Amongst present-day renewable energy sources, solar cells have been widely considered as the most viable solution. However, the energy conversion efficiency for the solar cells is limited to 30% or below due to the device physics. Rectifying antenna (rectenna) is an ideal supplement that is able to efficiently capture the abundant infrared (IR) energy from the solar radiation in part due to IR antenna’s inherent high efficiency. The rectenna system consists of two key elements: antenna and rectifying diode. The IR antenna captures the solar radiation within the wavelength of interest to be delivered to the ultrafast diode that rectifies the received signal into usable DC power.

 

Rectennas operating at microwave frequencies with efficiency up to 85% has been routinely demonstrated. However, the key remaining challenge for the infrared counterparts can be ascribed to the insufficient cutoff frequency of the semiconductor-based diodes owing to their excessive depletion-induced capacitance. In order to obtain the desired response times less than 10-12seconds, metal-insulator-metal (MIM) tunnel diodes with junction area in the range of 100nm×100nm were implemented herein to enable the coveted terahertz frequencies due to the greatly reduced junction capacitance and ultrafast quantum tunneling.

 

In this work, MIM tunnel diodes with sub-micron sized junction have been mass produced using CMOS-compatible processes without the need for E-beam lithography or sophisticated chemical etching. Standard photolithography and atomic layer deposition (ALD) were used to allow formation of a micrometer-wide finger in the second metal layer separated from the electrode in the first metal layer by an ALD-deposited sidewall dielectric spacer, thus forming a nm-thick vertical tunnel junction. The nano-scale junction is defined by the width of the finger and the thickness of the electrode, while the junction thickness is controlled by the ALD process.

 

On par to nano-scale devices, MIM tunnel diodes with micron-scale self-aligned cross-fingers have been successfully developed. Through this process, we have investigated a wide variety of metal and insulator materials such as Au, Cu, Pt, Ni, Al, Al2O3, HfO2to advance the performance of the MIM diode with particular focus on its efficiency. Some preliminary DC and RF characterization have been carried out to study the device characteristics such as responsivity, nonlinearity and asymmetry of I-V, and frequency responses. Ongoing research for modeling of MIM tunneling diode based on measured S-parameter data and further reduction of the device junction area will be detailed in the final manuscripts.