Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Elias K. Stefanakos, Ph.D.

Co-Major Professor

Shekhar Bhansali, Ph.D.

Keywords

MIM diode, Rectenna, Ni-NiO-Cr, Thin film insulator, Millimeter wave detection

Abstract

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.

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