Scalable ferroelectric MOS capacitors comprised of single crystalline SrZrxTi1-xO3 on Ge.*

The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, ferroelectric materials integrated on semiconductors could lead to field-effect devices that require very little power to operate, or that possess both logic and memory functionalities. The development of metal-oxide-semiconductor (MOS) capacitors in which the polarization of a ferroelectric gate is coupled to the surface potential of a semiconducting channel is essential in order to realize such field-effect devices. Here we demonstrate that scalable, ferroelectric MOS capacitors can be realized using single crystalline SrZrxTi1-xO3 (x$=$ 0.7) that has been epitaxially grown on Ge. Single crystalline SrZrxTi1-xO3 exhibits characteristics that are ideal for a ferroelectric gate material, namely, a type-I band offset with respect to Ge, large coercive fields and polarization that can be enhanced with electric field. The latter characteristic stems from the relaxor nature of SrZrxTi1-xO3. These properties enable MOS capacitors with 5 nm thick SrZrxTi1-xO3 layers to exhibit a nearly 2 V wide hysteretic window in the capacitance-voltage characteristics. The realization of ferroelectric MOS capacitors with technologically relevant gate thicknesses opens the pathway to practical field effect devices.