Built-In test of MEMS capacitive accelerometers for field failures and aging degradation.

Postprint (published version

Design Optimization of MEMS Comb Accelerometer

© ASEE 2007MEMS (Microelectromechanical Systems) refers to the technology integrating electrical and mechanical components with feature size of 1~1000 microns. MEMS comb accelerometers have been successfully applied for air-bag deployment systems in automobiles. In this paper, the design optimization of a polysilicon surface-micromachined MEMS comb accelerometer is discussed. The device uses folded-beam structure to enhance the sensitivity. The movable mass is connected to two anchors through folded-beams. There are movable fingers extruding from both sides of movable mass. Each movable finger has left and right fixed comb fingers surrounding it, so that a differential capacitance pair is formed. Any acceleration along the sensitive direction will induce inertial force on movable mass and deflect the beams. Hence the differential capacitance gap will change. By measuring this differential capacitance change, the experienced acceleration can be measured. ANSYS FEM simulation is used to extract the device sensitivity and resonant frequency of the device. By gradually varying the design parameters in ANSYS simulation, the relationship between the device sensitivity and various design parameters is derived. The curves of device sensitivity versus beam width, beam length and mass width are derived and they are in good agreement with theoretical prediction. From the analysis it is concluded that the device behavior strongly depends upon various design parameters. By adjusting design parameters, desired sensitivity can be obtained. Based on the simulation results, a set of optimized design parameters for the comb accelerometer is decided. The ANSYS simulation results show that the device has displacement sensitivity of 3nm/g. The above-proposed MEMS comb accelerometer may be used for many applications, such as automobile airbag deployment and navigations, fabrication sequence of the comb accelerometer is also proposed. The device is to be fabricated using surface-micro machining process with sacrificial layer technique

Sense/Drive Architecture for CMOS-MEMS Accelerometers with Relaxation Oscillator and TDC

Postprint (published version

A sigma-delta interface built-in self-test and calibration for microelectromechanical system accelerometer's utilizing interpolation method

This work presents the capacitive micromechanical accelerometer with a completely differential high-order switched capacitor sigma-delta modulator interface. Such modulation interface circuit generates one-bit output data using a third sigma-delta modulator low-noise front-end, doing away with the requirement for a second enhanced converter of resolution to encode the feedback route analog signal. A capacitive micromechanical sensor unit with just a greater quality factor has been specifically employed to give greater resolution. The closed-loop and electrical correction control are used to dampen the high-Q values to get the system's stability with high-order. This microelectromechanical system (MEMS) capacitive accelerometer was calibrated using a lookup table and Akima interpolation to find manufacturing flaws by recalculating voltage levels for the test electrodes. To determine the proper electrode voltages for fault compensation, COMSOL software simulates a number of defects upon that spring as well as the fingers of the sensor system. When it comes time for the feedback phase of a proof mass displacement correction, these values are subsequently placed in the lookup table

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

Comparison of Two Low-Power Electronic Interfaces for Capacitive Mems Sensors

The paper discusses the importance and the issues of interfacing capacitive sensors. Two architectures applicable for interfacing capacitive sensors are presented. The first solution was designed to interface a capacitive humidity sensor designed and built for a humidity-dependent monolithic capacitor developed at Budapest University of Technology and Economics. The second case presents the possible read-out solutions for a SOI-MEMS accelerometer. Both of the architectures were built and tested in a discrete implementation to qualify the methods before the integrated realization. The paper presents a detailed comparison of the two methodsComment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/EDA-Publishing

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Control Circuitry for Self-Repairable MEMS Accelerometers

A BISR (Built-in Self-Repairable) MEMS comb accelerometer with modularized design has been previously reported. In this paper, the differential capacitance sensing circuitry for MEMS comb accelerometer is discussed. The BISR control circuitry based on CMOS transmission gates (TGs) is proposed. Each BISR module is connected to the capacitance sensing circuitry through a transmission gate. By turning on or off a transmission gate, the corresponding module can be either connected to or isolated from the capacitance sensing circuitry. In this way, the faulty module can be easily replaced with a good redundant module for self-repair. The parasitic model for the BISR control circuitry is also analyzed. The analysis results show that the parasitic capacitance will not affect the proper operation of the BISR control circuitry. Furthermore, the signal strength will not be degraded due to the insertion of analog multiplexers. The control circuitry can effectively isolate the faulty module of the BISR MEMS comb accelerometer. Both BISR and non-BISR MEMS accelerometer designs are suggested and their performances are also extracted for comparison

Teaching MEMS Curriculum in Electrical Engineering Graduate Program

© ASEE 2010Microelectromechanical Systems (MEMS) refer to devices and systems in the size range of 1 micron (1 micron=10-6m) to 1000 microns. Due to their small size, MEMS technology has the advantages of low weight, low cost, low power consumption and high resolution. MEMS have found broad applications in automobile, inertial navigation, light display, optical and RF communications, biomedicine, etc. World’s MEMS market is growing rapidly each year. To meet the strong market demands on MEMS engineers and researchers, we developed MEMS curriculum in our master program in School of Engineering since Fall 2005. In this paper, we shared our experience in teaching the MEMS curriculum in master program of Electrical Engineering department. Three core courses have been developed for MEMS curriculum. The course description, goals, prerequisites, as well as the topics covered in these courses are discussed. Multimedia technology is used in the teaching to enhance the teaching results. Several MEMS course projects using ANSYS simulation are designed to help student accumulate experience in MEMS device design and simulation. Students are fascinated by the MEMS field and continue their master project/thesis research in MEMS. The MEMS curriculum attracted tremendous interest among students, and the students’ feedback on the course have been excellent. This is part of our efforts to prepare students for the future need of economy revival

A Self-repairable MEMS Comb Accelerometer

The final publication is available at www.springerlink.comIn this paper, a built-in self-repair technique for the MEMS comb accelerometer device is proposed. The main device of the comb accelerometer consists of n identical modules, and m modules are introduced as the redundancy. If any of the working module in the main device is found faulty during a built-in self-test (BIST), the control circuit will replace it with a good redundant module. In this way, the faulty device can be self-repaired through redundancy. The implementation of dualmode BIST on the BISR module is discussed. The sensitivity loss due to device modularization can be well compensated by different design alternatives. The yield model for MEMS redundancy repair is developed. The simulation results show that the BISR (built-in self-repair) design leads to effective yield increase compared to non-BISR design, especially for a moderate non-BISR yield. The yield as well as the reliability of the accelerometer can be improved due to the redundancy repair.http://link.springer.com/chapter/10.1007%2F1-4020-5261-8_1