Research On Sacrificial Layer-assisted Nanoscale Transfer Printing Method

Transfer printing is an emerging deterministic assembly technique.According to requirements,transfer printing can assembly micro-and nanomaterials into two or three-dimensional well-ordered structures to form micro-and nanodevices.Transfer printing has many advantages such as high compatibility,operate at room temperature and is of great interest for flexible electronics.While varieties of transfer printing methods have been developed,the resolution of most of those is at micrometer scale.Although a few methods allow the transfer of nanoscale patterns,the process is too complicated and poor universality,which greatly limits the application of micro-and nanodevices in flexible electronics.In this paper,a sacrificial layer-assisted micro-and nanoscale transfer printing method was put forward for the first time.The paper introduced nanoscale transfer printing method in detail.First,a sacrificial layer was deposited on the surface of the donor substrate and the ink was fabricated on the sacrificial layer.Second,a stamp was gently pressed onto the surface of the ink and the sacrificial layer.Third,the stamp was peeled off,the sacrificial layer and ink were transferred to the stamp.Finally,the sacrificial layer was chemically etched away.Using this method,47-nm-wide Au patterns can be easily transferred from silicon substrate using copper as a sacrificial layer.The method has two effects in transfer printing.First,it could develop the transfer resolution obviously.To understand the mechanism of the sacrificial layer during transfer printing process,the energy release rate theory was analyzed in the paper.With the decrease of the feature size of the ink,the stamp only partially contact with the ink,and the ink/donor interface continues to increase until G_{ink/substrate} is much larger than G_stamp/ink and the adhesion between the stamp and the ink is not large enough to pick up the ink when without sacrificial layer.The presence of sacrificial layer makes Gsacrificial layer/stamp is much larger than Gsubstrate/sacrificial layer,so the ink's feature size is not limited.Second,the presence of the sacrificial layer makes the ink remarkably obviate cracks during transfer printing process because of the bending stress.The presence of sacrificial layer makes the ink move close to the mechanical neutral plane,remarkably decreases the stretching strain.At the same time,a variety of complex structures and flexible LED circuits were fabricated and transferred,and no fracture was occurred,proving that the sacrificial layer could obviate cracks of the ink.To further demonstrate the versatility of transfer printing method based on sacrificial layer report here,various structure was fabricated and transferred on different donor substrates.Firstly,the single-layer silicon dioxide structure was transferred using copper as sacrificial layer.Secondly,three layers Au-SiNx-Au capacitors were fabricated by photolithography and transfer printing successfully.The capacitors were tested by I-V characters,showing it excellent performance.Finally,graphene and silver ink fabricated by electrohydrodynamic jet printing were successfully transferred by using gold as sacrificial layer,demonstrating the great potential applications of the method in the field of flexible electronics.