Printed degradable piezoelectric microsystems: From ink formulation to device fabrication and characterization

As the world moves further and further into the semiconductor era, the amount of waste generated from electronics ("e-waste") is increasing rapidly and unsustainably. Of particular note, alternatives to lead-based piezoelectric materials must be established. However, addressing e-waste reduction requires the development of both sustainable materials and green fabrication techniques, especially for high-volume, short-life uses. With low material waste and high scalability, additive manufacturing offers a greener alternative to conventional processing, and thus printed green piezoelectrics emerge as promising candidates to replace Pb-based counterparts. Even so, their integration into completely degradable devices has been hindered by processing complexity and high temperatures- alternative approaches must be established to enable entirely green printed piezoelectric devices.To that end, this thesis focuses on the development of degradable piezoelectric microsystems composed entirely of green materials and fabricated using eco-friendly printing technologies. We cover aspects from ink formulation to device fabrication and characterization, establishing a facile process for the low-temperature printing of KNbO3-based piezoelectrics and their integration into fully printed green devices.We begin with a down-selection of device and ink components, assessing several degradable piezoelectric materials (RS, ADP, ZnO, HA, KNbO3) in feasibility studies, and finally selecting potassium niobate (KNbO3) after successful proof-of-concept investigations validate low-temperature poling of screen-printed perovskite materials on degradable substrates.Next a screen-printing process for KNbO3 is developed and refined. Inks in a 58:8:34 wt% KN:EC:pentanol mixture are prepared and characterized by printing standardized designs on silicon with Au electrodes. We assess the influence of process and material parameters on print quality and device performance, with focusing on KNbO3 preparation via milling and post-processing. We achieve a piezoelectric response as high as 12.4 pC/N in 6 um thick screen-printed layers.The low-temperature printing process is then transferred onto degradable paper substrates. Performance evaluations are conducted on devices fabricated using paper and Si substrates with evaporated gold electrodes, employing both circular capacitor and cantilever device configurations. By optimizing poling parameters, we achieve piezoelectric coefficients as high as 18.4 pC/N, and averaging 13.6 pC/N on paper.In the final phase, printed zinc and carbon conductors are integrated into the process, leading to the successful fabrication of fully printed, green piezoelectric devices for the first time. The influence of electrode materials on device performance is studied, obtaining effective piezoelectric coefficients as high as 4.6 and 5.1 pC/N for printed devices on paper with C and Zn electrodes, respectively.The culmination of this research is the development of fully printed green demonstrator devices, including a paper-based force sensor array and an acoustic actuator integrated into entirely degradable headphones. These devices demonstrate the technological potential for practical applications.The research presented in this thesis contributes to the development of sustainable and eco-friendly printed electronic devices, paving the way for the reduction of environmentally harmful e-waste on a global scale.