Development of Flexible MEMS Pressure Sensors using Hierarchical Surface Structures for Texture Roughness Identification

Description

Wearable skin sensors have attracted significant attention due to their potential applications in robotics industry as they would allow intelligent machines or robots to have a sensation of touch like human beings. However, most of the reported skin sensors, mostly silicon-based MEMS, require complicated and costly fabrication procedures, and are too rigid to be wearable. In this project, we will develop a wearable skin sensor for measuring touch pressure for robotic skin applications using a simple, scalable, and cost-effective approach. We propose to create a novel hierarchically-structured thin-film-based piezoresistive skin sensor that could be directly conformed onto different geometric surfaces of robots to sense surface textures. The proposed hierarchically-structured piezoresistive layer is better than a conventional flat thin film structure because of its larger surface area and high density of distributed receptors, which is essential to sense surface textures. In addition, by judicious design and choice of materials, the mechanical properties (i.e. flexibility) and stability of the hierarchically-structured piezoresistive layer could be optimized, allowing easy fabrication and adherence of the sensor on surfaces of different shapes. Our ultimate goal is to develop a wearable sensor that mimics the human fingertip sensations, i.e., generating friction while sliding on a surface of test objects and sensing texture by measuring surface roughness/smoothness. The proposed sensor will detect changes in frictional force induced by dynamic interaction between the outer microstructure of the sensor and the sensing material surface. As different surface texture would interact with the sensor differently, the different signal patterns generated can be used to “recognize” the texture roughness. Specifically, our approach includes (i) development of composite materials for flexible, wearable, and stable piezoresistive sensor layer consisting of a graphite/polydimethylsiloxane composite (GPC) and microstructure engineering of polydimethylsiloxane (PDMS) substrate which mimics the micro-patterns of fingertip skin, (ii) simple and high-yield fabrication by micro-droplet printing of the GPC resistive layer into an array of sensors and (iii) hierarchical microstructure engineering of the GPC resistive layer so as to achieve large surface area for enhanced sensitivity; 4) fundamental understanding of skin sensor working mechanism on sensing various textures, the so-called “robotic sense” phenomena. Successful completion of these key objectives should lead to a new process for “structural skin sensor” fabrication using composite materials through a simple technique with high yield and low cost. In order to successfully complete these objectives, we will address the following key technical challenges in a span of three years: The following key technical challenges will be addressed as milestones in the next 3 years in order to successfully complete the project: (i) parametric investigation of micro-droplet printing of uniform GPC (Graphite/PDMS Composite) resistive layer array possessing high stability, mechanical flexibility, and durability over a wafer-scale area for quality control; (ii) comprehensive characterization of the skin sensors, including their sensitivity, limit of detection (LOD), response time, operational stability, and dynamic frequency response; (iii) quantitative analysis of the skin sensor performance under various pressure, temperature, humidity and mechanical properties of the pressure sensors under various bending and twisting angles; (iv) theoretical and experimental analysis of the temperature-strain relationship of the GPC-based sensors in order to compensate the temperature-dependent output of the sensors; (v) elucidate the fundamental mechanisms of microstructured sensors in sensing surface textures to explore possible applications of the fingertip skin sensors.We strongly believe that our proposed project will lead to the development of practical devices for robotic fingers for sensing pressure and texture roughness. Hong Kong and Mainland China have several small-scale industries looking for automation using robotics in which skin sensors would enable robots to feel and sense, development of which is the main scope of this project.