Apple Inc. is designing and producing its own device displays for the first time, using a secret manufacturing facility near its California headquarters to make small numbers of the screens for testing purposes, according to people familiar with the situation.

The technology giant is making a significant investment in the development of next-generation microLED screens, said the sources, who requested anonymity to discuss internal planning. MicroLED screens use different light-emitting compounds than the current OLED displays and promise to make future gadgets slimmer, brighter and less power-hungry.

The screens are far more difficult to produce than OLED displays, and the company almost killed the project a year or so ago, the people said. Engineers have since been making progress and the technology is now at an advanced stage, they said, though consumers will probably have to wait a few years before seeing the results.