Abstract
Post-metal annealing temperature-dependent forming-free resistive switching memory characteristics, Fowler-Nordheim (F-N) tunneling at low resistance state, and after reset using a new W/WO3/WOx/W structure have been investigated for the first time. Transmission electron microscope image shows a polycrystalline WO3/WOx layer in a device with a size of 150 × 150 nm2. The composition of WO3/WOx is confirmed by X-ray photo-electron spectroscopy. Non-linear bipolar resistive switching characteristics have been simulated using space-charge limited current (SCLC) conduction at low voltage, F-N tunneling at higher voltage regions, and hopping conduction during reset, which is well fitted with experimental current-voltage characteristics. The barrier height at the WOx/W interface for the devices annealed at 500 °C is lower than those of the as-deposited and annealed at 400 °C (0.63 vs. 1.03 eV). An oxygen-vacant conducting filament with a diameter of ~34 nm is formed/ruptured into the WO3/WOx bilayer owing to oxygen ion migration under external bias as well as barrier height changes for high-resistance to low-resistance states. In addition, the switching mechanism including the easy method has been explored through the current-voltage simulation. The devices annealed at 500 °C have a lower operation voltage, lower barrier height, and higher non-linearity factor, which are beneficial for selector-less crossbar memory arrays.
Highlights
Resistive random access memory (RRAM) has become a promising candidate to replace threedimensional FLASH for crossbar applications at a low cost owing to its simple structure, low power consumption, and high-speed operation [1,2,3,4]
Two positions marked (1) and (2) were leveled on the high-resolution transmission electron microscope (HRTEM) image in Fig. 1c, which were obtained from the X-ray photo-electron spectroscope (XPS) depth profile of the W top electrode (TE)/WOx/WO3/W bottom electrode (BE) sample
The binding energy peaks centered at 31.6 and 33.8 eV corresponded to the W f7/2 and W f5/2, respectively, whereas the peaks centered at 35.9 and 38.1 eV corresponded to the WO3 f7/2 and WO3 f5/2 core-level electrons, respectively
Summary
Resistive random access memory (RRAM) has become a promising candidate to replace threedimensional FLASH for crossbar applications at a low cost owing to its simple structure, low power consumption, and high-speed operation [1,2,3,4]. Many structures with different transport mechanism have been reported, a simple W/WO3/WOx/W RRAM device in the same material has not been reported yet. Nonlinear forming-free bipolar resistive switching characteristics using a simple W/WO3/WOx/W structure are observed for as-deposited, 400 °C, and 500 °C annealed devices. Temperature-dependent SCLC characteristics at low voltage and Fowler-Nordheim (F-N) tunneling at high voltage for both low-resistance state (LRS) and high-resistance state (HRS) are observed, even after reset. The switching mechanism is explained by oxygen-vacant conducting filament (CF) formation/ rupture into the WO3/WOx bilayer, and a new method of current-voltage (I-V) simulation is explored. Compared to other memory devices, the devices annealed at 500 °C have higher non-linearity factor, lower operation voltage, and lower barrier heights
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