Japanese firm Sharp has announced that it has begun production of 5-inch Full HD LCDs with a pixel density it claims to be among the "highest in the world".Production began at the start of September and the 1920 x 1080 LCD panels are intended for smartphones. They feature a pixel density of 443ppi (pixels per inch). Considering the iPhone 5 has a 1136 x 640 Retina display with 326ppi, you can only imagine just how clean and crisp Sharp's will be.What remains a mystery, however, is which phone(s) these LCD screens are intended for. While Sharp has said it will enter into full-scale production this month (October), it hasn't revealed the destination.\u00a0One good bet is HTC, for its HTC One X 5 or - as some have taken to calling it - the Google Nexus 5. It is known that this handset will sport a 5-inch screen - hence the name - and it has been leaked that the display will indeed be 1080p, just like Sharp's new panels.Pocket-lint knows that the One X 5 is a real handset, having been told so by our sources in the past, so we're feeling confident that this is a further piece to the puzzle.If so, it could well have the best smartphone screen seen to date.