Most modern touch screens in portable devices are made of glass.

This glass often breaks if accidentally dropped. Also, it is very reflective, making it difficult to use in strong light.

I know that touch screens without glass exist. For example, the multi-touch screen on my e-ink e-reader has a plastic front. I remember many other examples, such as the personal in-flight entertainment systems on many airplanes.

What are the reasons that most modern portable touch devices come with a glass panel on their fronts, rather than plastic or something else?

The cracking of glass seems to be a pretty big problem.

Edit: I've seen a lot of cracked touch devices, and it's nearly always only the front panel that's cracked. The actual display is usually fine underneath. Even the digitizer usually works perfectly.

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    1. Revenue from planned obsolescence, 2, see 1. – Passerby May 9 '16 at 7:55
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    @Passerby LOL. Thanks. If you are serious, you can post that as an answer, expanding on it. – Revetahw May 9 '16 at 7:56
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    If I could source or get a company to admit they purposely design their products to break in months, let alone years, I would. I'd also be heading a class action lawsuit, but that's another story. – Passerby May 9 '16 at 7:59
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    Re, your edit. The Glass/Digitizer is typically a few micrometers above the display, courtesy of the glue strips used to join the two. That accounts for why the display is saved. That distance is enough to blunt the damage. – Passerby May 9 '16 at 8:15
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    Modern glass is tough - really tough. It can take durable antireflection and anti-smudge coatings and it is extremely resistant to scratching. There is no suitable plastic that could work as well. corninggorillaglass.com – J... May 9 '16 at 23:16
up vote 37 down vote accepted

When decisions about consumer electronics are made, many reasons beyond technical come into play. There is no valid reason for a phone to be disassembled in 7 pieces in order to replace a battery, yet that's how one of the most popular phones is made. Mobile phones are as much a product of marketing as they are of electronics, and many design decisions become clear when you take a look at that perspective.

Glass looks good, so it sell good. And when it shatters, people have to pay again - either for a new phone, or for a glass replacement job.

Plastic doesn't shatter or otherwise fall apart, unless you try to cut or burn it on purpose. It can also be made matte, which makes the screen much more readable in presence of reflections and glares. Since plastic doesn't have to be hard, it can be made thinner than glass, improving touch sensitivity.

Unfortunately, it looks cheap even before it is scratched (and plain terrible after), so you can't make big money selling phones with plastic screens. Worse, people will carry these cheap-looking phones for ages (because the screen won't shatter), projecting that cheap-looking and outdated image of your brand everywhere they go. So you either go out of business, or switch to glass like everyone else.

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    "There is no valid reason for a phone to be disassembled in 7 pieces in order to replace a battery" -- untrue; all other things being equal, a non removable battery as in the iPhone allows for more battery volume (and therefore charge time) for a given overall package volume. Whether that's more or less valuable than the ability to swap the battery is a reasonable thing to debate, but it's a valid design decision. – Russell Borogove May 10 '16 at 3:22
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    @RussellBorogove I'm not arguing against the battery design, but about its location. A non-removable battery could still be located under a removable cover, not under several layers of LCD, PCB and flex cables. Take almost any Android tablet: they have non-removable batteries too (and often even require you to solder the new battery), but there's much less stuff to take apart, usually only the back cover. – Dmitry Grigoryev May 10 '16 at 7:26
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    It would still incur a volume penalty. Plastic has thickness. Connectors have volume. Engineering has tradeoffs. – Russell Borogove May 10 '16 at 12:06
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    I don't think the argument that it is marketing rather than technical constraints is very strong. There are lots of technical reasons for using glass screens given in other answers, and even yours (scratches). – dan1111 May 10 '16 at 13:08
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    @DmitryGrigoryev So is glass. I myself have a functional phone with cracked glass and if you look up classifieds you can find numerous examples of phones "touch cracked but working". And this is still unfair comparison - carrying in the pocket is the intended purpose while dropping is not. Scratch resistance is the #1 requirement here and plastic simply sucks for this. Planned obsolescence is everywhere but in the glass. – Agent_L May 10 '16 at 16:50

Title of question: Is there a technical reason why most touch screens use glass rather than plastic?

Note the word "technical" and not "marketing"

What are the reasons that most modern portable touch devices come with a glass panel on their fronts, rather than plastic or something else?

Glass (as a cheap and common material) has a good dielectric constant (more than most cheap plastics) and this makes the change in capacitance bigger for those devices using that technology. This makes life easier on the electronics that has to detect finger positions and movement.

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Taken from this article

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    Note that some cheaper/older devices do not use a capacitive touch screen but a resistive touchscreen. Usually these work best with a stylus or a fingernail. Capacitive touchscreens do not require any pressure to register a touch, resistive touchscreens do need some force (to make a connection between two resistive layers). – Bimpelrekkie May 9 '16 at 8:29
  • Correct but as for making plastic as sensitive as glass that is beyond my knowledge. – Andy aka May 9 '16 at 8:30
  • Alright, thanks for the info! Would it be on topic here to ask that as a sepreate question? – Revetahw May 9 '16 at 8:37
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    @FakeMoustache Resistive is going strong on medical sector and anywhere else where you may get the display wet. While you can in fact reject water droplets on display, this is hardly foolproof and requires combining self and mutual capacitance technologies in one display for best effect. Infrared is no good and it's mostly used for large size displays these days. There are various other technologies such as optical (they're watching you!) and various surface wave technologies but PCAP + resistive are dominating by vast margin. – Barleyman May 9 '16 at 14:24
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    @Andyaka You're not wrong with the dielectric constant, but it's not really an issue in most cases. But glass is generally the better display cover material. Plastic windows are not very popular. I commented on this here as well: electronics.stackexchange.com/questions/233141/… – Barleyman May 9 '16 at 14:36

You mention cracking as a downside to using glass, but most touchscreens will encounter far more potential scratch-causing events than crack-causing events.

