A. Y. Ahmed

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.

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.

Simulation and modeling the effect of temperature on resonant frequency of a CMOS-MEMS resonator

Simulation and modeling of the effect of temperature on resonant frequency of resonator that is maintained at high temperature (100 to 300°C) by a heater element using Coventor Ware software is presented in this paper. The principle of detection of the gaseous species is based on the change in resonant frequency of the microresonator due to change in mass induced by the adsorption of an analyte molecule onto the surface of the active material deposited on the microresonator. The theoretical resonant frequency is found to be 20.1 kHz. The frequency decreased from 20116.14 Hz to 19928.98 Hz with increasing temperature from 25°C to 300°C corresponding to a decrease in spring constant from 543.16 N/m to 533.1 N/m. The uniformity of the temperature distribution on the membrane area of the microresonator is also investigated and the temperature gradient is found to be 0.003°C/μm, which indicates a highly homogeneous temperature.

Characterization of CMOS-MEMS device for acetone vapor detection in exhaled breath

A MEMS vapor sensor for acetone detection in exhaled breath (EB) has been fabricated using 0.35 μm CMOS technology. Acetone vapor in EB is used as a non-invasive method for diabetes screening, which is currently conducted invasively by measuring blood glucose in blood. This paper studies the characterization of polysilicon piezoresistors, heater and temperature sensor embedded in the device. The measured resistances were found to be close to the modelled values within 1.1-6.8% error. Temperature coefficient of resistance (TCR) of the temperature sensor in a range of 25-100°C was found. TCR increases linearly with increasing the temperature and decreases linearly with decreasing the temperature. It was found to be 0.0033/°C for the increasing temperature and 0.0034/°C for the decreasing temperature, compared to 0.0038/°C reported in the literature, with an error of 13% and 10.5%, respectively.

Finite element analysis of a mass-sensitive CMOS-MEMS resonator using CoventorWare simulation software

The finite element analysis of a mass-sensitive CMOS-MEMS resonator using architect is presented in this paper. The principle of detection of the gaseous species is based on the change in resonant frequency of the microresonator as a result of the absorption/adsorption of an analyte molecule onto the surface of the active material deposited on the microresonator resulting into a change of the mass of the microresonator device. CoventorWare simulation software is used to design and simulate the micromachined resonator gas sensing platform/membrane. From simulation, the resonant frequency of the resonator is found to be 6.45 kHz and 23 kHz for mode 1 and mode 2 (in y and z direction), respectively. The frequency increases with decrease in the length of the beam. On the other hand the frequency decreases with increasing mass on the top of the CMOS-MEMS resonator. The sensitivity is determined to be 0.18 Hz/pg.

Design and simulation of mass-sensitive gas sensor based on CMOS-MEMS resonator

This paper is mainly focused on the design and simulation of a micromachined CMOS-MEMS resonator for gas sensing applications. The principle of detection of the gaseous species is based on the change in resonant frequency of the microresonator as a result of the adsorption of an analyte molecule onto the surface of the active material deposited on the microresonator resulting into a change of the mass of the microresonator device. Coventor Ware simulation software is used to design and simulate the micromachined microresonator gas sensing platforms. Simulation results show a resonant frequency of 20162.3 Hz for the resonator.

MetalMUMPs resonator for acetone vapor sensing

Acetone vapor monitoring is essential in workplace for human health and safety, where exposure to acetone concentration more than 176 parts per million (ppm) can cause damage to eyes, liver, kidneys and central nervous system. In addition, acetone in exhaled breath is known to be good biomarker for non-invasive screening of diabetes. The most common used acetone vapor sensors are based on metal oxide semiconductor sensors, which work at higher temperatures, and hence consume more power. This paper reports MetalMUMPs device for acetone vapor sensing for environmental monitoring. The device is based on electrothermal actuation and capacitive sensing using differential capacitance measurement technique. MS3110 universal capacitive readout circuit was used to readout the small change of the static capacitance when the device is actuated using 0.71 Vrms with a driving frequency range of 0.5 kHz–8 kHz. The output signal of the circuit is given as a voltage and it can be directly related to the capacitance change. The output voltage change was found to increase linearly with increasing the acetone vapor concentration from 100 ppm to 500 ppm with a concentration sensitivity of 0.65 mV/ppm.

CMOS-MEMS resonator parametric variation analysis through equivalent circuit modeling

In this paper, we report a micro electro mechanical system (MEMS) shuttle resonator fabricated on CMOS-MEMS wafer technique. The resonator operates at the resonant frequency when a current flows through the metal layers in the presence of an external magnetic field. We investigate the resonant frequency and amplitude shifts due to parametric variation in beam length, width, and structure thickness in resonator motion. The theoretical formulation of the equivalent circuit model is presented. Simulation of resonator with variations are carried out using equivalent circuit model, these variations are based on fabrication foundry tolerance range. Simulation results show a range of operational frequencies in which the resonator can perform under the fabrication tolerances provided by the foundry.

Characterization of embedded microheater of a CMOS-MEMS gravimetric sensor device

A CMOS-MEMS device for mass detection has been designed using 2008 CoventorWare software and fabricated using 0.35źm CMOS technology. This paper reports the characterization of the microheater and the temperature sensor embedded in the device. The measured resistances of the microheater and the temperature sensor were found to be close to the modeled values within ~4.2% error. The average temperature coefficient of resistance (TCR) of the temperature sensor of five dies was determined by increasing or decreasing the temperature in a range of 25°C-100°C. The resistance of the temperature sensor was found to increase with either an increase in ambient temperature or the voltage applied to the microheater, with a correlation factor of 0.99. The average TCR was found to be 0.0034/°C for the increasing temperature and 0.0036/°C for the decreasing temperature as compared to 0.0037°C reported in the literature, indicating an error of 8.1% and 3.5%, respectively. These differences between the measured and reported values are believed to be due to fabrication tolerances in the design dimensions or the material properties. The humidity was found to have a negligible effect on the resistance of the temperature sensor for increasing humidity levels from 40% to 90%. The repeatability of the measurements has shown low standard errors, which gives confidence in the reliability of the fabricated device.