Subject: LED TV s: The weak blue contribution!

From: [email-masked] (Bob Mueller)
Date: 18 Feb 95 13:12:47 GMT

Siemens has sold blue LED s for quite a few years.  These are based on SiC as
the semiconductor and had a major problem- extremely high price.  There seems
to have been no competition until the last few years (except for incandescent
lamps with blue envelopes, in LED sized packages).  Now that  others have
entered the market place the prices are an order of magnitude lower. Also,
brightness is getting better.  Thus, maybe the LED TV will be possible in the
not-too-distant future, though there remains the technical barrier of getting
arrays of these things.  Unlike many devices we have vastly different
substrates here.  Your typical IC is all silicon, or maybe all GaAs, with some
variation of low concentrations of foreign dopants from place to place.  The
different colors of LED are built around quite different materials requiring
quite different processing.  Either a very clever scheme is needed to lay down
hundreds of thousands of these very different spots of material using something
like lithographic techniques or else we'll need machines sticking all those
little chips on a substrate, one by one.  Will any company bother? Why? (A
color CCD contains nearly 500,000 sensing elements and the TV would need a
similar number to deliver the resolution given by the pick-up chip.)  It might
make sense for a military job, but nobody else can pay the bill.

  Sincerely,
  Bob