High Temperature Annealing Studies on the Piezoelectric Properties of Thin Aluminum Nitride Films
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1052-DD06-18
High Temperature Annealing Studies on the Piezoelectric Properties of Thin Aluminum Nitride Films R. Farrell1, V. R. Pagán1, A. Kabulski1, Sridhar Kuchibhatla1, J. Harman1, K. R. Kasarla1, L. E. Rodak1, J. Peter Hensel2, P. Famouri1, and D. Korakakis1 1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, PO BOX 6109, Morgantown, WV, 26506 2 USDOE/NETL, Morgantown, WV, 26505 ABSTRACT A Rapid Thermal Annealing (RTA) system was used to anneal sputtered and Metal Organic Vapor Phase Epitaxy (MOVPE)-grown Aluminum Nitride (AlN) thin films at temperatures up to 1000°C in ambient and controlled environments. According to Energy Dispersive X-Ray Analysis (EDAX), the films annealed in an ambient environment rapidly oxidize after five minutes at 1000°C. Below 1000°C the films oxidized linearly as a function of annealing temperature which is consistent with what has been reported in literature [1]. Laser Doppler Vibrometry (LDV) was used to measure the piezoelectric coefficient, d33, of these films. Films annealed in an ambient environment had a weak piezoelectric response indicating that oxidation on the surface of the film reduces the value of d33. A high temperature furnace has been built that is capable of taking in-situ measurements of the piezoelectric response of AlN films. In-situ d33 measurements are recorded up to 300°C for both sputtered and MOVPE-grown AlN thin films. The measured piezoelectric response appears to increase with temperature up to 300°C possibly due to stress in the film. INTRODUCTION Aluminum nitride is an attractive material for the fabrication of MicroElectroMechanical Systems (MEMS) due in part to its piezoelectricity, inertness and tolerance to high temperatures. AlN remains piezoelectric after annealing at temperatures as high as 1000°C, while other materials with a higher piezoelectric response (e.g. PZT) lose their properties after annealing above their Curie temperature well below 1000°C. Annealing AlN at high temperatures in an ambient environment causes the surface of the film to oxidize. AlN begins to oxidize in an ambient environment at 800°C and the oxidation abruptly increases at an annealing temperature of 1000°C [1]. This surface oxidation drastically reduces the displacement of piezoelectric films. In-situ measurements of AlN films using Laser Doppler Vibrometry are not widely reported. Kano et al used rf-sputtered 1200 nm thick AlN films to reveal that AlN can be used as an actuator with a constant output velocity up to 300°C [2]. They reported a constant d33 value of 1.38 pC/N at temperatures ranging from 20°C to 300°C. The results of high temperature measurements of sputtered and Metal Organic Vapor Phase Epitaxy (MOVPE)-grown AlN films as actuators will be discussed in this paper. EXPERIMENT This study reports the effects of high temperature annealing on sputtered and MOVPEgrown AlN thin films. Sputtered films were deposited onto a 350 µm thick (1 0 0)-oriented p-
type silicon substrate using a DC magnetron sputtering techniq
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