Piezoelectric Properties of Zinc Oxide Thin Films Grown by Plasma‐Enhanced Atomic Layer Deposition

• Published in: Physica status solidi. A, Applications and materials science Vol. 217; no. 21
• Main Authors: Abu Ali, Taher, Pilz, Julian, Schäffner, Philipp, Kratzer, Markus, Teichert, Christian, Stadlober, Barbara, Coclite, Anna Maria
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-11-2020
• Subjects: atomic layer deposition; Atomic layer epitaxy; Crystallography; Photovoltaic cells; Piezoelectricity; Polyethylene terephthalate; Properties (attributes); Room temperature; Substrates; Thin films; Zinc oxide; Zinc oxides
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.202000319

Zinc oxide (ZnO) thin films are deposited by plasma‐enhanced atomic layer deposition (PE‐ALD). This deposition method allows depositing stoichiometric and highly resistive ZnO films at room temperature. Despite such important requirements for piezoelectricity being met, not much is known in literature about the piezoelectric properties of ZnO thin films (<70 nm) deposited by PE‐ALD. The films are grown at different substrate temperatures to investigate the effect on crystalline and piezoelectric properties. Films deposited on flexible poly(ethylene terephthalate) (PET) generated a higher piezoelectric current (>1.8 nA) and charge (>80 pC) compared with films deposited on glass (>0.3 nA and >30 pC) due to bending effects of the substrate when mechanically excited. Furthermore, increasing the substrate temperature, during deposition, enhances the growth along the (002) crystallographic orientation, which further strengthens the generated piezoelectric current signal for mechanical excitations along the ZnO film's c‐axis.
The piezoelectric properties of ZnO thin films grown by plasma‐enhanced atomic layer deposition are investigated. Films grown on flexible substrates show enhanced piezoelectric output compared with rigid substrates due to possible bending effects. A higher growth temperature also leads to enhanced piezoelectric output due to preferential crystallographic orientation along the [002]‐axis.