High Temperature Annealing Studies on the Piezoelectric Properties of Thin Aluminum Nitride Films

Abstract

A Rapid Thermal Annealing (RTA) system was used to anneal sputtered and MOVPEgrown 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, d 33 , 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 d 33 . A high temperature furnace has been built that is capable of taking in-situ measurements of the piezoelectric response of AlN films. In-situ d 33 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.

Investigations of AlN thin film crystalline properties in a wide temperature range by in situ x-ray diffraction measurements: Correlation with AlN/sapphire-based SAW structure performance

“…evidenced by the present study should lead to an augmentation of the AlN thin film piezoelectric coefficients with temperature, which has been experimentally demonstrated up to 300°C [13].…”

Wide Bandgap Semiconductors for Sensing Within Extreme Harsh Environments

“…AlN and GaN can maintain their piezoelectric properties at elevated temperatures (7,14) as they are non-ferroelectric materials with no curie point. Commonly utilized ferroelectric piezoelectric materials, such as lead zirconate titanate (PZT), are limited to operation temperatures below 300 o C due to the Curie point and depolarization (15). Piezoelectric materials can be used as sensing elements or actuators.…”

“…In addition to the SiC-based sensors mentioned above, piezoelectric sensing elements and sensors utilizing AlN have been demonstrated at elevated temperatures (22). These devices exploit the ability of non-ferroelectric, hexagonal AlN to maintain it piezoelectric properties at temperatures as high as 1000 o C (14,15). It should be noted that hightemperature energy harvesters have been designed with AlN to harness energy from pressure pulses (e.g.…”