How to Make Micro/Nano Devices?

Transcription

1 How to Make Micro/Nano Devices? Science: Physics, Chemistry, Biology, nano/biotech Materials: inorganic, organic, biological, rigid/flexible Fabrication: photo/e-beam lithography, self-assembly, D/3D print Dimensions: quantum dots, nanowires, D, 3D Functions: logic, sensing, actuation, energy conversion Power: wired, wireless e-waste: 4.8 Mt (04), circular economy Nature 539, 84 (06) nm MoS transistor, Science 354, 99 (06) Soft-robotic ray Science 353, 58 (06) Mechanoreceptor Science 350, 33 (05) -

2 Cubic Systems Ref: Campbell:. Simple cubic (sc) Body-centered cubic (bcc) Face-centered cubic (fcc) Lattice point per unit cell: Lattice point per unit cell: Lattice point per unit cell: 4 Packing fraction: 5% Packing fraction: 68% Packing fraction: 74% -

3 Rocksalt Crystal Na Cl a NaCl can be described as a fcc lattice of lattice constant a, with a basis of a Cl atom at (000), and a Na atom at a/(,0,0) fcc structure can be viewed as sequence of planes of atoms arranged in a hexagonal pattern. -3

4 3D models at this website Diamond Structure a(/4,/4,/4) It can also be viewed as two interpenetrating fcc lattices. (0,0,0) a a Si = 5.43 Å Packing fraction: 34% Elemental crystal- C, Si, Ge a GaAs = 5.65 Å One can view a diamond lattice as a fcc lattice with a -point basis 0, and a x ˆ + yˆ + zˆ. ( ) 4 Distance between two atoms in Si:.35 Å 8 Si density = 3 cm -3 8 ( ) = 5 0-4

5 Diamond Structure Perovskite structure Ga As Ca O Ti Packing fraction: 34% CaTiO 3 (Calcium Titanate) Covalent compound- GaAs, AlAs, GaP, InP, ZnS, SiC [00] [00] [0] -5

6 Miller Indices of Crystal Planes Z c x a + y b + z c = b Y X a {(00), (00), (00), (00), (00), (00)}= {00} -6

7 Crystal Plane Directions Family of <> directions {[00], [00], [00], [00], [00], [00]}= <00> In cubic lattices, the [hkl] direction is always perpendicular to (hkl) plane. a The separation between two adjacent parallel planes (hkl) is d = h + k + l The separation is a for {00} planes, 0.707a for {0} planes, and 0.577a for {} planes. Thus the {} planes are the closest spaced among the low-index planes. -7

8 Crystal Structure of Al O 3 Nanoparticles h = kk = ll = dd = aa = 0.79 nnnn aa h + kk + ll =

9 Silicon Wafers The angle between two planes ( h k ) and ( h k ) is l l cosθ = ( h + k + l )( h + k + l ) Si <> directions has the fastest rate for crystal growth and the slowest etch rate. V-grooves can be etched in <00> wafers. h h + k k The tensile strength and modulus of elasticity are maxima in the <> directions. Thus, Si tends to cleave on the {} planes. + l l º () () -9

10 Silicon Wafers The angle between two planes ( h k ) and ( h k ) is l l cosθ = ( h + k + l )( h + k + l ) h h + k k + l l Ref: Campbell:.8 Si <> directions has the fastest rate for crystal growth and the slowest etch rate. V-grooves can be etched in <00> wafers. The tensile strength and modulus of elasticity are maxima in the <> directions. Thus, Si tends to cleave on the {} planes. Dangling bondssurface state density for <00> is lower than <> - device appl. -0

11 Crystal Growth Ref: Campbell:.4-.6 Czochralski growth Float zone growth Pull rate: 0µm/s O-contamination from quartz crucible Polycrystalline GaAs Bridgman growth of single crystal GaAs -

12 Crystal Defects (I) Ref: Campbell:.3 Point defects: vacancies, interstitials, impurity atoms could behave like acceptors or donors affecting device performance Dissolved oxygen: forming complexes and a donor level at 0. ev. Dissolved carbon: cm 6 3 cm forming microprecipitates of Si-C complexes E c Vacancy Substitutional impurity Interstitial impurity Substitutional impurity -

13 Line defects: Crystal Defects (II) It occurs when the crystal is subjected to stresses in excess of the elastic limit during the growth from a melt. Some dislocations can be annealed out. Defects have dangling bonds and behave like acceptors. compression tension Strain field GaN surface, dislocation density 8 0 cm Screw dislocation Dislocation line: AD Slip plane: ABCD JVST A 6, 64 (998) -3

14 Crystal Defects (III) Twinning: Composition plane: x-x -4

15 After fabrication Annealing Enhances Crystal Growth Cu: 300 nm Si (00) After vacuum anneal 58 ºC- 5 s After vacuum anneal 700 ºC- 5 min CuSi-5_0 Si (00) Cu: 300 nm CuSi-5_04-5