FEATURE MICROFABRICATION
Additive manufacture for microfabricated features
The micro-fabrication facility based in the School of Engineering at Durham University undertook a project to explore additive manufacturing for microfabricated features. Amy Tate reports
C
ommonly, fabrication of micro and nanostructures uses expensive
equipment sets, which tend to use some form of lithographic technique. Recently the market has developed such that there is the feasibility to use additive manufacturing technologies in the home environment to produce complex 3D features. The micro-fabrication facility based in the School of Engineering at Durham University are specialists in the development of processes. As part of an EPSRC funded project, engineers at the University have investigated how additive manufacture could fit into operations of a facility and work alongside more standard techniques. The work was structured into two main streams, the first to look at the use of bespoke equipment and the ultimate potential of this in terms of general fabrication, and the second to look at more generic printing and determine how far this technology was away in terms of resolution and feature structures from both the bespoke equipment and general lithography. Examination of high end equipment
was undertaken with two partners. The first partner (Optomec), make use of an aerosol jet technology to print structures. These allow production of features down to the 10s of microns produced out of a variety of both conductive and non- conductive materials. Using this technique as well as planer layers, it is possible to produce forms of 3D structures, which are perpendicular to the surface, which can be used as interconnects or active component in devices. The second partner (Nanoscribe) use a two—photon polymerisation (2pp) process to produce sub-micron structures as shown by the big ben structure with sub-micron features. These can be MEMS based structures or functional surfaces as part of a larger device. Example images can be seen in figure 1. Clearly high end bespoke equipment can offer an alternative to standard lithography which is in the micron regime. Figure 1a shows an aerosol jet
6 AUTUMN 2017 | MICROMATTERS Figure 1a:
Figure 1b: Figure 2a:
Figure 2b:
500micron tracks whilst figure 1b shows a 2pp microscale model of Big Ben. A series of test samples with a variety
of feature sizes were produced using conventional 3D printed technologies. It was found that depending upon the type of 3D printing did depend on the output quality of the structures. There was significant variation in minimum achieved features. Also, the surface structure was found to vary significantly showing rounding of features and significant surface topography. A typical structure can be seen in figure 2.
Figure 1a: Aerosol jet 500 micron tracks 1b: 2pp microscale model of Big Ben
Figure 2:
SEM imaging of typical 3D printed test
structures (left Direct Light projection/right Stereo Lithography)
As part of a collaborative work with its THz measurement group the Uni has looked at how the structures of a printed surface interact with the beam. These structures are a corrugated structure (of the order of 100microns in size). Examination of them showed that rather than well-defined vertical sidewalls, the structures tended to be more triangular in shape. It was observed the THz radiation couples from free space to these structures without the need of the commonly used prisms or knife-edge scattering to bridge the momentum gap from free space to the bound spoof Surface Plasmon Polaritons (SPPs) on the surface. While the SPPs are well confined to the surface the propagation lengths are only in the order of a few free-space wavelengths. Overall losses of at least 90% across a 3mm long structure were measured. Improvements in the printing quality will enable structures with a higher surface quality in the future where only a small defect-rich area is used to couple the free-space radiation and launch the SPPs into a high quality and low-loss structure with longer propagation lengths. Clearly there is limit of the order of several 100 microns currently for 3D printed structures with varying error in terms of feature size dependent on deposition method and material. However, as demonstrated there can be applications using this technology. The engineers at the University believe that simple surface structures (as shown by the THz results) or large scale features (for instance microfluidic devices), may be possible using this technology. However, there needs to be further collaborative work between equipment fabricator, material providers and end users in order to push this further. Bespoke systems currently bridge this gap and allow development of certain applications, however improvement in off the shelf systems would truly revolutionise the micro-fabrication. The group would like to thank EPSRC for funding of the project, Nanoscribe and Optomec for donation of samples and Members of the Department of Physics and School of Engineering at Durham Uni for their part in the work.
Durham University
www.dur.ac.uk/micro.fab 0191 334 1728
/ MICROMATTERS
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28
