From the organic thin film transistor to the 3-D textile organic cylindrical transistors - perspectives, expectations and predictions

In this paper we examine the possibility to simulate and study the behaviour of a fiber-based Textile Transistor in a commercial TCAD system. We also examine the capability of such transistors to operate in sufficiently low voltages, aiming to the potential realization of low-voltage wearable textiles in the future. We have seen that it is potentially feasible to build transistors which can operate in low voltages by using typical materials. Even if some of the selected typical materials have to be replaced by others more suitable for practical use in the textile industry, the simulation is a good starting point for estimating the device typical operation and parameters

Optimization of cylindrical textile organic field effect transistors using TCAD simulation tool

We used a commercial TCAD tool in order to simulate a cylindrical Textile Organic Field Effect Transistor (TOFET) and study the impact of different critical region sizes in its electrical characteristics. The simulation was based on models and parameters similar to those of previous simulations in Organic Thin Film Transistors. We have seen that it is potentially feasible to build transistors which can operate in low voltages by using typical materials. Even if some of the selected typical materials have to be replaced by others more suitable for practical use in the textile industry, the simulation is a good starting point for estimating the device typical operation and parameters. By optimizing critical region sizes of the device we conclude that the device should have an active layer thickness below 100 nm, channel length around 10 mu m and gate oxide thickness as small as possible (300 nm or less), in order to have optimum transistor performance

Soft capacitor fibers using conductive polymers for electronic textiles

A novel, highly flexible, conductive polymer-based fiber with high electric capacitance is reported. In its crossection the fiber features a periodic sequence of hundreds of conductive and isolating plastic layers positioned around metallic electrodes. The fiber is fabricated using fiber drawing method, where a multi-material macroscopic preform is drawn into a sub-millimeter capacitor fiber in a single fabrication step. Several kilometres of fibers can be obtained from a single preform with fiber diameters ranging between 500um -1000um. A typical measured capacitance of our fibers is 60-100 nF/m and it is independent of the fiber diameter. For comparison, a coaxial cable of the comparable dimensions would have only ~0.06nF/m capacitance. Analysis of the fiber frequency response shows that in its simplest interrogation mode the capacitor fiber has a transverse resistance of 5 kOhm/L, which is inversely proportional to the fiber length L and is independent of the fiber diameter. Softness of the fiber materials, absence of liquid electrolyte in the fiber structure, ease of scalability to large production volumes, and high capacitance of our fibers make them interesting for various smart textile applications ranging from distributed sensing to energy storage

Fabrication and optimization of hybrid field-effect transistors on fibres

Os dispositivos flexíveis à base de fibras prometem ter um impacto significativo na futura tecnologia wearable. Este trabalho, integrado no projeto 1D-NEON EU, documenta a fabricação e otimização de transístores de efeito de campo (FETs) em fios condutores para posterior implementação em fibras, promovendo o desenvolvimento dos smart textiles. Os transístores-fibra foram fabricados seguindo uma estrutura gate-all-around, usando fio de prata com diâmetro de 200 e 500 μm como núcleo (elétrodo de porta), parileno depositado por deposição química de vapor como isolante, óxido semicondutor pulverizado (óxido de índio-gálio-zinco ou óxido de zinco-estanho) e, como elétrodos de fonte-dreno, Al evaporado com máscara de sombra ou Ag por screen-printing. Realizou-se uma análise detalhada da espessura de parileno necessária para o bom funcionamento de estruturas metal-isolante-metal (MIM) e transístores, em configurações planares e em fibra. Enquanto que, em estruturas planares, se verificou uma boa qualidade das propriedades isolantes com filmes de 500 nm de espessura, os fios requerem filmes de ≈ 1 μm, devido à rugosidade inicial do fio. Foram desenvolvidas três diferentes gerações de estruturas, otimizando não só o empilhamento de materiais e os processos de deposição, mas também as configurações para medição, que foram consideradas críticas para aceder de forma confiável às propriedades elétricas das estruturas à base de fibras. Apesar da elevada tensão de operação, devido à espessa camada isolante, os transístores-fibra preparados abaixo de 150 °C apresentam mobilidades superiores a 10-2 cm2/V.s, Ion/Ioff > 102, sem degradação do desempenho após dobramento num raio de 45 mm

Modeling of physical and electrical characteristics of organic thin film transistors

