Inkjet-Printed Functionalization of CMUT-Based CO2 Sensors

Abstract

The trade-off between the functionalization shift of the informative parameters and sensitivity of capacitive micromachined ultrasound transducers (CMUT)-based CO2 sensors is addressed, and the CMUT surface modification process by thin inkjet-printed polyethyleneimine (PEI) films is optimized. It was shown that by the proper preparation of the active CMUT surface and properly diluted PEI solution, it is possible to minimize the functionalization shift of the resonance frequency and the quality of the resonance and preserve the sensitivity potential. So, after optimization, we demonstrated 23.2 kHz frequency shift readings of the sensor with 16 MHz nominal frequency while in the gas chamber and switching between pure N2 and CO2. After testing the sensors with different PEI film thickness, it was confirmed that a 200 nm average thickness of a PEI film is an optimum, because this is the practical limit of CO2 absorption depth at given conditions. Additionally, we note that modification of the hydrophilic/hydrophobic properties of the CMUT surface allows changing the nanoscale surface roughness of the printed PEI film and controlling the area resolution of the inkjet functionalization by reducing the diameter of a single dot down to 150 μm by a commercially available printer cartridge.

Design of Zeolitic Imidazolate Framework-8-Functionalized Capacitive Micromachined Ultrasound Transducer Gravimetric Sensors for Gas and Hydrocarbon Vapor Detection

“…However, this work did not detect any reasonable response with regards to dry N 2 to CH 4 , wet N 2 to CH 4 , or even air to CH 4 -switching compared with AZ-coated and bare CMUT sensors. Considering that the CH 4 -ZIF-8 interaction strength of 10 kJ/mol [36] is of the order of a typical H•••N hydrogen bond and CMUT-based sensors with H 2 O and CO 2 with a similar bond strength bound to other functional materials have already been demonstrated [25,31,38], the vibrational environment could be a suitable explanation for such results. The ZIF-8 cage aperture size was 0.34 nm.…”

“…This paper aimed to demonstrate the feasibility, characteristics, and versatility of a gravimetric MEMS capacitive micromachined ultrasound transducer (CMUT)-based ZIF-8-modified gas sensor. Successful gravimetric CMUT devices have been demonstrated before [25][26][27][28]. CMUTs are popular as a mass-sensing platform due to their sensitivity, ease of manufacture, scaling, and electronic response.…”

Significance of Various Sensing Mechanisms for Detecting Local and Atmospheric Greenhouse Gases: A Review

“…Barauskas et al used polyethylenimine or other gas adsorbing materials, and a capacitive, micromachined ultrasound transducer, referred to as CMUT, in order to bind and selectively detect up to five gases, including CO 2 , in the environment. [99] Assessed against the CO 2 gas concentration, a frequency response shift was detected, distinguishing the PEI-coated and uncoated CMUT in terms of their feedback to the amount of CO 2 . The PEI-modified transducer demonstrated an elevated signal output due to the CO 2 adsorption.…”

“…Highlighted in the sections above, a vast array of traditional, novel, and hybrid complex materials have been uncovered and adopted within the frameworks of sensors dedicated toward detecting GHGs. These include the carbon nanomaterials, polymers, metal oxide semiconductors, and transition metal dichalcogenides, in calorimetric sensors; [102,108,117,122]] the solid polymer electrolytes, pseudo-solid-state electrolytes, and carbon materials, in electrochemical sensors; [67][68][69]109,121,133,137]] pyroelectric elements, LEDs, and PDs, in IR/FTIR/NDIR sensors; [72][73][74][75][76]78,84,85,109,131]] metal oxides, carbon materials, polymers, and single-or multi-mode optical fibers, in opticalbased sensors; [86][87][88][89][90][92][93][94]109,134]] piezoelectric materials, piezoceramics, carbon materials, and polymers, in acoustic/ultrasonic sensors; [91,[95][96][97][98][99]100,110,111] as well as polymer films in calorimetric or gas chromatographic sensors. [103,104,…”