Evidence of High Remanent Polarization in Epitaxial Thin Film Ferroelectric BaTiO₃ Integrated onto Silicon

The computing world is approaching a global energy crisis due to the exponential growth of energy requirement as CMOS transistors scale to smaller dimensions. One path forward is to lower the device supply voltages. In this regard, low power beyond-CMOS technologies such as devices based on ferroelectric materials are receiving renewed interest from both the scientific and technological communities. Perovskite BaTiO3 (BTO) ferroelectric thin films are highly promising due to their low coercivity, large remanent polarization and environmental friendliness. Copious progress has been made towards optimizing ferroelectric BTO on oxide substrates including recent reports on BTO-based devices for ultra-low-voltage operation.¹ However, to be compatible with high volume manufacturing, integration of high quality BTO onto Silicon is key. Thus far, quantitative reports on the ferroelectric properties of BTO on Si substrates have been sparse. Properties tend to be degraded including higher leakage and low remanent polarization (Pr) of 5-12 µC/cm².^1-5 Additionally, films tend to be in the range of 50-200nm thick.^1-5 Ideally for scaled devices, films of BTO on Si would be as thin as possible, with low coercivity, low leakage, high endurance, and Pr close to the bulk value of 30 µC/cm². In this work, we report remanent polarization up to ~ 20 µC /cm² in Pulse laser deposition (PLD) grown ultrathin 30-nm-thick BTO films grown on Molecular Beam Epitaxial SrTiO3 (STO)-buffered Si (Si:STO) substrates, with leakage in the order of ~ 1A/cm². The Si:STO/SRO/BTO/Ti/Pd devices did not undergo dielectric breakdown up to 10⁹ cycles, with only a 5% reduction in Pr observed after cycling. Structural characterizations revealed epitaxial growth of BTO films with relaxed lattice parameters. The quality of the STO buffer on Si was found to be critical for optimizing the ferroelectricity in BTO. This improved remanent polarization in ultrathin BTO with low leakage paves the way towards integrating a semiconducting channel with this device to create the next generation transistor. Nevertheless, a pursuit towards a 300 mm compatible perovskite process entails a concerted effort among academia, semiconductor manufacturers and tool manufacturers.<br/><br/>Reference:<br/>1. Jiang, Y., <i>et al.</i> Enabling ultra-low-voltage switching in BaTiO₃. <i>Nat. Mater.</i> 21, 779–785 (2022)<br/>2. Scigaj M. <i>et al.</i>, Ultra-flat BaTiO₃ epitaxial films on Si(001) with large out-of-plane polarization. <i>Appl. Phys. Lett.</i> 102 (11): 112905 (2013)<br/>3. Scigaj M. <i>et al.</i>, High ferroelectric polarization in <i>c</i>-oriented BaTiO₃ epitaxial thin films on SrTiO3/Si (001). <i>Appl. Phys. Lett.</i> 109, 122903 (2016)<br/>4. Lyu J. <i>et al.</i>,<b> </b>Tailoring Lattice Strain and Ferroelectric Polarization of Epitaxial BaTiO3 Thin Films on Si(001). <i>Scientific Reports</i>. 8, 495 (2018)<br/>5. Singamaneni S.R. <i>et al.</i>, Ferroelectric and ferromagnetic properties in BaTiO3 thin films on Si (100), J<i>. Appl. Phys.</i> 116, 094103 (2014)