The most studied and widely employed material for electronics is undoubtedly silicon. Its semiconductor properties and its associated costs make it an ideal candidate for most of the needs of today electronics. However, several different materials have been studied in the last years. In 1977, Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa discovered a new, carbon based, highly-conductive polymer: the oxidized, iodine-doped polyacetylene. For their discovery, which was one of the most important milestones for organic electronics, they were jointly awarded the chemistry Nobel Prize in 2000. In this doctoral thesis, a theoretical framework for the electronics of organic transistors is developed. In chapter 2 an overview of the topic is presented: starting from the fundamental properties of the organic semiconductors, the chapter develops to provide a thorough analysis of the underlying physics and the electrical models which describe the behavior of organic thin film transistors. The next chapters describe models for organic thin film transistors with a cylindrical geometry, with short channel, and as a function of time. Chapter 6 concludes the doctoral thesis. The most important achievements and considerations are here summarized, and possible future activities on the topic are exposed

Enhancing the Performance of Poly(3-Hexylthiophene) Based Organic Thin-Film Transistors Using an Interface Engineering Method

An original design and photolithographic fabrication process for poly(3-hexylthiophene-2, 5-diyl) (P3HT) based organic thin-film transistors (OTFTs) is presented. The structure of the transistors was based on the bottom gate bottom contact OTFT. The fabrication process was efficient, cost-effective, and relatively straightforward to implement. Current–voltage (I-V) measurements were performed to characterize the primary electronic properties of the transistors. The measured mobility of these transistors was significantly higher than most results reported in the literature for other similar bottom gate bottom contact P3HT OTFTs. The higher mobility is explained primarily by the effectiveness of the fabrication process in keeping the interfacial layers free from contamination, as well as the proper annealing of the P3HT. An interface engineering method is investigated to further enhance the performance of the OTFTs. Three interfacial materials were used for this purpose: graphene oxide (GO), poly(oligo (ethylene glycol) methyl ether methacrylate- glycidyl methacrylate- lauryl methacrylate) (P(OEGMA-GMA-LMA)) or POGL, and a composite of GO and P(OEGMA-GMA-LMA) or GO-POGL. The OTFTs with a GO interfacial layer were observed to have a higher drain current and field-effect mobility than the OTFTs with no interfacial layer. The enhanced drain current and mobility are associated with the particular structure of the P3HT layer on the dielectric surface and the reduction in the contact resistance between the GO-covered electrodes and the P3HT. The OTFTs with a POGL interfacial layer were observed to have a smaller threshold voltage than the OTFTs with no interfacial layer. The POGL OTFTs were also observed to have much more ideal drain current saturation characteristics with very small I-V curve slope. This is explained by the deep trap states on the POGL surface and the reduction of the contact resistance at the electrode/organic semiconductor interface. The OTFTs with a GO-POGL composite layer were observed to have a higher drain current and mobility, and a smaller threshold voltage than the OTFTs without an interfacial layer, which is the optimum case for these two device parameters. The higher drain current and field-effect mobility are attributed to the larger interconnecting grains of the P3HT that is deposited onto the GO-POGL surface and the smaller interfacial tension between the GO-POGL and the P3HT. The smaller threshold voltage is attributed to the deep trap states on the GO-POGL layer and the smaller contact resistance between the GO-POGL modified electrodes and the P3HT. Furthermore, experiments that could be performed to advance this research work and enhance the performance of the OTFTs even further are proposed

Optik litografi ile organik alan etkili transistörlerin kanal aralığının hassas şekilde oluşturulması ve elde edilen cihazların elektriksel karakterizasyonu

