John Ojur Dennis

Design and modeling of MEMS resonator for magnetic field sensing using hybrid actuation technique

A novel design of 0.751MHz MEMS resonant magnetic field sensor of mass 0.775pg based on hybrid actuation technique (Lorentz force and Electrostatic force) is presented and simulated using Coventor Ware and CADENCE simulators. The sensor consists of Aluminum paddle resonator, two supporting beams, driving electrodes, sensing electrode and silicon substrate with a capacitive CMOS readout amplifier. Working in a resonant condition, the sensors vibration amplitude is converted into the sensing capacitance change, which reflects the outside magnetic flux-density. Based on the simulation, the key structure parameters are optimized and the resonant frequency is estimated. The results of the device are in accordance with the theoretical results of the designed model. The resolution of the sensor is 1 nT. The results indicate its sensitivity more than 0.01 nV/nT, when operating at a normal atmosphere. The sensitivity and resolution can be enhanced through vacuum packaging.

Fabrication and Characterization of a CMOS-MEMS Humidity Sensor

This paper reports on the fabrication and characterization of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) device with embedded microheater operated at relatively elevated temperatures (40 °C to 80 °C) for the purpose of relative humidity measurement. The sensing principle is based on the change in amplitude of the device due to adsorption or desorption of humidity on the active material layer of titanium dioxide (TiO2) nanoparticles deposited on the moving plate, which results in changes in the mass of the device. The sensor has been designed and fabricated through a standard 0.35 µm CMOS process technology and post-CMOS micromachining technique has been successfully implemented to release the MEMS structures. The sensor is operated in the dynamic mode using electrothermal actuation and the output signal measured using a piezoresistive (PZR) sensor connected in a Wheatstone bridge circuit. The output voltage of the humidity sensor increases from 0.585 mV to 30.580 mV as the humidity increases from 35% RH to 95% RH. The output voltage is found to be linear from 0.585 mV to 3.250 mV as the humidity increased from 35% RH to 60% RH, with sensitivity of 0.107 mV/% RH; and again linear from 3.250 mV to 30.580 mV as the humidity level increases from 60% RH to 95% RH, with higher sensitivity of 0.781 mV/% RH. On the other hand, the sensitivity of the humidity sensor increases linearly from 0.102 mV/% RH to 0.501 mV/% RH with increase in the temperature from 40 °C to 80 °C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%. The sensitivity is also frequency dependent, increasing from 0.500 mV/% RH at 2 Hz to reach a maximum value of 1.634 mV/% RH at a frequency of 12 Hz, then decreasing to 1.110 mV/% RH at a frequency of 20 Hz. Finally, the CMOS-MEMS humidity sensor showed comparable response, recovery, and repeatability of measurements in three cycles as compared to a standard sensor that directly measures humidity in % RH.

Analysis of frequency up-conversion based vibration energy harvesting

Mechanical frequency up-conversion has been suggested by many researchers in order to increase power density of kinetic energy harvesters. In this paper analytical analysis of frequency up-conversion mechanism has been carried out in some detail. It has been shown that sources of actuation for a frequency increased generator can be categorized as force limited and displacement limited sources. Maximum energy transferring conditions have been investigated for both types. The settling time of the transient motion of the high frequency oscillator has been shown to be dependent on the seismic mass. Effects of premature excitation and natural frequency of high frequency resonator on average power have also been investigated. A relationship has been developed between frequency of ambient vibration and optimal natural frequency of frequency increased generator.

Design and simulation of mechanical behavior of MEMS-based resonant magnetic field sensor with piezoresistive output

This study scopes in the application of Lorentz force for the magnetic field detection using micromachined device. The device is designed and simulated using CoventorWare simulation software. The design is based on CMOS technology and surface micromachining. The response of the device in external magnetic field is discussed in two situations: static and dynamic. It was observed in static case a displacement of 47.4 nm, while for the dynamic case it was 0.237 µm in the center of beam. The device has a resonant frequency of 66.64 MHz and a quality factor 6 with important features such as small device size. Earths magnetic field is used as source of actuation and sensor response towards the variation in external magnetic field is 99.9 % linear with sensitivity of 0.05 µA/µT.

A CMOS-MEMS cantilever sensor for capnometric applications

Capnometers monitor the concentration of CO2 in exhaled breath, which can be a life saving modality. High cost, big size and high power consumption of the conventional capnometers limit their scope and adaption. To overcome these issues, a CMOS MEMS microcantilever based CO2 sensor is proposed for capnometric applications. The microcantilever is manufactured using CMOSMEMS technology and its critical parameters are analytically investigated. The optimized microcantilever has a quality factor, sensitivity and resolution of 3116, 16 mHz/ppm and 0.31 ppb, respectively.

