Inkjet-Printed Functionalization of CMUT-Based CO₂ Sensors

Area of Science:

• Materials Science
• Chemical Engineering
• Sensor Technology

Background:

• Capacitive micromachined ultrasound transducers (CMUTs) are promising for gas sensing applications.
• Optimizing surface functionalization is crucial for balancing sensor sensitivity and signal stability.
• Polyethyleneimine (PEI) is a suitable material for CO2 functionalization of CMUT surfaces.

Purpose of the Study:

• To optimize the surface modification process of CMUTs using inkjet-printed PEI films for CO2 sensing.
• To address the trade-off between functionalization-induced parameter shifts and sensor sensitivity.
• To achieve high-performance CO2 detection with CMUT-based sensors.

Main Methods:

• Inkjet printing of polyethyleneimine (PEI) films onto CMUT surfaces.
• Optimization of PEI solution dilution and CMUT surface preparation.
• Characterization of CMUT resonance frequency, quality factor, and sensitivity.
• Testing sensor response to CO2 gas under varying PEI film thicknesses.

Main Results:

• Minimized functionalization shift in resonance frequency and quality factor.
• Preserved sensitivity potential of the CMUT-based CO2 sensor.
• Demonstrated a 23.2 kHz frequency shift for a 16 MHz sensor switching between N2 and CO2.
• Identified an optimal PEI film thickness of 200 nm for CO2 absorption.
• Controlled inkjet functionalization resolution down to 150 μm dot diameter.

Conclusions:

• The optimized PEI functionalization process effectively balances CMUT sensor performance for CO2 detection.
• A 200 nm PEI film thickness represents the practical limit for CO2 absorption, maximizing sensor performance.
• Inkjet printing offers precise control over functionalization, enabling tailored CMUT sensor design.