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Publication Date

Spring 2011

Degree Type

Thesis - Campus Access Only

Degree Name

Master of Science (MS)


Electrical Engineering


David Parent

Subject Areas

Electrical Engineering


In order to use a transistor as a neural interface, the transistor must be protected from the sodium and potassium present in the culture medium [1]. Fluctuations or shifts in capacitance affect the electrical characteristics of the transistor causing changes to the threshold voltage, thus making the transistor an unstable amplifer or sensor. In this study, hafnium oxide (HfO2) metal oxide semiconductor (MOS) capacitors were fabricated, and their ability to maintain a stable capacitance over time was evaluated in the presence of sodium. HfO2 is a high-κ material that has the added advantage of increasing the gain of the transistor. The capacitance-voltage (C-V) method was used to evaluate fixed oxide charge, dielectric constant, and threshold voltage of experimental samples. The capacitance-time (C-t) method was used to measure capacitance shifts over time due to ionic contamination, and the triangular voltage sweep (TVS) test was used to measure the baseline sodium contamination present in the grown oxides.

Refectometry methods were used to measure the index of refraction and oxide thicknesses. HfO2 was shown to be highly resistant to corrosion. The permittivity of the stacked dielectric, including HfO2 measured, was 10.5 and the index of refraction was 2.1 for a 333 Å film. The capacitance from the C-t test was found to be stable when using the 0.1M NaCl physiological saline solution on a 197 Å film.