Given that our LCD screens are also "solid-state", how come they don't wear out more easily. [actually, i still find it surprising to learn that SSD drives don't last a lot longer.]
The specifics of the problem with Flash memory has to do with the type of electronic circuit in it.
Flash memory uses a basic storage element called a "floating gate transistor." A floating gate transistor can basically be thought of as an on/off switch; leaving technical details aside, the transistor either conducts electricity (on) or it doesn't (off), and it will stay in whatever state you put it in even when there is no power going to it.
It's called a "floating gate" transistor because each switch has a tiny bit of conductive material, a few microns wide, that is separated from the rest of the transistor by an insulator. The little sliver of conducting material can be charged full of electrons, and when it is charged, it holds the charge for a very long time, because it's surrounded by insulator on all sides. When it's charged, the rest of the transistor "senses" the charge and it acts like a closed switch. When it isn't charged, it acts like an open switch.
Make sense so far? Here's where the funky bit comes in:
You charge or discharge the gate by pushing electrons into it or draining electrons out of it. Now, the gate is surrounded by insulating material, in a very thin layer, so you would normally think there is no way to get electrons in or out, since the electrons can't pass through the insulator.
But electrons have the ability to teleport, jumping from one place to another without passing through the space in between. They can only do this over very tiny distances; the phenomenon is called "electron tunneling," and it happens because electrons are not hard round little balls like billiard balls. They are quantum particles, and as such they do not have definite, precise position in space--they have a wavelength, and they can appear to act as through they are located anywhere within that wavelength. (That's the quick and dirty overview, anyway; the reality is a bit more complicated, but that is the basic gist.)
Because electrons can tunnel, they can be made to pass through the insulator and into or out of the gate without actually moving through the space in between. You can force electrons to tunnel into the gate or tunnel out of the gate even though it's surrounded by insulating material, because the width of the insulating material is smaller than the wavelength of an electron.
When you do this, though, you end up damaging the insulator. You have to provide a pretty good push on the electron in order to get it to tunnel--it takes more power to write to a Flash cell than it takes to read one--and applying a higher voltage field across the insulator causes it to degrade.
Eventually, the insulating layer degrades so much that it no longer acts as an insulator. That particular cell shorts out; the floating gate is no longer floating and no longer stores a charge.
Things like LCDs aren't made from floating gate transistors. They're made from thin-film field effect transistors, which are entirely different in their structure and in how they work. Field effect transistors don't have a charged floating gate, which means they don't retain their state when you remove power to them but also means that they aren't damaged by the process of changing states.