CMOS Compatible Bulk Micromachining

The last two decades have seen the emergence and prevalence of Micro-Electro-Mechanical Systems (MEMS) technology. The reduction in size, low power consumption and low cost is the ultimate goals of application specific MEMS devices. One way to achieve these goals is the monolithic integration of MEMS technology with the standard integrated circuit (IC) technol‐ ogy. The utilization of the conventional IC technology as a platform for design of the fastgrowing MEMS technology has led to development of numerous devices and technologies in the past years. Much effort has been made and large capital has been invested into mainstream Complementary Metal-Oxide Semiconductor (CMOS) compatible MEMS technology. This approach has enabled MEMS devices to be directly integrated with CMOS circuits, allowing smaller device sizes and higher performances. This integration of MEMS technology with the mainstream CMOS technology is referred to as CMOS-MEMS technology [1].

A CMOS MEMS Resonant Magnetic Field Sensor with Differential Electrostatic Actuation and Capacitive Sensing

This paper is about CMOS MEMS resonant magnetic field sensor in which differential electrostatic actuation, capacitive sensing, resonant frequency, quality factor and sensitivity of interdigitated comb resonator is investigated. Information is embedded in the output signal frequency because it is robust against the interference from other sources during transmission. At damping ratio of 0.0001, resonant frequency of the comb resonator is 4.35 kHz with quality factor 5000 and amplitude 18.45 μm. Sensitivity of the device towards external magnetic field is 9.455 mHz/nT which is 10,000 times improved than recently published data.

Design, simulation, modeling and characterization of micromachined microcantilever using coventorware software

Modeling and simulation of a microcantilever designed to achieve high resonant frequency on the sensing area is presented in this paper. Simple analytical models of the microcantilever are generated to achieve estimates of the device performance and to check the validity of the subsequent simulation. CoventorWare simulation software is used to design and process the micromachined microcantilever gas sensing platforms. Results indicate that with a periodic force of amplitude 0.05 N applied at the top of microcantilever, increasing its thickness from 1 µm to 5 µm increases the natural frequency from 10.203 KHz to 50.709 KHz. On the other hand an increase in the lengths of the microcantilever from 90 µm to 170 µm decreases its natural frequency from 30.437 KHz to 17.70 KHz, while increasing its widths from 60 µm to 140 µm increases its natural frequency from 23.854 KHz to 35.84 KHz. A comparison between simulation and mathematical model results for frequency showed close agreement.

A monolithic, low-noise, capacitive readout interface circuit for CMOS-MEMS resonator-based gravimetric chemical gas sensors

This paper presents a monolithic, low-noise capacitive readout interface circuit for CMOS-MEMS resonator based gravimetric chemical gas sensors. In these sensor devices, where the sense capacitances are usually very weak, the readout interface circuit plays a crucial role in determining the overall sensor performance. Noise is observed in various active and passive devices affecting circuit performances. Particularly at low frequencies, flicker noise is dominant in degrading the quality of output signals. A dual stage, open-loop continuous time voltage sensing with chopper stabilization technique is proposed in this work to cope with it and improve the total output signal SNR. The proposed circuit is designed based on MIMOS 0.35 μm AMS 3.3V CMOS technology. Cadence Spectre circuit simulator simulation results show, the proposed circuit achieves an input inferred noise of 11.6 n V/√(Hz), total gain of 48.1 dB and consumes a total power of 3.385 mW. The designed circuit is able to detect minute capacitance changes as low as 0.0365 aF with total sensitivity of 67.95 μV/aF.

Design, modeling and simulation of CMOS MEMS cantilever for carbon dioxide gas sensing

Carbon dioxide sensors have potential applications in medical diagnoses, health care, environmental monitoring, food and medicine industry. In recent years, many novel biological, physical and chemical sensors have employed microcantilevers due to their simplicity, ease of fabrication and integration with electronics. This paper presents design, modeling and simulation of a microcantilever working in dynamic mode for CO2 gas sensing with electromagnetic actuation and capacitive sensing using comb fingers. The sensor is based upon 0.35 micron CMOS technology. CoventorWare and MATLAB have been used as simulation software. According to the developed model and simulation results the resonator has a quality factor of 3333 in air and mass sensitivity of 3.2 Hz/ng.