Epitaxial BaTiO₃ on Si(100) with In-Plane and Out-of-Plane Polarization Using a Single TiN Transition Layer

Abstract

The integration of BaTiO3 with Si(100) is essential to exploit its ferroelectric capabilities in the well-established Si-complementary metal–oxide–semiconductor (CMOS) technological platform. To enable this goal, epitaxial BaTiO3 films with both in-plane and out-of-plane polarization are demonstrated on Si(100) with just a single TiN layer that is also CMOS-compatible. This change in polarization direction is brought about very simply by changing the growth temperature. Piezo force microscopy and optical second-harmonic generation measurements confirm the presence of out-of-plane and in-plane polarization. Films deposited at relatively higher temperatures of 800 °C have polarization lying in-plane at room temperature. The nonlinear dielectric susceptibilities were found to be comparable to the state-of-the-art films integrated with more complex transition schemes. Films deposited at a relatively lower temperature of 600 °C are defective and revert to 800 °C like films on annealing. The defects however confer on them an out-of-plane polarization with a large tetragonality of 1.6% at 500 °C. The changes in anomalous lattice expansion in out-of-plane coupled with coefficient of thermal expansion (CTE) strain result in orientation selection in our films.

Giant electromechanical response from defective non-ferroelectric epitaxial BaTiO3 integrated on Si (100)

“…The unit cell volume of the lm (65. 35 Å 3 ) is larger than that of bulk ceramic BTO (a = 3.99 Å, c = 4.04 Å, 64.31 Å 3 ), as a result of chemical expansion due to defects 24 . The polarization maps obtained from HAADF STEM (Fig.…”

“…Our defective BTO is not ferroelectric, as we do not see any ferroelectric switching peaks in large signal AC I-V plots (Fig 4a and S4 a, b, c). We also measure a large coefficient of thermal expansion (CTE), α33=2.36  10 -5 /K, through in situ XRD measurements on these films (results published elsewhere 24 , also reproduced in Fig S6c). Coincidentally, large CTE and large electrostriction are both related to lattice anharmonicity, in this case induced by defects.…”

“…This work is a significant step in achieving lead-free CMOS compatible materials with giant EM response. The effect of deposition conditions on epitaxy and growth of the defective complex oxides on Si studied here was previously developed by Vura et al and has been reported elsewhere 23,24 . A buffer layer of epitaxial TiN ((100) oriented, 40-60 nm) was deposited on n++ Si (100) using reactive pulsed laser deposition in N2 (99.9999% pure) atmosphere in eclipsed off-axis configuration 23 analysis reveals the presence of a TiOx (18-20 nm) layer between TiN and BTO, formed via interfacial redox reaction during annealing.…”

PLD Epitaxial Thin‐Film BaTiO3 on MgO − Dielectric and Electro‐Optic Properties

“…[6a], it becomes apparent that r 33 = r zzz is about a factor 30 weaker than r 42 = r yzy , and that r 13 = r xzx is even smaller. Thus, the two coefficients r 13 and r 33 can be considered negligible andr 13…”

“…When BTO is grown on substrates with a slightly larger lattice constant above 700 °C, usually its layer stack initially comprises in‐plane BTO. [ 13 ] Here, its c‐axis crystalline structure lies in‐plane and tends to grow in domains that are aligned by 0 o and 90 o against the crystalline structure of the substrate, see Figure 1d,e. To fully exploit the largest Pockels coefficient r 42 = r yzy = r xzx in such perpendicularly oriented domains, one orients the waveguide at a 45° angle with respect to the in‐plane axis.…”