Current Research

Monochromatic high-resolution micro-LED micro-display

1700 pixels per inch (PPI) passive-matrix (PM) blue micro-display and a 400 × 240 active-matrix (AM) blue micro-display

Monochromatic high-resolution micro-LED micro-displays have been monolithically fabricated on both GaN-on-Sapphire and GaN-on-Si platforms, including a world-first 1700 pixels per inch (PPI) passive-matrix (PM) blue micro-display and a 400 × 240 active-matrix (AM) blue micro-display.

Related publications:

  1. W. C. Chong, W. K. Cho, and Z. J. Liuet al.et al., “1700 pixels per inch (PPI) passive-matrix micro-LED display powered by ASIC,” in IEEE Compound Semiconductor Integrated Circuit Symposium (IEEE, 2014), pp. 1–4.

  2. L. Qi, X. Zhang, W. C. Chong, P. Li, and K. M. Lau, “848 ppi high-brightness active-matrix micro-LED micro-display using GaN-on-Si epi-wafers towards mass production,” Opt. Express 29, 10580-10591 (2021).

A world-first 1700 pixels per inch (PPI) passive-matrix (PM) blue micro-display

The first 1700 pixels per inch (PPI) blue passive-matrix light-emitting diodes on silicon micro-displays powered by ASIC with 6-bit grayscale is realized by flip-chip bonding of a micro-LED array onto a CMOS-based ASIC display driver. The micro-display consists of 256 x 192 pixels within a display area of 0.19 inch in diagonal.

Fig.1. (a) I-V curve of single pixel with inset of its light emitting image. (b) Architecture of ASIC driver. Top-down view of (c) ASIC driver and (d) 256 × 192 LEDs array. (e) Final assembly wire-bonded on a flex cable. (f) Source images (top) and its corresponding display images (bottom) on this micro-display.

Related publications:

  1. W. C. Chong, W. K. Cho, Z. J. Liu, C. H. Wang, and K. M. Lau, "1700 pixels per inch (PPI) passive-matrix micro-LED display powered by ASIC," in Technical Digest - IEEE Compound Semiconductor Integrated Circuit Symposium, CSIC, 2014.

  2. K. M. Lau, Z. Liu, W. C. Chong, W. K. Cho, and C. H. Wang, "Passive-matrix light-emitting diodes on silicon micro-display," ed: Google Patents, 2019.

400 × 240 active-matrix (AM) blue micro-display

A blue GaN micro-LED array featuring 400 × 240 pixels with a pixel size of 30 × 30 μm2 was implemented on a single sapphire substrate using monolithic fabrication process. Active-matrix driving was achieved by hybridizing the micro-LED array with a CMOS backplane.

Fig.2. (a) Layout of 400 × 240 LEDs array and (b) zoomed-in image of LED array edge area. (c) I-V curve of single pixel. (d) Final assembly wire-bonded on PCB driving board. (e) 16-level gray scale images shown on this micro-display.

Related publications:

  1. X. Li, L. Wu, Z. Liu, B. Hussain, W. C. Chong, K. M. Lau, et al., "Design and Characterization of Active Matrix LED Microdisplays With Embedded Visible Light Communication Transmitter," Journal of Lightwave Technology, vol. 34, pp. 3449-3457, 2016/07/15 2016.

848 ppi active-matrix micro-LED micro-display using GaN-on-Si epi-wafers

A 0.55-inch high-brightness high-resolution monolithic GaN-on-Si micro-LED micro-display with a pixel density of 848 ppi is demonstrated. The GaN thin film grown on Si substrate was integrated with a custom-designed Si CMOS driver through Au-Sn flip-chip bonding, in which Si growth substrate was removed using a crack-free wet etching method.

Fig. 3 (a) GaN-thin film integrated with Si CMOS driver after Si growth substrate removal (b) Yield of the Micro-LED micro-display panel and pixel uniformity

Fig. 4 (a) EL spectra and wavelength shift of the micro-LED display under different driven current (b) Color difference in u’v’ space

Fig. 5 (a) Setup of luminance and angular dependence measurement (b) Brightness and LER V.S driven current density (c) The far-field luminance distribution of the micro-LED display

Fig. 6 Original grayscale images and displayed images

Related publications:

  1. X. Longheng Qi, Xu Zhang, Wing Cheung Chong, Peian Li, and Kei May Lau, "848 ppi high-brightness active-matrix micro-LED micro-display using GaN-on-Si epi-wafers towards mass production", Optics Express, vol. 29, no. 7, pp.10580-10591, 2021

64 × 36 active-matrix red LED micro-display

A thin film active-matrix red LED micro-display fabricated from AlGaInP-on-GaAs LED epi-wafers is demonstrated. The resolution is 64 × 36 with a 40 μm pixel pitch. The maximum brightness is 23,500 nits at < 0.5 W power consumption.

Fig. 7 (a)Thin film red LED micro-display, (b) Driver PCB and (c) Displayed images

Related publications:

  1. Peian Li, Xu Zhang, Wing Cheung Chong, and Kei May Lau, “Monolithic Thin Film Red LED Active-Matrix Micro-Display by Flip-Chip Technology”, IEEE Photonics Technology Letters, Vol. 33, no. 12, pp.603-606, 2021