Is there a technical reason why most touch screens use glass rather than plastic?

Question

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.

@Passerby LOL. Thanks. If you are serious, you can post that as an answer, expanding on it. — Fiksdal, May 09 '16 at 07:56
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 09 '16 at 07:59
@Passerby LOL... Just make a phone call to Apple or Samsung, I'm sure they'll admit it in writing... — Fiksdal, May 09 '16 at 08:00
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 09 '16 at 08:15
@Passerby I see, thanks. On devices that feature a plastic front, rather than glass, is the glass in the inner glass of the LCD more likely to break in the case of a drop? (Compared to the glass front device.) — Fiksdal, May 09 '16 at 08:17
In terms of user experience, glass screens also feel nicer and are less yielding. — JAB, May 09 '16 at 13:17
@JAB Some people actually think plastic feels better, though. So it's a matter of taste. — Fiksdal, May 09 '16 at 13:19
I would imagine the use of plastic screens on in-flight entertainment systems was influenced by weight concerns. Saving 100g per seat is a win. — TMN, May 09 '16 at 15:25
@TMN Good point! Saving 100g per iPad would also be a win though, but probably not a big enough one. Also, the in flight screens are in little or no danger of getting scratched, as they t won't be lying around in backpacks, etc. — Fiksdal, May 09 '16 at 15:31
@Passerby Someone did pretty much make that an answer. http://electronics.stackexchange.com/a/233193/108245 — Fiksdal, May 09 '16 at 17:41
There are different touchscreen technologies. Most likely this is referring to capacitive touch? Resistive touch requires a flexible panel (as far as I know). — Steve, May 09 '16 at 20:18
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. http://www.corninggorillaglass.com/ — J..., May 09 '16 at 23:16
My Lumia820 broke the inner AMOLED display and the inside layer of glass (with polarizer), but the front glass (with touch) remained intact and I'm still using it after replacing the display. — Agent_L, May 10 '16 at 16:16
@Fiksdal It felt perfectly flat screen down on a wooden floor. This is an old and thick model with front glass not bonded to the display. I guess the g-force broke the inner screen and then the broken screen hit the front glass from the inside as it lost rigidity. Because cracks on the display and the screen were pretty good matching. — Agent_L, May 10 '16 at 16:26
@Agent_L But I thought only one component, the display, was cracked? What was the second component with matching cracks? — Fiksdal, May 10 '16 at 16:39
@Fiksdal The front glass have 2 layers: outside with digitizer and inside with polarizer (not counting the display). The digitizer is intact but polarizer is broken in exactly same way as the screen. Cracks can be seen with correct angle and can be felt with fingernail (after disassembling the phone ofc). This is how I found out the glass have 2 layers. — Agent_L, May 10 '16 at 16:56
Also I am not sure if a drop of hot coco would create a melting spot in my display? Though many plastics can withstand heat but may be they will increase the cost. — Tanmoy, May 11 '16 at 11:33

Andy aka · Answer 1 · 2016-05-11T17:03:36.487

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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.

