Article Highlight | 6-May-2024

High-sensitivity force sensors based on novel materials

Advanced Devices & Instrumentation

Due to limitations in the performance of traditional materials, force sensors face challenges in terms of miniaturization and low sensitivity. With advancements in materials science and micro-nano fabrication technologies, novel force sensors based on the unique structures of three-dimensional materials, two-dimensional materials, and one-dimensional materials have emerged as a solution to address these issues. Consequently, this field has been increasingly explored and researched. The article provides a comprehensive and detailed summary of high-sensitivity force sensors based on new materials. It begins by introducing various types of novel materials and the criteria for material selection in force sensors. The article then outlines device structures and fabrication processes, encompassing the preparation of low-dimensional materials, sensor electrode fabrication, and methods for transferring low-dimensional materials. Subsequently, the article places emphasis on summarizing the key characteristics of force sensors, along with the testing principles, equipment setups, and pros and cons of electrical, optical, and direct-motion measurement methods. Furthermore, the article categorically presents a variety of applications for force sensors, including mass sensors, pressure sensors, flexible tactile sensors, as well as other specialized applications represented by accelerometers and torsion balances. Finally, the article concludes by summarizing the challenges and future opportunities in this cutting-edge field.

There are still numerous challenges and issues in the field of novel force sensors. Firstly, the compatibility of force sensor processes with CMOS integrated circuit processes presents a major challenge for achieving large-scale production and widespread applications. As high-performance force sensors often employ suspended structures, ensuring a smooth transition from laboratory-scale to fabrication with high yield and performance is crucial. Among these challenges, achieving high-quality wafer-level growth of low-dimensional materials remains a notable hurdle. Additionally, due to the demanding growth conditions of low-dimensional materials, directly growing them on pre-fabricated sensor electrodes can result in electrode damage. Therefore, developing methods for wafer-level transfer of low-dimensional materials is also an urgent issue to address. Currently, methods for wafer-level electrode transfer have been developed, which can prevent damage to two-dimensional materials, significantly enhancing device quality and yield. Secondly, while force sensors exhibit exceptional performance, the complexity of measurement equipment hinders the integration of the entire sensing system. Achieving the integration of measurement equipment poses a challenge for novel force sensors. Developing advanced electrical testing methods to replace optical testing would facilitate the integration of testing systems.Thirdly, expanding the applications of force sensors and further enhancing sensor accuracy remain challenges. Incorporating heterostructures of two-dimensional materials, such as adding a layer of specific-functionalized two-dimensional materials to the existing structure, introduces new physical parameters to the entire sensor system or enhances its performance, enabling new applications. Additionally, encapsulating special materials on or attaching specific loads to CNTs can expand the applications of CNT-based force sensors and provide a deeper understanding of physical phenomena.

Currently, force sensors based on common 3D materials have been widely studied. However, due to limitations in the physical properties of these materials, it is challenging to improve the performance of sensors while achieving device miniaturization. With the advancement of MEMS/NEMS technology, especially the invention of new fabrication processes and designs, the use of novel 3D material structures or force sensors based on low-dimensional materials has become a captivating focal point of research. These materials naturally possess large surface-to-volume ratios and exhibit unique electrical, mechanical, and optical properties, enabling significant performance enhancements while reducing device sizes. Despite many challenges still present in this field, it is believed that in the foreseeable future, force sensors based on novel materials will become an integral part of everyone's life.

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