Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Ashok Kumar, Ph.D.

Co-Major Professor

Shekhar Bhansali, Ph.D.

Keywords

Chemical vapor deposition, Nucleation, Mems, Field emission, Pressure sensor

Abstract

Diamond is widely known for its extraordinary properties, such as high thermal conductivity, energy bandgap and high material hardness and durability making it a very attractive material for microelectronic and mechanical applications. Synthetic diamonds produced by chemical vapor deposition (CVD) methods retain most of the properties of natural diamond. Within this class of material, nanocrystalline diamond (NCD) is being developed for microelectronic and microelectromechanical systems (MEMS) applications. During this research, intrinsic and doped NCD films were grown by the microwave plasma enhanced chemical vapor deposition (MPECVD) method using CH4/Ar/H2 gas mixture and CH4/Ar/N2 gas chemistries respectively. The first part of research focused on the growth and characterization of NCD films while the second part on the application of NCD as a structural material in MEMS device fabrication.

The growth processes were optimized by evaluating the structural, mechanical and electrical properties. The nature of chemical bonding, namely the ratio of sp²:sp³ carbon content was estimated by Raman spectroscopy and near edge x-ray absorption fine structure (NEXAFS) techniques. The micro-structural properties were studied by x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties of the pure NCD films were evaluated by nano-indentation. The electrical properties of the conductive films were studied by forming ohmic as well as schottky contacts. In second part of this study, both free-standing and membrane capped field emitter devices were fabricated by a silicon mold technique using nitrogen incorporated (i.e., doped) NCD films. The capped field emission devices act as a prototype vacuum microelectronic sensor.

The field emission tests of both devices were conducted using a diode electrical device model. The turn-on field and the emission current of free-standing emitter devices was found to be approximately 0.8 V/µm and 20 µA, respectively, while the turn-on fields of capped devices increased by an order of magnitude. The emission current in the field emission sensor changed from 1 µA to 25 µA as the membrane was deflected from 280 µm to 50 µm from the emission tip, respectively.

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