Technical Overview

1
Tritiated 3D Diode Betavoltaic Microbattery Larry
L. Gadeken, Ph.D. IAEA Workshop Advanced
Sensors for Safeguards 23-27 April 2007
2
3D Betavoltaic Technology

• Long Life Batteries Converting Tritium Beta
  Energy to Electricity
• Tritiated Polymer
  3D Porous Silicon Diode

p-n junction conversion layer
3
Beta-Emitting Isotopes
Note 145 keV is damage threshold for silicon.
4
Tritium Selection Criteria

• Tritium is cheap
• 3 per Curie (30,000 per gram)
• Tritium is available commercially
• Canada produces 1.5 kg/year (gt20 kg on hand)
• Russia, unknown production (50 kg on hand)
• Korea to produce 0.5 kg/year (0 kg on hand)
• No radiation hardness issues
• 145 keV damage threshold for crystalline silicon
• Safety considerations
• All radioactive material contained in silicon
  pores
• Polymer form is a stable lump (decomposes in
  flame)
• Helium-3 decay product requires venting

5
Phase I Results Published in Journal, Advanced
Materials

• Phase I Feasibility Configuration
• Used tritium gas
• Porous silicon with 16 Million pores/cm2 
• Average pore was  lt1 µm diameter and 50 µm deep
• Measured Conversion Efficiency
• 3D BetaBatt pores 0.22 efficiency
• 2D planar surface 0.023 efficiency
• Results Factor of 10 Efficiency Gain from
  BetaBatt 3D Geometry
• ? nearly every decay electron entered
  conversion layer in pore walls

6
3D Diode in Wafer Test Fixture
7
Extraordinarily Efficient DEC Cell
8
Energy Density Improvements

• Basis for significant efficiency gains in
  pre-commercial prototypes
• 1) Increase energy density using a tritiated
  polymer
  (not tritium gas filling the pore space)
• ? Estimated improvement factor 20
  
  (Solid energy density gt1000 ? T2 gas)
• 2) Increase pore channel density to 25M
  pores/cm2
  (increase from 16M
  pores/cm2 )
• 3) Lengthen pore channel dimension to 250-300
  µm (up from 50
  µm )
• ? Estimated improvement factor 8
• ? Overall energy density improvement factor
  160

9
Device Performance Improvements

• Basis for significant efficiency gains in
  prototypes (continued)
• 4) Increased energy density improves
  semiconductor Fill Factor ? Goal is 70 or
  more
• 5) Reduce series resistance and minimize
  parasitic resistances
• ? Overall efficiency target 7-9 or greater
• Target electrical power density
• ? 50 - 125 µW/cm3 for prototype BetaBatteries

10
BetaBattery Features

• Small or Big For hearing aids.or much larger
  arrays
• High Efficiency - From Direct Energy Conversion
• Green - No harmful radiation, leaching,
  contamination
• Long Life 5 to 15 years for tritium (100
  years for 63Ni energy source)
• Scalable Wide form factor variety standard
  chemical batteries or special cases
• Extreme Environments -100C to 150C, shock
  tolerant
• Manufacturable - Well known semiconductor
  techniques

11
Betavoltaic Characteristics

• Semiconductor conversion efficiency
• Maximum versus observed performance
• Real devices have loss mechanisms
• Exponential decay and performance
• Constant power plus headroom cusp
• Hybrid BetaBattery
• Constant current output
• Energy storage options
• Duty Cycle Chart

12
Betavoltaic Maximum Efficiencies
13
BetaBattery Power Parameters
Headroom Power Cusp
Constant Power Rectangle
14
Application Space
BetaBatteries
20
Low Power, Very Long Life
18
Hybrid BetaBatteries Energy Storage with Pulse
Power Delivery
16
14
Years of Battery Life
12
10
8
Chemical Batteries
6
High Power, Short Life
4
2
0
0
0.001 0.01 0.1
1.0 10
100
Watts (Power)
Watts (Power)
15
Self-Recharging Battery
Hybrid BetaBattery Concept

• First Customer Defense contractor developing
  anti-tamper hardware
• Prevent reverse engineering or theft of military
  and intelligence property
• Requires power source with very long useful life
  25 µW _at_ 15 years

16
BetaBattery Weekly Energy Output
17
Product and Technology

• Purpose
• BetaBatt founded to commercialize 3D porous
  silicon diodes in betavoltaic and photovoltaic
  applications.
• Differentiating Novelty
• 3D geometry gives very efficient energy
  conversion.
• Self-recharging Hybrid BetaBattery combines
  betavoltaic energy generation with secondary
  Lithium energy storage chemistry.
• Compelling Features
• Long useful life of 5-15 years.
• Performs exactly like a normal chemical battery.
• Rugged wide temperature range, survives shock
  and vibration
• Critical Needs
• Short battery life is a limiting factor for many
  sensor and mesh network applications in
  Defense/Intelligence, Process Industry and
  Medical Implant arenas.

18
BetaBattery Production

• Maturity of conversion technology
• Semiconductor manufacturing is very mature.
• 3D porous silicon diodes are a new geometry
  requiring production engineering development.
• Tritiated polymer synthesis is new application of
  well established hydrogenation chemistry.
• Reliable infiltration of tritiated polymer into
  pore channels requires further development.
• Licensing and recovery Issues
• Seek General License for BetaBatteries.
• Need to develop recovery procedures for spent
  BetaBatteries.
• BetaBattery Production schedule
• Prototype samples --- August 2007
• Initial production --- January 2008
• Volume production --- December 2008

19
Business Case

• What are the market drivers for commercial
  success?
• Safe
• Long life
• Easy to use
• Familiar form factor
• Rugged
• Reliable
• Cheap

20
Light Bulb vs LED Comparison

• Tritium Exit Signs
• Mature Technology
• Inexpensive Components
• Easy to Handle Fill Gas
• Existing Production Facilities
• BetaBatteries
• New Technology
• Improve 3D Diode Performance (Geometry,
  Materials, Process, etc.)
• Refine Tritiated Polymer Synthesis Methods
• Perfect Infiltration Into Pore Space
• Hermetic Packaging Similar to Medical Batteries
• Production Engineering for Thin Film Lithium
  Batteries
• Low Volume Production Initially
• Multi-Step Chemistry With Nuclear Materials
• New Production Facilities Needed

21
Acknowledgements

• National Science Foundation SBIR Program
• University Collaborators
• University of Rochester
• Rochester Institute of Technology
• Rice University
• Scientific Consultants and Mentors
• Business Advisors
• Legal and Patent Counsel

22
Contact Information
BetaBatt Larry L. Gadeken, Ph.D.,
Founder and President
larrygad_at_betabatt.com 281-450-5449