Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures, fabricated in MUMPs and SUMMiT processes, were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance, contrary to the effect predicted by linear models. In addition, tensile, compressive, and bending loads combine in their effects on resistance. The experimental data illustrate the inability of linear piezoresistance models to predict the piezoresistive trends of polysilicon in bending and combined loads, indicating the need for more complete nonlinear models appropriate for these loading conditions.

Many applications in microelectromechanical systems require physical actuation for implementation or operation. On-chip sensors would allow control of these actuators. This paper presents experimental evidence showing that a certain class of thermal actuators can be used simultaneously as an actuator and a sensor to control the actuator's force or displacement output. By measuring the current and voltage supplied to the actuator, a one-to-one correspondence is found between a given voltage and current and a measured displacement or force. This integrated sensor/actuator combination will lead to efficient on-chip control of motion for applications including microsurgery, biological cell handling, and optic positioning.[ 2007-0299]Index Terms-Microelectromechanical system (MEMS), piezoresistance, thermal actuator.

Many applications in microelectromechanical systems require physical actuation for implementation or operation. On-chip sensors would allow control of these actuators. This paper presents experimental evidence showing that a certain class of thermal actuators can be used simultaneously as an actuator and a sensor to control the actuator’s force or displacement output. By measuring the current and voltage supplied to the actuator, a one-to-one correspondence is found between a given voltage and current and a measured displacement or force. This truly integrated sensor/actuator combination will lead to efficient, on-chip control of motion for applications including microsurgery, biological cell handling, and optic positioning.

This paper presents the design, fabrication, and testing of a force sensor for integrated use with thermomechanical in-plane microactuators. The force sensor is designed to be integrated with the actuator and fabricated in the same batch fabrication process. This sensor uses the piezoresistive property of silicon as a sensing signal by directing the actuation force through two thin legs, producing a tensile stress. This tensile load produces a resistance change in the thin legs by the piezoresistive effect. The resistance change is linearly correlated with the applied force. The device presented was designed by considering both its piezoresistive sensitivity and outof-plane torsional stability. A design trade-off exists between these two objectives in that longer legs are more sensitive yet less stable. Fabrication of the sensor design was done using the MUMPs process. This paper presents experimental results from this device and a basic model for comparison with previously attained piezoresistive data. The results validate the concept of integral sensing using the piezoresistive property of silicon.

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