Getting to the SUMMiT Sandia National Lab. A team of scientists led by Jeff Sniegowski developed SUMMiT, a microfabrication process geared specifically towards 3D structures and MEMS devices. By depositing these various layers, masking and defining each layer through photolithography and etch processes, using chemical mechanical polishing for planarization at appropriate levels, and then etching away sacrificial material, Sandia has produced the world's most complex, electrically actuated gear systems, moveable mirrors, plates and bearings, and many other structures. That could be an arming system for a weapon or a high-energy power supply on a photocopier. You can make electronic locks easily, but they have mixed failure modes where the result can be a short circuit or electrical spark.
Mechanical systems stand up to mixed failure modes better.
SUMMiT's improvements from just a few layers to five may not initially seem like such a big deal. However, like a microchip, making a five-layer device takes up to 140 individual patterning, polishing, and etching steps. This permits significant interactions to occur between various subassemblies, thereby allowing the mechanical systems' aspect of MEMS to be much more realizable. When two of these systems are placed orthogonal to each other and linked to a rotary gear in a third and fourth layer of mechanical material, the linear motion can be coupled to a free gear capable of driving many more interactions. Now, microengines driving gear boxes can generate enough energy to power movement among many subassemblies.