Neuromorphic computing has the potential to accelerate high performance parallel and low power in-memory computation, artificial intelligence, and adaptive learning. Despite emulating the basic functions of biological synapses well, the existing artificial electronic synaptic devices have yet to match the softness, robustness, and ultralow power consumption of the brain. Here, we demonstrate an all-inorganic flexible artificial synapse enabled by a ferroelectric field effect transistor based on mica. The device not only exhibits excellent electrical pulse modulated conductance updating for synaptic functions but also shows remarkable mechanical flexibility and high temperature reliability, making robust neuromorphic computation possible under external disturbances such as stress and heating. Based on its linear, repeatable, and stable long-term plasticity, we simulate an artificial neural network for the Modified National Institute of Standards and Technology handwritten digit recognition with an accuracy of 94.4%. This work provides a promising way to enable flexible, low-power, robust, and highly efficient neuromorphic computation that mimics the brain.

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The ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO/FeO fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO have been confirmed by macro- and microscale measurements, for which FeO serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe and Fe at O sites and Fe at T sites in FeO, while the room-temperature magnetic domains of FeO are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of FeO can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in FeO, and thus its magnetic state, making it attractive for electrically written magnetic memories.

Magnetic materials and devices that can be folded and twisted without sacrificing their functional properties are highly desirable for flexible electronic applications in wearable products and implantable systems. In this work, a high‐quality single crystalline freestanding Fe3O4 thin film with strong magnetism has been synthesized by pulsed laser deposition using a water‐dissolvable Sr3Al2O6 sacrificial layer, and the resulting freestanding film, with magnetism confirmed at multiple length scales, is highly flexible with a bending radius as small as 7.18 µm and twist angle as large as 122°, in sharp contrast with bulk magnetite that is quite brittle. When transferred to a polydimethylsiloxane support layer, the Fe3O4 film can be bent with large deformation without affecting its magnetization, demonstrating its robust magnetism. The work thus offers a viable solution for flexible magnetic materials that can be utilized in a range of applications.

Multiferroic materials with flexibility are expected to make great contributions to flexible electronic applications, such as sensors, memories, and wearable devices. In this work, super-flexible freestanding BiMnO 3 membranes with simultaneous ferroelectricity and ferromagnetism are synthesized using water-soluble Sr 3 Al 2 O 6 as the sacrificial buffer layer. The super-flexibility of BiMnO 3 membranes is demonstrated by undergoing an ≈180°folding during an in situ bending test, which is consistent with the results of first-principles calculations. The piezoelectric signal under a bending radius of ≈500 μm confirms the stable existence of electric polarization in freestanding BiMnO 3 membranes. Moreover, the stable ferromagnetism of freestanding BiMnO 3 membranes is demonstrated after 100 times bending cycles with a bending radius of ≈2 mm. 5.1% uniaxial tensile strain is achieved in freestanding BiMnO 3 membranes, and the piezoresponse force microscopy (PFM) phase retention behaviors confirm that the ferroelectricity of membranes can survive stably up to the strain of 1.7%. These super-flexible membranes with stable ferroelectricity and ferromagnetism pave ways to the realizations of multifunctional flexible electronics.

Flexible ferroelectric field effect transistors (FeFETs) with multiple functionalities and tunable properties are attractive for low power sensing, nonvolatile data storage, as well as emerging memristor applications such as artificial synapses, though the state-of-art flexible FeFETs based on organic materials possess low polarization, large coercivity, and high operating voltage, and suffer from poor thermal stability. Here, developed is an all-inorganic flexible FeFET based on epitaxial Pb(Zr 0.1 Ti 0.9 )O 3 /ZnO heterostructure on a mica substrate, which not only operates under a small voltage (±6 V) and thus consumes low power with an excellent on/off ratio of 10 4 as well as retention characteristics, but also shows robust FeFET performance under large bending deformation (4 mm), extended bending cycling (500 cycles), and high temperature operation at 200 °C. Importantly, the FeFET characteristics depend on temperature, but not on temperature history, critical for operation under repeated thermal loading. The excellent mechanical flexibility and functional robustness of the flexible FeFET originate from the unique van der Waals bonded layer structure of mica, facilitating a small bending radius yet modest strain. This work demonstrates the great promise of mica as a universal platform to integrate complicated functional devices for flexible electronics, especially under harsh environment.

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