NS Nanotech was at the SID Vehicle Displays and Interfaces conference to talk about the development of their nanowire microLED technology for use in automotive displays. They have now developed an encapsulation technique for the nanowires that will significantly aid in planarization and contact formation.

CEO Seth Coe-Sullivan started by noting that they have already commercialized UV nanowire microLEDs for use as disinfection applications. But for Head-up Displays, full-color microLEDs are needed.

Their nanowire growth process starts with a GaN epi layer on top of a silicon substrate, which may contain display circuitry. The nanowire template, or growth starting points, are defined with a deep UV lithography method.  These are hexagonal patterns where the size of the hexagonal defines its color.  The smaller the hexagonal, the shorter the emitted wavelength. Nanowires are typically 50 to 250 nm in size with multiple nanowires needed to make a display pixel (1 to 10 microns).

An MBE growth phase is then initiated to create multiple quantum wells in each nanowire. This is a single growth operation allowing the fabrication of red, green and blue nanowires on the substrate.

Next, the space between the nanowires is filled with an inorganic material to better enable the planarization of the nanowires and fabrication of top p-type contacts. The company experimented with several processes and materials and finally settled an Atomic Layer Deposition process to deposit Aluminum Oxide (AL2O3).

Close packing each nanowire also creates a photonic crystal structure, which aids in the emission directionality, brightness and efficiency. Coe-Sullivan showed results for their green device which he says is a world record for devices of less than 1 micron. They have achieved an EQE of over 25%  (at ~ 0.3 A/cm2 current density) and an IQE of over 70%. The linewidth and directionality are also impressive with a green photoluminescence FWHM of 2-3 nm, and electroluminescence FWHM of ~4nm (peak at ~547nm).

Red EQE is 13% (at ~1 A/cm2) which corresponds to around 500K nits of red (wavelength not specified).

Alternative microLED structures like nanowires and pyramids are being explored by several companies and may offer a very exciting path forward. Demonstrating scalable processes like planarization for consistent p-contact formation is a good step forward.