Piezoresponse Measurements for Pb(Zr,Ti)O 3 Island Structure Using Scanning Probe Microscopy
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Piezoresponse Measurements for Pb(Zr,Ti)O3 Island Structure Using Scanning Probe Microscopy H.Fujisawa, K.Morimoto, M.Shimizu, H.Niu, K.Honda1 and S.Ohtani1 Department of Electronics, Faculty of Engineering, Himeji Institute of Technology, Shosha 2167, Himeji, Hyogo 671-2201, JAPAN 1 Fujitsu Laboratory Ltd, 10-1 Wakamiya Morinosato, Atsugi, Kanagawa 243-0197, JAPAN ABSTRACT Piezoresponse measurements using scanning probe microscopy (SPM) were performed for island structures at the initial growth stage of Pb(Zr,Ti)O3 (PZT) (Zr/Ti=0/100, 24/76 and 74/26) thin films prepared by metalorganic chemical vapor deposition(MOCVD). Deposition times were varied from 5s to 7min to control the size of PZT islands. When deposition times were shorter than 3min, (111)-oriented triangular-shaped PZT islands were observed before forming a continuous film. The width and height of PZT islands deposited at 3min were 160 and 70nm for Zr/Ti = 0/100, 100 and 30nm for Zr/Ti = 24/76, and 80 and 20nm for Zr/Ti = 74/26, respectively. The size of islands decreased with increasing the Zr composition. Hysteresis loops due to polarization switching were observed in the phase difference and displacement of piezoresponse measured using scanning probe microscopy (SPM). This result proves that nano-size PZT islands have weak ferroelectricity. The minimum width and height of PZT islands which showed ferroelectricity were 70 and 30nm for Zr/Ti=24/76. INTRODUCTION Recently, many efforts have been made toward the realization of megabit scaled non-volatile ferroelectric random access memories (NV-FeRAMs) using 1 transistor and 1 capacitor (1T1C) cell structure. To go beyond megabit NV-FeRAMs, will require the reduction in the capacitor size and thickness of ferroelectric thin films below 1µm2 and 100nm, respectively. In such small ferroelectric capacitors, size effects will have large influences on electrical properties of ferroelectric thin films. There have been a variety of reports on the size effects of thin films. For example, the calculated value of remanent polarization was reported for SrBi2Ta2O9 films with decreasing grain size and film thickness [1]. We have also reported on the thickness dependence of electrical properties of epitaxial Pb(Zr,Ti)O3 (PZT) thin films grown on SrRuO3/SrTiO3(100) [2-4]. In these studies, it was found that PZT thin films with thickness of 40nm showed D-E hysteresis loops with high remanent polarization (Pr~40µC/cm2) [2-4]. However, the area (>φ50µm) of capacitors was much larger than that expected in high-integrated NV-FeRAMs. Therefore, it is still unknown whether capacitors show good ferroelectricity or not when the capacitor area is CC10.4.1
reduced below 1µm2. At the initial stage of metalorganic chemical vapor deposition (MOCVD) growth of PbTiO3 (PTO) and PZT thin films, island structures are observed before a continuous film is formed [5, 6]. These island structures are isolated from each other and can be considered as sub-micron ferroelectric capacitors except for the absence of top electrodes. Therefore, usin
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