School of Mechanical Engineering Asaf Asher

School of Mechanical Engineering Seminar
Wednesday, November 29, 2017 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Cold Forming of Shallow Spherical Micro Caps by Nano Imprinting

Asaf Asher

MSc. student of Prof. Slava Krylov

The seminar will be given in Hebrew

Many micro- and nanoelectromechanical (MEMS/NEMS) structures are distinguished by bistability, which manifests itself as the coexistence of two or more equilibria under the same loading. Applications include electrical and optical switches, sensors, non-volatile memories, micro-pumps, micro-resonators and deformable mirrors. While beam-type bistable micro structures were intensively investigated much less attention was paid to two-dimensional structures such as initially curved plates and shells (caps). One of the reasons is that fabrication of these devices is challenging. Lithography-based processes commonly used in MEMS are essentially planar and are not suitable for fabrication of cap-like structures.

In this work we explore cold forming techniques for fabrication of shallow micro caps. While multiple variations of this process were used at the macro scale, much less works reported the implementation of this technique in MEMS. In the framework of the fabrication process used in our work, a layer of Al or Cu is deposited on top of a Si wafer. Sputtering is implemented for the creation of a thin seed layer, followed by electrodeposition used to increase the layer thickness to a desired value. Next, an opening in the Si substrate is created by means of deep reactive ion etching (DRIE).  Finally, the forming process is performed using nano-imprinting lithography tool. We discuss suitability of different structural materials, deposition methods and stamping techniques for the formation of non-planar micro structures. Compact reduced order models are used for the evaluation of the design parameters. Prior to forming, residual stress of the thin suspended membranes is estimated using a resonance method, by means of comparison of the measured natural frequencies of the device with the model predictions. The bistablity of the shallow caps is demonstrated experimentally.