1,384 research outputs found
Test of dual axis accelerometers based on specifications compliance
Postprint (published version
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
Optimal and Robust Design Method for Two-Chip Out-of-Plane Microaccelerometers
In this paper, an optimal and robust design method to implement a two-chip out-of-plane microaccelerometer system is presented. The two-chip microsystem consists of a MEMS chip for sensing the external acceleration and a CMOS chip for signal processing. An optimized design method to determine the device thickness, the sacrificial gap, and the vertical gap length of the M EMS sensing element is applied to minimize the fundamental noise level and also to achieve the robustness to the fabrication variations. In order to cancel out the offset and gain variations due to parasitic capacitances and process variations, a digitally trimmable architecture consisting of an 11 bit capacitor array is adopted in the analog front-end of the CMOS capacitive readout circuit. The out-of-plane microaccelerometer has the scale factor of 372 mV/gâŒ389 mV/g, the output nonlinearity of 0.43% FSOâŒ0.60% FSO, the input range of ±2 g and a bias instability of 122 ÎŒgâŒ229 ÎŒg. The signal-to-noise ratio and the noise equivalent resolution are measured to be 74.00 dBâŒ75.23 dB and 180 ÎŒg/rtHzâŒ190 ÎŒg/rtHz, respectively. The in-plane cross-axis sensitivities are measured to be 1.1%âŒ1.9% and 0.3%âŒ0.7% of the out-of-plane sensitivity, respectively. The results show that the optimal and robust design method for the MEMS sensing element and the highly trimmable capacity of the CMOS capacitive readout circuit are suitable to enhance the die-to-die uniformity of the packaged microsystem, without compromising the performance characteristics
Interface Circuits for Microsensor Integrated Systems
ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.
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
Remote photothermal actuation for calibration of in-phase and quadrature readout in a mechanically amplified Fabry-PĂ©rot accelerometer
A mechanically amplified Fabry-PeÌrot optical accelerometer is reported in which photothermal actuation is used to calibrate the in-phase and quadrature (I&Q) readout. The Fabry-PeÌrot interferometer (FPI) is formed between a gold-coated silicon mirror, situated in the middle of a V-beam amplifier, and the end surface of a cleaved optical fiber. On the opposite side of the silicon mirror, a further cleaved optical fiber transmits near-infrared laser light (λ = 785 nm), which is absorbed by the uncoated silicon causing heating. The thermal expansion of the V-beam is translated into an amplified change in cavity length of the FPI, large enough for the 2Ï-phase variation necessary for I&Q calibration. A simple 1D thermal analysis of the structure has been developed to predict the relationship between laser power and change in cavity length. A device having a V-beam of length 1.8 mm, width 20 ÎŒm, and angle 2 ° was found to undergo a cavity length change of 785 nm at 30 mW input power. The device response was approximately linear for input accelerations from 0.01 to 15 g. The noise was measured to be ~ 60 ÎŒg/âHz from 100 Hz to 3.0 kHz, whereas the limit of detection was 47.7 mg from dc to 3.0 kHz
Inertial MEMS: readout, test and application
This thesis moves towards the investigation of Micro Electro-Mechanical Systems
(MEMS) intertial sensors from different perspectives and points of view: readout,
test and application.
Chapter 1 deals with the state-of-the-art for the interfaces usually employed for 3-
axes micromachined gyroscopes. Several architecture based on multiplexing schemes
in order to extremely simplify the analog front-end which can be based on a single
charge amplifier are analysed and compared. A novel solution that experiments an
innovative readout technique based on a special analog-Code Division Multiplexing
Access (CDMA) is presented; this architecture can reach a considerable reduction of
the Analog Front-End (AFE) with reference to other multiplexing schemes. Many
family codes have been considered in order to find the best trade-off between
performance and complexity. System-level simulations prove the effectiveness of
this technique in processing all the required signals. A case study is also analysed: a
comparison with the SD740 micro-machined integrated inertial module with tri-axial
gyroscope by SensorDynamics AG is provided.
MEMS accelerometers are widely used in the automotive and aeronautics fields
and are becoming extremely popular in a wide range of consumer electronics
products. The cost of testing is a major one within the manufacturing process,
because MEMS accelerometer characterization requires a series of tests that include
physical stimuli. The calibration and the functional testing are the most challenging
and a wide selection of Automatic Test Equipments (ATEs) is available on the
market for this purpose; those equipments provide a full characterization of the
Device Under Test (DUT), from low-g to high-g levels, even over temperature.
Chapter 2 presents a novel solution that experiments an innovative procedure to
perform a characterization at medium-g levels. The presented approach can be
applied to low-cost ATEs obtaining challenging results. The procedure is deeply investigated and an experimental setup is described. A case study is also analysed:
some already trimmed Three Degrees of Freedom (3DoF)-Inertial Measurement
Unit (IMU) modules (three-axes accelerometer integrated with a mixed signal ASIC),
from SensorDynamics AG are tested with the experimental setup and analysed, for
the first time, at medium-g levels.
Standard preprocessing techniques for removing the ground response from vehicle-
mounted Ground Penetrating Radar (GPR) data may fail when used on rough
terrain. In Chapter 3, a Laser Imaging Detection and Ranging (LIDAR) system
and a Global Positioning System (GPS)/IMU is integrated into a prototype system
with the GPR and provided high-resolution measurements of the ground surface.
Two modifications to preprocessing were proposed for mitigating the ground bounce
based on the available LIDAR data. An experiment is carried out on a set of
GPR/LIDAR data collected with the integrated prototype vehicle over lanes with
artificially rough terrain, consisting of targets buried under or near mounds, ruts
and potholes. A stabilization technique for multi-element vehicle-mounted GPR is
also presented
Performance improvement of MEMS accelerometers in vibration based diagnosis
Vibration measurement and analysis has been an accepted method since decades to meet a number of objectives - machinery condition monitoring, dynamic qualification of any designed structural components, prediction of faults and structural aging-related problems, and several other structural dynamics studies and diagnosis. However, the requirement of the vibration measurement at number of locations in structures, machines and/or equipments makes the vibration measurement exorbitant if conventional piezoelectric accelerometers are used. Hence, there is a need for cheaper and reliable alternative for the conventional accelerometers. The Micro-Electro-Mechanical Systems (MEMS) accelerometers are one such cheap alternative. However, a significant deviation in the performance of the MEMS accelerometers has been observed in earlier research studies and also confirmed by this presented study when compared with well known conventional accelerometer. Therefore, two methods have been suggested to improve the performance of the existing MEMS accelerometers; one for correction in time domain and other in frequency domain. Both methods are based on the generation of a characteristic function (CF) for the MEMS accelerometer using well known reference accelerometer in laboratory tests. The procedures of both methods have been discussed and validations of these methods have been presented through experimental examples. In addition, a Finite Element (FE) model of a typical MEMS accelerometer has been developed and modal analysis has been carried out to understand the dynamics of capacitive type MEMS accelerometer and to identify the source of errors. It has been observed that the moving fingers behave like a cantilever beam while the fixed fingers showed rigid body motion. This cantilever type of motion seems to be causing non-parallel plates effect in the formed capacitors between moving and fixed fingers which results in errors in the vibration measurement. Hence, design modifications on finger shape have been suggested to remove the cantilever motion and results showed remarkable improvement. Moreover, the effect of using synchronous amplitude modulation and demodulation in the readout circuit has been studied. The experimental study showed that this circuit also introduces errors in amplitude and phase of the output signal compared with the input signal. Thus, in the new design of MEMS accelerometers, improvements in both mechanical design and electronic circuit are required.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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