DESIGN AND MICROFABRICATION OF A CMOS-MEMS PIEZORESISTIVE ACCELEROMETER AND A NANO-NEWTON FORCE SENSOR

DESIGN AND MICROFABRICATION OF A CMOS-MEMS PIEZORESISTIVE ACCELEROMETER AND A NANO-NEWTON FORCE SENSOR by Mohd Haris Md Khir Adviser: Hongwei Qu, Ph.D. This thesis work consists of three aspects of research efforts: I. Design, fabrication, and characterization of a CMOS-MEMS piezoresistive accelerometer 2. Design, fabrication, and characterization of a CMOS-MEMS nano-Newton force sensor 3. Observer-based controller design of a nano-Newton force sensor actuator system A low-cost, high-sensitivity CMOS-MEMS piezoresistive accelerometer with large proof mass has been fabricated. Inherent CMOS polysilicon thin film was utilized as piezoresistive material and full Wheatstone bridge was constructed through easy wiring allowed by three metal layers in CMOS thin films. The device fabrication process consists of a standard CMOS process for sensor configuration and a deep reactive ion etching (DRIE) based post-CMOS microfabrication for MEMS structure release. Bulk single-crystal silicon (SCS) substrate was included in the proof mass to increase sensor sensitivity. Using a low operating power of 1.67 m W, the sensitivity was measured as 30.7 mV/g after amplification and 0.077 mV/g prior to amplification. With a total noise floor of 1.03 mg!-!Hz, the minimum detectable acceleration is found to be 32.0 mg for a bandwidth of I kHz which is sufficient for many applications. The second device investigated in this thesis work is a CMOS-MEMS capacitive force sensor capable ofnano-Newton out-of-plane force measurement. Sidewall and fringe capacitance formed by the multiple CMOS metal layers were utilized and fully differential sensing was enabled by common-centroid wiring of the sensing capacitors. Single-crystal silicon (SCS) is incorporated in the entire sensing element for robust structures and reliable sensor deployment in force measurement. A sensitivity of 8 m V /g prior to amplification was observed. With a total noise floor of 0.63 mg!-IHz, the minimum detection acceleration is found to be 19.8 mg, which is equivalent to a sensing force of 449 nN. This work also addresses the design and simulation of an observer-based nonlinear controller employed in a CMOS-MEMS nano-Newton force sensor actuator system. Measurement errors occur when there are in-plane movements of the probe tip; these errors can be controlled by the actuators incorporated within the sensor. Observerbased controller is necessitated in real-world control applications where not all the state variables are accessible for on-line measurements. V

Modal analysis and condition monitoring for an electric motor through MEMS accelerometers

Piezoelectric accelerometers are commonly employed for diagnosing machine faults, due to their accuracy. In the last few years, however, MEMS (Micro Electro-Mechanical Systems) accelerometers have attracted strong interest thanks to their low cost. In this work, a synchronous electric motor with an integrated MEMS sensor is studied and results are compared from both MEMS and piezoelectric sensors. A modal analysis is performed, using data from all available sensors. Comparing the frequency response functions and the natural frequencies shows the limitations of the MEMS sensor. One can then correct the MEMS measurements, by using global statistical parameters calculated on the data or by defining a “filter” function between the signals, thus improving the signal-to-noise ratio. It is found that MEMS sensors may replace piezoelectric ones for diagnostic applications. This way, an inexpensive measurement system (which needs to be calibrated only once, before installation, against higher-accuracy sensors) can be used for vibration monitoring of electric motors

Out-of-plane Characterization of Silicon-on-insulator Multiuser MEMS Processes-based Tri-axis Accelerometer

In this paper, we discuss the analysis of out-of-plane characterization of a capacitive tri-axis accelerometer fabricated using SOI MUMPS (Silicon-on Insulator Multi user MEMS Processes) process flow and the results are compared with simulated results. The device is designed with wide operational 3 dB bandwidth suitable for measuring vibrations in industrial applications. The wide operating range is obtained by optimizing serpentine flexures at the four corners of the proof mass. The accelerometer structure was simulated using COMSOL Multiphysics and the displacement sensitivity was observed as 1.2978 nm/g along z-axis. The simulated resonant frequency of the device was found to be 13 kHz along z axis. The dynamic characterization of the fabricated tri-axis accelerometer produces the out-of-plane vibration mode frequency as 13 kHz which is same as the simulated result obtained in z-axis

