An electrical energy generator with improved efficiency has a base on which is mounted an elastically deformable micromechanical element that has a section that is free to be displaced toward the base. An absorber of radioactively emitted particles is formed on the base or the displaceable section of the deformable element and a source is formed on the other of the displaceable section or the base facing the absorber across a small gap. The radioactive source emits charged particles such as electrons, resulting in a buildup of charge on the absorber, drawing the absorber and source together and storing mechanical energy as the deformable element is bent. When the force between the absorber and the source is sufficient to bring the absorber into effective electrical contact with the source, discharge of the charge between the source and absorber allows the deformable element to spring back, releasing the mechanical energy stored in the element. An electrical generator of improved efficiency includes a first energy source comprising a piezoelectric transducer secured to the deformable element to convert the released mechanical energy to electrical energy. A second energy source comprises a betavoltaic cell carried on the deformable element or electron collector cantilever beam to provide a direct current (DC) power output that can be added to the piezo-electric circuit's alternating current (AC) power output, such that there is a continuous power output that can be used to provide power to electronic circuits.