Taken from this article

edited May 11 '16 at 17:03

answered May 09 '16 at 08:17

Andy aka

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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 09 '16 at 08:29
Correct but as for making plastic as sensitive as glass that is beyond my knowledge. – Andy aka May 09 '16 at 08:30
Alright, thanks for the info! Would it be on topic here to ask that as a sepreate question? – Fiksdal May 09 '16 at 08:37
Is it an EE question or a physics question? – Andy aka May 09 '16 at 08:38
I would phrase the question: "Is it possible to make a plastic touch screen as sensitive and accurate as a glass touch screen?" This sounds like an EE question? (Although of course, all engineering involves physics.) – Fiksdal May 09 '16 at 08:41
Ask it then but it's not something I can answer. – Andy aka May 09 '16 at 08:49
OK :) Maybe someone else can :) – Fiksdal May 09 '16 at 08:50
@FakeMoustache I see. As you said, I think resistive is quite rare these days? – Fiksdal May 09 '16 at 09:05
Yes resistive touchscreens are getting rare these days because of their bad performance, they're not made of glass so scratch easily and look worse, capacitive touch screens have become cheaper making the resistive variant mostly obsolete. – Bimpelrekkie May 09 '16 at 09:11
@FakeMoustache Then there is infrared, which I have on my plastic eReader. – Fiksdal May 09 '16 at 13:23
@Andyaka I think you're reading a bit too much on the dielectric constant. If you look at chapter 2.3.3 in the same document they go on to say that 10mm plastic cover"glass" is quite usable. So for your average <1mm thick mobile device "glass" this is bit of a non-issue. On the other hand if you want teenager-resistant display you want to go with thick materials.. – Barleyman May 09 '16 at 14:15
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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 09 '16 at 14:24
@Barleyman - I genuinely look forward to seeing your answer. – Andy aka May 09 '16 at 14:28
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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: http://electronics.stackexchange.com/questions/233141/is-it-possible-to-make-a-plastic-touch-screen-as-sensitive-and-accurate-as-a-gla/233171#233171 – Barleyman May 09 '16 at 14:36
@fiksdal After reviewing some technical material, it turns out the actual touch sensor sometimes uses plastic but glass is more popular and actually cheaper these days. Plastic can be made thinner on the other hand. – Barleyman May 10 '16 at 08:38
@fiksdal Geoff Walker has more information on touch technology than anyone else and it's all available free of charge right here: http://www.walkermobile.com/PublishedMaterial.htm – Barleyman May 10 '16 at 08:42
@Barleyman: Resistive in medical sector is just backwardsness/resistance to change. The UX for resistive touch screens is utterly awful. – R.. GitHub STOP HELPING ICE May 11 '16 at 00:17
@R.. Possibly they're resistive to change because having a drug dispenser et al go haywire because the display got some body fluid on it is a non-issue. – Barleyman May 11 '16 at 08:41
@Barleyman: If that's an issue, the possibility of a visitor or other non-qualified person accidentally doing something dangerous via the UI is also an issue, and there should be proper access controls to ensure that it doesn't happen... But of course the medical sector is utterly backwards on security and access control, too... – R.. GitHub STOP HELPING ICE May 11 '16 at 17:27
Andy, I want to comment on this vs. the answer of @DmitryGrigoryev . My opinion, as well as which answer I accept, is largely irrelevant, as I have near zero knowledge on EE. Anyway, I think the two answers highlight two different things, and both seem important. I believe Dmitry's answer is also technical. I believe you probably agree that vulnerability to scratches and aesthetics are part of the reason why plastic is not widely used. Similarly, Dmitry probably agrees with your points regarding the sensitivity and accuracy of glass. It seems to me that both answers are very valid, – Fiksdal May 12 '16 at 06:13
@Andyaka I also found this very relevant: http://electronics.stackexchange.com/a/233171/108245 – Fiksdal May 12 '16 at 06:16
@Fiksdal this is an EE site and I have provided technical answers based purely on electronic or electrical standpoints. How you choose to select the best answer is down to you but don't expect everyone to agree!! – Andy aka May 12 '16 at 07:38
@Andyaka No, of course not, it would be insane to expect everyone to agree. I just wanted to say that I believe both answers seem very valid to me. Actually, an ideal answer might even include both aspects. But as I said, I have nearly zero knowledge on EE. – Fiksdal May 12 '16 at 07:43
@Fiksdal having virtually zero knowledge on EE puts you in a very unique position for judging the best answer LOL. – Andy aka May 12 '16 at 07:58
@Andyaka lol, yeah it's funny, because I can choose which answer is on the top, and that answer often gets more votes simply because it's what people see first. And this question has been featured in the "hot" category all over SE, so a lot of non EE users have probably seen and voted on it. If one answer gets a lot more upvotes than the accepted answer, then it should probably rise to the top regardless. But that has probably been discussed in meta. – Fiksdal May 12 '16 at 08:03

Dmitry Grigoryev · Accepted Answer · 2016-05-10T16:29:30.920

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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.

