Development of Aluminum Nitride/Platinum Stack Structures for an Enhanced Piezoelectric Response
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Development of Aluminum Nitride/Platinum Stack Structures for an Enhanced Piezoelectric Response Adam Kabulski, John Harman, Parviz Famouri, and Dimitris Korakakis Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV, 26506
ABSTRACT Aluminum nitride (AlN) films are being investigated for piezoelectric and high temperature applications, but the piezoelectric response is still much lower than that of more common piezoelectric materials such as lead zirconate titanate or zinc oxide. A method of maximizing the piezoelectric response of aluminum nitride has been explored by depositing stack structures composed of aluminum nitride and platinum. These stack structures were created by depositing a thin, ~50nm, metal layer in between thicker, ~150-350nm, layers of the piezoelectric film. Platinum was chosen as the metal interlayer due to the tendency of AlN to become highly c-oriented when deposited on Pt. An electric field was applied across the structure and displacements were measured using a Laser Doppler Vibrometer. A maximum piezoelectric coefficient d33 was found to be over two times larger than the theoretical value for AlN (3.9pm/V). However, some of the stack structures were found to be conductive when measuring the displacement. I-V measurements as well as Fowler-Nordheim theory and plots were applied to investigate tunneling due to high electric fields in the structures. INTRODUCTION Aluminum nitride (AlN), a material that is being considered for deep ultraviolet optoelectronics due to its wide bandgap of 6.2eV, is also currently being examined for uses based on its piezoelectric behavior [1,2]. AlN is an attractive material for MEMS applications because of its piezoelectric response (d33 = 3.9pm/V) as well as its stability to high temperatures in inert atmospheres [2]. More commonly used piezoelectric materials such as lead zirconate titanate (PZT) and zinc oxide (ZnO) have higher values for the piezoelectric coefficient d33 (60130pm/V and 5.9pm/V respectively) but have Curie points lower than 400°C [3]. For high temperature or high power applications, a piezoelectric material such as AlN (with no known Curie point up to this date) is a much better candidate. AlN has been deposited using various techniques with sputtering being one of the most common deposition methods. These sputtered films range from being amorphous to polycrystalline. Crystalline structure is of great importance to piezoelectric materials with more crystalline materials exhibiting a much larger piezoelectric response. Increased polycrystalline behavior through maximized deposition parameters can aid in increasing this piezoelectric response. While the piezoelectric response is lower for polycrystalline films, the response can be large enough to fabricate useful devices. This response can be further increased by maximizing the crystalline orientation of the films and by creating stack structures which amplify the
piezoelectric effect. Platinum(Pt) was chosen as the metal inter
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