Fabrication and characterization of diamond-like carbon/Ni bimorph normally closed microcages

Normally closed microcages based on highly compressively stressed diamond-like carbon (DLC) and electroplated Ni bimorph structures have been simulated, fabricated and characterized. Finite-element and analytical models were used to simulate the device performance. It was found that the radius of curvature of the bimorph layer can be adjusted by varying the DLC film stress, the total layer thickness and the thickness ratio of the DLC to Ni layers. The angular deflection of the bimorph structures can also be adjusted by varying the finger length. The radius of curvature of the microcage was in the range of 18-50 mu m, suitable for capturing and confining micro-objects with sizes of 20-100 mu m. The operation of this type of device is very efficient due to the large difference in thermal expansion coefficients of the DLC and the Ni layers. Electrical tests have shown that these microcages can be opened by similar to 90 utilizing a power smaller than 20 mW. The operating temperatures of the devices under various pulsed currents were extracted through the change in electrical resistance of the devices. The results showed that an average temperature in the range of 400-450 degrees C is needed to open this type of microcage by similar to 90, consistent with the results from analytical simulation and finite-element modelling.