Polysilicon Piezoresistive Tactile Sensor Array Fabricated by PolyMUMPs Process

This paper discusses the design, fabrication and testing of a 5x5 micromachined tactile sensor array for the detection of an extremely small force (micrometer-Newton range). Central contacting pads that are trampoline-shape suspended structures and sensor beams are formed using an anisotropic etching of silicon substrate of a MUMPs process chip. A piezoresistive layer of polysilicon embedded in sensor beams is used to detect the displacement of the suspended contacting pad. Each square tactile has dimension of 200 mum x 200 mum with 250 mum center-to-center spacing. The entire sensor area is 1.25 mm x 1.25 mm. The device was characterized under various normal force loads using weight microneedles. The individual sensor element shows the linear response to normal force with good repeatability.

I Introduction

One of mostly sensitive human perceptions is tactile perception. Good example of tactile perception is how we feel when our finger tip contact to the object. Micro-Electro-Mechanical Systems (MEMS) technologies have found the broad field in intelligent solid-state microsensors, the sensing devices that are batch-fabricated by micromachining techniques and integrated with electrical circuits on the same chip. A micromachined tactile sensor is a promising area in the field of physical MEMS sensors. It has a function similar to the surface of a human fingertip. The measurement and processing of a contact stress found useful in robotic dexterous manipulation applications. When a robot grasps object, information on contact, shear force and torque determination are needed for feedback control of robot. Other potential applications of this sensor would be such as sensing of organic tissue on a small scale at the end of catheter or on the fingers of an endoscopic-surgery telemanipulator [1]. Recently, various micromachined tactile sensors capable of measuring normal and shear stress are individually developed by many research groups [2], [3] but none of them are foundry-fabricated for potential low cost devices. In this paper, we present a novel piezoresistive tactile sensor array designed for measurement in medium-density sub-millimeter tactile sensing and fabricated by a commercial available Multi-Users MEMS Process (MUMPs) with bulk etching in post processing step.