Low-power front-ends for capacitive three-axis accelerometers

This thesis consists of six publications and an overview of the research topic. The overview concentrates on background information of the capacitive accelerometers and front-ends. The publications focus on two low-power front-ends that were implemented for capacitive three-axis accelerometers and their operation as a part of an interface. The switched-capacitor front-ends that were implemented are based on the charge-balancing structures, namely a self-balancing bridge and a ΔΣ front-end, which convert the capacitive acceleration information to analog and digital signals, respectively. Both structures operate mechanically in open-loop configuration and are capable of reducing the effects of the electrostatic forces and displacement-to-capacitance conversion. According to the performance comparison presented in this thesis, both interfaces, which were implemented around the front-ends, exhibit competitive performance when compared to the commercial products of the day

Development of a Miniature Electrostatic Accelerometer /MESA/ for low g applications Summary report

Design, fabrication, and testing of miniature digital electrostatic accelerometer for low gravity measurements in spac

Degree-per-hour mode-matched micromachined silicon vibratory gyroscopes

The objective of this research dissertation is to design and implement two novel micromachined silicon vibratory gyroscopes, which attempt to incorporate all the necessary attributes of sub-deg/hr noise performance requirements in a single framework: large resonant mass, high drive-mode oscillation amplitudes, large device capacitance (coupled with optimized electronics), and high-Q resonant mode-matched operation. Mode-matching leverages the high-Q (mechanical gain) of the operating modes of the gyroscope and offers significant improvements in mechanical and electronic noise floor, sensitivity, and bias stability. The first micromachined silicon vibratory gyroscope presented in this work is the resonating star gyroscope (RSG): a novel Class-II shell-type structure which utilizes degenerate flexural modes. After an iterative cycle of design optimization, an RSG prototype was implemented using a multiple-shell approach on (111) SOI substrate. Experimental data indicates sub-5 deg/hr Allan deviation bias instability operating under a mode-matched operating Q of 30,000 at 23ºC (in vacuum). The second micromachined silicon vibratory gyroscope presented in this work is the mode-matched tuning fork gyroscope (M2-TFG): a novel Class-I tuning fork structure which utilizes in-plane non-degenerate resonant flexural modes. Operated under vacuum, the M2-TFG represents the first reported high-Q perfectly mode-matched operation in Class-I vibratory microgyroscope. Experimental results of device implemented on (100) SOI substrate demonstrates sub-deg/hr Allan deviation bias instability operating under a mode-matched operating Q of 50,000 at 23ºC. In an effort to increase capacitive aspect ratio, a new fabrication technology was developed that involved the selective deposition of doped-polysilicon inside the capacitive sensing gaps (SPD Process). By preserving the structural composition integrity of the flexural springs, it is possible to accurately predict the operating-mode frequencies while maintaining high-Q operation. Preliminary characterization of vacuum-packaged prototypes was performed. Initial results demonstrated high-Q mode-matched operation, excellent thermal stability, and sub-deg/hr Allan variance bias instability.Ph.D.Committee Chair: Dr. Farrokh Ayazi; Committee Member: Dr. Mark G. Allen; Committee Member: Dr. Oliver Brand; Committee Member: Dr. Paul A. Kohl; Committee Member: Dr. Thomas E. Michael

