Apple’s upcoming iPhone models—the OLED-based iPhone 8 and the iterative LCD-based iPhone 7s and iPhone 7s Plus handsets—have been hit in a global shortage of 3D NAND flash chips, forcing the Cupertino giant to call on Samsung in an effort to secure more.

According to a new report Thursday from DigiTimes, the overall supply of 3D NAND flash components for 2017 iPhones has fallen short of Apple’s orders by as much as thirty percent.

That’s because the company’s current flash chip suppliers SK Hynix and Toshiba have both experienced lower-than-expected yield rates for their 3D NAND technologies.

SK Hynix is among the bidders for Toshiba’s lucrative flash chip unit.

Here’s an excerpt from the DigiTimes report:

Apple has turned to Samsung for more NAND chip supplies for its upcoming phones, since Samsung has relatively stable yield rates for 3D NAND technology and has scaled up its output of 3D NAND chips.

TrendForce estimated that supplies of the 3D NAND flash storage chip won’t ease until the middle of 2018. “The NAND Flash industry’s manufacturers will continue to devote their attention to the development of 3D 64L NAND Flash technology in 2017,” said TrendForce.

In the second half of 2018, some suppliers will also begin to shift their attention towards the industry’s newer and more advanced 96L flash storage products. Samsung, Toshiba and Micron Technology are currently transitioning to 64-layer 3D NAND flash products, while SK Hynix plans to jump straight to supplying 72-layer 3D chips.

“These gradual changes are all expected to have a potentially beneficial effect on the productions of NAND Flash in 2018,” added TrendForce. “As a result, their prices could start to fall as early as next year”. However, the global supply of NAND flash chips is set to remain tight through the end of 2017.

Business Korea said that Samsung Electronics (which leads the global NAND flash market), Toshiba, Western Digital and SK Hynix are accelerating the development of these three-dimensional NAND flash chip technologies, which basically stack more memory cells than 2D chips while utilizing existing mass production facilities.

The 128GB iPhone 7 model, for example, uses Toshiba’s 3D BiCS NAND technology, which stores three bits of data per transistor and stacks 48 NAND layers onto a single die, bringing accelerated read and write performance compared to 2D flash memory chips.