| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeE |
| Session: | Emerging Topics: Growth and Properties of Electronic Materials, 2D Layers, and Metallic-glass Thin Films |
| Presenter: | John Conley, Jr., Oregon State University |
| Authors: | M.A. Jenkins, Oregon State University J.F. Conley, Jr., Oregon State University |
| Correspondent: | Click to Email |
Metal/insulator/metal (MIM) structures are used as high speed diodes for rectenna based harvesting and sensing of IR radiation, capacitors, resistive memory, and hot-electron transistors. To better control electric fields and improve performance of these devices, there is growing interest in integrating metallic glassy (amorphous) thin films as smooth electrodes with uniform work function. Precise knowledge of metal/insulator barrier heights, φBn, is critical for predicting, understanding, and optimizing MIM device charge transport and operation. In the simplest model, charge transfer across the interface is neglected, and φBn should vary with the vacuum work function of the metal, ΦM,vac, so that φBn=ΦM,vac-χi where χi is the insulator electron affinity. In induced gap state theory, charge transfer at intrinsic interface traps which create an interfacial dipole that drives the metal Fermi level, EFM, towards the charge neutral level of the insulator, ECNL,i, the energy at which the dominant character of the interface states switches from donor-like to acceptor-like. A metal on an insulator will behave as if it has an effective work function, ΦM-eff, different from ΦM,vac, so that ΦM,eff=ECNL,i+S(ΦM,vac-ECNL,i).1 S is the slope that describes how much ΦM,eff on a given dielectric will change in response to ΦM,vac. Empirically, S=1/(1+0.1(εhf-1)2. As the high frequency dielectric constant, εhf, increases, S decreases and the insulator more effectively "pins" EFM at ECNL,i. Finally, actual φBn's depend on deposition method and can deviate substantially due to extrinsic interface traps. Thus it is necessary to directly measure φBn for a given metal-insulator combination.
In this work, we use IPE spectroscopy to measure φBn of the thin film glassy metals ZrCuAlNi, TaWSi, and TaNiSi in MIM stacks with various insulators deposited via ALD.2,3 To date, there have been few reports of IPE measurements of MIM structures and only one an amorphous metal.4 Results are referenced to TaN, Al, and Au barriers on the same devices.
Ta-based metal φBn's change with ΦM for Al2O3, but HfO2 φBn are relatively constant, likely due to pinning. The asymmetry in the I-V response is qualitatively consistent with the IPE determined φBn. TaWSi and TaNiSi electrodes showed consistently higher φBn's than ZCAN electrodes and comparable performance to TaN. With low roughness and thermal stability approaching 900 °C, TaWSi is a promising electrode for MIM diodes.
1 Yeo et al. J. Appl. Phys. 92, 7266 (2002).
2 N. Alimardani et al. J. Vac. Sci. Technol. A 30, 01A113 (2012).
3 McGlone et al. MRS Commun. 7 (2017).
4. M.A. Jenkins et al. Physica Status Solidi (RRL) 12, 1700437 (2018).