The objective of this thesis is to successfully design, fabricate, and characterize an optimum metal-insulator-metal diode that can be used as a fast switching diode in various applications such as solar energy conversion. The improvements of this type of diode will result in rectification of a wider spectrum of AC signals to usable electricity. In this project, several proposed designs of MIM diodes were successfully fabricated and characterized. Pt-Al2O3-Al metal-insulator-metal diode was fabricated to have high asymmetry in I-V curve. Additionally, in an attempt to study the effect of material properties on MIM diode???s performance, four different combinations of MIIIIM diode were compared and discussed. Many processes were involved in the fabrication of these diodes such as E-beam evaporation, photolithography, reactive ion etching RIE, and Atomic Layer Deposition (ALD) technique. The fabricated tunneling diodes are intended to operate in the GHz regime and can also operate at higher frequencies (THz) by changing and scaling the dimensions. In addition to MIM diode work, this project attempted to engineer the contrast curve of polystyrene as a negative resist used for E-beam lithography using multi layer resist stack. If the resist stack has a very high contrast and its sensitivity differs between the various layers, it can be ideal for the fabrication of multi-level zone-plate/Fresnel lens.

Metal Insulator Metal (MIM) diodes that work on fast mechanism of tunneling have been used in a number of very high frequency applications such as (Infra-Red) IR detectors and optical Rectennas for energy harvesting. Their ability to operate under zero bias condition as well as the possibility of realizing them through printing makes them attractive for (Radio Frequency) RF applications. However, MIM diodes have not been explored much for RF applications. One reason preventing their widespread RF use is the requirement of a very thin oxide layer essential for the tunneling operation that requires sophisticated nano-fabrication processes. Another issue is that the reliability and stable performance of MIM diodes is highly dependent on the surface roughness of the metallic electrodes. Finally, comprehensive RF characterization has not been performed for MIM diodes reported in the literature, particularly from the perspective of their integration with antennas as well as their rectification abilities. In this thesis, various metal deposition methods such as sputtering, electron beam evaporation, and Atomic Layer Deposition (ALD) are compared in pursuit of achieving low surface roughness. It is worth mentioning here that MIM diodes realized through ALD method have been presented for the first time in this thesis. Amorphous metal alloy have also been investigated in terms of their low surface roughness. Zinc-oxide has been investigated for its suitability as a thin dielectric layer for MIM diodes. Finally, comprehensive RF characterization of MIM diodes has been performed in two ways: 1) by standard S-parameter methods, and 2) by investigating their rectification ability under zero bias operation. It is concluded from the Atomic Force Microscopy (AFM) imaging that surface roughness as low as sub 1 nm can be achieved reliably from crystalline metals such as copper and platinum. This value is comparable to surface roughness achieved from amorphous alloys, which are non-crystalline structures and have orders of magnitude lower conductivities. Relatively lower resistances of the order of 1 k ohm with a sensitivity of 1.5 V-1 have been obtained through DC testing of these devices. Finally, RF characterization reveals that input impedances in the range of 300 Ω to 25 Ω can be achieved in the low GHz frequencies (from 1-10 GHz). From the rectification measurements at zero bias, a DC voltage of 4.7 mV has been obtained from an incoming RF signal of 0.4 W at 2.45 GHz, which indicates the suitability of these diodes for RF rectenna devices without providing any bias. It is believed that with further optimization, these devices can play an important role in RF energy harvesting without the need to bias them.

One of the untapped energy sources is the thermal energy available either from solar irradiance which is still not fully utilized or from the ambient heat temperature. Both resources share the nature of infrared (IR) radiation but with different range of wavelengths. The rectenna (rectifying antenna) concept is presented to harvest these IR radiations. The rectenna is simply an antenna connected to a diode. The diode has to be able to follow and rectify the ultra-fast received AC signal. This condition promotes the use of metal-insulator-metal (MIM) diodes due to their ultra-fast tunneling mechanism. The impedance matching between the diode an antenna is to be considered. The resistance practical ranges of both nano-antenna and MIM diode are generally far. The diode responsivity determines the MIM rectification capability. By building MIM diodes with multiple insulator layers the trade-off between the resistance and responsivity can be resolved. An optimization algorithm to select the qualified materials to build an MIIM diode with high responsivity and low resistance is introduced. A Ti-TiO2/ZnO-Al MIIM diode with ultra-thin oxide layers is fabricated. Also, a global optimization approach is carried out to maximize the impedance matching between the diode and the nano-antenna while improving the capacitance effect on the device’s cut-off frequency. The optimal results reveal a maximum coupling efficiency of 5.5%, a responsivity of 6.4 A/W, and a cut-off frequency of ~34 THz. A symmetric MIM metamaterial perfect absorber is introduced. The design has larger resistance than conventional nano-antennas. The near unity absorptivity is achieved through an optimization approach. A novel Chand-Bali nano-antenna that supports dual polarization and wide angle of reception is presented. The rectenna based on this nano-antenna is expected to achieve more than one magnitude of efficiency higher than ones fabricated in literature. / Thesis / Doctor of Philosophy (PhD)

