# Presentation: 016827

## Tritiated 3D Diode Betavoltaic Microbattery

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

## 3D Betavoltaic Technology

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

***p-n***** junction **
**conversion layer**

**+**

## Beta-Emitting Isotopes

| Isotope | T1⁄2 
(year) | Emission | Eave
 (keV) | Emax
 (keV) | Psp
 (μW/Ci) | Element |
| --- | --- | --- | --- | --- | --- | --- |
| 3H | 12.3 | β- | 5.7 | 18.6 | 34 | Hydrogen
 (tritium) |
| 63Ni | 100 | β- | 17.6 | 62 | 100 | nickel |
| 14C | 5710 | β- | 59 | 156 | 290 | carbon |
| 147Pm | 2.7 | β-, weak γ | 62 | 224 | 367 | promethium |
| 45Ca | 0.44 | β- | 77 | 257 | 456 | calcium |
| 208Tl | 3.8 | β-, X | 243 | 763 | 1440 | thallium |

**Note: 145 keV is damage threshold for silicon.**

## Tritium Selection Criteria 

**Tritium is “cheap”**
- ~$3 per Curie (~$30,000 per gram)
**Tritium is available commercially**
- Canada produces 1.5 kg/year (>20 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

## 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  <1 μm diameter and ~50 μm deep
*Measured Conversion Efficiency:*
- 	3D BetaBattTM pores = 0.22% efficiency
- 	2D planar surface     = 0.023% efficiency
- Results: Factor of _*10*_ Efficiency Gain from BetaBattTM 3D Geometry:
- 	 *→* nearly every decay electron entered conversion layer in pore walls

## 3D Diode in Wafer Test Fixture

## Extraordinarily Efficient DECTM Cell

## 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 >1000 ************ T******2****** gas)***
**	****2) Increase pore channel density to 25M pores/cm****2                                                                ****	****	****(increase from 16M pores/cm****2**** *****)***
**	****3) Lengthen pore channel dimension to 250-300 ****μ****m****	****                              ****	****	****	****(up from 50 ****μ****m *****)***
**	****	**** *****→***** *****Estimated improvement factor: ~8***
**	**** ****	**** *****→***** ****O*****verall energy density improvement factor: ~160***

## 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/cm****3 ****for prototype**** ****BetaBatteries****TM**** **

## BetaBatteryTM 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** -100°C to +150°C, shock tolerant
**Manufacturable **- Well known semiconductor techniques

## Betavoltaic Characteristics

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

## Betavoltaic Maximum Efficiencies

## BetaBatteryTM Power Parameters

_***Constant***_*** Power Rectangle***

_***Headroom***_*** Power Cusp***

## Application Space

** ****0.001****       ****          0.01                0.1           ****    ****1.0             **     **10                  100**

**Watts (Power)**

**Years of Battery Life**

-   20

- 18

- 16

- 14

- 12

- 10

-   8

-   6

-   4

-   2

- 0

**BetaBatteries****TM****:**

**Chemical Batteries:            **

**High Power, Short Life**

**Watts (Power)**

- 0

**Low Power,**
**Very Long Life**

***Hybrid BetaBatteries*****TM*****: ***
***Energy Storage ***_***with ***_***Pulse Power Delivery***

## Self-Recharging Battery

**Hybrid BetaBattery****TM**** 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 @ 15 years

## BetaBatteryTM Weekly Energy Output

## 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 BetaBatteryTM 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.

## BetaBatteryTM 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 BetaBatteriesTM.
- Need to develop recovery procedures for “spent” BetaBatteriesTM.
**BetaBattery****TM** **Production schedule**
- Prototype samples ---  August 2007
- Initial production     --- January 2008
- Volume production ---  December 2008

## Business Case

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

## “Light Bulb” vs “LED” Comparison

- Tritium Exit Signs
- Mature Technology
- Inexpensive Components
- ‘Easy to Handle’ Fill Gas
- Existing Production Facilities
- BetaBatteriesTM
- 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

## 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

## Contact Information

***BetaBatt***
- 	         Larry L. Gadeken, Ph.D.,
- 		 Founder and President
- 	         _[larrygad@betabatt.com](mailto:larrygad@betabatt.com)_
- 	         	281-450-5449