The Design And Fabrication Of Betavoltaic Battery Based On Wide Bandgap Semiconductors

Betavoltaic batteries have unique advantages such as high energy density,strong environmental adaptability,the long service life of several years to decades,and no need for maintenance,making them an excellent choice for micro-power sources in MEMS.However,due to the lack of in-depth research on semiconductor selection and device preparation of transducer components,the energy conversion efficiency of experimental devices of betavoltaic batteries is relatively low at present,which cannot meet the development needs of MEMS well.This study has addressed the above-mentioned issues by conducting in-depth theoretical analysis of the selection direction of wide bandgap semiconductor materials in betavoltaic batteries.Drawing on research achievements in the fields of photovoltaic cells and power devices,the study has clarified the direction of device preparation optimization for betavoltaic batteries and successfully prepared highperformance betavoltaic battery devices.Finally,the long-term operational stability and temperature adaptability of the prepared batteries were evaluated in consideration of the application scenarios of betavoltaic batteries.The main research contents and innovative achievements are summarized as follows:1)Theoretical research on the selection of semiconductor materials for betavoltaic batteries:Based on the transport processes of various particles inside the betavoltaic battery,the key factors that affect the output performance of the betavoltaic battery were analyzed and simulated in depth by using MCNP simulation and theoretical formula.The results showd that indirect band-gap semiconductor materials with low mean ionization energy,low mass number and density,such as SiC,diamond and BN,have higher energy conversion efficiency.Combined with the current material preparation level,SiC was selected as the wide bandgap semiconductor material for the betavoltaic battery in this study.Through MCNP optimization design,using a 63Ni isotope source with an activity of 5 mCi/cm2,the theoretical short-circuit current density of the SiC-based betavoltaic battery in this study was 18.67 nA.cm-2,the open-circuit voltage was 1.89 V,the fill factor was 0.91,and the theoretical energy conversion efficiency was 6.14%.2)Study on optimization and preparation of SiC-based betavoltaic battery transducer:Based on research achievements in the fields of photovoltaic cells and power devices,the P-type ohmic contact process was studied,and Ni/Ti/Al/Ni metal was selected as the P-type ohmic contact metal in this study.The effects of surface passivation process,ohmic contact electrode process,and device effective size on the output performance of the betavoltaic battery were experimentally investigated.The results showed that the surface passivation process can reduce the boundary trap charges of SiC semiconductors,reduce the reverse saturation current and the ideality factor of SiC devices;the ohmic contact electrode affects the series resistance of the battery,leading to changes in the short-circuit current;increasing the effective area will increase the reverse saturation current,and reduce the open-circuit voltage and short-circuit current density.By optimizing the dry oxygen oxidation surface passivation process,the Ni/Ti/Al/Ni metal electrode,and the 4 mm×4 mm effective area,the energy conversion efficiency of the SiC-based betavoltaic battery in this study reached 3.8%,which is about 2.4 times higher than that of experimental devices of betavoltaic batteries at home and abroad.3)Study on the weatherability of SiC-based betavoltaic battery:Based on theoretical analysis,a weather resistance evaluation plan was developed for SiCbased betavoltaic batteries,and its long-term operational stability and temperature adaptability were experimentally tested and evaluated.The results showed that within the 10-year service life,the equivalent input energy decay of the 63-Ni isotope source was only 3.4%,which would not affect the output performance of the betavoltaic battery.After the electron beam accelerated aging experiment of equivalent operation for 5-8 years,the maximum variation range of filling factor and open-circuit voltage of the prepared SiC-based betavoltaic battery was less than 10%,which shows good long-term stability.Meanwhile,temperature changes will significantly affect the open-circuit voltage and maximum output power of the SiCbased betavoltaic battery.After high and low temperature performance tests,the SiCbased betavoltaic battery prepared has an open-circuit voltage temperature variation coefficient of 1.6～2.8 mV/K,which is lower than other photovoltaic cells and has good temperature adaptability.This study has provided a clear direction for the future selection of wide bandgap semiconductor materials in betavoltaic batteries through in-depth theoretical analysis.By drawing on research achievements in the fields of photovoltaic cells and power devices,high-performance SiC-based betavoltaic battery devices were successfully prepared.The weather resistance of the prepared betavoltaic battery was tested and evaluated in consideration of the application scenarios of betavoltaic batteries.The research achievements in this study can provide theoretical support and experimental reference for the future development of wide bandgap semiconductor-based betavoltaic batteries,especially SiC-based betavoltaic batteries.