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From: henry@hpcvci.HP (Henry Nielsen)
Newsgroups: sci.electronics
Subject: Re: Liquid Crystals
Message-ID: <3340001@hpcvci.HP>
Date: Sat, 18-Apr-87 19:11:37 EST
Article-I.D.: hpcvci.3340001
Posted: Sat Apr 18 19:11:37 1987
Date-Received: Sun, 19-Apr-87 20:57:44 EST
References: <337@sdics.ucsd.EDU>
Organization: Hewlett-Packard Co., Corvallis, Oregon
Lines: 66



> I'm interested in homebrewing a portable terminal including a liquid
> crystal display, suitable for 80x24 characters or whatever I can get.
> Got any good sources for these and the driver chips required?
> Manufacturers' or distributors' names, cities, and part numbers would
> be great, along with whatever comments you have from actually using
> such devices.  Like everybody else, I'm looking for low power, excellent
> readability, and easy to drive screens :-).
> 
> All I need is quantity 1 -- if it ever works and becomes a product,
> I'll be sure to let you all know.
>
> I could always buy a laptop and disassemble it but that seems a waste
> (of money and a laptop).
> -- 
> Copyright 1987 John Gilmore; you can redistribute only if your recipients can.

First, some background information:  

There are three types of liquid crystals:  smectic, nematic, and cholesteric.
Smectic LCs line up in a fundamentally 1-dimensional ordering.
Nematic LCs line up in sheets (2-d ordering) and have an orientation that
can be controlled by an extermal electric field.  These are the ones that
you'll find in LC displays.
Cholesteric LCs also line up, but their key property derives from their
helical structure - they reflect light at the wavelength equal to the pitch
of the helix.  This pitch is controlled by the ambient temperature and
is EXTREMELY sensitive.

O.K.  So much for background.  Don't try to make a LC display.  In principle
it is very easy, in practice quality control will keep you up nights,
making you unpopular with you neighbors... :-)  Seriously, there are little
problems like control of static-electric fields on the inside of the glass
plates enclosing the LC material, proper sealing (they don't work well if
moisture gets inside), etc.  So, the best way to use such a display is
to buy one.  Now, in quantities of 1, I'm not aware of anyplace you could
get a Japanese display (I'm pretty sure they've wiped out any other
American manufacturers...).  Also, these displays take about 10 volts to
drive (15V is better), and that makes the display drivers a little tricky.
For low power, you want CMOS drivers.  For Hi-res, you need lots of data
handling capability in the drivers - this means very small geometries on
the chips - and this means thin gate oxides and that spells out a problem
because you now have 10 volts across a (nominally) 400 Angstrom gate oxide.
This makes a E-field of ~2.5 Megavolts/cm and requires a very high
integrity gate oxide...  In English - you probably can't find a source
for these (we make them, but don't sell them outside the company...).
As for readability - I'll assume you mean a wide viewing angle - don't
hold your breath.  Even with tricks like lenses in front of the display 
AND backlighting, its very tough to improve the performance you see in
current LC display products.

Bottom line:  It sounds like an interesting project.  I don't think you'll
be able to find the materials you need to put it together (I'll be happily
surprized if you do).  Your best bet is, most probably, to buy a laptop
like the HP Portable Plus or the Toshiba 1100+ (I know the HP is good and
has a reasonable terminal emulator; I've only heard rumors about the
Toshiba unit, but what I have heard is positive and I do know that they're
quite competent at IC manufacturing so that the reliability should be
acceptable - I assume that they have an on-board terminal emulator...).

Disclaimer:  This is really NOT intended as a sales-pitch for laptops.

Henry Nielsen
Hewlett-Packard Company, Corvallis Oregon.
hplabs!hp-pcd!henry