Graduation Year

2014

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Stephen E Saddow, Ph.D.

Committee Member

Christopher Frewin, Ph.D.

Committee Member

Andreas Muller, Ph.D.

Committee Member

Andrew Raij, Ph.D.

Committee Member

Mark Jaroszeski, Ph.D.

Keywords

Biomaterials, BMI, Brain Machine Interface, SiC

Abstract

Silicon carbide (SiC) has been used for centuries as an industrial abrasive and has been

actively researched since the 1960's as a robust material for power electronic applications.

Despite being the first semiconductor to emit blue light in 1907, it has only recently been

discovered that the material has crucial properties ideal for long-term, implantable biomedical

devices. This is due to the fact that the material offers superior biocompatibility and

hemocompatibility while providing rigid mechanical and chemical stability. In addition, the material

is a wide-bandgap semiconductor that can be used for optoelectronics, light delivery, and optical

sensors, which is the focus of this dissertation research.

In this work, we build on past accomplishments of the USF-SiC Group to develop active

SiC-based Brain Machine Interfaces (BMIs) and develop techniques for coating other biomaterials

with amorphous SiC (a-SiC) to improve device longevity. The work is undertaken to move the

state of the art in in vivo biomedical devices towards long term functionality. In this document we

also explore the use of SiC in other bio photonics work, as demonstrated by the creation of the

first reported photosensitive capacitor in semi-insulating 4H-SiC, thus providing the mechanism

for a simple, biocompatible, UV sensor that may be used for biomedical applications.

Amorphous silicon carbide coatings are extremely useful in developing agile biomaterial

strategies. We show that by improving current a-SiC technology we provide a way that SiC

biomaterials can coexist with other materials as a biocompatible encapsulation strategy. We

present the development of a plasma enhanced chemical vapor deposition (PECVD) a-SIC

process and include material characterization analysis. The process has shown good adhesion

to a wide variety of substrates and cell viability tests confirm that it is a highly biocompatible

coating whereby it passed the strict ISO 10993 standard tests for biomaterials and biodevices.

In related work, we present a 64-channel microelectrode array (MEA) fabricated on a cubic

3C-SiC polytype substrate as a preliminary step in making more complex neurological devices.

The electrode-electrolyte system electrical impedance is studied, and the device is tested against

the model. The system is wire-bonded and packaged to provide a full neural test bed that will be

used in future work to compare substrate materials during long-term testing.

Expanding on this new MEA technology, we then use 3C-SiC to develop an active,

implantable, BMI interface. New processes were developed for the dry etching of SiC neural

probes. The developed 7 mm long implantable devices were designed to offer four channels of

single-unit electrical recording with concurrent optical stimulation, a combination of device

properties that is indeed at the state-of-the-art in neural probes at this time.

Finally, work in SiC photocapacitance is presented as it relates to radio-frequency tuning

circuits as well as bio photonics. A planar geometry UV tunable photocapacitor is fabricated to

demonstrate the effect of below-bandgap optical tuning. The device can be used in a number of

applications ranging from fluorescence sensing to the tuning of antennas for low-power

communications.

While technology exists for a wide variety of in vivo interfaces and sensors, few active

devices last in the implantable environment for more than a few months. If these devices are

going to reach a long-term implant capability, use of better materials and processing strategies

will need to be developed. Potential devices and strategies for harnessing the SiC materials family

for this very important application are reviewed and presented in this dissertation to serve as a

possible roadmap to the development of advanced SiC-based biomedical devices.

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