A New Approach to Capacitive Sensing: Repulsive Sensors

项目目标简介：本研究旨在设计一种新的电容传感方法，并证明其在MEMS麦克风中的有效性。摘要：非技术助听器是老年人提高生活质量的有效工具。微型麦克风是助听器的关键部件，其声学性能决定了助听器在嘈杂环境中帮助听障人士交流的有效性。微机电系统（MEMS）麦克风由于其小巧的外形以及与大批量制造工艺的兼容性，已经发展成为手机等便携式电子设备中微型麦克风的主导市场。虽然MEMS麦克风有潜力为助听器提供显着的性能改进，但它们通常还没有表现出足够的性能来满足这种要求苛刻的应用。提出的研究目标是更好地利用MEMS技术，使高性能MEMS麦克风的设计发生革命性的变化。如果这项研究成功，将为助听器带来更灵敏的MEMS麦克风，并将对听障人士的生活产生巨大影响。MEMS麦克风的噪声性能将得到重大改善，可以帮助老年人更好地倾听。利用静电斥力手指进行电容传感是一种新颖的概念，它可以改变许多应用中由于传统平行板传感器的拉入不稳定性而导致的功能限制。自1916年发明电容式麦克风以来，拉入电压的限制大大降低了这些设备在噪声性能和灵敏度方面的功能。我们建议使用一种基于斥力的微机电系统（MEMS）电容传感机制，与传统的电容传感器不同，它不受拉入电压的影响。这种方法允许显著增加偏置电压，这将大大提高麦克风的信噪比和电灵敏度。本文所研究的MEMS麦克风由一个硅膜片组成，在声压下围绕一个轴旋转。膜片包含许多电容传感器单元，它们的电容变化在前置放大器中转换为电压。一个传感器单元由一个可移动的手指在一个垂直对齐的固定手指上，旁边是一个不对齐的固定手指。当在对齐和未对齐的手指中产生电位差时，在活动手指上产生不对称电场，产生排斥力，将其推离基底。我们的初步研究表明，单元传感器单元的初始间隙可以设计为使活动手指上的力保持排斥性，从而防止活动手指在基板上塌陷（拉入）。由于动指上电场的不对称分布，使得电容量与机械位移之间存在复杂的耦合关系。因此，为了获得对耦合系统行为的基本理解，我们将创建电容式MEMS传感器的分析和数值模型。利用模型仿真，我们将设计出所需灵敏度的传感器。使用微加工技术，我们将建立传感器，并使用激光多普勒振动计表征其行为。将传感器与前置放大器电路集成后，我们将在消声室中测试系统，以验证传感器提高了麦克风的性能和灵敏度。

Proposal Title: A New Approach to Capacitive Sensing: Repulsive SensorsBrief Description of Project Goals: This research aims to devise a new approach to capacitive sensing and to demonstrate its effectiveness in MEMS microphones.Abstract:Nontechnical Hearing aids are useful tools an aging population can use to improve their quality of life. Miniature microphones are a key component in hearing aids and their acoustic performance determines the effectiveness of hearing aids in helping the hearing impaired communicate in noisy environments. Micro-Electro-Mechanical Systems (MEMS) microphones have grown to dominate the market for miniature microphones in portable electronic devices such as cell phones due to their small form factor as well as their compatibility with high-volume manufacturing processes. While MEMS microphones have the potential of providing significant performance improvements in hearing aids, they have generally not yet demonstrated sufficient performance for this demanding application. A goal of the proposed research is to take better advantage of MEMS technology to enable a revolutionary change in the design of high-performance MEMS microphones. If successful, this research will lead to more sensitive MEMS microphones for hearing aids and will have a tremendous impact on the lives of hearing impaired. Noise performance of the MEMS microphone will be the major improvement that can help the aging population hear better.Technical Capacitive sensing using electrostatic repulsive fingers is a novel concept that can transform many applications suffering from limited functionality due to the pull-in instability of conventional parallel plate sensors. Since the invention of capacitive microphones in 1916, the limitation of pull-in voltage has significantly diminished the functionality of these devices in terms of noise performance and sensitivity. We propose using a Micro-Electro-Mechanical Systems (MEMS) capacitive sensing mechanism based on the repulsive force that, unlike conventional capacitive sensors, does not suffer from pull-in voltage. This approach allows significantly increased bias voltages that will substantially improve the signal-to-noise ratio and electrical sensitivity of microphones. The MEMS microphone examined here is composed of a silicon diaphragm that rotates about an axis upon exposure to sound pressure. The diaphragm incorporates a number of capacitive sensor unit cells, and their change in capacitance converts to a voltage in the preamplifier. A unit sensor cell consists of a movable finger above a vertically aligned fixed finger next to an unaligned fixed finger. When potential differences are made in the aligned and unaligned fingers, an asymmetric electric field is created on the movable finger, generating a repulsive force that pushes it away from the substrate. Our preliminary studies show that the initial gap of the unit sensor cell can be designed so the force on the movable finger remains repulsive, which prevents the collapse of the movable fingers on the substrate (pull-in). The asymmetric electric field distribution on the movable finger causes a complicated coupled relationship between the capacitance and mechanical displacement. Therefore, to gain a fundamental understanding of the coupled system behavior, we will create analytical and numerical models of the capacitive MEMS sensor. Using the model simulations, we will design the sensor for desired sensitivity. Using microfabrication techniques, we will build the sensor and characterize its behavior using a Laser Doppler Vibrometer. After integrating the sensor with preamplifier circuitry, we will test the system in an anechoic chamber to verify the sensor improves the performance and sensitivity of microphones.