# Investigation of the Influence of Sublayer Thickness on Pairing of Metallic MEMS Shutter Blades
## 5 Summary and Outlook  
An investigation has been performed on the geometrical changes in the freestanding and 3D self-assembled paired shutter blades due the influence of changing the thickness of the metal stack building system of the shutters. The investigation reveals the nonlinearity and dynamics of the process, as well as its complexity. For metallic MEMS shutter blades with dimensions of 150 \(\times\) 400 \(\upmu\)m\({}^{2}\), the freestanding shutter blades have been analysed, and a technological processing window for 3D self-assembling pairing shutter blades was identified for the highest Al layer thickness \(d_{\text{Al2}}\) range of between 70 and 88 nm. The influence of the thickness changes has been observed in the geometrical shape changes for both the unpaired and paired shutter blades. The main results are presented in measurements of RoCs for the unpaired shutters, revealing a decreasing trend with a decaying \(d_{\text{Al2}}\) and a decreasing measure of eccentricity for the paired shutters, thereby showing the influence of pairing on the geometry of the shutters. The RoC of the unpaired shutters ranges between 17 and 79 \(\upmu\)m, and the eccentricity of the paired shutters is between 0.35 and 0.67. The paired shutters have been categorised into three different pairing scenarios with respective overlapping lengths ranging between 8 \(\upmu\)m and 31 \(\upmu\)m. For 3D self-assembly with the tightest attachment due to a maximum overlapping area of the shutter blades, the following optimum parameters have been identified: the highest Al layer thickness of \(d_{\text{Al2}}\) of between 80 and 88 nm and an RoC of between 40 and 60 nm. It has been noticed that once the shutter blades are paired, they can only be reopened with massive effort, e.g., an electrostatic actuation of \(>\)100 Volts [16]. Morevoer, ongoing studies with variable FIB trenches show that a threshold area is necessary to keep them attached using the Casimir force. Additionally, roughness studies in the overlapping region of the shutter blades are currently under work, and they will be published in a forthcoming publication. In terms of the future of that field, various applications can be considered: (a) Particle transport in magnetic stray field tubes [28; 32] for mass transport and sensorics. The Yin and Yang shape is superior to the circular diameter used in [28], and it introduces additional attractive research fields. (b) Shock absorbers for mobile systems. (c) Lightweight construction for material resource efficiency and weight reduction in macro and micro fields. Other applications are, e.g., in the fields of buildings and mobile systems, such as planes, cars, and drones. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13031538/s1](https://www.mdpi.com/article/10.3390/app13031538/s1)]([https://www.mdpi.com/article/10.3390/app13031538/s1](https://www.mdpi.com/article/10.3390/app13031538/s1)), Figure S1: SEM micrographs of fabricated micro-shutters with different thicknesses of the top Al layer \(d_{\mathrm{Al2}}\): (a) Sample with \(d_{\mathrm{Al2}}=92\) nm, unpaired and curled with high radius of curvature, (b) Sample with \(d_{\mathrm{Al2}}=55\) nm, the shutter blade is rolled on itself, forming a tube, (c) Sample with \(d_{\mathrm{Al2}}=80\) nm, showing an unpaired microshutter and the third pairing scenario between two shutter blades, (d) Sample with \(d_{\mathrm{Al2}}=70\) nm, showing also the third pairing scenario and unpaired shutter blades behind, (e) Sample with \(d_{\mathrm{Al2}}=88\) nm, showing the first and second pairing scenario for neighbouring shutter blade rows, and (f) Sample with \(d_{\mathrm{Al2}}=88\) nm, showing an overview of homogeneous rows of 3D self-assembled paired shutters with the second pairing scenario; Figure S2: Image of the drying setup in real-time scale; side and top views; Figure S3: Represents a standard ellipse and the eccentricity, \(\varepsilon\), for a selection of different cases. For \(\varepsilon=0\) a circle is resulting.