Millimeter wave imaging systems are the next generation imaging systems being developed for security and surveillance purposes. In this work, thin film metal-insulator-metal (MIM) tunnel junction based detector using Ni-NiO-Cr has been developed for the first time for millimeter wave detection operating at 94 GHz. Extensive process development has been carried out to fabricate the MIM junctions. Arrays of MIM junctions with 1 µm² contact area and ultra-thin insulator layer of ~3 nanometer have been developed using e-beam lithography and reactive sputtering, respectively. MIM diodes were also fabricated in a bulk-micromachined diaphragm configuration to minimize surface wave loss. DC and millimeter wave measurements were carried out on the fabricated diodes to determine the device characteristics and performance. The current-voltage (I-V) measurements yielded current in the range of few µA with significant non-linearity and asymmetry. A maximum sensitivity of 7 V-1 was also obtained from the fabricated diode. These tunnel junctions showed a positive response to millimeter wave signal, with output current in the range of few µA. By controlling the input power of the millimeter wave signal, the output current from the device could be varied. Additionally, MIM diodes with 100 µm² contact area were developed using optical lithography technique. The I-V characteristics of diode demonstrated a uniform behavior, with a sensitivity value of 15 V-1. Furthermore, the diodes were utilized to observe the effects of post-deposition annealing on the diode I-V behavior. The I-V measurement provided evidence of diode operation up to 350°C, with optimal operation at 250°C. Finally, the feasibility of using an organic insulator was also investigated. MIM junctions were fabricated with a thin layer of polyaniline using Langmuir-Blodgett deposition process. The electrical characteristics of the polyaniline based MIM junction was determined by evaluating its I-V response. The use of an alternate dielectric proved successful, yielding a significant non-linearity and asymmetry. However, the output current obtained from these junctions was in the order of nano-Amperes. By optimizing the deposition process, the organic MIM junctions can be developed to yield better device characteristics.

This dissertation presents the rectifying antennas potential for harvesting solar power, along with a novel design for a solar rectenna. The suns general features and the characteristics of solar radiation as an electromagnetic wave are treated in depth in order to determine the deficiencies of traditional rectennas as a solar cell. A closed form equation for a MIM rectifiers efficiency as a function of its input power was developed and verified by a simulated behavioral model and measurements. A unique calculation method was also developed to determine the available solar power at the terminal of a [lambda]/2 dipole antenna as a function of its bandwidth. The available power for each diode at the antennas terminal was found to be insufficient for a MIM diode to operate in its high efficiency region. It was concluded that the MIM diode requires an array of high gain antennas to increase the solar power captured at its input in order to operate in its high efficiency region. A dielectric rod antenna is proposed as the high gain antenna element for the solar antenna. In order to minimize losses due to the skin effect in the feed system of the array, a non-radiative dielectric (NRD) wave guide is proposed as the feed structure for the solar array antenna. To increase the rectification efficiency of the solar rectenna, two improvements were introduced: 1) the solar antenna was modified to function as a dual polarized antenna; and 2) a novel technique was used to achieve full-wave rectification. Test results of prototypes of the proposed solar antennas and arrays, show them to be potentially far superior to traditional [lambda]/2 dipole antennas for collecting solar radiation. The interconnection method for rectennas in an array – as well as their associated dc losses – were also investigated. Based on the theoretical results, a novel interconnection method is proposed here, which has the potential to minimize the dc losses in the grid. A series of experiments were conducted to verify the proposed concepts, which yielded promising results.