[igorsk]

viktorz over at the-ebook.org forums dug out an old PR from PVI which might explain how Sony made a touch screen without layer on top:

PVI’s new Touch EPD uses the innovative “force sensing” touch technology. In this technology, several force sensors are placed under the e-paper display. When a user touches the display, proprietary software calculates the location and intensity of the touch with input from the sensors. There is no additional layer of materials on top of he display as there is in traditional touch technologies; as such, there is no impact to the reflective qualities of the display. This technology requires no ITO (the most fragile component in traditional touch panels), hence exhibits superior robustness. Unlike capacitive touch panels which requires the touch medium be conductive (such as a finger), this force sensing technology works with either stylus or fingers. The cost of the technology is competitive with resistive and lower than capacitive touch panels. In other words, the force sensing technology is highly competitive against all existing touch technology in the market, especially for the e-paper application.