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A radioisotope power generator with a potential lifetime of decades is demonstrated by employing a 100.3-year half-lifetime 63Ni radioisotope thin-film source to electrostatically actuate and cause reciprocation in a microfabricated piezoelectric unimorph cantilever. The radioisotope direct-charged electrostatic actuation of the piezoelectric unimorph cantilever results in the conversion of radiation energy into mechanical energy stored in the strained unimorph cantilever. The gradual accumulation of the actuation charges leads to the pull-in of the unimorph cantilever into the radioisotope thin-film, and the resulting discharge leads to vibrations in the unimorph cantilever. During the vibrations, the stored mechanical energy is converted into electrical energy by the piezoelectric thin-film. The generator was realized by using both microfabricated lead zirconate titanate oxide-silicon (PZT-Si) and aluminum nitride-silicon (AIN-Si) unimorph cantilevers. The radioisotope direct-charged electrostatic actuation of the AIN-Si unimorph cantilevers by a 2.9-mCi 63Ni thin-film radiating 0.3 muW led to charge-discharge-vibrate cycles that resulted in the generation of 0.25% duty cycle 12.95-muW power pulses (across an optimal load impedance of 521 kOmega) at an overall energy conversion efficiency of 3.97%. These electrical power pulses can potentially be useful for periodically sampling sensor microsystems.