Ferroelectric properties of SOS and SOI pseudo-MOSFETs with HfO2 interlayers

The formation of a multi-crystalline HfO2 film, containing the ferroelectric phase OII (Pmn21) after a high-temperature annealing at 1100 °C, was experimentally observed by HREM for the first time in silicon-on-sapphire (SOS) structures obtained by direct bonding and a hydrogen transfer of silicon layer on Si or C-sapphire substrates, respectively. PEALD HfO2 interlayers with the thickness of 20 nm were deposited on silicon before bonding to reduce the defects and magnitude of their charge at the SOS and silicon-on-insulator (SOI) interfaces. SOS pseudo-MOS transistors demonstrate standard drain-gate characteristics with the same charge carrier mobility as in bulk silicon and a small positive fixed charge (≤1.2 × 1012 cm−2). Moreover, a stable ferroelectric hysteresis with ΔVG ∼700 V observed only in SOS FETs is promising for the embedded memory formation and it extends the functionality of logic circuits. It was concluded that the OII phase is stabilized mainly by a high compressive stress and it can be responsible for the hysteresis in the case of SOS pseudo-MOSFETs opposite to the SOI-structure.