| AVS 60th International Symposium and Exhibition | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM+PS-WeM |
| Session: | Oxides and Dielectrics for Novel Devices and Ultra-dense Memory II |
| Presenter: | N. Alimardani, Oregon State University |
| Authors: | N. Alimardani, Oregon State University J.F. Conley, Jr., Oregon State University |
| Correspondent: | Click to Email |
Thin film metal-insulator-metal (MIM) tunnel devices have seen renewed interest for high speed applications such as infrared (IR) detectors, optical rectennas for energy harvesting, and hot electron transistors. For many of these applications, desired properties include high asymmetry (η) and non-linearity (fNL) of current vs. voltage (I-V) behavior and small turn-on voltage (VON). The standard approach to achieving these characteristics in tunnel devices is M1IM2 diodes - the use of electrodes with different workfunctions to induce a built-in field across the insulator. VON is influenced by the choice of the dielectric layer. In theory, small band-gap dielectrics with large electron affinity (χ) are desired to achieve small VON in tunnel diodes as they make small energy barriers with electrodes. Regarding this, Nb2O5 and Ta2O5 are widely considered to be promising candidates as tunnel dielectrics. In this work, we investigate Nb2O5 and Ta2O5 MIM diodes. Atomic layer deposition (ALD) was used to deposit 5 nm and 10 nm thick Nb2O5 and Ta2O5 tunnel barriers with sputtered amorphous bottom electrodes (ZrCuAlNi) and evaporated Al top electrodes. The I-V responses were found to be asymmetric for diodes made with 5 nm and 10 nm of either of these dielectrics. Although a lower VON was observed, the maximum asymmetry was 3 orders of magnitude smaller than what we previously reported for similar diodes with ALD Al2O3 as the dielectric layer. High speed operation of MIM devices is typically based on Fowler-Nordheim tunneling (FNT). Conduction mechanisms were investigated as a function of temperature and electric field. By fitting I-V curves to FNT, Schottky emission (SE), and Frenkel-Poole (FP) emission plots, the dominant conduction mechanism in these diodes was found to be SE in the small bias regime (0.1 V to 0.3 V) and FP emission in the large bias regime (≥ 0.75 V). These assignments were confirmed by the close match of the optical dielectric constants extracted from the SE and FP plots with spectroscopic ellipsometry. Finally, Arrhenius plots show temperature dependence of current at both small and large bias regimes, indicating that tunneling is not the dominant conduction mechanism. In conclusion, we find that the small low-voltage asymmetric I-V behavior in MIM diodes made with Nb2O5 and Ta2O5 dielectrics is due to SE, rather than FN tunneling. A comparison will be made to bi-layer dielectric MIIM diodes, which we recently reported to show improved low voltage η and fNL. This work indicates that the choice of dielectric is critical as high χ dielectrics may not exhibit conduction mechanisms appropriate for high speed applications of MIM tunnel diodes.