Sub-100 nm integrated ferroelectric tunnel junction devices using hydrogen silsesquioxane planarization (original) (raw)
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Scientific reports, 2015
The quest for solid state non-volatility memory devices on silicon with high storage density, high speed, low power consumption has attracted intense research on new materials and novel device architectures. Although flash memory dominates in the non-volatile memory market currently, it has drawbacks, such as low operation speed, and limited cycle endurance, which prevents it from becoming the "universal memory". In this report, we demonstrate ferroelectric tunnel junctions (Pt/BaTiO3/La0.67Sr0.33MnO3) epitaxially grown on silicon substrates. X-ray diffraction spectra and high resolution transmission electron microscope images prove the high epitaxial quality of the single crystal perovskite films grown on silicon. Furthermore, the write speed, data retention and fatigue properties of the device compare favorably with flash memories. The results prove that the silicon-based ferroelectric tunnel junction is a very promising candidate for application in future non-volatile m...
Scaling of electroresistance effect in fully integrated ferroelectric tunnel junctions
Applied Physics Letters, 2016
Systematic investigation of the scalability for tunneling electroresistance (TER) of integrated Co/ BaTiO 3 /SrRuO 3 ferroelectric tunnel junctions (FTJs) has been performed from micron to deep submicron dimensions. Pulsed measurements of the transient currents confirm the ferroelectric switching behavior of the FTJs, while the hysteresis loops measured by means of piezoresponse force microscopy verify the scalability of these structures. Fully integrated functional FTJ devices with the size of 300 Â 300 nm 2 exhibiting a tunneling electroresistance (TER) effect of the order of 2.7 Â 10 4 % have been fabricated and tested. Measured current density of 75 A/cm 2 for the ON state and a long polarization retention time of ON state (>10 h) show a lot of promise for implementation of high-density BaTiO 3-based FTJ memory devices in future.
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Ferroelectric tunnel junction devices based on ferroelectric thin films of solid solutions of hafnium dioxide can enable CMOS integration of ultra-low power ferroelectric devices with potential for memory and emerging computing schemes such as in-memory computing and neuromorphic applications. In this work, we present ferroelectric tunnel junctions based on Hf 0.5 Zr 0.5 O 2 with materials and processes compatible with CMOS back-end-of-line integration. We show a device architecture based on W-Hf 0.5 Zr 0.5 O 2-Al 2 O 3-TiN stacks featuring low temperature annealing at 400°C with performance comparable to those obtained with higher temperature annealing conditions.
Ultrathin BaTiO3-Based Ferroelectric Tunnel Junctions through Interface Engineering
Nano Letters, 2015
The ability to change states using voltage in ferroelectric tunnel junctions (FTJs) offers a route for lowering the switching energy of memories. Enhanced tunneling electroresistance in FTJ can be achieved by asymmetric electrodes or introducing metal− insulator transition interlayers. However, a fundamental understanding of the role of each interface in a FTJ is lacking and compatibility with integrated circuits has not been explored adequately. Here, we report an incisive study of FTJ performance with varying asymmetry of the electrode/ferroelectric interfaces. Surprisingly high TER (∼400%) can be achieved at BaTiO 3 layer thicknesses down to two unit cells (∼0.8 nm). Further our results prove that band offsets at each interface in the FTJs control the TER ratio. It is found that the off state resistance (R Off) increases much more rapidly with the number of interfaces compared to the on state resistance (R On). These results are promising for future low energy memories.
Ferroelectric tunnel junctions (FTJs) based on ultrathin HfO 2 have great potential as a fast and energy-efficient memory technology compatible with complementary metal oxide semiconductors. FTJs consist of a ferroelectric film sandwiched between two distinct electrodes, the properties of which are intricately linked to the electrical properties of the FTJs. Here we utilize a W crystallization electrode (CE) to achieve a high and reproducible remanent polarization, combined with a metal replacement process in which the W is carefully removed and replaced by another top electrode (TE). In this way we separate the ferroelectric film properties from the device design and can thereby evaluate the effect of the TE work function (WF) and conduction band electron density (n e) on the tunneling electroresistance (TER) and device reliability. We compare FTJs designed with a TiN bottom electrode and W, Cr, or Ni TE and find that the use of high electron density metals such as Ni or Cr as TE allows for an improved TER, albeit at the cost of reliability due to a large built-in electric field. To bypass this effect, a bilayer Cr/Ni TE is implemented, which allows for a high TER and minimal built-in field, leading to excellent retention and endurance beyond 10 8 cycles. The results presented here thus highlight a process flow for reliable design and implementation of FTJs.
Ferroelectric Tunnel Junction for Dense Cross-Point Arrays
ACS applied materials & interfaces, 2015
Cross-point array (CPA) structure memories using a memristor are attracting a great deal of attention due to their high density integration with a 4F2 cell. However, a common significant drawback of the CPA configuration is crosstalk between cells. To date, the CPA structure using a redox-based memristor has restrictions to minimize the operating current level due to their resistive switching mechanism. This study demonstrates suitable characteristics of a ferroelectric tunnel junction (FTJ) for the memristor of the CPA structure using an electrostatic model. From the FTJ of the Au/ p-type Pr0.98Ca0.02MnO3 (4 nm)/ BiTiO3 (4.3 nm)/ n-type Ca0.98Pr0.02MnO3 (3 nm)/ Pt(111) structure, which has a higher and thicker potential barrier, a good memristive effect for the CPA structure with a high non-linear I-V curve and low current operation, was obtained by Δ Fowler-Nordheim tunneling with effectively blocked direct tunneling and thermionic emission. The FTJ demonstrated reduced sneak curr...