Also known as quantum mechanical black holes, the micro black holes are hypothetical. The fact that black holes smaller than stellar mass can form was first theorized by Stephen Hawking in 1971. These micro black holes have a certain mass limit. According to the concept of Schwarzchild radius and Compton wavelength, the minimum mass of a micro black hole is 22 micro-grams, also known as the Planck mass.
The quantum mechanical black holes must have played an important role in the early universe in tremendous energy and density. Such black holes, however, were unstable and must have evaporated through the Hawking radiation. In 1975, Hawking showed that due to quantum mechanical effects, smaller the black hole, faster it will evaporate. So it results in a sudden burst of particles as the micro black hole suddenly explodes. Mathematics tells us that the energy required to create these micro black holes is of the order of 10^19 GeV. This is far more than the maximum energy we can achieve with current technology
