Rosana A. Dias

High-Resolution MEMS Inclinometer Based on Pull-In Voltage

High-resolution pull-in-based microelectromechanical system (MEMS) inclinometers are presented in this paper. Pull-in is characterized by the sudden loss of stability in electrostatically actuated parallel-plate structures, and since pull-in voltage is stable and easy to measure, it enables an effective transduction mechanism that does not require complex and stable capacitive readout electronics. The MEMS devices used to test the novel architecture have differential actuation electrodes resulting in two pull-in voltages that change differentially with applied acceleration. Dedicated MEMS microstructures with extra proof mass show high sensitivity; 269 mV/° with a nonlinearity <;0.5% FS (Full Scale of ±23°). The measured noise is limited by the actuation mechanism, setting the sensors resolution at 75

Design of a Time-Based Micro-g Accelerometer

\mu

CMOS Optical Sensors for being incorporated in Endoscopic Capsule for Cancer Cells Detection

°; high above state-of-the-art MEMS devices. [2014-0156].

Bi-directional extended range parallel plate electrostatic actuator based on feedback linearization

Closed-loop pull-in time operated devices are a good alternative for high sensitivity accelerometers. This paper proposes the use of time measurement as the transduction mechanism for the realization of a high-precision accelerometer. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. The main design challenges for a pull-in time parallel-plate capacitive microelectromechanical system (MEMS) accelerometer are related to the damping and the associated tradeoff between sensitivity and noise is discussed. Parallel-plate MEMS structures designed and fabricated in a 25 μm-thick SOI micromachining process (SOIMUMPS) are used to demonstrate the accelerometer time-based approach and experimental results demonstrate a sensitivity of 0.25 μs/μg.

Real-Time Operation and Characterization of a High-Performance Time-Based Accelerometer

This paper describes the design, fabrication and characterization of CMOS optical sensors for cancer detection based on autofluorescence emission spectra. These optical sensors were fabricated for being an integrated part of an endoscopic capsule used in diagnosis of gastrointestinal diseases. Cells and tissues show autofluorescence, in a part of the visible spectrum, when excited by ultraviolet or short-wavelength visible light. The emission spectrum of cancer tissue is different from the one of the healthy tissue, and, it is dependent on the cancer development stage. CMOS photodetectors can be used to measure that spectrum. Once they are small and easily integrated with readout electronics, they can be placed around all the surface of the endoscopic capsule. While, nowadays, a locomotion and stop mechanism is a challenge, this scheme can cover a large area of the gastrointestinal tract examination during the natural movement of the capsule. The complete system will innovate the way of physicians diagnose the gastrointestinal diseases.

FPGA controlled MEMS inclinometer

In this paper, we present a bi-directional extended range parallel-plate electrostatic actuator using feedback linearization control. The actuator can have stable displacements up to 90% of the full-gap (limited by mechanical stoppers) on both directions, i.e., the device can move ±2μm within a ±2.25μm gap. The system has successfully tracked references until 1kHz (limited by the dynamics of the device) and it presents a capacitor tuning range of 17, using an actuation voltage from 0 to 10V. The results presented here are a clear advance in respect to the current state-of-the-art in terms of tracking capabilities, total stable displacement and tuning range.

A novel soi-mems “micro-swing” time-accelerometer operating in two time-based transduction modes for high sensitivity and extended range

An accelerometer based on the electrostatic pull-in time of a microstructure is presented in this paper. The device uses a parallel-plate overdamped microstructure, and real-time control operation is performed using a field programmable gate array and high precision digital-to-analog converters. Both open-loop and closed-loop measurements are presented. The low noise is a key feature of this approach, which is limited only by the mechanical-thermal noise of the microstructure used, 2 μg/√Hz as shown in the open-loop results (3 μg/√Hz in closed-loop operation). The time readout method has extremely high-resolution capabilities. The pull-in time sensitivity can be adjusted up to 1.6 μs/μg, and the electrostatic feedback voltage sensitivity is 61.3 V2/g. The closed-loop control allows operation of the accelerometer in a much larger range than in open-loop (±500 mg have been achieved) and the linearity is greatly improved (<;1%FS). The current closed-loop control algorithm allows operation up to 2 Hz. A bias stability of 50 μg has been measured over 45 h in open loop and 250 μg in closed loop.

Sensitivity linearization technique for a time based MEMS accelerometer

A FPGA (Field Programmable Gate Array) controlled inclinometer based on MEMS structures is presented in this paper. Pull-in voltage measurements are used in this work as the transduction mechanism. The pull-in phenomenon is characterized by the sudden loss of stability in electrostatically actuated parallel-plate actuators and since pull-in voltage is stable and easy to measure, it enables an interesting transduction mechanism. By successively bringing the microstructure to pullin while measuring the pull-in voltage allows the detection of external accelerations. A FPGA is responsible to control the entire system increasing its performance and reliability. The sensor resolution is defined by the resolution of the measured pull-in, i.e., resolution of the actuation voltage. Experimental results show a sensitivity of 50 mV/o with the resolution of the actuation voltage set below 1 μV using a 24-bit Digital-to-Analog Converter (DAC).

Time-based micro-g accelerometer with improved damper geometry

Here we report the design, modelling, fabrication and initial characterisation results of a new SOI-MEMS “micro-swing” time-accelerometer. Time-based acceleration sensing can be performed using either the embedded piezoresistors or the capacitive sense electrodes. The accelerometer can be operated in two distinct time-based transduction modes aimed at high sensitivity and extended operation range, depending on the applied drive voltage (α.VPull-In). A high sensitivity of 0.914µs/μg is achieved using the pull-in time metastable (PITMS) region (for, a = 1.01) over a small acceleration range from ±0.02g–±0.79g. Extended operation range up to ±2g can be achieved through mechanical time-of-flight (TOF) sensing (for, α ≥ 1.4). Preliminary measurements indicate device functionality and a pull-in transit time of 11ms for a tilt-acceleration corresponding to 70mg.

On-Chip Integrated Optical Sensors for Fluorescence Detection of Cancer Tissue: Application to Capsule Endoscopy

A high-resolution, high-sensitivity capacitive accelerometer based on pull-in time measurement is described in this paper. The high sensitivity of pull-in time is being explored to implement high performance accelerometers, and non-linearity is the main characteristic compromising device performance. An electrostatic compensation technique that addresses the non-linearity problem, based on pull-in time duration control, is presented and tested. Capacitive parallel-plates MEMS structures were used and the measured sensitivities for different acceleration ranges confirm the potential of this technique and the overall accelerometer concept. The results show an accelerometer with 0.26 µs/μg sensitivity, over a 120 dB dynamic range.