While all-screen smartphones have undoubtedly become the mainstream of the handset industry, many industry watchers are now wondering whether notch smartphones - models with a u-shape notch on the top of the display as inspired by Apple's iPhone X - could gain further momentum in 2018.

A number of Android smartphone vendors including more established brands such as Asustek Computer, Huawei and Oppo, and little known China-based makers such as UleFone, Leagoo, and Doogee, have rolled out models with notch-type displays.

But not all users have been pleased by the u-shape design, which does not have full support from app interfaces, said the observers.

Sales of the iPhone X have reportedly been lower than expected, prompting Apple to reduce its purchase of AMOLED panels for the first half of 2018 to 25 million units from 40 million units set previously, the sources indicated.

Even so, Apple is expected to continue to adopt the notch technology for all of its three iPhone models reportedly to be rolled out in 2018: a 6.05-inch LTPS LCD model, a 5.85-inch OLED version and a 6.45-inch OLED device, said the sources.

However, the sources also pointed out that patent issues may force Android-based smartphone makers to refrain themselves from developing notch smartphones relentlessly in the near future as Apple holds related patents for the u-shape display.

The higher production cost and complicated manufacturing processes for notch-type displays will also compel Android phone makers to limit the number of notch phones targeting primarily on the high-end segment.

Given such considerations, the penetration rate of notch smartphones is unlikely to experience an explosive growth in 2018, with the ratio likely to reach 20% and mostly contributed by Apple, commented the sources.