Controllable Direct-Writing of Serpentine Micro/Nano Structures via Low Voltage Electrospinning

Feiyu Fang, Xin Chen, Zefeng Du, Ziming Zhu, Xindu Chen, Han Wang, Peixuan Wu
2015 Polymers  
Micro/nanofibers prepared by direct-writing using an electrospinning (ES) technique have drawn more attention recently owing to their intriguing physical properties and great potential as building blocks for micro/nanoscale devices. In this work, a wavy direct-writing (WDW) process was developed to directly write serpentine micro/nano structures suitable for the fabrication of micro devices. This fabrication ability will realize the application of electrospun-nanofiber-based wiring of
more » ... wiring of structural and functional components in microelectronics, MEMS, sensor, and micro optoelectronics devices, and, especially, paves the way for the application of electrospinning in printing serpentine interconnector of large-area organic stretchable electronics. Polymers 2015, 7 1578 serpentine interconnects enable reversible levels of stretch ability as high as 300% [3] and the substantial resistive strain sensitivity reduction ("1100%) with the encapsulated serpentine pattern [5] . Conventional methods, such as electron beam lithography, focused ion beams (FIB), and dip-pen nanolithography (DPN), are capable of generating well-defined micro/nano patterns [6-8], but they are inefficient and require special equipment and complex processes. Inkjet printing is an attractive method of depositing patterns while the minimum reliable printing resolution ranges from 20 to 30 µm [9]. A size limitation, which prevents the fabrication of smaller patterns, does exist. Electrohydrodynamic (EHD) printing is a technique that has the potential to print high resolution patterns [10]. However, due to the discontinuous feature, precise continuous patterning is still unable to be achieved with EHD printing. Thus, there is a significant need to produce continuous serpentine structures in a simpler, more cost-effective way. The efficiency and low-cost production of micro/nanostructures by electrospinning (ES) via a direct-writing process has gained popularity recently, owing to its enormous potential for application in many areas including light-emitters [11, 12] , field-effect transistors [13], piezoelectric devices [14] , and supercapacitors [15] . ES is considered to be a straightforward, low-cost technique to fabricate ultra-thin fibers with diameters ranging from tens of nanometers to several micrometers [16, 17] . In particular, having the ability to deposit functional materials directly and without contact on a variety of substrates, including flexible substrates, ES can be used to directly print large-area organic semiconducting nanowire arrays on device substrates, enabling sophisticated large-area nanowire lithography for nanoelectronics [18, 19] . Thus, ES is considered to be a promising alternative to traditional lithography technology to produce microelectronic devices in an ingenious and cost-effective way. While a conventional ES system is simple, the physics of the process is extremely complex. Owing to the bending instability of a charged jet under coupled multi-field forces, the ES process is unstable and almost uncontrollable. A revolutionary technology breakthrough has been developed to increase the controllability of a single fiber by shortening the needle-to-collector distance. This improved process, near-field electrospinning (NFES), has been developed to write smooth microfibers in a direct manner [20] . However, a challenge to precisely write different patterns using NFES still exists [21] . In order to obtain a specific serpentine/helical structure to meet the requirements for the manufacture of micro/nano devices, several exploratory studies have been carried out, yielding remarkable results [22] [23] [24] [25] [26] [27] . However, challenges remain in producing micro/nano scale serpentine patterns stably, where frequency, amplitude, and wavelength can be control precisely. In this study, we developed the wavy direct-writing (WDW) process, a simple but effective method, to directly write high-resolution serpentine patterns. This fabrication ability has potential application in many fields, including stretchable energy harvesters [28, 29] , stretchable strain sensors [24], light-emitters [12, 30] , photonics, electronics, and micromechanics [31]. Experimental Section Polyethylene oxide (PEO) with an average molecular weight of 2,000,000 (Aladdin, Shanghai, China) was chosen for the preparation of the solutions. PEO fibers were electrospun using 3%-8% (w/w) concentrations of PEO in deionized water with 4 h stirring at 20˝C. The ground collector
doi:10.3390/polym7081471 fatcat:pdpdmhnbprhf3escmspnmyj2lm