Meanwhile, the CMOS- incompatible film growth technique makes the current state of the art of Fe diode unable to be implemented in the 3D structure. However, it is still too low to be detected by a periphery circuit in chip. reported a Fe-diode current density up to 5.4 A/cm 2 in Pt/BiFeO 3/SrRuO 3 thin-film capacitors by a plate-like growth mode 18. The ultralow readout currents in the orders of 20 mA/cm 2 and low on/off ratio limited their miniaturization. The concept of Fe diode was first proposed in PbTiO 3 perovskite thin films 16 and later in bulk BiFeO 3 single crystals 17. In contrast, the ferroelectric diode (Fe diode), with the working principle governed by Schottky barrier modulation as polarization reversal, has the potential to gain inherent nonlinearity and realize selector-free cross-point integration. In principle, both the on and off states of FTJ obey linear or quasi-linear I– V relationship, which makes it need extra selector device to diminish the sneaking current in the crossbar array. The FTJ device takes the advantage of a ferroelectric as the barrier material, and has a giant tunnel electroresistance (TER) effect by switching the ferroelectric polarization, which was generally formulated by quantum mechanical electron-tunneling mechanism. On the other hand, two terminal devices, such as the ferroelectric tunneling junction (FTJ) and Fe diode, have the potential to achieve high- density crossbar array 12, 13, 14, 15. However, it cannot be used as a random-access memory. FeFET can realize non-distructive read and 3D vertical stack 9, 10, 11. As shown in Supplementary Table 1, the 1T1C FeRAM requires a large capacitor area (“footprint”) and undergoes destructive readout. Up to now, ferroelectric HfO 2-based memories in the forms of one access transistor–one ferroelectric capacitor (1T1C) 5, 7 and ferroelectric transistor (FeFET) structures have been demonstrated, with excellent scalability down to 10-nm node 8. The discovery of ferroelectricity in doped HfO 2 has renewed the interest in FeRAM by offering a possible solution to bridge the scaling gap between perovskite ferroelectric materials and complementary metal–oxide–semiconductor (CMOS) technology 4, 6. The development of FeRAM in semiconductor industry has been stopped at 130-nm node for a long time 4, 5. However, the scaling limitation of perovskite ferroelectric materials has hindered their widespread applications 3. To effectively solve the memory wall problem, a desired way is to configure a memory with high speed and high-density features.Īmong various types of nonvolatile memories, ferroelectric random-access memories (FeRAM), which achieve nonvolatility by switching and sensing the polarization state of a ferroelectric capacitor, have been thought of as an excellent memory solution due to its outstanding features of low power, high speed, high endurance, and good retention. However, the frequent data transfer between different memories leads to the decreased bandwidth and degraded computing efficiency, especially in the case of massive data computing, resulting in the well-known “memory wall” issue. It could achieve an optimal trade-off between performance and density in different types of memory 2. Memory hierarchy composed of volatile and nonvolatile solid-state memories is the main building block of the computing system 1. This work opens up new opportunities for future memory hierarchy evolution. The built-in nonlinearity of more than 100 guarantees its self-selective property that eliminates the need for external selectors to suppress the leakage current in large array. Operation speed as high as 20 ns and robust endurance of more than 10 9 were demonstrated. We further implemented this ferroelectric diode in an 8 layers 3D array. By visualizing the hafnium/zirconium lattice order and oxygen lattice order with atomic-resolution spherical aberration-corrected STEM, we revealed the correlation between the spontaneous polarization of Hf 0.5Zr 0.5O 2 film and the displacement of oxygen atom, thus unambiguously identified the non-centrosymmetric Pca2 1 orthorhombic phase in Hf 0.5Zr 0.5O 2 film. Here we demonstrated a highly scalable, three-dimensional stackable ferroelectric diode, with its rectifying polarity modulated by the polarization reversal of Hf 0.5Zr 0.5O 2 films. Memory devices with high speed and high density are highly desired to address the ‘memory wall’ issue.
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