Title: Deposition and characterisation of ultralow-stress ZnO thin films for application in FBAR-based gravimetric biosensors

Authors: L. García-Gancedo; G.M. Ashley; X.B. Zhao; J. Pedrós; A.J. Flewitt; W.I. Milne; J.K. Luo; J.R. Lu; C.J.B. Ford; D. Zhang

Addresses: Electrical Engineering Division, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FA, UK. ' IMRI, University of Bolton, Deane Road, Bolton BL3 5AB, UK. ' School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK. ' Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK. ' Electrical Engineering Division, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FA, UK. ' Electrical Engineering Division, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FA, UK. ' IMRI, University of Bolton, Deane Road, Bolton BL3 5AB, UK. ' School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK. ' Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK. ' State Key Laboratory of Powder Metallurgy, Central South University, Lushan Road South, Changsha 410083, China

Abstract: Zinc oxide (ZnO) thin films were deposited at high rates (> 50 nm min?1) using a unique technique known as high target utilisation sputtering (HiTUS). The films obtained possess good crystallographic orientation, low surface roughness, very low stress and excellent piezoelectric properties. We have utilised the films to develop highly sensitive biosensors based on thickness longitudinal mode (TLM) thin film bulk acoustic resonators (FBARs). The FBARs have the fundamental TLM at a frequency near 1.5 GHz and quality factor Q higher than 1,000, which is one of the largest values ever reported for ZnO-based FBARs. Bovine Serum Albumin (BSA) solutions with different concentrations were placed on the top of different sets of identical FBARs and their responses to mass-loading from physically adsorbed protein coatings were investigated. These resonators demonstrated a high sensitivity and thus have a great potential as gravimetric sensors for biomedical applications.

Keywords: high target utilisation sputtering; HiTUS; zinc oxide; ZnO thin films; film bulk acoustic resonator; FBAR; biosensors; crystallographic orientation; surface roughness; surface quality; stress; piezoelectric properties; bovine serum albumin; BSA solutions; gravimetric sensors; biomedical applications; nanotechnology.

DOI: 10.1504/IJNM.2011.042478

International Journal of Nanomanufacturing, 2011 Vol.7 No.3/4, pp.371 - 382

Available online: 14 Sep 2011

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