J. O. Dennis

Low-noise, low-offset modulator demodulator circuit for chopper stabilization technique in CMOS-MEMS sensor applications

This paper presents a design and technique for low noise, low offset modulation demodulation circuit for chopper stabilized amplifiers use in CMOS-MEMS sensor applications. In these sensors, where the sensed signals are usually very weak, a low-noise interface readout circuit plays a crucial role in determining the overall sensor performance and success in the market. Amplifiers are the core building blocks of these circuits and hence there is a growing demand for low noise and low offset designs and fabrication. Chopper stabilization technique has been widely used in amplifiers for flicker (1/f) noise and offsets reduction purposes using the principles of modulation and demodulation. Thus, the functionality and performance of the modulation and demodulation circuit determines the realization and attainment of chopper stabilization. The demonstrated circuits in this work are designed in MIMOS 0.35 μm AMS CMOS 3.3 V CMOS process technology. Cadence Spectre simulation results show the presented circuit achieves chopper stabilization with total noise contribution of 0.885 nV√Hz and minimized offset.

Mass detection using a macro-scale piezoelectric bimorph cantilever

Piezoelectric cantilevers have found a wide usage in sensor technologies for mass sensing and energy harvesting. This paper reports theoretical calculations, Finite Element Method (FEM) simulation and experimental measurements of mass detection using piezoelectric bimorph cantilever (PZT-5H) in macro (mm) scale. The dimensions of the cantilever are 33mm, 10mm, and 0.5mm for length, width, and thickness, respectively. The cantilever has 1.325g static mass with resonance frequency of 240.036 Hz, mass sensitivity of 377 Hz/g and quality factor of 390. The calculated resonance frequency of the device was 1% and 5% higher than the measured and the simulated frequencies, respectively. Air damping is believed to be the reason for lowering values of the simulated and measured resonance frequencies. In addition the extra masses due to the material coating the piezoelectric layer of the cantilever also play a role. Attachment of 8.96mg mass on the tip of the cantilever found to induce ~4 Hz frequency shift. Due to the reasonable mass sensitivity of the cantilever, it could be used for mass sensing applications.

Design, modeling and simulation of CMOS-MEMS resonator for biomedical application

CMOS-MEMS resonators have found a broad usage in mass sensing applications especially in biomedical field. This paper reports theoretical calculations and Finite Element Method (FEM) simulation for a proposed microresonator for detection of acetone in exhaled breath as biomarker for diabetes. The resonator is 760 μm long and 340 μm wide with 1.461ng effective mass, 21.331 kHz natural resonance frequency, and 8.867 mHz/pg mass sensitivity. Deposition of 4 μm sensitive layer gives 781 μHz/ppm gas concentration sensitivity with minimum concentration detection of 1.28 ppm. The operating voltage of this resonator is below 50 V and the static sensing capacitance is 90.84 fF. Due to the reasonable mass sensitivity of the resonator, it could be used for mass sensing applications.

Design and characterization of embedded microheater on CMOS-MEMS resonator for application in mass-sensitive gas sensors

In utilizing CMOS-MEMS resonators as mass-sensitive platforms, a uniform temperature distribution on the membrane surface is critical. In this paper, a novel design of CMOS-MEMS resonator with embedded microheater to control the temperature over the sensing layer was successfully designed and characterized. The CMOS-MEMS resonator was fabricated using 0.35 μm CMOS and post-CMOS micromachining process. Temperature coefficient of resistance (TCR) of aluminum temperature sensor embedded in the membrane was determined by measurement of resistance variation as a function of temperature from 27°C and 150°C. The TCR of the temperature sensor is found to be 0.00386 and 0.00379 for measurements carried out while temperature is increasing and decreasing, respectively. The total resistance of the temperature sensor and the wire interconnects was theoretically determined to be 74.23 Ω and 94.82 Ω, respectively, making a total resistance of 169.05 Ω when measurements are made through the pads. On the other hand the measured resistance at 27°C is found to be 169.06 Ω which is in very good agreement with a difference of 0.006 %. The experimental results and analytical values of resistance of the temperature sensor as a function of temperatures shows a good agreement (1.07%). TCR of Al is found to 0.00382 with percentage difference of about 2.05 % from standard value (39 ×10-4 C-1).

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.

Modelling and Simulation of Polysilicon Piezoresistors in CMOS-MEMS Resonator for Biomarker Detection in Exhaled Breath

This research studies longitudinal and transverse polysilicon resistors deposited in the maximum stress points of a CMOS-MEMS resonator for mass detection. The longitudinally mounted resistors were found to increase with the stress and giving maximum of resistance change of 10 to 23 O when the actuation voltage was varied from 50 to 180 V, while the transverse resistors were found to decrease from 0.8 to 0.4 O for the given voltages. Possible Wheatstone bridge configurations were studied to get the maximum output voltage, which was found to be 14 mV when two equal longitudinal resistors are connected with two equal external resistors to form a half bridge configuration.

Noise and Bandwidth analysis for PMOS based wide swing cascode current mirror using 0.35 um CMOS-MEMS technology

In this work, we propose a PMOS based wide swing cascode current mirror (WSSCM) for 0.35 um CMOS-MEMS technology. The proposed circuit shows a high bandwidth current mirror with high output resistance capability operating at low voltage levels. Noise, output resistance and bandwidth analysis are presented. CADENCE SPECTRE circuit design tool using MIMOS 0.35 um and BSIM3 transistor models is used to carry out the simulations. The circuit achieves an amplification of 120.04 uA, the input referred noise of the circuit is 75.77 nV/√Hz with a minimum power consumption of 0.33 mW and a high output resistance of 15 MO .

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.

Design of PolyMUMPS device for diabetes screening via acetone vapor detection in exhaled breath

Diabetes is a chronic disease that occurs due to deficiency or improper use of insulin by body tissues. It is currently diagnosed invasively by measuring blood glucose. This paper reports modelling and simulation of a PolyMUMPS device proposed for a non-invasive screening of diabetes. The device is electromagnetically driven at its resonance frequency using Lorenz force, while the output is detected by capacitive means. The resonance frequency of the first mode was obtained by CoventorWare software and it was found to be 18.552 kHz compared to its modelled value of 17.211 kHz, within an error of 7.2 %. Maximum displacement of 8.35 µm and capacitance of 29.57 fF were obtained when the device was driven by applying 15 mA current and 50 mT magnetic field.

Modeling and simulation of two modes of vibration in MEMS devices based on embedded piezoresistors

Piezoresistive effect is commonly used as transduction mechanism in microelectromechanical systems (MEMS) and Wheatstone bridge as readout circuit. This paper presents modeling and simulation of two modes of vibration in the MEMS device through embedded piezoresistors which are arranged in Wheatstone bridge configuration, modeling is extended up to n branches for wide range of applications in MEMS. The comparative analysis of fully and half differential setups even with one variable resistor with balanced form of the two branch bridge is modeled as well as simulated using Multisim8. The sensitivity of the bridge in fully, half and with one variable resistor configuration is found to be 2 μV/mΩ, 1 μV/mΩ and 0.49 μV/mΩ respectively. It is found that fully differential set up is the most sensitive one. This output is amplifiable by using 1000 gain amplifier.