FRONTIERS PHOTONICS


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CONSUMER


across the supply chain, such as ams Osram for microLED components, LG Display for the substrates and Taiwan Semiconductor Manufacturing for 12-inch wafers.


Overcoming manufacturing bottlenecks In May, LA-based start-up Q-Pixel introduced a new microLED process achieving pixel densities of more than 5,000 pixels (PPI) per inch. The company aims to overcome manufacturing barriers that have inhibited the technology’s adoption in the consumer market. The Polychromatic RGB microLED achieves full-colour tunability across a single four-micron pixel, which, the company says, negates the need for pick-and-place assembly as with single- colour LEDs. Selectively placing millions


of tiny RGB LEDs is a challenging and cost-prohibitive process. The process could ultimately decrease costs, streamline manufacturing, and minimise the occurrence of dead pixels. MIT researchers proposed a similar


process in February that also achieved a density of more than 5,000 PPI. The process involves growing vertically stacked ultrathin red, green, and blue membranes to achieve multiple colours in a four-micron pixel. Porotech, based in Cambridge, UK, launched a single-panel, full-colour microdisplay in May, using a process that overcomes manufacturing challenges. It is based on dynamic pixel tuning (DPT) technology, whereby microLED pixels can emit any visible colour when driven with a


specific current density. The new active- matrix 0.26in microLED display offers 1,280 x 720 resolution, which uses a driving method developed by Porotech that rapidly displays red, green and blue light to enable a full-colour RGB display. Based on existing backplane technology,


the 3.5-micron microLEDs are fabricated on a 4.5-micron pixel pitch. The emitter size of Porotech’s microLED can be larger and keep the resolution because subpixels are no longer required. With DPT technology, full- colour native microLED displays can now be unlocked with a single LED epitaxial growth and a one-step wafer-to-wafer bonding to the CMOS backplane. This removes complex and low-yield manufacturing barriers inherent with alternative approaches. l


SMARTPHONE SENSORS


VCSELs deliver mega impact in consumer space


T rumpf Photonic


Components has been named by Apple as a key


supplier for its work supporting the proximity sensor in the iPhone. The iPhone’s proximity sensor turns off the screen when it detects an object that is close by, such as when a user holds an iPhone up to their ear, to save battery life. To date, Trumpf has


manufactured and delivered more than one billion vertical- cavity surface-emitting lasers (VCSELs) to Apple. VCSELs offer the benefit


of high-performance data transmission with a comparatively low power input, and because they are manufactured using semiconductor processes, they are inexpensive to produce at scale. With the VCSEL laser diode, the light is emitted perpendicular to the plane of the semiconductor chip, in contrast to the edge-emitting laser diode, where the light exits at one or two edges of the chip. When VCSELs first appeared


in the iPhone in 2017, they were integrated with the sensors on top of the display, usually in a notch bar. This created some initial kickback as the space it took up was not compatible with the popular aesthetic of


Trumpf has manufactured and delivered more than one billion VCSELs to Apple


full-screen displays. Recently, however – in the iPhone 14 – it has been possible to integrate the proximity sensor underneath the OLED screen. This is thanks to Trumpf using an InP-based long-wavelength emitter and receiver at 1,380nm, which fits the optical transmission window of OLED screens. Trumpf gained VCSEL


technology and a dedicated production plant in Ulm, Germany, when it acquired Philips Photonics in 2019. The company has invested €40m in the Ulm facility since the purchase, and is planning further expansion within the next year. Apple announced in May that its spend with European


suppliers has increased more than 50% since 2018, totaling €85bn over the past five years and more than €20bn in 2022 alone.


The consumer market for


VCSELs is expected to reach $1.7bn in 2027, according to the ‘VCSELs market and technology trends 2022 report’ by Yole Group. l


42 Photonics Frontiers 2023


TRUMPF Group


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