Abstract— In this paper, real-time feedback control of a nov- el micro-machined 1-degree-of-freedom (1-DoF) thermal nano- positioner with on-chip electrothermal positioning sensors is presented. The actuation works based on thermal expansion of silicon beams. The sensing mechanism works based on the dif- ference between the electrical resistances of two electrically biased identical Silicon beams. The difference increases with displacement as the heat conductance of the sensor beams vary oppositely with position, resulting in different beam tempera- tures and resistances. The sensor pair is operated in a differen- tial way to reduce low-frequency drift. The nanopositioner has a nonlinear static input-output characteristic. An open-loop control system is first designed using polynomials that approx- imately compensate the nonlinear characteristics. It is experi- mentally shown that plant uncertainties and sensor drift result in unacceptable performance for open-loop control of the thermal nanopositioner. Hence, feedback control methods are necessary for accurate nanopositioning. A closed-loop feedback control system was then designed using a proportional-integral (PI) controller and the nonlinear compensator used for the open-loop control system. The closed-loop system provides ac- ceptable and robust tracking performance for a wide range of set point values. For triangular reference tracking, which is needed in raster-scanned SPM, the tracking performance of the closed-loop system is further improved by incorporating a suit- able pre-filter. Index Terms-Thermal actuation, thermal position sensing, micro- electromechanical system (MEMS), nanopositioning, feedback control. I. INTRODUCTION igh precision nanopositioners have been used exten- sively in many applications such as scanning probe microscopy (SPM) [1], atomic force microscopy (AFM) [2], and emerging ultrahigh density probe storage system [3, 4]. Although macro-scale nanopositioners can achieve nanome- ter-scale positioning resolution and accuracy, they are rela- tively large and expensive [5, 6]. Microelectromechanical System (MEMS) nanopositioners have attracted increasing research interest recently due to their small size, low cost, Manuscript received September 28, 2010. This research was funded by Australian Research Council (ARC) discovery grant- DP0774287. Y.Zhu is with the School of Engineering, Griffith University, Australia (email: y.zhu@griffith.edu.au). A.Bazaei, S.O.R.Moheimani, and M.R.Yuce are with the School of Elec- trical Engineering and Computer Science, the University of Newcastle, Australia (email: {ali.bazaei, reza.moheimani, mehmet.yuce} @newcastle.edu.au). and highly parallel nanoscale manipulation and assembly strategies [7]. Closed-loop feedback control of the position- ers is highly desirable if a high degree of displacement pre- cision is required, and such a control system needs an accu- rate source of position information [8]. However, many of the MEMS nanopositioners reported in the literature have no on-chip sensors due to the restrictions associated with mi- cro-fabrication processes [9]. Thus, the in-plane movements are often measured by laser reflectance microscopes [10, 11] or optical microscopes [12], making the footprint of the whole system fairly large. There are several exceptions in the literature, for example, an embedded on-chip capacitive displacement sensor was integrated in a thermally actuated positioner in [13]. Nevertheless, only open-loop results were obtained, and a complex fabrication process was required for electrical insulation between electrical heating and sens- ing circuits. Recently, a thermal sensing scheme was used in a probe-based storage device [14]. Micro-heaters were used to measure the motion of a MEMS micro-scanner with reso- lution of less than 1 nm. Compared to a comb capacitive sensor, a thermal sensor is more compact and can be easily integrated with actuators in a MEMS device. In [15, 16], off-chip electromagnetic coil actuators were adopted for scanner actuation, and a complex mass-balanced structure was designed for vibration resistance purposes. In this paper, a novel electrothermal position sensor is in- tegrated with a thermal actuator in the same MEMS chip without the need for inclusion of extra electrical insulation fabrication process as reported in [13], or assembling two chips as reported in [15]. Compared to other MEMS actua- tion mechanisms, the thermal actuators have advantages of low voltage operation, large forces, and a high vibration resistance due to their stiff structures [17]. A MEMS device with integrated electrothermal actuation and sensing has been micro-fabricated in a bulk silicon process. To reduce the low frequency thermal drift, the sensors are operated in a pair and measured by a differential circuitry. The on-chip displacement sensing enables a feedback control capability. A model of the positioner is derived and a proportional- integral (PI) feedback controller is implemented digitally in a dSPACE rapid prototyping system to investigate the closed-loop performance of the positioner. Open-loop and closed-loop step displacement tracking were investigated. The closed-loop step response results show a positioning resolution of 7.9 nm and a time constant of 1.6 ms, while the Design, Prototyping, Modeling and Control of a MEMS Nanopositioning Stage Y. Zhu, Member, IEEE, A. Bazaei, S. O. R. Moheimani, Fellow, IEEE, and M. R. Yuce, Senior Mem- ber, IEEE H 2011 American Control Conference on O'Farrell Street, San Francisco, CA, USA June 29 - July 01, 2011 978-1-4577-0079-8/11/$26.00 ©2011 AACC 2278