Some recent mobile phones use piezo actuators, driven by dedicated haptics drivers at various voltages (50 to 200 Volts peak to peak). This provides precise vibration feedback, such as you may feel when using a Swype touchscreen keypad on some Android phones.
The advantages of these actuators:
- Very small size and light weight for given level of vibration feedback
- Very low power consumption compared to vibration motors
- Extremely short start and stop times (1.5 mS) and duration resolution
- Fine frequency control and wide frequency range: e.g. 1 Hz to 350 Hz vibration
- No magnetic field hence no risk of erasing magnetic stripes on credit cards etc
While online stores like Digikey do not seem to have the really small haptic piezos, only their larger cousins, the piezo benders (coin piezo speakers), you could actually use a bender for your purpose. Also, I know at least one local business that hand-fabricates their own piezo haptic actuator sheets using piezo materials bought from ebay or AliExpress. It's pretty low-tech and not a recent development at all.
This article gives an outline of the various haptic feedback options commonly used, from motors to piezos.
To drive a piezo actuator, you can build an oscillator + voltage boost solution of your own, or use a highly integrated single-chip solution such as TI's DRV8662 which pretty much takes care of everything, from PWM input through to voltage boost up to 200 Volts.
One of my projects incorporated a piezo haptic feedback solution using a regular peizo coin speaker, which was acceptable because a really strong vibration was not needed, just perceivable touch notification.