Capacitors made of interdigitated electrodes (IDEs) as a transducer platform for the sensing of volatile organic compounds (VOCs) have advantages due to their lower power operation and fabrication using standard micro-fabrication techniques. Integrating a micro-electromechanical system (MEMS), such as a microhotplate with IDE capacitor, further allows study of the temperature- dependent sensing response of VOCs. In this paper, the design, fabrication, and characterization of a low-power MEMS microhotplate with IDE capacitor to study the temperature-dependent sensing response to methanol using Zeolitic imidazolate framework (ZIF-8), a class of metal-organic framework (MOF), is presented. A Titanium nitride (TiN) microhotplate with aluminum IDEs suspended on a silicon nitride membrane is fabricated and characterized. The power consumption of the ZIF-8 MOF-coated device at an operating temperature of 50 ∘ C is 4.5 mW and at 200 ∘ C it is 26 mW. A calibration methodology for the effects of temperature of the isolation layer between the microhotplate electrodes and the capacitor IDEs is developed. The device coated with ZIF-8 MOF shows a response to methanol in the concentration range of 500 ppm to 7000 ppm. The detection limit of the sensor for methanol vapor at 20 ∘ C is 100 ppm. In situ study of sensing properties of ZIF-8 MOF to methanol in the temperature range from 20 ∘ C to 50 ∘ C using the integrated microhotplate and IDE capacitor is presented. The kinetics of temperature-dependent adsorption and desorption of methanol by ZIF-8 MOF are fitted with double-exponential models. With the increase in temperature from 20 ∘ C to 50 ∘ C, the response time for sensing of methanol vapor concentration of 5000 ppm decreases by 28%, whereas the recovery time decreases by 70%.@en

A MEMS gas sensor consists of a transducer, mainly a resistive or capacitive transducer coated with a thin film of specific functional materials. Functional materials can change their electrical, optical, magnetic, or mechanical properties based on the stimuli received. In a chemi-resistive or chemi-capacitive gas sensing system, thin film of functional materials coated on the transducers are a class of materials that can change the resistivity or dielectric properties of the adsorption or chemisorption of volatile organic compounds such as methanol and ethanol. A combination of efficient design of the MEMS transducer, read-out system, and robust sensing material is a key requirement for the development of good and reliable sensors. In this thesis, the study of thin-film dielectric and semiconducting nanoparticles integrated on MEMS transducers for the detection of volatile organic compounds (VOCs), namely ethanol and methanol vapors are presented.@en

In this paper, we present electro-thermal analysis and design of a combined MEMS micro hotplate and interdigitated-capacitance impedance sensor for gas sensing application using nano-porous materials like metal organic framework (MOF). The effects of design parameters of interdigitated electrodes such as width(W) and gap(G) of the capacitor, metallization ratio, number of electrodes and area of the capacitor. The influence of height of the electrode material, thickness of the insulation layer between the capacitance electrodes and the micro hotplate electrodes are studied. These design parameters are optimized to obtain a high bare capacitance of the electrodes using analytical and electric and thermal domain simulations in COMSOL 5. The design and thermal analysis of the micro hotplate for a temperature range of (150-300°C) and low power consumption is modelled and results are discussed.@en

In this paper, we present electro-thermal analysis and design of a combined MEMS micro hotplate and interdigitated-capacitance impedance sensor for gas sensing application using nano-porous materials like metal organic framework (MOF). The effects of design parameters of interdigitated electrodes such as width(W) and gap(G) of the capacitor, metallization ratio, number of electrodes and area of the capacitor. The influence of height of the electrode material, thickness of the insulation layer between the capacitance electrodes and the micro hotplate electrodes are studied. These design parameters are optimized to obtain a high bare capacitance of the electrodes using analytical and electric and thermal domain simulations in COMSOL 5. The design and thermal analysis of the micro hotplate for a temperature range of (150-300°C) and low power consumption is modelled and results are discussed.@en

The in situ electrochemical growth of Cu benzene-1,3,5-tricarboxylate (CuBTC) metal-organic frameworks, as an affinity layer, directly on custom-fabricated Cu interdigitated electrodes (IDEs) is described, acting as a transducer. Crystalline 5-7 μm thick CuBTC layers are grown on IDEs consisting of 100 electrodes with a width and a gap of both 50 μm and a height of 6-8 μm. These capacitive sensors are exposed to methanol and water vapor at 30 °C. The affinities show to be completely reversible with higher affinity toward water compared to methanol. For exposure to 1000 ppm methanol, a fast response is observed with a capacitance change of 5.57 pF at equilibrium. The capacitance increases in time followed diffusion-controlled kinetics (k = 2.9 mmol s-0.5 g-1 CuBTC). The observed capacitance change with methanol concentration follows a Langmuir adsorption isotherm, with a value for the equilibrium affinity Ke = 174.8 bar-1. A volume fraction fMeOH = 0.038 is occupied upon exposure to 1000 ppm of methanol. The thin CuBTC affinity layer on the Cu-IDEs shows fast, reversible, and sensitive responses to methanol and water vapor, enabling quantitative detection in the range of 100-8000 ppm.@en

The in situ electrochemical growth of Cu benzene-1,3,5-tricarboxylate (CuBTC) metal-organic frameworks, as an affinity layer, directly on custom-fabricated Cu interdigitated electrodes (IDEs) is described, acting as a transducer. Crystalline 5-7 μm thick CuBTC layers are grown on IDEs consisting of 100 electrodes with a width and a gap of both 50 μm and a height of 6-8 μm. These capacitive sensors are exposed to methanol and water vapor at 30 °C. The affinities show to be completely reversible with higher affinity toward water compared to methanol. For exposure to 1000 ppm methanol, a fast response is observed with a capacitance change of 5.57 pF at equilibrium. The capacitance increases in time followed diffusion-controlled kinetics (k = 2.9 mmol s-0.5 g-1 CuBTC). The observed capacitance change with methanol concentration follows a Langmuir adsorption isotherm, with a value for the equilibrium affinity Ke = 174.8 bar-1. A volume fraction fMeOH = 0.038 is occupied upon exposure to 1000 ppm of methanol. The thin CuBTC affinity layer on the Cu-IDEs shows fast, reversible, and sensitive responses to methanol and water vapor, enabling quantitative detection in the range of 100-8000 ppm.@en

The in situ electrochemical growth of Cu benzene-1,3,5-tricarboxylate (CuBTC) metal-organic frameworks, as an affinity layer, directly on custom-fabricated Cu interdigitated electrodes (IDEs) is described, acting as a transducer. Crystalline 5-7 μm thick CuBTC layers are grown on IDEs consisting of 100 electrodes with a width and a gap of both 50 μm and a height of 6-8 μm. These capacitive sensors are exposed to methanol and water vapor at 30 °C. The affinities show to be completely reversible with higher affinity toward water compared to methanol. For exposure to 1000 ppm methanol, a fast response is observed with a capacitance change of 5.57 pF at equilibrium. The capacitance increases in time followed diffusion-controlled kinetics (k = 2.9 mmol s-0.5 g-1 CuBTC). The observed capacitance change with methanol concentration follows a Langmuir adsorption isotherm, with a value for the equilibrium affinity Ke = 174.8 bar-1. A volume fraction fMeOH = 0.038 is occupied upon exposure to 1000 ppm of methanol. The thin CuBTC affinity layer on the Cu-IDEs shows fast, reversible, and sensitive responses to methanol and water vapor, enabling quantitative detection in the range of 100-8000 ppm.@en

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