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Organik alan etkili transistör (OFET), üretim kolaylığı, düşük bütçeli yatırım ve esnek yüzeye uygulanabilmesi gibi avantajlarından dolayı, bilinen silisyum temelli transistörlerin pek çok uygulama alanında yerini almaya aday bir elektronik devre elemanıdır. OFET; bir alt tabaka üzerine önce iki iletken kontak (kaynak ve Savak) sonra üzerine yarıiletken polimer, bunun üzerine yalıtkan polimer ve en üste de kapı kontağı kaplanarak üretilir. Bu üretim sıralaması; kapının altta olması veya yarıiletken malzemenin kaynak ve Savak arasında olması gibi 4 farklı geometride de oluşturulabilmektedir. Elde edilen OFET'lerde Kaynak kapı arasına uygulanan gerilim ile kaynak Savak arasından geçen akım kontrol edilmektedir. Tez kapsamında öncelikle literatürde yer alan P tipi P3HT polimeri ile litografi yöntemi kullanılarak transistörler üretilmiş ve literatürde bulunan sonuçlarla karşılaştırılmıştır. Ticari bir polimer olan P3HT ile elde edilen transistörlerin karakteristik davranışları literatürde bulunan karakteristik davranışlarla son derece uyumlu çıkmıştır. Daha sonra özgün sentez bileşikler kullanılmıştır. Bu tezde, özgün malzemeler kullanılarak kapı/yalıtkan/kaynak Savak/yarıiletken yapılı yüksek performanslı OFET üretimi gerçekleştirilmiş ve sentezin özgün olmasının yanısıra performansın yüksek olması ile de literatüre büyük katkı sağlanmıştır. Yapılan çalışmada P3HT polimeri ile üretilen OFET'in kanal aralığına bağlı olarak eşik voltajı (VTh), açma kapama akım oranı(ION/IOFF), maksimum çıkış Savak akımı (IDS)max ve alan etkili mobilitesi µFET gibi transistör parametreleri incelenmiştir. Eşik voltajı küçük ve büyük kanal aralıklarında sapma gösterirken genelde -7 V civarında elde edilmiştir. ION/IOFF değeri, 6 µm için 1,01x103 olarak bulunurken 70 µm için 0,18x103 olarak elde edilmiş ve kanal aralığının artmasıyla azaldığı gözlenmiştir. (IDS)max değeri yine 6 µm için 4,24 µA bulunurken 70 µm için 0,34 µA olarak elde edilmiştir. Buradan kanal aralığının artmasıyla (IDS)max değerinin azaldığı anlaşılmaktadır. µFET değeri ise 6 µm için 2,1x10-3 cm2/Vs olarak bulunurken 70 µm için 6,3x10-3cm2/Vs olarak elde edilmiş ve kanal aralığıyla birlikte lineer olmayan bir artış gözlenmiştir. Yeni sentez malzeme ile üretilen OFET'in VTh, ION/IOFF, µFET ve geçiş iletkenliği (gm) değeri, sırasıyla 1,37 V, 0,7x103, 5,02 cm2/Vs ve 5,64 µS/mm olarak elde edilmiştir.Because of the advantages such as ease of production, low budget investment and applicability on flexible surfaces; organic field effect transistors ( OFET) are used as electronic circuit components that are candidate to take silicon based transistors' place in many applications. An OFET is fabricated by depositing two conducting contacts on substrate (source and drain) and then a semiconducting polymer on these contacts and later an insulating polymer on semiconducting polymer and lastly gate contact on insulating polymer. This fabrication order could be in four different geometry such as gate's being at the bottom or semiconductor materials being between source and drain. The voltage between source and gate, and the current passing through source and drain are controlled in fabricated OFET. Within the scope of dissertation, firstly transistors were fabricated by using P type P3HT polymer that is encountered in literature via lithography method and the results were compared with those in the literature. The performance of transistors fabricated with P3HT, which is a commercial polymer, has beeen found considerably compatible with the results of literature. Afterwards, novel synthesized compounds were used. In this dissertation, high performance OFET of gate/insulator/source drain/semiconductor structure were fabricated and considerable contribution was made to the literature through novel synthesized compounds and obtained high performance. In the study conducted, depending on channel length of OFET fabricated by P3HT polymer, transistor parameters such as threshold voltage (VTh), on off current ratio (ION/IOFF), maximum output drain current (IDS)max and field effect mobility (µFET) are investigated. Threshold voltage values are generally at about -7 V though there are deviations for small and large channel gaps. The value of ION/IOFF for 6 µm is 1,.01x103 whereas it is 0,18x103 for 70 µm, and it has been observed that it decreases with increasing the channel length. Similarly, value of (IDS)max for 6 µm is 4,24 µA whereas it is 0,34 µA for 70 µm, and it has been concluded that it decreases with increasing the channel length. As to the value of µFET, it is 2,1x10-3 cm2/Vs for 6 µm whereas it is 6,3x10-3 cm2/Vs for 70 µm, and it exhibits non linear increase with increasing the channel length. VTh, ION/IOFF, µFET and transconductance (gm) values of the OFET fabricated by newly synthesized compound are 1,37 V, 0,7x103, 5,02 cm2/Vs and 5,64 µS/mm, respectively