS) between the SiO 2 gate dielectric and the pentacene active layer [6]....
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206 citations
"Stacked pentacene layer organic thi..." refers background in this paper
...less than 10 6, and subthreshold slope greater than 5 V/decade [2], [3]....
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...The log – characteristics show the maximum on/off current ratio is greater than 108 at 20 V and the subthreshold slope is about 1.6 V/decade at 20 V....
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...Typically, a-Si : H TFT’s have field-effect mobility larger than 0.5 cm2/V-s, on/off current ratio greater than 108, near zero threshold voltage, and subthreshold slope less than about 1.0 V/decade....
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...Although the result obtained here, 1.6 V/decade, is larger than that typically observed for a-Si : H devices, it is low enough to allow OTFT use in many applications....
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...For example, OTFT’s usingsexithienyl as the active material typically have field-effect mobility less than 0.1 cm2/V-s, current on/off ratio near or less than 106, and subthreshold slope greater than 5 V/decade [2], [3]....
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