>Normalizing for density, monocrystalline silicon is stronger than steel!
So's glass, and silicon's a lot like glass (very brittle)
So's glass, and silicon's a lot like glass (very brittle)
You're right that fracture toughness is comparable, but that's not usually as relevant in a MEMS context: for one thing there's less potential for unanticipated collisions, but also crack propagation is significantly inhibited at microscopic length scales.