Fabrication of Rectifying Optical Rectenna Array for Sensing and Light Energy Harvesting

Abstract

Since the advent of microwave power transmission in the 1960s, rectifying optical antennas, also referred to as Rectenna, has been pursued as a means to convert light into direct current (DC) output for sensing and possibly even light energy harvesting applications. Rectenna is a combination of antenna and rectifier and it has been tried to use in visible-near infrared (near IR) spectrum nowadays. The extension from microwave to higher frequencies (few hundreds of THz) has remained a challenge, because of complicated fabrication for smaller feature sizes. In this dissertation, it is introduced that the initial successes in fabricating rectenna arrays using a special projection e-beam approach and conventional e-beam lithography. A key element in the designed function of rectenna device is the built-in rectification with the MIM junction arrays, to convert the alternating current (AC) in the nano antenna into DC output. For this built in MIM structure, two different metals with a large work function difference are used: aluminum and gold. Aluminum oxide of 10nm thickness was used as the insulating layer, formed by atomic layer deposition (ALD). As it is mentioned previously, the nanowires patterning process was done by the special projection e-beam lithography method – atomic image projection e-beam lithography (AIPEL) developed over the years in our group (nanofabrication laboratory, NFL), at Seoul National University. The conventional e-beam lithography was also tried to pattern the nanowires. It was followed by the metal electrodes and metal pads, which were made by conventional e-beam lithography and photolithography, respectively. Each nanowire serves as an element antenna of the device, which varies in length from 300nm to 480nm. The target of frequency for operation is within near IR region. The aim is to complement the prevailing pn diode and solar cell technologies by providing a much broader spectral coverage. Since the visible-IR spectrum would reach the surface of Earth more than other waves, our rectenna device is expected to be more efficient. A series of measurement was carried out in order to characterize the device structure and the current voltage dependence, as well as its optical response. The representative I-V characteristic shows a dramatic increase in current response, by ~3 orders of magnitude, to incident broad-band light (white light from a microscope). With experimental results, the spectral response to incident light in the near IR range is also discussed as well as spectral resonance.