All‐Carbon Thin‐Film Transistors as a Step Towards Flexible and Transparent Electronics

Abstract

silicon wafer, TFTs can be fabricated on various types of rigid or flexible substrates. [1] TFTs fabricated on glass are primarily used for driving circuits in the liquid-crystal displays of televisions, computer monitors, and mobile phones, etc. Well-established TFT technologies based on amorphous silicon and polycrystalline silicon are well-suited for large-area, highresolution panels, e.g., six pieces of 65-and 75-inch TFT arrays can be fabricated on a 10.5th generation glass substrate. [2] However, TFTs based on these silicon-based semiconductors still face challenges in flexible and transparent applications, which would allow circuit integration on curved and non-rigid surfaces and in multi-layer packaging, e.g., head-up displays on windshields, informational displays on eyeglasses and transparent electronic skin in wearable electronics. [3] In terms of the materials used to construct flexible and transparent devices, not only the transistor channel but also the dielectric layers and metallic interconnects should have excellent flexibility and transparency. [4] The following factors play critical roles in the selection of channel materials: carrier mobility, temperature of material preparation, flexibility, large area availability, cost and stability. Carrier mobility is an important parameter to characterize the drift velocity of electrons or holes in a semiconductor under an applied electric field. [5] A high mobility corresponds to a high operating speed of the TFTs and their circuits. The only advantage of low-temperature polycrystalline silicon is its relatively high mobility. [6] Amorphous oxide semiconductors, including indium gallium zinc oxide, have a modest mobility and are costly due to the use of noble metal elements. [7] Hydrogenterminated amorphous silicon has modest properties in carrier mobility, large-area and flexibility, [1] and organic semiconductors are better suited for flexible and transparent TFTs except for their shortcomings of low mobility and poor environmental stability. [8] On the other hand, normal metal electrodes, such as gold, silver, aluminum and copper, cannot be used to form transparent electrodes due to their poor light transmittance. Both transparent indium tin oxide (ITO) electrodes and opaque metal electrodes suffer from flexibility constraints and can usually tolerate strains of less than 2%. [9][10][11] Therefore, the discovery of new types of robust channel and electrode materials is essential to achieve transparent, flexible, and even stretchable electronics. [12] Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, have attracted great attention for potential use in flexible and transparent electronics since their discovery in the last two decades, [13,14] owing to their excellent properties Carbon nanotubes and graphene have attracted great attention for potential applications in flexible and transparent electronics, owing to their exceptional properties including very high electrical conductivity, optical transmittance, mechanical strength and f...

Solution Processed Metal Oxide High‐κ Dielectrics for Emerging Transistors and Circuits

“…Employing spin coated ZrO x film (500 °C) as the dielectric layer, Dodabalapur et al demonstrated complementary inverters ( Figure a) and high speed ring oscillators (Figure b) using inkjet printed SWCNTs (p‐type) and ZTO (n‐type) semiconductors . CNTs have been attracting great interest for TFT integration over past two decades due to their high mobility, chemical stability, excellent mechanical flexibility, and potential for various applications (e.g., ICs, displays, and sensors) . Figure c shows output and transfer curves for ZTO and SWCNT TFTs, exhibiting μ FE = 4.4 and 1.7 cm 2 V −1 s −1 in the saturation region, respectively.…”

Recent Progress in Inkjet‐Printed Thin‐Film Transistors

“…In particular, the ability to realize flexible thin‐film transistors (TFTs), which are key driving/switching component of wearable electronics, offers much freedom on the target substrates. Therefore, a variety of functional materials focusing on semiconductors have been extensively explored for realizing competitive flexible TFTs, including traditional silicon, organics, oxides, carbon nanotubes (CNTs), and emerging 2D materials . Furthermore, because representative flexible or stretchable platforms, such as polymer‐based plastic and polydimethylsiloxane (PDMS) substrates, are difficult to utilize in traditional microfabrication, the development of alternative processes that can be employed for implementing low‐cost, large‐area, flexible, and biocompatible electronics is key to meet this demand.…”

“…This review highlights recent progress in inkjet‐printed TFTs to achieve improved electrical performance and their emerging electronics applications. Although several excellent reviews have already introduced printable organic, oxide, and 2D materials for large‐area TFT applications, for example, high‐speed printed circuits and transparent CNT‐based applications, the overarching aim of this review is to provide an overview of the recent efforts to realize high‐performance inkjet‐printed TFTs based on various channel materials and switching mechanisms as well as fundamental inkjet printing technology. The issues raised in the field of inkjet‐printed organic, metal‐oxide, low‐dimension thin‐film transistors in electronic and material perspectives would be systematically described, and then the currently promising strategies to address these issues will be introduced.…”

Transparent Flexible Nanoline Field-Effect Transistor Array with High Integration in a Large Area

“…Transparent transistor arrays with sufficient mechanical flexibility − have been spotlighted as key technologies for flexible opto- and nanoelectronic devices such as light-emitting diode, display, touch panel, and electronic skin . Use of transparent materials − and dimensional reduction of nontransparent materials − have been the main approaches in fabrication of transparent flexible transistors.…”