Apple is reportedly looking at sputtering first to build the HMO OLED transistors it is developing for future Mac displays. The final mass-production process has not been chosen because the alternative, atomic layer deposition (ALD), costs more.
HMO, short for high-mobility oxide, could replace some silicon steps in the LTPO transistor layers of premium OLED panels, which would simplify manufacturing and lower costs. The MacBook Pro with PROLED XDR Display announced on October 28 already uses a full oxide transistor layer, and HMO is a candidate for later panels such as the MacBook and iMac, The Elec reported.
Apple Is Looking at the Cheaper Sputtering Route for HMO OLED
Sputtering uses plasma to knock atoms off a solid material and stack them on the substrate, and OLED makers already run that equipment on their lines. Reaching high electron mobility and reliability together still needs better material composition and film structure.
ALD builds the semiconductor layer one atomic layer at a time from gas precursors, which gives tighter control over thickness and composition. The equipment and precursor materials cost more, and since ALD’s performance edge has already shown up in research, cost is what is steering the tests toward sputtering.
Samsung Display and LG Display Are Developing Both Methods
Samsung Display is building sputtering-based HMO while also validating ALD, to see whether the electron mobility and reliability Apple requires hold up on large substrates. Apple reviewed the technology at its own research facility in Taiwan and asked Samsung Display to check whether it works on a Gen 8-class large-area process.
Samsung Display already makes the MacBook Pro’s OLED panels on its 8.6-generation OLED line. LG Display is developing sputtering-based HMO on its Gen 6 line for small and medium-size OLED panels, runs ALD research alongside it, and leans toward the existing sputtering equipment because ALD would need extra capital spending. LG Display is also developing a five-layer OLED panel for an iMac, an emitter stack that is separate from the transistor layer.
HMO Must Keep Its Electron Mobility in the Finished Panel
Each pixel’s thin-film transistor switches the pixel on and off and sets its brightness. Conventional oxide transistors reach roughly 10 cm²/Vs of electron mobility, while HMO targets 30 to 50, which lets the transistor supply more current for high-resolution, high-refresh-rate screens.
Hitting the number on a test device is not enough, because later manufacturing steps and exposure to heat and light can change a transistor’s electrical behavior. Samsung Display and LG Display are checking performance and stability for each deposition method for that reason. LG Display’s ALD-built oxide transistor reached about 40 cm²/Vs last year, inside the target range, and the company showed an OLED prototype built with it.
