Control of a Novel 2-DoF MEMS Nanopositioner With Electrothermal Actuation and Sensing

This paper presents the full characterization, modeling, and control of a 2-degrees-of-freedom microelectromechanical systems (MEMS) nanopositioner with fully integrated electrothermal actuators and sensors. Made from nickel Z-shaped beams, the actuators are able to move the device's stage in positive and negative directions (contrary to classical V-shaped electrothermal actuators) and along two axes (x and y). The integrated electrothermal sensors are based on polysilicon resistors, which are heated via Joule heating due to an applied electrical bias voltage. The stage displacement is effectively measured by variations in their resistance, which is dependent on the position of the stage. The characterization tests carried out show that the MEMS nanopositioner can achieve a range of displacement in excess of ±5 μm for each of the x and y axes, with a response time better than 300 ms. A control scheme based on the combination of feedforward and internal model control-feedback is constructed to enhance the general performance of the MEMS device, and in particular to reject the cross-coupling between the two axes and to enhance the accuracy and the response time. The experimental results demonstrate the efficiency of the proposed scheme and demonstrate the suitability of the designed device for nanopositioning applications.