AVS 56th International Symposium & Exhibition
    Thin Film Wednesday Sessions
       Session TF-WeA

Paper TF-WeA2
Fabrication and Characterization of Point Contact Metal-Insulator-Metal Diodes for Potential Applications in Energy Harvesting

Wednesday, November 11, 2009, 2:20 pm, Room B4

Session: ALD/CVD: Novel Applications, Mechanical Properties
Presenter: P. Periasamy, Colorado School of Mines
Authors: P. Periasamy, Colorado School of Mines
A. Dameron, National Renewable Energy Laboratory
J. Bergeson, National Renewable Energy Laboratory
J. Berry, National Renewable Energy Laboratory
P. Parilla, National Renewable Energy Laboratory
D.S. Ginley, National Renewable Energy Laboratory
R. O'Hayre, Colorado School of Mines
Correspondent: Click to Email
A rectenna is a device that can convert electromagnetic radiation such as visible light to DC power using a rectifier and an antenna component. Our focus in this paper is on fabrication and characterization of the rectifier component. Metal-Insulator-Metal (MIM) diodes are an excellent choice for the rectifier, since MIM diodes rectify via tunneling. Thus, a properly optimized MIM may be able to rectify signals in femto seconds (10-15 s), which enables rectification of visible light (400-790 THz). A point contact MIM diode (PCD) configuration is adopted in order to achieve the small diode capacitance necessary for high-frequency rectification. In the PCD, a planar metal/insulator bilayer “sandwich” is contacted by a second metal in the form of a sharp tip, resulting in a diode contact area as small as µm2 – nm2. For our initial studies we are using blunt wire tips, since our initial objectives are to optimize the planar metal/insulator layers. PCD devices with different metal 1, insulator and metal 2 (wire tip) combinations were fabricated and characterized for the desired I-V characteristics.

The PCD diodes were fabricated as follows. First, 100nm films of metal 1 candidates such as Ni, Nb, Sm, Hf were deposited by DC sputtering. The insulator layer (NiOX, NbOX, SmOX, HfOX) was grown by anodization of the metal films and by atomic layer deposition. Devices were characterized as a function of thickness of the insulator layer. In addition, dual insulators (MIIM) were grown and compared with single insulator (MIM) devices. TiO2 and Al2O3 were used for the second insulator layer. The deposition parameters of the metal and the insulator films were optimized to obtain films that are pinhole free and have low surface roughness. The films were characterized using scanning electron microscopy, atomic force microscopy, x-ray reflectivity and x-ray photoelectron spectroscopy. Pt, Au and Ag wire tips were used for Metal 2. PCD IV characteristics were analyzed in terms of non-linearity (NL) [(dI/dV)*(V/I)], asymmetry (AS), responsivity (RY) [(d2I/dV2)*(dI/dV)] and turn-on voltage (TOV) [based on positive current]. From the matrix of different material combinations and the fabricated MIM devices, an attempt was made to identify critical parameters that influence the desired I-V curve characteristics.

The NL, RY and TOV values for the Nb-NbOX (5.2 nm thick)-Pt system were 2.3, 3.8 A/W and 0.1 V respectively. But the AS value was not as good as found in Nb-NbOX (22.81 nm thick)-Pt system. At the same time, however, the turn-on voltage was relatively higher (1.7 V) in the latter system. Such results would help us fabricate a diode suitable for solar energy harvesting.