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We present a comprehensive study of the design, modeling, and characterization of an on-chip piezoresistive displacement sensor. The design is based on the bulk piezoresistivity of tilted clamped-guided beams without the need for additional steps to generate doped regions. The sensor is implemented in a one-degree-of-freedom microelectromechanical system (MEMS) nanopositioner, where the beams also function as the suspension system. A standard MEMS fabrication process is used to realize the device on single-crystalline silicon as the structural material. The beams are oppositely tilted to develop tensile and compressive axial forces during stage movement, creating a differential sensing feature. An analytical approach is proposed for modeling and design of the tilted clamped-guided beams. The linearity of the sensor in the differential configuration is investigated analytically. The static, dynamic, and noise characteristics of the sensor are presented, followed by a model-based investigation of the measured dynamic feedthrough. [2015-0030] [ABSTRACT FROM PUBLISHER]

We report the design of a two-degree-of-freedom microelectromechanical systems nanopositioner for on-chip atomic force microscopy (AFM). The device is fabricated using a silicon-on-insulator-based process to function as the scanning stage of a miniaturized AFM. It is a highly resonant system with its lateral resonance frequency at ~850 Hz. The incorporated electrostatic actuators achieve a travel range of 16 μm in each direction. Lateral displacements of the scan table are measured using a pair of electrothermal position sensors. These sensors are used, together with a positive position feedback controller, in a feedback loop, to damp the highly resonant dynamics of the stage. The feedback controlled nanopositioner is used, successfully, to generate high-quality AFM images at scan rates as fast as 100 Hz. [ABSTRACT FROM AUTHOR]

The sensitivity of an electrothermal displacement sensor increases with its temperature, whereas a higher temperature range leads to higher thermal noise level, which imposes a tradeoff on the sensor's achievable resolution. We have developed a multiple sensor displacement measurement technique on a 1-degree-of-freedom silicon-on-insulator microelectromechanical systems nanopositioner that mitigates the mentioned tradeoff. To obtain maximum improvement, it is necessary to supply equal power to all of the sensors to ensure equal sensitivity. By combining three identical sensors, we have successfully achieved a 4-dB improvement in signal-to-noise ratio, which is in a good agreement with the averaging theory. Experiments show that the displacement resolution is improved from 0.3 to 0.15 nm/ √(Hz) in the prototype nanopositioner. Furthermore, improvement is possible by increasing the number of sensors around the stage. [ABSTRACT FROM AUTHOR]

We report a novel piezoresistive microelectromechanical system (MEMS) differential displacement sensing technique with a minimal footprint realized through a standard MEMS fabrication process, whereby no additional doping is required to build the piezoresistors. The design is based on configuring a pair of suspension beams attached to a movable stage so that they experience opposite axial forces when the stage moves. The resulting difference between the beam resistances is transduced into a sensor output voltage using a halfbridge readout circuit and differential amplifier. Compared with a single piezoresistive flexure sensor, the design approximately achieves 2, 22, and 200 times improvement in sensitivity, linearity, and resolution, respectively, with 1.5-nm resolution over a large travel range exceeding 12 μm. [ABSTRACT FROM AUTHOR]