Fully Transparent and Rollable Electronics

Abstract

Major obstacles toward the manufacture of transparent and flexible display screens include the difficulty of finding transparent and flexible semiconductors and electrodes, temperature restrictions of flexible plastic substrates, and bulging or warping of the flexible electronics during processing. Here we report the fabrication and performance of fully transparent and rollable thin-film transistor (TFT) circuits for display applications. The TFTs employ an amorphous indium-gallium-zinc oxide semiconductor (with optical band gap of 3.1 eV) and amorphous indium-zinc oxide transparent conductive electrodes, and are built on 15-μm-thick solution-processed colorless polyimide (CPI), resulting in optical transmittance >70% in the visible range. As the CPI supports processing temperatures >300 °C, TFT performance on plastic is similar to that on glass, with typical field-effect mobility, turn-on voltage, and subthreshold voltage swing of 12.7 ± 0.5 cm(2)/V·s, -1.7 ± 0.2 V, and 160 ± 29 mV/dec, respectively. There is no significant degradation after rolling the TFTs 100 times on a cylinder with a radius of 4 mm or when shift registers, each consisting of 40 TFTs, are operated while bent to a radius of 2 mm. For handling purposes, carrier glass is used during fabrication, together with a very thin (∼1 nm) solution-processed carbon nanotube (CNT)/graphene oxide (GO) backbone that is first spin-coated on the glass to decrease adhesion of the CPI to the glass; peel strength of the CPI from glass decreases from 0.43 to 0.10 N/cm, which eases the process of detachment performed after device fabrication. Given that the CNT/GO remains embedded under the CPI after detachment, it minimizes wrinkling and decreases the substrate's tensile elongation from 8.0% to 4.6%. Device performance is also stable under electrostatic discharge exposures up to 10 kV, as electrostatic charge can be released via the conducting CNTs.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…90 Multi-layer metals offer, in general, a compromise between good adhesion and high conductivity, especially in the case of Ti/Au, 23,96,181 Ti/Cu, 135 Cr/Au, 174 or Ti/Au/Ti gate stacks. 162 Besides metals and metal alloys, ITO, 29,69,78,80,135,139,165,177,180,184,188,205 IZO, 77,79,133,160,208 In 2 O 3 , 171 and aluminum zinc oxide (AZO) have been used to fabricate transparent gate contacts. 93,134 Furthermore, duallayers of metal and ITO 40 or IZO have also been employed.…”

“…162 In alternative to flexible substrates manufactured independently from the TFTs, it is also possible to create the flexible substrate by covering a host substrate with a polymer using either evaporation, 80,81,141 spin, slot or blade coating techniques. 23,39,133,135,137,142,144,147,155,161,164,179 The advantages of these fabrication techniques based on a rigid support are a high compatibility with the standard fabrication processes on Si or glass wafers, a reduction of the expansion of the substrate during the manufacturing process, as well as the possibility to realize devices on very thin (%1 lm) substrates. After the TFT fabrication is completed, the flexible foils or thin deposited polymer layers carrying the devices can be separated from the rigid support using: (1) mechanical peeling, 38,142,155,158,161,164,166,168,179 (2) a low adhesion releasing layer, 133,144 (3) a supporting laser, 137 or (4) a sacrificial layer between the host carrier and the polymer.…”

HCI meets Material Science

“…An exciting prospect for rollable structures is in the development of flexible electronics, with advances in thin, flexible display technology enabling the concept of rollable displays to be explored [143]. This is perhaps the application of rollable structures that has been of most interest within HCI to date.…”

“…This is perhaps the application of rollable structures that has been of most interest within HCI to date. Several studies have focused on developing the technology, including [34,97,143,229,252]. Typically metal foils, ultrathin glasses and plastic films are considered ideal materials for the flexible substrate, with rollable polymer films showing particular promise due to their flexibility, low cost and excellent optical clarity, in addition to being amenable to a wide range of manufacturing processes such as roll-to-roll processing and inkjet printing [103].…”

Recent Progress in Electronic Skin

“…In addition to the functions mentioned above that attempt to mimic human skin, such as strain, pressure, temperature, and humidity sensing, additional features of intelligent e‐skin should be exploited in the future beyond the basic functions and physiognomy of human skin, which are the advantages of e‐skin 102. Hence, the high level of integration of the e‐skin system is an urgent topic of investigation, indicating that flexible electronic‐integrated circuits and other chemical or physical sensors should keep pace with the development of e‐skin to meet the demands of applications in robotics, human–machine interactions, health monitoring, and medical implant services 103.…”