One of the big advantages of resistive touch panels is that they are relatively inexpensive to make. Another is that you can use almost anything to create an input signal: finger tip, fingernail, stylus -- just about anything with a smooth tip. (Sharp tips would damage the film layer.)

This technology has a lot of disadvantages, however. First, the analog system is susceptible to drift, so the user may have to recalibrate the touch panel from time to time. (If you owned a PalmPilot or other PDA, you may remember having to occasionally go through the recalibration process on their PalmPilot.) Next, the ITO material used for the conductors is brittle and not well suited for bending. Over time, repeated use can cause the ITO to crack, which disrupts the flow of electricity and can result in a dead spot on the touch screen.

In addition, there needs to be a gap between the two sensor planes that must be bridged in order to make contact between the two. Just about the only material suitable for this gap is air, but this presents some problems of its own.

First, the gap adds to the combined thickness of the display and touch module. As the consumers demand thinner and thinner devices, a single millimeter can be a big deal.

Another problem has to do with the optical properties of the different layers. If you look at a drinking straw in a glass of water, it will look as though it is slightly bent where it enters the water, even though it is straight. This is because light can bend, or "refract," when it makes the transition from one material to another. If the materials have the same index of refraction, the light won't change its path, but if the index of refraction is different, the light will bend.