For all the reasons the author stated, I think piezos are a much better solution than motors for haptic feedback.
From the user's perspective, the idea is to emulate the feel of pushing a mechanical key. Vibrating the touchscreen with a motor doesn't come anywhere close to achieving that feel. Motor-driven haptic feedback "buzzing" on a touchscreen is, at least for me, unnatural -- something I'd rather disable than enable.
The peizos can do both, create audible feedback and/or haptics (tap). The waveshape will determine the type of response. If you want the audible response along with the haptics, use a faster rise/fall time on the waveform. If you do not want an audible click, use a slower rise/fall time.
In general, as panel size increases, the number of piezos required increases due to increased mass that needs to be moved.
This is a very nice use of pizzo effect, in fact most of the non technical person seeks the similar kind of effect after key press they feel in the computer keyboard or some other physical keypad, but in case of touch sceens it is not possilble to have that effect, present touch screen devices are simulating that effect using the bass speaker, but otherway round this consumes a lot of power from battery.
This use of pizzp electric effect will greatly solve this problem.
@Luis, are you sure you are not referring to audible clicks? This article is about a more LF physical 'tap' under the keyboard/screen.
I'd be interested to know if just one driver can produce the same level of feedback across the whole panel, or if it is stronger in particular positions.
I experienced this haptic feedback on one mobile phone once and to be honest I prefer not to have it. I think the silence and the delicate feeling once gets when using a capacitive touchscreen is nice. Nonetheless, that's my appreciation, there might be some folks out there that due prefer the mechanical feedback...