The Birth of the Sapphire POS Terminal Window

It is a well-known fact that a thin layer of sapphire forms the top surface of almost all point-of-sale (POS) scanner windows.  I had the privilege of making the prototype for this component around 1978 when I worked for Allied Chemical in their synthetic crystal products division in Charlotte, North Carolina.
Among other oxide crystals that we were growing at the time was r-plane sapphire for SOS substrates.  We grew nominally 3 inch wide ribbons by the EFG process that had been licensed from Tyco’s Saphikon division.  We cut and polished 3” wafers from these ribbons for the SOS market.

We were approached by IBM who was finding that their glass windows on the POS terminals were scratching fairly quickly after being installed.  Imagine a supermarket where canned vegetables and six-packs of beer were dragged across the window on a continuous basis.  A typical glass window would have to be replaced every month at least.  IBM asked us if we could bond a sapphire layer to glass so that they could test fire their laser through it and see if there was no distortion in the beam so that it could read the bar code on the products.

A typical SOS wafer was polished only on one side, so I asked my guys to polish a few wafers on both sides.  I then took them and a piece of ordinary window glass that I bought at a hardware store.  I cleaned them both with window cleaner and then mixed up some 5 minute epoxy.  I smeared the epoxy on the glass, put the wafer on it and put it in a hydraulic press with a large rubber stopper on each side to spread out the force.  I cranked up the pressure as high as I dared to squeeze as much of the epoxy from between the glass and the sapphire wafer.

After the epoxy had enough time to set up, I removed the pieces from the press, cleaned away the excess epoxy from the glass with a razor blade and sent the piece off to IBM for testing.  The results were positive, and the sapphire POS window was born.  I still have the original (pictured here) which I have been using as a coaster for a ceramic coffee mug for about 35 years.  The glass around the sapphire is scratched, but the sapphire itself is nearly as pristine as the day that I first made the sample.  If you look at it obliquely, some faint scratches are visible.  But, as sapphire is the second hardest material in nature after diamond, it should remain virtually unscratched for all time.

After I came to Santa Rosa I had a friend who was a store manager for Safeway, the big supermarket chain.  Apparently they were well aware of the availability of the sapphire windows, but were put off by the price.  I got him to explain to his management that, although the sapphire windows were more expensive, they were a one-time purchase, as opposed to replacing the glass windows on a monthly basis.  Soon after, Safeway switched over to the sapphire POS windows which can now be found virtually everywhere that counter level scanners are used.