edited May 10 '16 at 16:29

answered May 09 '16 at 14:58

Dmitry Grigoryev

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Ah, my old Game Boy Color comes to mind :) – Fiksdal May 09 '16 at 15:02
@Fiksdal I don't think your GBC has a touchscreen (though it does have a plastic screen finish). – Dmitry Grigoryev May 09 '16 at 15:07
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Yeah, I was talking about the not-so-pretty plastic screen and it getting worse over time. – Fiksdal May 09 '16 at 15:08
FYI, it can be polished with the same product they use on scratched CDs, if you feel nostalgic enough. – Dmitry Grigoryev May 09 '16 at 15:13
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Cool :) Unfortunately it's no longer with me. But that polish would probably be useful for plastic screen phones too? – Fiksdal May 09 '16 at 15:20
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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 03:22
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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 07:26
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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
Regarding the battery being under the LCD, etc., is this something new? I remember one time I had to change the battery in an iPhone 4(S?). All I had to do was remove two screws, take off the back cover, remove a third screw inside, and change the battery, then put everything back on. Of course, that's still way more work than changing the battery on my Samsung S3, which can be done by hand. But is it even more complicated in newer iPhones? – Fiksdal May 10 '16 at 12:46
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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
Plastic scratch resistance is abysmal compared to glass. And what's the intended use of a touch screen? - yep, scratching it with the dust under your fingertips. Sorry, I had to downvote because you're simply wrong. Russell is also right and arguing with his fine points only shows your answer is based on faith, not facts. – Agent_L May 10 '16 at 16:13
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@Agent_L Plastic scratch resistance is abysmal compared to glass - isn't that what I say in my answer as well? Or do you disagree with the word "terrible"? – Dmitry Grigoryev May 10 '16 at 16:16
@DmitryGrigoryev No, you wrote "Plastic is virtually indestructible". Then it's "If it's scratched" - but that's a very big "if" considering the paragraph before states it can't be damaged at all. – Agent_L May 10 '16 at 16:22
@Agent_L Well, a scratched screen remains readable and otherwise functional, contrary to a shattered screen. I rephrased that part of the answer. – Dmitry Grigoryev May 10 '16 at 16:34
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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
@Agent_L Well, if you can read on a shattered screen, good for you. I can't. – Dmitry Grigoryev May 10 '16 at 17:01
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There is a major valid reason for making the battery hard to replace: it destroys the profit margins for stores removing the factory battery from every device, replacing it with a used, virtually-dead one, and selling the removed battery as a replacement. This is widespread practice in certain markets. – R.. GitHub STOP HELPING ICE May 10 '16 at 19:22
This has probably more to do with the fact that most plastic touchscreens are cheap or don't care too much about usability, but I have yet to see any plastic touchscreen that had acceptable performance. I mean those industry handhelds, airplane screens, old navigation devices - all plastic touchscreens, all horrible beyond recognition. Recognize prints slowly, low accuracy, you can press into the screen, no multi-touch support,.. Most of those are presumably resistive and not capacitive though. – Voo May 11 '16 at 12:07
@Voo Slow input recognition is almost certainly due to a slow CPU processing touchscreen input. Delay in touchscreen electronics in unnoticeable. – Dmitry Grigoryev May 11 '16 at 12:21
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people have to pay again - either for a new phone, or for a glass replacement job.- well, that's a horrible strategy because most people will buy a phone from a different company, because they have first-hand experience of poor build quality from the company whose phone they just had break on them. And over time, people will eventually flock to buy phones from the one company whose screens do not break easily. – Juha Untinen May 28 '17 at 12:18

score 36 · Answer 3 · answered May 09 '16 at 22:17

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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).

answered May 09 '16 at 22:17

Mark

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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 07:36
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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
@WarrenYoung Sapphire is too expensive for screens, but most cost-effective for the objective lenses on many phone cameras. – Eric Lloyd May 11 '16 at 22:20

score 18 · Answer 4 · answered May 09 '16 at 07:57

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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.

answered May 09 '16 at 07:57

pjc50

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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. – Fiksdal May 09 '16 at 08:03
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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 09 '16 at 08:16
@FakeMoustache Thanks! BTW, I just read on Wikipedia that glass-free Amoled is in the works. – Fiksdal May 09 '16 at 08:24
Let us continue this discussion in chat. – Fiksdal May 09 '16 at 10:19
FYI, Apple did wind up using the synthetic sapphire, but only for the Home button (or whatever that button is called on an iPhone) and maybe also the rear camera. I watched a YouTube video about it a few weeks ago, a guy took steel wool and sandpaper to the screen and the button to show the difference in how much it scratched. – Dan Henderson May 09 '16 at 12:22
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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 09 '16 at 13:34
@DanHenderson I think they also used the sapphire on the Apple Watch? – Fiksdal May 09 '16 at 13:36
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@IhavenoideawhatI'mdoing I've also heard that sapphire shatters easily. – Fiksdal May 09 '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 09 '16 at 13:41
Relevant story to your answer: http://www.businessinsider.com/steve-jobs-new-iphone-screen-2012-1 – childofsoong May 09 '16 at 20:39
@FakeMoustache - what do you mean by that? Look around the office and you'll see plastic LCDs literally everywhere. You're probably using one right now. – Jasmine May 11 '16 at 21:42
@Jasmine You should look again, those displays are themselves are made using glass. Maybe there's a plastic window on top of it but the LCD itself will have glass plates. Smash one with a hammer and you'll see I'm right. – Bimpelrekkie May 12 '16 at 05:42

undo · Answer 5 · 2016-05-11T12:02:32.503

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

score 3 · Answer 6 · answered May 09 '16 at 17:42

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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)

answered May 09 '16 at 17:42

user109531

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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 07:31
Dell P2418HT uses a projected capacitive system and it's made from plastic (the brochure says "Eliminate the need for glass screen found in traditional monitors with an anti-glare surfaces which reduces distracting reflections and fingerprints"). – Cristian Ciupitu Dec 06 '19 at 00:35

Is there a technical reason why most touch screens use glass rather than plastic?

6 Answers6

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

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