Comparative Study of Thin PZT Sol-gel Films Deposited on Pt and GaN Substrates
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Comparative Study of Thin PZT Sol-gel Films Deposited on Pt and GaN Substrates Serguei A. Chevtchenko1, Francisco A. Agra1, Jinqiao Xie1, and Hadis Morkoç2 1 Electrical Engineering, Virginia Commonwealth University, 601 West Main Street, Richmond, VA, 23284-3072 2 Electrical Engineering and Physics, Virginia Commonwealth University, 601 West Main Street, Richmond, VA, 23284-3072 ABSTRACT We provide a comparative study of the piezoresponse in thin Pb(ZrxTi1-x)O3 (PZT) films deposited onto GaN/sapphire and Pt/Ti/SiO2/Si substrates using the sol-gel process. The effective piezoelectric coefficient was measured by Piezoresponse Force Microscopy. The resulting effective piezoelectric coefficient obtained for PZT(~180 nm)/GaN/sapphire structure is 16.7 ± 3.4 pm/V and for PZT(~180 nm)/Pt/Ti/SiO2/Si structure is 7.8 ± 0.8 pm/V. We also discuss the substrate clamping effect of both structures and explain the relatively stronger piezoresponse of PZT on GaN by different orientation of films formed on the two types of substrates. In this investigation, the PZT thin films crystallized with preferred (100) and (110) orientations on platinum and GaN, respectively. The phase mode of the Piezoresponse Force Microscopy was used to demonstrate remanent polarization in PZT/GaN/sapphire structure. INTRODUCTION The perovskite Pb(ZrxTi1-x)O3 or PZT material is one of the promising candidates for the development of non-volatile ferroelectric random access memories (FeRAM) and microelectromechanical systems (MEMS) due to its excellent ferroelectric and piezoelectric properties.1,2 Considerable research efforts in the recent years have focused on the integration of ferroelectric materials on Si substrates. Beside the development of non-volatile memory devices these efforts are stimulated by potential use of metal-ferroelectric-semiconductor (MFS) interfaces in integrated optoelectronic, piezoelectric, and microwave devices.3,4,5 It was found that the ferroelectric/Si interface is unstable most probably due to high interface trap concentration which increases with increasing processing temperature made necessary for the formation of thin ferroelectric films.5,6 A thermally stable semiconductor is required in general for such an application. Recently, GaN received considerable attention as a promising candidate to develop a usable ferroelectric/semiconductor interface.7 Applications of such a structure include ferroelectric nanomechanical resonators8 and metal-ferroelectric-semiconductor fieldeffect transistors (MFSFETs)9. In the last case the structure is analogous to GaN metal-oxidesemiconductor FETs with the advantage of the high dielectric constant of ferroelectric material serving as an insulator. The study of piezoelectric and ferroelectric properties of PZT films deposited on GaN is important. The residual stress in thin piezoelectric/ferroelectric layers can significantly affect the properties of layers. The effect associated with the residual stresses is known as “clamping effect” of the substrate and depends on the subst
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