Simple solution in driving vibration motors, an app note from Precision Microdrives. Link can be found here
This bulletin covers the circuitry required to drive vibration motors from a high impedance signal source (for example an output pin of a micro controller / digital device).
There are several integrated IC’s that can do this job, but if there is already a power supply of appropriate voltage in the application design, it is often cheaper to use discrete components.
Circuits like this are common in handheld applications where one may want to alert users and operators of an event. This is generally known as vibration feedback. For haptic feedback which is used more commonly with things like touch-screen interfaces, a more advanced drive circuit is usually employed.