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

Mems Accelerometer Design

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2005Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2005Bu çalışmada, analog kapasitif MEMS ivme ölçer sisteminin teori, tasarım süreci ve analizi incelenmiş ve yüzey mikro makine tekniği olan MUMPS prosesi kullanılarak geniş ölçme dinamiğine sahip MEMS ivme ölçer sistemi gerçeklenmiştir. Mekanik sistemin optimizasyonu için Bölüm 2 ‘de elde edilen analitik modeller kullanılarak C++ programla dilinde MABEMS isimli görsel tabanlı bir program yazılmıştır. Mekanik sistemlerin sonlu eleman analizlerinde ticari bir yazılım olan ANSYS kullanılmıştır. Davranışsal seviyedeki simulasyonlar içinse sistemin MATLAB Simulink modeli oluşturulmuştur. Elektronik algılama kısmında, parazitik kapasitelerin etkisini azalttığı için yük kuvvetlendiricisi yapısı kullanılmıştır. İvme ölçerin Bölüm 3’te elde edilen matematik modeli, analog davranışsal modelleme kütüphanesi (ABM) kullanılarak PSPICE içerisinde gerçeklenmiş ve bu da elektronik algılama devresi ile mekanik elemanın aynı ortamda simulasyonuna olanak vermiştir. Geleneksel yöntemlerde, MEMS ivme ölçerler, ölçme dinamiği, bant genişliği ve lineerlik gibi performans ölçütlerinin iyileştirilmesi için geri beslemeli çevrimde çalıştırılır. Bu çalışmada, bu yönteme alternatif olarak ölçme hassasiyeti düşük olan bir sistemin, hassasiyeti daha yüksek olanın dinamik ofsetini (sıfırını) oluşturması prensibine dayanan ve “Kuvvet İleri Beslemesi” diye isimlendirdiğimiz yöntem önerilmiş ve kavramsal olarak tanımlanmıştır. Bu amaçla biri daha hassas fakat belli bir yer değiştirme değerinden sonra lineerliği bozulan, diğeri de daha az hassas fakat her zaman lineer çıkış veren iki farklı mekanik sistem tasarlamıştır. Tasarımlara ilişkin bütün sonuçlar Bölüm 3’te verilmiştir.In this work, the theory, design process, and analysis of analog capacitive MEMS accelerometer system is examined and a high dynamic range MEMS accelerometer system is implemented by using MUMPS surface micromachining process. For the optimization of the mechanical system, by using the analytical models obtained in Section 2, a visual software, named MABEMS, is implemented in C++ programming language. Finite element analysis of the mechanical systems are made by using a commercially available simulation package ANSYS. MATLAB Simulink model of the system is realized for the behavioral level simulations. The charge amplifier topology is used in electronic sensing interface since this configuration eliminates the effect of the parastic capacitances. Mathematical model of the accelerometer, obtained in Section 3, is implemented in PSPICE by using the Analog Behavioral Modelling (ABM) library so, this allowed the simulation of the mechanical device and electronic interface in the same environment. In conventional methods, accelerometers are operated in closed loop by applying feedback signals to increase the performance parameters like dynamic range, bandwidth, and linearity. In this work, a new method, is offered and described conceptually as an alternative to the conventional closed loop systems and this method is named as Force Feed forward Mechanism. In this method, less sensitive system, forms the dynamic offset of the more sensitive device. For this reason, two different mechanical devices are designed such that one of them has high sensitivity but nonlinear output above a certain displacement and the other one has low sensitivity but linear even for large displacements. All the results about the designed systems are given in Section 3.Yüksek LisansM.Sc

System design of a low-power three-axis underdamped MEMS accelerometer with simultaneous electrostatic damping control

Recently, consumer electronics industry has known a spectacular growth that would have not been possible without pushing the integration barrier further and further. Micro Electro Mechanical Systems (MEMS) inertial sensors (e.g. accelerometers, gyroscopes) provide high performance, low power, low die cost solutions and are, nowadays, embedded in most consumer applications. In addition, the sensors fusion has become a new trend and combo sensors are gaining growing popularity since the co-integration of a three-axis MEMS accelerometer and a three-axis MEMS gyroscope provides complete navigation information. The resulting device is an Inertial measurement unit (IMU) able to sense multiple Degrees of Freedom (DoF). Nevertheless, the performances of the accelerometers and the gyroscopes are conditioned by the MEMS cavity pressure: the accelerometer is usually a damped system functioning under an atmospheric pressure while the gyroscope is a highly resonant system. Thus, to conceive a combo sensor, aunique low cavity pressure is required. The integration of both transducers within the same low pressure cavity necessitates a method to control and reduce the ringing phenomena by increasing the damping factor of the MEMS accelerometer. Consequently, the aim of the thesis is the design of an analog front-end interface able to sense and control an underdamped three-axis MEMSaccelerometer. This work proposes a novel closed-loop accelerometer interface achieving low power consumption The design challenge consists in finding a trade-off between the sampling frequency, the settling time and the circuit complexity since the sensor excitation plates are multiplexed between the measurement and the damping phases. In this context, a patenteddamping sequence (simultaneous damping) has been conceived to improve the damping efficiency over the state of the art approach performances (successive damping). To investigate the feasibility of the novel electrostatic damping control architecture, several mathematical models have been developed and the settling time method is used to assess the damping efficiency. Moreover, a new method that uses the multirate signal processing theory and allows the system stability study has been developed. This very method is used to conclude on the loop stability for a certain sampling frequency and loop gain value. Next, a 0.18μm CMOS implementation of the entire accelerometer signal chain is designed and validated

Multi-Physics Simulation Platform and Multi-Layer Metal Technology for CMOS-MEMS Accelerometer with Gold Proof Mass

This chapter describes technical features and solutions to realize a highly sensitive CMOS-MEMS accelerometer with gold proof mass. The multi-physics simulation platform for designing the CMOS-MEMS device has been developed to understand simultaneously both mechanical and electrical behaviors of MEMS stacked on LSI. MEMS accelerometer fabrication process is established by the multi-layer metal technology, which consists of the gold electroplating and the photo-sensitive polyimide film. The proposed MEMS accelerometers are fabricated and evaluated to verify the effectiveness of the proposed techniques regarding sub-1G MEMS and arrayed MEMS devices. The experimental results show that the Brownian noise of the sub-1G MEMS accelerometer can achieve 780 nG/(Hz)1/2 and the arrayed MEMS accelerometer has a wide detection, ranging from 1.0 to 20 G. Moreover, using the developed simulation platform, we demonstrate the proposed capacitive CMOS-MEMS accelerometer implemented by the multi-layer metal technology. In conclusion, it is confirmed that the multi-physics simulation platform and the multi-layer metal technology for the CMOS-MEMS device have a potential to realize a nano-gravity sensing technology

