High piezoelectricity in epitaxial BiFeO3 microcantilevers

Abstract

The large switchable ferroelectric polarization and lead-free composition of BiFeO3 make it a promising candidate as an active material in numerous applications, in particular, in micro-electro-mechanical systems (MEMS) when BiFeO3 is integrated in a thin film form on a silicon substrate. Here, 200-nm-thick Mn-doped BiFeO3 thin films have been epitaxially grown on a SrRuO3/SrTiO3/Si substrate and patterned into microcantilevers as prototype device structures for piezoelectric actuation. The devices demonstrate excellent ferroelectric response with a remanent polarization of 55 μC/cm2. The epitaxial BiFeO3 MEMS exhibit very high piezoelectric response with transverse piezoelectric coefficient d31 reaching 83 pm/V. The BiFeO3 cantilevers show larger electromechanical performance (the ratio of curvature/electric field) than that of state-of-art piezoelectric cantilevers, including well-known PZT (Pb(Zr,Ti)O3) and the hyper-active PMN–PT (Pb(Mg1/3Nb2/3)O3-PbTiO3). In addition, the piezoelectricity in BiFeO3 MEMS is found to depend on the ferroelectric polarization direction, which could originate from the flexoelectric effect and be exploited to further enhance the electromechanical performance of the devices. These results could potentially lead to a replacement of lead-based piezoelectrics by BiFeO3 in many microdevices.

Coupling oxygen vacancy gradient distribution and flexoelectric effects for enhanced photovoltaic performance in bismuth ferrite films

“…More recently, multiferroic BiFeO 3 with a narrow bandgap (E g ∼ 2.7 eV) and giant ferroelectric polarization (P > 100 μC cm −2 ) has great advantages in the photovoltaic application, making it the most promising ferroelectric photovoltaic material with potential breakthrough results. [10][11][12] Previous literature [13][14][15][16] works mainly focused on exploring the origin of the ferroelectric photovoltaic effect in BiFeO 3 . For example, (i) bulk photovoltaic mechanism: the emergence of a stable photocurrent in a homogeneous medium with an asymmetric center is the so-called "bulk photovoltaic effect" (BPVE).…”