Abstract
The charge-trapping memory devices with a structure Pt/Al2O3/(Ta2O5)x(TiO2)1−x/Al2O3/p-Si (x = 0.9, 0.75, 0.5, 0.25) were fabricated by using rf-sputtering and atomic layer deposition techniques. A special band alignment between (Ta2O5)x(TiO2)1−x and Si substrate was designed to enhance the memory performance by controlling the composition and dielectric constant of the charge-trapping layer and reducing the difference of the potentials at the bottom of the conduction band between (Ta2O5)x(TiO2)1−x and Si substrate. The memory device with a composite charge storage layer (Ta2O5)0.5(TiO2)0.5 shows a density of trapped charges 3.84 × 1013/cm2 at ± 12 V, a programming/erasing speed of 1 µs at ± 10 V, a 8% degradation of the memory window at ± 10 V after 104 programming/erasing cycles and a 32% losing of trapped charges after ten years. The difference among the activation energies of the trapped electrons in (Ta2O5)x(TiO2)1−x CTM devices indicates that the retention characteristics are dominated by the difference of energy level for the trap sites in each TTO CTM device.
Highlights
Charge trapping memory (CTM) devices like silicon-oxide-nitride-oxide -silicon (SONOS) type memory devices have attracted much attention in recent years
A 3-nm Al2O3 thin film was deposited on wafers as the tunneling layer by using atomic layer deposition (ALD) system by using the precursors of trimethylaluminum (Al(CH3)[3], TMA) and water reacting on the surface of wafers at 200 °C
The cross-sectional morphologies of four TTO CTM devices were observed by using high resolution transmission electron microscopy (HRTEM)
Summary
Please see the following production note; XRD patterns of four TTO films all show an amorphous structure. Compared with Si substrate, Al2O3 films both in the tunneling layer and the blocking layer as well as the TTO film in the charge trapping layer show an amorphous structure, favorable to the performance of CTM devices. A memory window of about 3.6 V was obtained in a sweeping cycle of gate voltage from −12 V to +12 V for Ta2O5 CTM device, corresponding to a density of trapped charges 1.0 × 1013/cm[2], much lower than that obtained in TTO CTM devices. In TTO(1:1) film with the most effective mixing between Ta2O5 and TiO2, the largest density of defect states should be expected, TTO(1:1) CTM device gets the largest density of trapped charges, similar with that observed in (Ta2O5)x(Al2O3)1−x system[19]. Al2O3, TTO(3:1)/Al2O3 and TTO(1:1)/Al2O3 are calculated as 2.74 eV, 0.25 eV, 0.44 eV, and 0.5 eV, respectively, by using the following formula:
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