Mohammed Zakriya, Elfadel Ibrahim Abe M, Rasras Mahmoud
Department of Electrical and Computer Engineering, New York University-Tandon School of Engineering, Brooklyn, NY 11201, USA.
Department of Electrical and Computer Engineering, Khalifa University, Abu Dhabi 54224, UAE.
Micromachines (Basel). 2018 Nov 16;9(11):602. doi: 10.3390/mi9110602.
With the continuous advancements in microelectromechanical systems (MEMS) fabrication technology, inertial sensors like accelerometers and gyroscopes can be designed and manufactured with smaller footprint and lower power consumption. In the literature, there are several reported accelerometer designs based on MEMS technology and utilizing various transductions like capacitive, piezoelectric, optical, thermal, among several others. In particular, capacitive accelerometers are the most popular and highly researched due to several advantages like high sensitivity, low noise, low temperature sensitivity, linearity, and small footprint. Accelerometers can be designed to sense acceleration in all the three directions (X, Y, and Z-axis). Single-axis accelerometers are the most common and are often integrated orthogonally and combined as multiple-degree-of-freedom (MDoF) packages for sensing acceleration in the three directions. This type of MDoF increases the overall device footprint and cost. It also causes calibration errors and may require expensive compensations. Another type of MDoF accelerometers is based on monolithic integration and is proving to be effective in solving the footprint and calibration problems. There are mainly two classes of such monolithic MDoF accelerometers, depending on the number of proof masses used. The first class uses multiple proof masses with the main advantage being zero calibration issues. The second class uses a single proof mass, which results in compact device with a reduced noise floor. The latter class, however, suffers from high cross-axis sensitivity. It also requires very innovative layout designs, owing to the complicated mechanical structures and electrical contact placement. The performance complications due to nonlinearity, post fabrication process, and readout electronics affects both classes of accelerometers. In order to effectively compare them, we have used metrics such as sensitivity per unit area and noise-area product. This paper is devoted to an in-depth review of monolithic multi-axis capacitive MEMS accelerometers, including a detailed analysis of recent advancements aimed at solving their problems such as size, noise floor, cross-axis sensitivity, and process aware modeling.
随着微机电系统（MEMS）制造技术的不断进步，诸如加速度计和陀螺仪之类的惯性传感器能够以更小的尺寸和更低的功耗进行设计和制造。在文献中，有若干基于MEMS技术并利用诸如电容式、压电式、光学式、热式等多种传感方式的加速度计设计报道。特别是，电容式加速度计因其具有高灵敏度、低噪声、低温度灵敏度、线性度以及小尺寸等诸多优点而最为流行且得到了广泛研究。加速度计可设计用于感测所有三个方向（X、Y和Z轴）的加速度。单轴加速度计最为常见，并且通常正交集成并组合为多自由度（MDoF）封装，以感测三个方向的加速度。这种类型的MDoF增加了整个器件的尺寸和成本。它还会导致校准误差，并且可能需要昂贵的补偿措施。另一类MDoF加速度计基于单片集成，并且已被证明在解决尺寸和校准问题方面是有效的。根据所使用的质量块数量，此类单片MDoF加速度计主要有两类。第一类使用多个质量块，其主要优点是不存在校准问题。第二类使用单个质量块，这使得器件紧凑且本底噪声降低。然而，后一类存在高交叉轴灵敏度问题。由于机械结构复杂和电接触布局，它还需要非常创新的版图设计。由非线性、制造后工艺以及读出电子学导致的性能复杂性影响了这两类加速度计。为了有效地比较它们，我们使用了诸如单位面积灵敏度和噪声 - 面积乘积等指标。本文致力于对单片多轴电容式MEMS加速度计进行深入综述，包括对旨在解决其尺寸、本底噪声、交叉轴灵敏度和工艺感知建模等问题的最新进展进行详细分析。
