Thinned SiC Betavoltaic Cell Design for High Power Density
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Solution Overview
Problem
Conventional betavoltaic batteries suffer from low power density due to inefficient use of semiconductor material and high leakage currents caused by etching processes, resulting in wasted electrons and reduced conversion efficiency.
Innovation Solution
A very thin betavoltaic cell design using thinned SiC wafers with optimized doping layers and radioisotope integration, allowing for cascading of cells to achieve higher voltage and power density, with a thickness of the N+ doped SiC substrate limited to less than 100 micrometers and the use of low melting temperature adhesion layers for stacking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional planar betavoltaic devices use thick semiconductor wafers (150-500 μm), then structural strength and manufacturing ease are improved, but most of the volume (over 90%) is wasted as only the top 20 μm is active
Solution Approach 1:
The device is segmented into multiple thin active layers (drift region, depletion region, contact region) stacked in series, with each layer optimized for its specific function. This allows the total active thickness to be reduced to match electron penetration depth while maintaining structural integrity through the layered architecture.
Solution Approach 2:
The invention transitions from a single thick wafer to a multi-layer stacked structure, effectively using the vertical dimension to stack multiple functional regions. This dimensional reorganization maximizes the active volume fraction by ensuring every portion of the semiconductor contributes to electron collection.
2Quantity of substance
If etching processes are used to pattern and increase fuel fill factor, then device area utilization is improved, but leakage currents increase significantly due to semiconductor material damage
Solution Approach 1:
The semiconductor layers are grown with predetermined doping profiles and thicknesses that pre-establish the depletion region geometry and fuel fill factor before any patterning. This preliminary structuring allows for optimized electron-hole pair generation and collection without requiring damaging etching processes.
Solution Approach 2:
The invention changes the doping concentration parameters across different layers (heavily doped contact region, lightly doped drift region, undoped depletion region) to create the desired electric field distribution and fuel fill factor without mechanical etching, thereby avoiding material damage and leakage currents.
3Power
If high energy beta-emitting isotopes (137Cs, 90Sr) are used to increase fuel power density, then energy output is improved, but shielding volume increases significantly decreasing overall power density
Solution Approach 1:
The invention changes the beta particle energy parameter by selecting low-energy isotopes (63Ni with 17.3 keV average energy, 147Pm with 62 keV) that emit electrons with penetration depths matching the thin semiconductor structure. This parameter optimization achieves high power density without requiring extensive shielding, as the electrons are fully absorbed within the device structure itself.
4Ease of manufacture
If thick semiconductor substrates are used, then manufacturing robustness is improved, but electron collection efficiency decreases as electrons are wasted irradiating away from substrate
Solution Approach 1:
Different regions of the semiconductor structure have locally optimized properties: the bottom contact region is heavily doped for robust electrical connection, the drift region has intermediate doping for electron transport, and the depletion region is undoped or lightly doped for maximum electron-hole pair collection efficiency. This local quality optimization ensures high productivity throughout the structure.
Solution Approach 2:
The electric field distribution is dynamically optimized through the doping profile design, creating strong field regions near the depletion region where electrons are generated and gradually weaker fields in the drift region for efficient electron transport to the contact. This dynamic field structure maximizes electron collection while minimizing losses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The thin cell design achieves a significant increase in fuel-fill efficiency and power density, with measured conversion efficiencies up to 22.3% and a 170% increase in power density compared to regular thickness devices, while minimizing material waste and shielding requirements.
Implementation Method 1
A betavoltaic battery consists of a semiconductor diode that is exposed to electrons emitted from a beta-emitting radioisotope thin film
Implementation Method 2
The electrons penetrate the semiconductor material and generate electron-hole pairs by different ionization processes
Implementation Method 3
electrons emitted from a beta-emitting radioisotope thin film. The electrons penetrate the semiconductor material and generate electron-hole pairs
Implementation Method 4
collected across a built-in depletion layer electric field leading to current output with net power
Implementation Method 5
a low melting temperature conductive adhesion layer of material such as a metal layer, for example, is disposed between the electrically conductive layer of the one betavoltaic device and the radioisotope layer of the other betavoltaic device
Data Source
AI summary
An exemplary thinned-down betavoltaic device includes an N+ doped silicon carbide (SiC) substrate having a thickness between about 3 to 50 microns, an electrically conductive layer disposed immediately adjacent the bottom surface of the SiC substrate; an N− doped SiC epitaxial layer disposed immediately adjacent the top surface of the SiC substrate, a P+ doped SiC epitaxial layer disposed immediately adjacent the top surface of the N− doped SiC epitaxial layer, an ohmic conductive layer disposed immediately adjacent the top surface of the P+ doped SiC epitaxial layer, and a radioisotope layer disposed immediately adjacent the top surface of the ohmic conductive layer. The radioisotope layer can be 63Ni, 147Pm, or 3H. Devices can be stacked in parallel or series. Methods of making the devices are disclosed.