High-temperature dielectric energy-storage properties are crucial for polymer-based capacitors for harsh environment applications. However, biaxially oriented polypropylene (BOPP), a state-of-the-art commercial capacitor dielectric, can work only below 105 °C. Here, we present a versatile method to enhance its working temperature by depositing alumina (Al2O3) layers onto BOPP films via magnetron sputtering. Compared with a pure BOPP film, the sandwiched Al2O3/BOPP/Al2O3 structure shows a higher dielectric constant, a lower electrical conduction loss, stronger mechanical properties, higher thermal conductivity, and especially increased working temperature. As a result, the composite film delivers a high discharged energy density of 0.45 J/cm3 under 200 MV/m (the actual operating electric field in hybrid electric vehicles) at 125 °C. The discharged energy density and energy-storage efficiency (∼97.7%) are highly stable over 5000 cycles at 125 °C. This work provides an effective route to develop high-temperature polymer-based capacitors.

HfO 2 -based ferroelectric materials are good candidates for constructing next-generation nonvolatile memories and high-performance electronic synapses and have attracted extensive attention from both academia and industry. Here, a Hf 0.5 Zr 0.5 O 2based ferroelectric tunnel junction (FTJ) memristor is successfully fabricated by epitaxially growing a Hf 0.5 Zr 0.5 O 2 film on a 0.7 wt % Nb-doped SrTiO 3 (001) substrate with a buffer layer of La 2/3 Sr 1/3 MnO 3 (∼1 u.c.). The FTJ shows a high switching speed of 20 ns, a giant electroresistance ratio of ∼834, and multiple states (eight states or three bits) with good retention >10 4 s. As a solid synaptic device, tunable synapse functions have also been obtained, including long-term potentiation, long-term depression, and spike-timingdependent plasticity. These results highlight the promising applications of Hf 0.5 Zr 0.5 O 2 -based FTJ in ultrafast-speed and high-density nonvolatile memories and artificial synapses.

The endurance degradation of HfO2-based ferroelectric films limits their development toward practical applications. In this work, we systematically investigate the ferroelectric endurance properties of Hf0.5Zr0.5O2 (HZO) film under various pulse voltages and pulse widths, and it is found that the fatigue severity increases first and then decreases with increasing pulse voltage or width. The nonmonotonic fatigue trend explains the controversial results in the literature that both faster and slower fatigues with increasing voltage were observed in HZO. Accordingly, low voltages of ±1.6 V/100 ns are applied for cycling the HZO device to achieve weaker fatigue and a sufficiently switched ferroelectric polarization (7–12 μC cm−2), and a recovery method by introducing wake-up effect is utilized to realize an enhanced endurance >1.01 × 1012 (>5.0 × 1013 in expectation). Our work provides a universal way to weaken fatigue and improve endurance performance of HfO2-based ferroelectric random access memory devices.

Further scaling of dynamic random-access memory (DRAM) faces critical challenges because of the lack of materials with both high dielectric constant and low leakage. In this work, engineering Hf1−xZrxO2 (HZO) films to the morphotropic phase boundary (MPB) and inserting Al2O3 interface layers with a wide bandgap are utilized to overcome this bottleneck. By tuning Zr composition and the woken-up process, the ratio of tetragonal and orthorhombic phases is manipulated to achieve the desired high dielectric constant MPB state. On this basis, Al2O3 ultrathin layers are inserted to further enhance the dielectric constant as well as reduce the leakage current. As a result, a high dielectric constant of ∼ 46.7 (equivalent oxide thickness ∼ 5.1 Å) and low leakage current density (<10−7 A/cm2 at ±0.5 V) are achieved in TiN/Al2O3 (0.2 nm)/Hf0.5Zr0.5O2 (5.6 nm)/Al2O3 (0.3 nm)/TiN capacitors. Furthermore, long dielectric breakdown time of the heterostructure confirms its application potential. These results are useful for developing next generation DRAM capacitor devices.

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