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Novel Device Structure for Increased Power Density in Betavoltaic Cells

Detailed Technology Description

Cornell researchers have developed a betavoltaic cell generating 500 times more power density than current planar designs.

Others

Patent: 7,663,288; 7,939,986

*Abstract

Cornell researchers have developed a betavoltaic cell generating 500 times more power density than current planar designs. The increased power density is achieved through a novel device structure and the use of SiC as the substrate. The novel device structure incorporates high aspect ratio micromachined pillars to provide a very large surface area in a relatively small volume of SiC, and provide ample space for the radioactive beta-emitting fuel material. Silicon carbide provides an energy conversion efficiency an order of magnitude higher than silicon.

Standard fabrication techniques are used to manufacture the novel device structure with smooth pillar side walls. P or N type dopants can be added to the pillars to produce shallow junctions with increased cell efficiency. A novel doping process utilizing borosilicate glass has also been developed that helps the device achieve its impressive power density. The technology will find wide application in a variety of areas requiring on-chip or low-accessibility power supplies.

Figure 1. Open circuit voltage for a Ni-63 source over a range of bandgaps.

Technical Merits

• Nickel 63 as a β source provides a mean E of 17 keV and 100 year half life
• 4H SiC is the ideal cell material with a bandgap of 3.3 eV, extreme radiation durability and good temperature stability
• The expected output current density is 13 nA/cm²
  • For a Tritium source, one would expect a current density output of 3.7μA/cm²
• Due to the half life of the nickel isotope, the cell is expected to last at least 50 years before the output starts to degrade substantially
• Efficiencies of 5.76% measured with Ni-63 source
• Power density gain equal to aspect ratio
• Deep etching required- standard processes available
• Boron is the only practical diffusion dopant
  • Silicon atom substitution EA=6.1eV and D0=3.2cm²/s (shallow dopant Ea ~250 meV)
  • Carbon vacancy EA=4.6eV and D0=0.1cm²/s
  • deep dopant Ea~700 meV
  • For 1 hour diffusion at 1500°C, junction depth ~70nm
  • Good electrical characteristics reported for B-diffused junctions
• Power density of ~1.0 μW/cm² demonstrated
• Can scale to ~1mW/cm² for single layer by utilizing high aspect ratio structures

Technical Results

• 4H SiC (bandgap = 3.3eV) cell with Ni-63 (avg. energy = 17 keV) provides:
  • 5.76% efficiency
  • 13 nA/cm² current density
• Tritium (H-3) cell demonstrated the following:
  • ~1.0 µW/cm² power density and ~10% efficiency

Applications

• Power supply for low accessibility sensor nodes
• On-chip power source for MEMS
• Standby power for cell-phones

Advantages

• Low cost, long lasting, high current, energy efficient cell
  • Stable energy output for at least 50 years (Ni-63 half life = 100 years)
• Safe power source
• Insensitive to harsh environmental and production conditions while maintaining:
  • High thermal conductivity, good electronic mobility and low leakage currents
• Other semiconductor substrates can be used

*Licensing

Patrick Govangpjg26@cornell.edu(607) 254-2330

Country/Region

USA