Process steps for Field Emitter devices built on Silicon wafers And 3D Photovoltaics on Silicon wafers

Process steps for Field Emitter devices built on Silicon wafers And 3D Photovoltaics on Silicon wafers David W. Stollberg, Ph.D., P.E. Research Engineer and Adjunct Faculty GTRI_B-1

Field Emitters GTRI_B-2

Doped Si GTRI_B-3

Deposit SiO2 (~10mm) Variable for Height SiO 2 Doped Si GTRI_B-4

Deposit gate (poly Si or Cr, ~200nm) poly-si SiO 2 Doped Si GTRI_B-5

Doped SiO 2 Si poly-si plan view Spincoat Photoresist poly-si SiO 2 Doped Si elevation view GTRI_B-6

Doped SiO 2 Si Pattern Develop poly-si plan view Resist poly-si SiO 2 Doped Si elevation view GTRI_B-7

Etch gate and insulator isotropically Doped SiO 2 Si poly-si poly-si SiO 2 plan view Resist Doped Si elevation view GTRI_B-8

Deposit catalyst metal Fe shown Ni possible with barrier layers Doped SiO 2 Si poly-si poly-si SiO 2 plan view Fe catalyst Resist Doped Si elevation view GTRI_B-9

Doped SiO 2 Si poly-si Lift off & Dice plan view poly-si SiO 2 Doped Si elevation view GTRI_B-10

Doped SiO 2 Si poly-si Grow CNTs plan view poly-si SiO 2 Doped Si elevation view GTRI_B-11

Connect and test @ HPEPL Langmuir Probe Doped SiO 2 Si poly-si e- plan view e- e- poly-si SiO 2 V Doped Si Measure I, V elevation view GTRI_B-12

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CNT growth parameter for CNTs 2µm CVD growth: N 2 and NH 3 flowed at 100sccm and 160scmm Temperature ramp of 300 C/min until 650 C (top and bottom heat) Annealed at 650 C for 2min Plasma Ignited: 80W, 15kHz, 800V Pressure controller activated: P chamber = 6mbar Annealed under NH 3 plasma for 3 min while T raised to 750 C at rate of 200 C/min C2H2 (40sccm) introduced at end of plasma anneal Growth time = 6min Plasma extinguished, cooled under N 2 flow until T <400 C. Opened to atmosphere GTRI_B-14

Influence of Temperature on CNT growth Below 725 C Catalyst does not sufficiently create synthesis islands. Short, fat Carbon Fiber like CNTs result Around 725 C islands initiate growth, but rate of growth is limited 750 C - growth rate of ~0.3µm/min 775 C some smaller islands, higher growth rate of smaller diameter CNTs 800 C increased Ni diffusion into Si, few catalyst island remain on surface, sparse CNT growth, much lower diameter. Rate is similar to 750-775 range with larger variance 650 C 675 C 700 C 725 C GTRI_B-15 750 C 775 C 800 C

Ion Electric Propulsion G. Pirio, et al, Nanotechnology, vol. 13, pp. 1-4, 2002. Electron-induced Surface Plasmon Resonance (Chem-Bio Sensor) MRE Antibodies Y Y Y Y Y Gold Foil Gate CNTs TiW/Mo/TiW electrode GTRI_B-16

84 Emitter Capacity 2.1 A at 25 ma/cm2 Busek BHT-200 Modified for use with CNT Emitters GTRI_B-17

Thrust! GTRI_B-18

3D Solar Cells GTRI_B-19

Multiple bounce light trapping Light Trapping= more absorbance Thinner layers = less recombination orthogonalize absorption and carrier extraction Solves thick-thin conundrum GTRI_B-20

CNT-Based Approach PR spun on PR Si GTRI_B-21

CNT-Based Approach UV PR spun on Mask and expose to UV PR Mask Si GTRI_B-22

CNT-Based Approach PR spun on Mask and expose to UV Develop PR PR PR Si GTRI_B-23

CNT-Based Approach PR spun on Mask and expose to UV Develop PR Fe deposited metal PR PR Si GTRI_B-24

CNT-Based Approach Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst metal metal Si GTRI_B-25

CNT-Based Approach CNT Tower metal CNT Tower metal Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) Si GTRI_B-26

CNT-Based Approach Pattern generated on Si substrate via photolithography CNT Tower metal p-type Si CNT Tower metal Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) p-type material (CdTe) applied via Molecular Beam Epitaxy (MBE) GTRI_B-27

CNT-Based Approach CNT Tower metal n-type p-type Si CNT Tower metal Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) p-type material (CdTe) applied via Molecular Beam Epitaxy (MBE) n-type material (CdS) applied via MBE or CBD GTRI_B-28

CNT-Based Approach CNT Tower metal TCO n-type p-type Si CNT Tower metal Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) p-type material (CdTe) applied via Molecular Beam Epitaxy (MBE) n-type material (CdS) applied via MBE or CBD Transparent Conductive Oxide applied via ion assisted deposition (IAD) GTRI_B-29

CNT-Based Approach CNT Tower metal TCO n-type p-type Si CNT Tower metal h u Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) p-type material (CdTe) applied via Molecular Beam Epitaxy (MBE) n-type material (CdS) applied via MBE Transparent Conductive Oxide applied via ion assisted deposition (IAD) V GTRI_B-30

CNT-Based Approach h u Pattern generated on Si substrate via photolithography Metal catalyst (Fe) applied Lift-off photoresist to leave only patterned catalyst atop interconnect layer CNT towers are formed in Chemical Vapor Deposition (CVD) furnace (~720 C; 20 min.) p-type material (CdTe) applied via Molecular Beam Epitaxy (MBE) n-type material (CdS) applied via MBE Transparent Conductive Oxide applied via ion assisted deposition (IAD) GTRI_B-31

Molecular Beam Epitaxy for CdTe and CdS deposition (p/n junction) CdTe CNTs CNTs Si substrate GTRI_B-32

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Reflectance, R (%) Light Reflection 3.0 2.5 2.0 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 1.5 1.0 0.5 0.0 400 600 800 1000 1200 1400 1600 1800 Wavelength, (nm) GTRI_B-35

Extra Slides on CNT Batteries GTRI_B-36

Silicon Battery Si-coated Carbon Nanotubes for Li - ion battery anodes (with Yushin in MSE) Silicon has an order of magnitude greater capacity compared to graphite anodes But Silicon has very poor cyclability (pulverizes with Lithium insertion) Solution = Reinforce Silicon (with Carbon Nanotubes) 1 5 kc 1 Li e Si LixSi x 22 ka x 5 22 GTRI_B-37

Vertically aligned carbon nanotubes Act as rebar to strengthen internal structure of Si-battery Pictures of Si-coated Carbon Nanotubes Demonstrates conformal coatings are possible GTRI_B-38

Dealloying Capacity (mah/g) Coulombic Efficiency (%) Charge/Discharge Results 3000 2500 2000 1500 1000 500 0 C-Si-VACNTs Theoretical capacity of graphite 0 5 10 15 20 Cycle Number 100 80 60 40 20 0 Stable performance and reversible dealloying capacity in excess of 2000 mah/g (over 5x more than graphite) has been demonstrated. VACNTs provide structural support for Si as well as dramatically improved electrical conductivity therefore higher power Sicontaining electrodes are possible. GTRI_B-39

: Sensors Cultures Scaffolds 100 mm Heat Sink Batteries 20 mm Fuel Cells Logic circuits Hydrogen storage Waveguide/Filter Many, MANY more... 1 mm GTRI_B-40