Low-temperature processing of screen-printed piezoelectric KNbO3 with integration onto biodegradable paper substrates

Abstract

The development of fully solution-processed, biodegradable piezoelectrics is a critical step in the development of green electronics towards the worldwide reduction of harmful electronic waste. However, recent printing processes for piezoelectrics are hindered by the high sintering temperatures required for conventional perovskite fabrication techniques. Thus, a process was developed to manufacture lead-free printed piezoelectric devices at low temperatures to enable integration with eco-friendly substrates and electrodes. A printable ink was developed for screen printing potassium niobate (KNbO3) piezoelectric layers in microns of thickness at a maximum processing temperature of 120 °C with high reproducibility. Characteristic parallel plate capacitor and cantilever devices were designed and manufactured to assess the quality of this ink and evaluate its physical, dielectric, and piezoelectric characteristics; including a comparison of behaviour between conventional silicon and biodegradable paper substrates. The printed layers were 10.7–11.2 μm thick, with acceptable surface roughness values in the range of 0.4–1.1 μm. The relative permittivity of the piezoelectric layer was 29.3. The poling parameters were optimised for the piezoelectric response, with an average longitudinal piezoelectric coefficient for samples printed on paper substrates measured as d33, eff, paper = 13.57 ± 2.84 pC/N; the largest measured value was 18.37 pC/N on paper substrates. This approach to printable biodegradable piezoelectrics opens the way forward for fully solution-processed green piezoelectric devices.

Additively Manufactured Degradable Piezoelectric Microsystems for Sensing and Actuating

“…[ 25 ] For the reference samples, a 10/100 nm Cr/Au layer was deposited via thermal evaporation, following previous work on this system. [ 22 ]…”

“…In line with the results of previous investigations on low‐temperature contact poling, the poling duration was fixed for all samples to be 5 min. [ 22 ] Figure S9 (Supporting Information) provides more information on the poling process.…”

“…The magnitude of the piezoelectric response for the reference samples with gold electrodes match well with prior studies on this piezoelectric, with a maximum of 11.6 ± 0.8 pC N −1 when poled at 15 V µm −1 (compared to 13.6 ± 2.8 pC N −1 reported previously). [ 22 ] Samples with gold electrodes were not evaluated for piezoelectric coefficients when poled at 20 V µm −1 or above due to breakdown events resulting in damage to the electrodes. A maximum piezoelectric response was obtained for samples poled with an applied field of 15 V µm −1 for samples with zinc or carbon electrodes, where the average effective piezoelectric coefficient was 5.1 ± 0.8 pC N −1 for zinc electrode devices and 4.6 ± 0.2 pC N −1 for carbon electrode devices.…”

“…Preparation of KNbO 3 -Based Ink: Prior to ink manufacture, the KN powder was ground in order to reduce average particle diameter and improve the homogeneity of the particle sizing, following the procedure previously described by Monroe. [22] Five grams of KN powder was placed in a Teflon grinding vessel (72 mL volume, fabricated in-house), along with 10 mL of 1-propanol and 125 g of ZrO 2 grinding media (2 mmØ, Retsch). Grinding was conducted in a planetary ball mill (QM-3SP2), for a total duration 24 h, with a directional switching period of 0.3 h and a jar rotational speed of 200 rpm.…”

“…As a non-toxic perovskite material, KNbO 3 is an excellent choice for printed piezoelectrics, with comparatively high values reported for both bulk KNbO 3 and screenprinted KNbO 3 of 109 and 13.6 pC N −1 respectively. [22][23][24] For printed conductive materials, both carbon and zinc are promising candidates, with degradable screen-printing inks realized for both conductive materials in recent years. [25][26][27] Readily degradable, carbon is the standard for many biodegradable electronics applications, however its poor conductivity makes carbon non-ideal for widespread industrial use.…”