Wikipedia: Microelectronics

Microelectronics is a subfield of Electronics. Microelectronics, as the name suggests, is related to study of electronic components which are very small. Microelectronics is the science of producing solid-state electronic devices. These devices are made from semiconductors. The basic units are transistors, capacitors, inductors, resistors, diodes and insulators and conductors.

Transistors are active devices, in that they amplify power. There are other posibilities for active devices, but they are rare. ([Josephson junction]?s and nanotubes? comes to mind).

Digital integrated circuits consist mostly of transistors. Analog circuits contains resistors and capacitors as well. Inductors are used in high frequency analog circuits, but tend to occupy large chip area if used at low frequencies.

Passive devices are ideally two-terminal devices: resistors, capacitors, inductors and diodes. Parasitic (unwanted) components may form additional terminals towards e.g., the substrate.