The combination of multiaxis and multiparameter microelectromechanical systems (MEMS) in the same technology would result in very cheap and smart inertial measurement units (IMUs). In this paper, a $Z$ -axis Lorentz-force-based magnetometer whose design and optimization are reviewed taking into account the constraints of an industrial MEMS technology (process and packaging) already used for accelerometers and gyroscopes is presented. How this impacts the design guidelines is shown; in particular, a very compact device that can fit in the same package of the gyroscope to realize an all-MEMS seven-degree-of-freedom IMU is proposed and experimentally tested. The device shows a mechanical sensitivity of around 0.8 $\hbox{aF}/(\mu\hbox{T} \cdot \hbox{mA})$ with a resolution of 520 $(\hbox{nT} \cdot \hbox{mA})/\sqrt{\hbox{Hz}}$ over a signal bandwidth of 50 Hz at room temperature. Coupled to a transimpedance amplifier, the system shows an overall sensitivity of 150 $\mu\hbox{V}/\mu\hbox{T}$ at 250 $\mu\hbox{A}$ of peak driving current.

$Z$ -Axis Magnetometers for MEMS Inertial Measurement Units Using an Industrial Process

This paper proposes a new design method to achieve adverse-resistant microwave sensors using balanced structure of two sensors. Any kinds of sensors can be used in the presented balanced architecture. However, a new kind of high-resolution microwave material sensor, based on the injection locking phenomenon, is presented and used in this paper. By injecting a low-power level and low-phase noise signal to an oscillator, an injection-locked oscillator with a very small lock range is achieved with a very high sensitivity to its resonator condition. In the balanced structure, for a standard sample over one branch and an arbitrary sample over the other, the difference between center frequencies and lock ranges of oscillators can be measured at once. Therefore, the dielectric constant and loss tangent of unknown samples are calculated while the adverse environmental variations have the same effects on both branches and are compensated automatically without additional sensors and environmental controlling system. Moreover, it is indicated that using a simple frequency comparator with an output voltage instead of a spectrum analyzing system makes the system more practical and low cost. As an example for validation, a system is fabricated at 1 GHz and results of various states have been presented.

High-Resolution Balanced Microwave Material Sensor With Extended Dielectric Range

Vapor detection using highly sensitive miniaturized resonant sensors is of great interest for many applications, including consumer, industrial, and environmental applications. An operational-amplifier-based multichannel oscillator that interfaces with a 50-MHz capacitive micromachined ultrasonic transducer array is presented for chemical sensing applications. The circuit was implemented in a 0.18-μm CMOS technology to reduce power consumption, number of wires, and active area per channel. The presented integrated circuit also addresses the potential-frequency-locking problem between channels by allowing the open-loop gain to be adjustable off-chip. The feasibility of the developed oscillator for the chemical sensing application is demonstrated. Two channels that were operated simultaneously achieved excellent volume sensitivities of 8.5 × 10-4%/Hz and 3.9 × 10-4%/Hz, respectively, to relative humidity in N2.

A Multichannel Oscillator for a Resonant Chemical Sensor System

This article presents a novel method to derive and identify an accurate small perturbation model of a comb-actuated resonant microelectromechanical system (MEMS) mirror with highly nonlinear dynamics. Besides the nonlinear stiffness and damping, the comb-drives add nonlinearities due to their electrostatic nature and their effect on the dynamic mirror amplitude over frequency behavior. The proposed model is based on a period to period energy conservation and applies for most nonlinearities present in an oscillator such as MEMS mirrors. It is shown that for specific nominal operation points with square wave excitation, the small perturbation model is linear for a wide range. The full dynamics of the derived linear model are parametrized by three constants, that can be estimated by the phase locked loop (PLL), performing a proposed identification method only based on phase measurements. An analysis of control laws usually applied in a PLL provides important information for the proper design of controllers to meet the desired behavior for individual applications.

Linear Modeling and Control of Comb-Actuated Resonant MEMS Mirror With Nonlinear Dynamics

In this paper, we report on the new design of an electric field sensor based on piezoelectric bending effect in a capacitive-sensing method. The bipolar electric field sensor with a range from −22 to 22 kV/cm concentrates on a bending structure to enlarge the piezoelectric effect and to control its bending orientation. It performs with a much higher sensitivity of 0.448 pF/(kV/cm) or 5.78%/(kV/cm) and has a better resolution of 7.0 V/cm at $E=0$ . Factors influencing the capacitance response are also discussed, which might further optimize the sensitivity. Moreover, the analytical model and experimental results make an agreement on the reasonability of this electric field sensor, gaining an insightful guide to the potential capacitive-sensing electric field chip sensor widely distributed in sensor networks.

Electric Field Sensor Based on Piezoelectric Bending Effect for Wide Range Measurement

Many microelectromechanical systems (MEMS) devices possess charged capacitor structures where the suspension system allows relative electrode motion due to internal or external stimuli. When such a device is subjected to external mechanical vibrations present in a harsh operating environment, unwanted movement between the capacitor plates can generate a noise current which is injected into the connected circuitry. This paper analyzes this phenomenon and presents a model for the dynamics of a MEMS device with capacitive plates experiencing relative motion due to external stimuli. A Fourier series expansion of the current is developed to characterize the frequency content of the signal in closed form for a given vibration frequency, and simulation and experimental results are presented.

S J Reeves

Papers

Electrical Noise in MEMS Capacitive Elements Resulting From Environmental Mechanical Vibrations in Harsh Environments