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MECH466-Lecture-3

# MECH466-Lecture-3 - MECH 466 Systems University of Victoria...

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1 MECH 466 Microelectromechanical Systems University of Victoria Dept. of Mechanical Engineering Lecture 3: Basic Concepts: Semiconductors May 14th, 2007 Mech 466, N. Dechev, UVic 2 Silicon Structural Properties Crystal Planes Bulk Micromachining Semiconductor Properties Doped Semiconductors Overview Mech 466, N. Dechev, UVic

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3 Silicon Structural Properties Silicon solid exists in three different forms: Amorphous Randomly oriented atoms, e.g. Glass Polycrystalline Crystal grains/ domains oriented in random directions, which meet at grain boundaries Crystal Entire solid is made of an ordered array of atoms Mech 466, N. Dechev, UVic 4 Silicon Structural Properties Silicon crystal lattice is cubic. Silicon atoms form covalent bonds with four adjacent atoms, in the form of a diamond lattice structure. Si Atoms Covalent Bonds Note: Bonds outside of Cubic Lattice are not shown Mech 466, N. Dechev, UVic
5 Silicon Structural Properties Silicon exhibits different properties along different crystal planes. Properties such as E (young’s modulus), electron mobility, piezoresistivity, and chemical etch rates (for fabrication purposes). z x y a a a Mech 466, N. Dechev, UVic 6 Miller Indices, Planes The Miller Indices are a common notation used to identify the planes and directions in a crystal lattice. To determine the Miller Index of a plane, we use the following procedure: z x y a Step 0: Identify the plane of interest. For example, the plane shown in pink is one face of the cubic structure. Mech 466, N. Dechev, UVic Crystal Plane (100) Step 3: Reduce these numbers to the smallest set of integers h , k and l , by multiplying all by a , which yields (1 0 0). Parentheses are used to denote a crystal plane. Step 2: Take the reciprocals of the three numbers found in step 1. In this example: 1/ a , 1/ ! (=0), and 1/ ! (=0). Step 1: Identify the intercepts of the plane with the x , y and z axes. In this example, we have x = a , y = infinite, z = infinite.

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