Glass is highly scratch-resistant: at a Mohs hardness of 5.5, it's harder than anything else in your pocket (steel is around 4). Synthetic sapphire is even more scratch-resistant: at a hardness of 9, the only common material that can scratch it is diamond. In contrast, most plastics have a hardness less than 1, and will get scratched up in short order (among other hazards, fingernails have a hardness between 2 and 3).

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    BTW this site says that steel can scratch minerals of up to 6.5 hardness, and my phone screen has several tiny scratches by now, so it's definitely NOT harder than anything in my pocket – Dmitry Grigoryev May 10 '16 at 7:36
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    According to the Walter Isaacson biography of Steve Jobs the original iPhone prototype had a plastic screen but go so scratched up in Jobs' pocket by his keys that Jobs insisted on the iPhone having a glass screen – Matthew Lock May 10 '16 at 12:20
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    @DmitryGrigoryev, steel comes in a wide range of hardness grades. Mild and stainless steels tend towards the lower end of that range, while a hardness of 6.5 is for a steel file (ie. tool steel specifically engineered for maximized scratch hardness). – Mark May 10 '16 at 20:28
  • You should add Gorilla Glass and other such highly-engineered materials to that answer. As far as I'm aware, no smartphone yet uses synthetic sapphire for the screen — phones are still too big for that to be economical — but there are materials commonly used in high-end smartphones that approach the hardness of sapphire, splitting the difference between your Mohs numbers. – Warren Young May 11 '16 at 12:56
  • I sent a Wacom bamboo touch/tablet back as not fit for purpose as it scratched the first time I touched it. I didn't have it long enough to drop it. – Pete Kirkham May 11 '16 at 13:09

Glass is hard, and therefore brittle, so it shatters.

Plastic (acrylic or polycarbonate) is softer, so more prone to scratches. It's certainly a possibility and some cheap phones have plastic touchscreens.

But the underlying LCD behind the transparent touchscreen has to be made of glass, due to high temperature parts of the process. So that's still vulnerable to breaking.

The ultimate is synthetic sapphire, which Apple were going to use but abandoned for some reason. Much harder and harder to shatter than glass.

  • Thanks! Are all LCD's made of glass? What about Amoled, etc? Also, I've seen hundreds of shattered touch devices, and it's nearly always the front panel that's shattered. The actual display is usually fine underneath. Even the digitizer usually works perfectly. – Revetahw May 9 '16 at 8:03
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    I have not seen any LCDs that are not made using glass. That does not mean these do not exist of course. But it would surprise me if they did. LCDs need electrically conductive patterns on the glass. Maybe these patterns cannot be made so easily on something which is not glass. I do not expect that an Amoled display needs glass as it consists of LEDs on a substrate. – Bimpelrekkie May 9 '16 at 8:16
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    @pjc50 What makes you think sapphire will be harder to shatter, though? Doesn't hardness come with brittleness? – I have no idea what I'm doing May 9 '16 at 13:34
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    @IhavenoideawhatI'mdoing I've also heard that sapphire shatters easily. – Revetahw May 9 '16 at 13:37
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    @IhavenoideawhatI'mdoing I have shattered sapphire (actually cleaving wafers), and it is no more difficult to do than for glass. In fact it may be easier, because making "toughened sapphire" is impossible, and unlike glass, sapphire is a crystalline material so cracks propagate readily along the lattice plane directions. Its only advantage in this application seems to be its hardness. A sputtered coating of (amorphous) alumina on top of ordinary glass would seem to be a better choice for toughness. Polycrystalline diamond is very tough but mass production is constrained by economics. – Oleksandr R. May 9 '16 at 13:41

Resistive touch screens are plastic

Capacitive are glass - for capacitive touchscreen to work, there is wires manufactured on the glass itself - this up to just recently was possible on glass only so this is why it is glass.

Also LCDs are from glass for the same reason, there are already plastic film LCDs but are pretty new (like flexible amoleds and flexible epaper)

Most ereaders uses IR touch sensing(which enables to use plastic covering of the display, but the epaper module itself is glass based again)

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    This is false: plastic PCAP displays existed for a long time. I own one of the first android smartphones and it has plastic finish. – Dmitry Grigoryev May 10 '16 at 7:31

Here's some history:

Back in the day, almost all of the early touch (not-so-smart) phones used plastic displays. It was, in fact, Steve Jobs, who demanded that the first iPhones use unscratchable glass.

He said that consumers would carry their smartphones with keys in their pockets and products which were easily damaged weren't acceptable from a corporation like Apple.

This was less than 3 months before the iphone's launch date.
“I want a glass screen," Steve is quoted as saying. "And I want it perfect in six weeks.”

Obviously, other companies followed suit.

Source: http://www.businessinsider.com/steve-jobs-new-iphone-screen-2012-1?IR=T

protected by W5VO May 11 '16 at 13:48

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