Integrated Piezoresistive Force and Position Detection Sensors for Micro-Handling Applications

This paper presents two integrated piezoresistive sensors capable of detecting simultaneously both the contact force and the contact position of a micro-object in micro-handling applications. The first sensor detects the 1-D contact position in vertical direction along a contact surface. The second sensor extends the sensing principle and detects the contact position on a 2-D contact surface. The devices combine the outputs of two groups of piezoresistors in Wheatstone bridge configurations, allowing the computation of the contact force and the contact position. The sensors are fabricated with an IC-compatible process and can be integrated in micro-handling tools such as micro-grippers. The two devices are characterized by applying forces onto the contact surface at pre-defined positions. With an applied contact force ~ 1 mN, the first sensor has a force resolution of 1 μN and a vertical position detection accuracy of 2-3 μm. The estimated force range detectable is 3 mN and a sensitivity of 2.8 V/N is obtained with an effective supply voltage of 177 mV across the Wheatstone bridge. The second sensor has a force detection range up to 3 mN with a resolution of 20 μN under a measured noise of 30 μV. The theoretical spatial resolution is ~ 5μm in both x and y directions with a contact force of 1 mN. The devices are designed to handle micro-objects with sizes of 25-250 μm. The concept and the principle of the device are not limited to applications in micro-grippers and can be used in other micro-handling tools.