Laser-assisted direct ink writing of planar and 3D metal architectures

Abstract

The ability to pattern planar and freestanding 3D metallic architectures at the microscale would enable myriad applications, including flexible electronics, displays, sensors, and electrically small antennas. A 3D printing method is introduced that combines direct ink writing with a focused laser that locally anneals printed metallic features "on-the-fly." To optimize the nozzle-to-laser separation distance, the heat transfer along the printed silver wire is modeled as a function of printing speed, laser intensity, and pulse duration. Laser-assisted direct ink writing is used to pattern highly conductive, ductile metallic interconnects, springs, and freestanding spiral architectures on flexible and rigid substrates. T he ability to create planar and freestanding 3D metal structures on demand at the microscale would enable myriad applications, including electronics (1-8), microelectromechanical systems (MEMS) (9, 10), metamaterials (11-13), and biomedical devices (14-16). For example, many electronic devices, such as inductors and antennas (4, 7), operate more efficiently in 3D form. However, that format is not well suited to standard photolithographic techniques. A onestep process for directly writing conductive, ductile metal wires and complex 3D architectures, such as freestanding spiral motifs, onto low-cost plastic and rigid substrates would enable highperformance, customizable electronic and other devices to be manufactured in a cost-effective and space-efficient manner. To date, several printing approaches have been developed to directly deposit conductive features, including roll-to-roll (17-19), inkjet printing (20, 21), meniscus printing (8), and direct ink writing (DIW) (1,22). Although DIW has demonstrated spanning linear traces or short arcs printed out-of-plane, only meniscus-based electrodeposition printing has been used to generate freestanding 3D solid metal structures in arbitrary geometries. However, its ultralow print speed (<1 μm/s) coupled with the need for a conductive substrate have limited its widespread adoption (8).Here, we introduce laser-assisted direct ink writing (laser-DIW), which combines printing of concentrated silver nanoparticle inks with focused infrared laser annealing to rapidly create high conductivity, ductile metallic wires and 3D architectures "on-the-fly" in a one-step, additive process. Laser-DIW offers three key advantages over other 3D printing techniques. First, by combining patterning and annealing in a single step, the printed metallic features exhibit the requisite mechanical properties needed to precisely fabricate arbitrary objects in midair, enabling complex curvilinear structures to be generated without the need for support material. Due to localized annealing, such features can be printed on low-cost plastic substrates, such as poly(ethylene terphthalate) (PET). Finally, the patterned features exhibit high electrical conductivity approaching that of bulk silver. Results and DiscussionDuring laser-DIW, an 808-nm IR laser is focused to a 100-μm spot adjacent ...

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

“…After debinding (30 minutes at 600°C) and sintering (2 hours at 1600°C), the green parts of 57 %TD yielded final products of 98 %TD with a flexural strength of 363.5 MPa. Recently, laser sintering has been combined with direct ink printing to produce complex shaped 3D metal structures . The technique could be readily adapted to producing ceramic materials.…”

3D printed optics with nanometer scale surface roughness

“…Complex to fabricate optical devices [8][9][10] and systems can similarly benefit from the ability of 3D printing to create low-cost structures of nearly arbitrary shape 11,12 . Optical designs are often complicated by the need to conform to shape constraints imposed by fabrication technologies, e.g., spherically polished lenses, flat imagers, and shapes that can be efficiently molded and cast.…”

Self-peeling of impacting droplets

“…In many applications, avoiding adhesion of impacting droplets around designated target surfaces can be as crucial as bonding onto them to minimize waste or cleaning. These insights have broad applicability in processes ranging from thermal spraying 12,15 and additive manufacturing [16][17][18][19] to extreme ultraviolet lithography 20 .…”

“…In many applications, avoiding adhesion of impacting droplets around designated target surfaces can be as crucial as bonding onto them to minimize waste or cleaning. These insights have broad applicability in processes ranging from thermal spraying 12,15 and additive manufacturing [16][17][18][19] to extreme ultraviolet lithography 20 .We release molten tin droplets of millimetric size (R = 0.95 ± 0.03 mm) from a nozzle, such that they hit a target surface with moderate velocity (v = 1.9 ± 0.1 m s −1 , see Methods). Figure 1a shows a comparison between the deposition and subsequent solidification of a droplet (initial temperature T d,0 = 240 • C) onto a silicon wafer (top) and a glass slide with ∼200 times lower thermal conductivity (bottom).…”