Integrated reference circuits for low-power capacitive sensor interfaces

This thesis consists of nine publications and an overview of the research topic, which also summarizes the work. The research described in this thesis concentrates on the design of low-power sensor interfaces for capacitive 3-axis micro-accelerometers. The primary goal throughout the thesis is to optimize power dissipation. Because the author made the main contribution to the design of the reference and power management circuits required, the overview part is dominated by the following research topics: current, voltage, and temperature references, frequency references, and voltage regulators. After an introduction to capacitive micro-accelerometers, the work describes the typical integrated readout electronics of a capacitive sensor on the functional level. The readout electronics can be divided into four different functional parts, namely the sensor readout itself, signal post-processing, references, and power management. Before the focus is shifted to the references and further to power management, different ways to realize the sensor readout are briefly discussed. Both current and voltage references are required in most analog and mixed-signal systems. A bandgap voltage reference, which inherently uses at least one current reference, is practical for the generation of an accurate reference voltage. Very similar circuit techniques can be exploited when implementing a temperature reference, the need for which in the sensor readout may be justified by the temperature compensation, for example. The work introduces non-linear frequency references, namely ring and relaxation oscillators, which are very suitable for the generation of the relatively low-frequency clock signals typically needed in the sensor interfaces. Such oscillators suffer from poor jitter and phase noise performance, the quantities of which also deserve discussion in this thesis. Finally, the regulation of the supply voltage using linear regulators is considered. In addition to extending the battery life by providing a low quiescent current, the regulator must be able to supply very low load currents and operate without off-chip capacitors

Integrated interface electronics for capacitive MEMS inertial sensors

This thesis is composed of 13 publications and an overview of the research topic, which also summarizes the work. The research presented in this thesis concentrates on integrated circuits for the realization of interface electronics for capacitive MEMS (micro-electro-mechanical system) inertial sensors, i.e. accelerometers and gyroscopes. The research focuses on circuit techniques for capacitive detection and actuation and on high-voltage and clock generation within the sensor interface. Characteristics of capacitive accelerometers and gyroscopes and the electronic circuits for accessing the capacitive information in open- and closed-loop configurations are introduced in the thesis. One part of the experimental work, an accelerometer, is realized as a continuous-time closed-loop sensor, and is capable of achieving sub-micro-g resolution. The interface electronics is implemented in a 0.7-µm high-voltage technology. It consists of a force feedback loop, clock generation circuits, and a digitizer. Another part of the experimental work, an analog 2-axis gyroscope, is optimized not only for noise, but predominantly for low power consumption and a small chip area. The implementation includes a pseudo-continuous-time sense readout, analog continuous-time drive loop, phase-locked loop (PLL) for clock generation, and high-voltage circuits for electrostatic excitation and high-voltage detection. The interface is implemented in a 0.35-µm high-voltage technology within an active area of 2.5 mm². The gyroscope achieves a spot noise of 0.015 °/s/√H̅z̅ for the x-axis and 0.041 °/s/√H̅z̅ for the y-axis. Coherent demodulation and discrete-time signal processing are often an important part of the sensors and also typical examples that require clock signals. Thus, clock generation within the sensor interfaces is also reviewed. The related experimental work includes two integrated charge pump PLLs, which are optimized for compact realization but also considered with regard to their noise performance. Finally, this thesis discusses fully integrated high-voltage generation, which allows a higher electrostatic force and signal current in capacitive sensors. Open- and closed-loop Dickson charge pumps and high-voltage amplifiers have been realized fully on-chip, with the focus being on optimizing the chip area and on generating precise spurious free high-voltage signals up to 27 V

STEP: Satellite Test of the Equivalence Principle. Report on the phase A study

During Phase A, the STEP Study Team identified three types of experiments that can be accommodated on the STEP satellite within the mission constraints and whose performance is orders of magnitude better than any present or planned future experiment of the same kind on the ground. The scientific objectives of the STEP mission are to: test the Equivalence Principle to one part in 10(exp 17), six orders of magnitude better than has been achieved on the ground; search for a new interaction between quantum-mechanical spin and ordinary matter with a sensitivity of the mass-spin coupling constant g(sub p)g(sub s) = 6 x 10(exp -34) at a range of 1 mm, which represents a seven order-of-magnitude improvement over comparable ground-based measurements; and determine the constant of gravity G with a precision of one part in 10(exp 6) and to test the validity of the inverse square law with the same precision, both two orders of magnitude better than has been achieved on the ground