By Jennifer Colegrove – Director, Display Technologies, DisplaySearch
Apple’s announcement of the iPhone 4 at WWDC 2010 confirms the rumors that the display is 3.5” with a 960 x 640 pixel format (double VGA). This is the first time this format, and its resulting 324 dpi (dots per inch) display, is being mass produced. It is an impressive breakthrough.
The first generation iPhone, released in 2007, had a 3.5” HVGA (480 x 320 pixel) display, which was pretty advanced at the time. However, the successive iPhone 3G and 3GS models used the same display. Meanwhile, other smart phone displays surpassed the iPhone with 3.5” or 3.7” WVGA (800 x 480 pixel) formats. Smart phones such as in the Samsung Omnia II and Google’s Nexus One more than doubled this resolution, and also utilized the new AMOLED technology. There have been side-by-side comparisons of the iPhone 3GS with Google’s Nexus One, which put pressure on the display engineers at Apple. Well, they have responded definitively with the new iPhone 4 display, leapfrogging the competition with nearly twice the resolution of WVGA.
The previous iPhones used both a-Si and LTPS TFT LCD technologies. Any customer could end up with either a-Si or LTPS in their iPhone. The LTPS versions might have slightly better battery life or higher brightness, but most consumers could not tell the difference. The iPhone 4 uses LTPS TFT only. A-Si can’t obtain a high enough resolution yet, mainly because of its lower electron mobility and larger TFT size.
The touch screen on the iPhone 4 is still multi-touch projected capacitive. Improvements have been made to the touch screen by gluing together the LCDs to remove air gaps. This enhances optical transmittance, picture quality and sunlight readability. Actually, the touch screen and LCD were also glued together in the first generation iPhone, but the bonding process reduced yields and added material and labor costs. Since late 2007, the iPod touch and iPhones used designs in which the touch screen and LCD were separated by an air gap. It is likely that Apple’s suppliers have been able to increase the bonding yield rate to an acceptable level, or at least are confident that they can do so.
