Submicron Ferroelectric Elements Fabricated by Direct Electron Beam Lithography
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Submicron Ferroelectric Elements Fabricated by Direct Electron Beam Lithography Dong-Joo Kim1, Jin Seo Im1,2, Carol Thompson1,3, S. K. Streiffer1, G. Wiederrecht2, and O. Auciello1 1 Materials Science Division, Argonne National Laboratory, Argonne, IL 2 Chemistry Division, Argonne National Laboratory, Argonne, IL 3 Dept. of Physics, Northern Illinois University, DeKalb, IL ABSTRACT To realize Gigabit density ferroelectric memory devices, downscaling issues involving processing, materials, and fundamental ferroelectric behavior must be resolved. To address patterning and characterizing ferroelectric films at the nanoscale, we have prepared different lateral sizes of ferroelectric PZT capacitors down to 120 nm, using direct-write electron beam lithography. Characterization of the piezoelectric activity of the patterned elements was performed by means of piezoelectric-sensitive scanning probe microscope in the contact mode. Switching of single 120 nm cells was achieved. INTRODUCTION Ferroelectric materials continue to draw considerable attention due to the wide range of their potential applications in microelectronics, especially in non-volatile ferroelectric random access memories (NV-FeRAM) [1]. Low-density NV-FeRAMs are now incorporated in commercial products. This technological achievement has been possible because of the advances in the synthesis and characterization of ferroelectric thin films, which provides the basis for understanding the material microstructure-property relationships and the associated physics of polarization domain dynamics, and integration into submicron capacitors. For high density NVFeRAMs of 1 Gbit and greater, development of nanoscale capacitors of the order of 100 nm by 100 nm is required. For such a prospective design, there are several downscaling issues including processing, materials, and fundamental size effects. However, fabrication by a conventional lithography process has practical limitations in decreasing feature size given typical lab-scale cleanroom equipment. In addition, dry etching processes may result in reduction of observed polarization, separate from any intrinsic size effects which must be addressed to understand the physics of ferroelectric materials and to design and engineer the next generation of NV-FeRAM. The fabrication of 3-D submicron ferroelectric elements has been demonstrated by several techniques [2-6]. Okamura et al. have shown patterned Bi4Ti3O12 with a lateral dimension of 300 nm by electron beam direct writing [2]. Alexe et al. also used electron beam lithography to fabricate individual Pb(Zr,Ti)O3 (PZT) structure on conducting SrTiO3:Nb substrates with lateral sizes down to 100 nm [3]. Stanishevsky et al. used focused ion beam patterning for fabricating ferroelectric capacitors [4]. Epitaxial ferroelectric structures produced using e-beam lithography and physical etching techniques [5], and self-assembled ferroelectric cells have been demonstrated [6]. In this paper, we report a fabrication protocol for sharply defined submicron Pb(Zr0.3Ti0.7
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