Python-based MEMS inertial sensors design, simulation and optimization

With the rapid growth in microsensor technology, a never-ending range of possible applications emerged. The developments in fabrication techniques gave room to the creation of numerous new products that significantly improve human life. However, the evolution in the design, simulation, and optimization process of these devices did not observe a similar rapid growth. Thus, the microsensor technology would benefit from significant improvements in this domain. This work presents a novel methodology for electro-mechanical co optimization of microelectromechanical systems (MEMS) inertial sensors. The developed software tool comprises geometry design, finite element method (FEM) analysis, damping calculation, electronic domain simulation, and a genetic algorithm (GA) optimization process. It allows for a facilitated system-level MEMS design flow, in which electrical and mechanical domains communicate with each other to achieve an optimized system performance. To demonstrate the efficacy of the co-optimization methodology, an open-loop capacitive MEMS accelerometer and an open-loop Coriolis vibratory MEMS gyroscope were simulated and optimized - these devices saw a sensitivity improvement of 193.77% and 420.9%, respectively, in comparison to its original state

Bio-inspired hair-based inertial sensors

In biology, hair-based sensor systems are used regularly for measurement of physical quantities like acceleration, flow, rotational rate, and IR light. In this chapter, two different types of bio-inspired sensors for inertial measurement are discussed, which have been developed using surface micromachining and SU-8 lithography. First, an accelerometer inspired by the cricket’s clavate hair is presented. Second, a gyroscope inspired by the fly’s haltere is treated. For both, sensors are the necessary models presented, and guidelines are derived for optimization. Also, their performance is compared to their biological counterpart and the biomimetic potential is discussed

3D Energy Harvester Evaluation

This paper discusses the characterization and evaluation of an MEMS based electrostatic generator, a part of the power supply unit of the self-powered microsystem[1,2,3]. The designed generator is based on electrostatic converter and uses the principle of conversion of non-electric energy into electrical energy by periodical modification of gap between electrodes of a capacitor [4]. The structure is designed and modeled as three-dimensional silicon based MEMS. Innovative approach involving the achievement of very low resonant frequency of the structure (about 100Hz) by usage of modified long cantilever spring design, minimum area of the chip, 3D work mode, the ability to be tuned to reach desired parameters, proves promising directions of possible further development

Evaluation of low-cost MEMS accelerometers for SHM : frequency and damping identification of civil structures

Trabalho apresentado no CILAMCE 2018: IBERO-LATIN AMERICAN CONGRESS ON COMPUTATIONAL METHODS IN ENGINEERINGSensing techniques based on accelerometers for modal parameters identification are among the most studied and applied in Structural Health Monitoring of civil structures. The advent of low-cost MEMS accelerometers and open-source electronic platforms, such as Arduino, have facilitated the design of low-cost systems suitable for modal identification, although there is still a lack of studies regarding practical application and comparison of commercially available low-cost accelerometers under SHM conditions. This work presents an experimental performance evaluation of six low-cost MEMS accelerometers for the identification of natural frequencies and damping ratios of a three-storey frame model and a reinforced concrete slab, as well as their noise characteristics. A low-cost Arduino-based data acquisition system was used. The results showed an overall good performance of the MEMS accelerometers, with identified natural frequencies errors within 1.02% and 7.76% of reference values, for the three-storey frame and concrete slab, respectively, and a noise density as low as 108 g/√Hz

A three-axis accelerometer for measuring heart wall motion

This thesis presents the work carried out in the design, simulation, fabrication and testing of miniaturised three-axis accelerometers. The work was carried out at the Faculty of Science and Engineering at Vestfold University College (Tønsberg, Norway), the MIcroSystems Engineering Centre (MISEC) at Heriot-Watt University and in collaboration with the Interventional Centre at Rikshospitalet University Hospital (Oslo, Norway). The accelerometers presented in this thesis were produced to be stitched to the surface of human hearts. In doing so they are used to measure the heart wall motion of patients that have just undergone heart bypass surgery. Results from studies carried out are presented and prove the concept of using such sensors for the detection of problems that can lead to the failure of heart bypasses. These studies were made possible using commercially available MEMS (MicroElectroMechanical Systems) three-axis accelerometers. However, the overall size of these sensors does not meet the requirements deemed necessary by the medical team (2(W) 2(H) 5(L) mm3) and fabrication activities were necessary to produce custom-made sensors. Design verification and performance modelling were carried out using Finite Element Analysis (FEA) and these results are presented alongside relevant analytical calculations. For fabrication, accelerometer designs were submitted to three foundry processes during the course of the work. The designs utilise the piezoresistive effect for the acceleration sensing and fabrication was carried out by bulk micromachining. Results of the characterisaton of the sensors are presente