Introduction to micro-LEDs

Introduction to micro-LEDs

High speed GaN micro-LED arrays for data communications N. Laurand(1), J.J.D. McKendry(1), A.E. Kelly(2), S. Zhang(1), J. Vinogradov(3), D. Massoubre(1), B.R. Rae(4), R.P. Green(5), E. Gu(1), O. Ziemann(3), R.K. Henderson(4) and M.D. Dawson(1) 1: 2: 3: 4: 5: Institute of Photonics, University of Strathclyde, Glasgow, UK

School of Engineering, University of Glasgow, Glasgow, UK POF-Application Center, Georg Simon Ohm University, Nrnberg, Germany School of Engineering, University of Edinburgh, Edinburgh, UK Department of Physics, University College Cork, Cork, Ireland Introduction to micro-LEDs 0.5m m Micro-stripes Matrix-addressable

III-nitride wafers grown on sapphire UV (370nm), violet (405nm) blue (450 and 470nm) and green (520nm) Patterned by standard photolithography M.D. Dawson and M.A.A. Neil, Micro-pixellated LEDs for science and instrumentation J Phys D. 41 090301 (2008). Individually-addressable micro-LEDs 16 16 array 72m diameter

100m pitch 370, 405, 450nm emission 8 8 array 10, 2080m diameter 200m pitch 370, 405, 450, 520, 560nm emission CW power output Diameter (nm)

Maximum absolute power (mW) 14 24 44 64 84 0.48 0.85

2.52 3.8 4.94 Up to 5mW from a single micro-LED pixel (450nm peak emission) Smaller pixels higher output power densities & current densities Micro-LEDs for communications Our GaN-based micro-LEDs emit at wavelengths corresponding to attenuation minimum in POF Data transmission using white LEDs also topical Possible advantages of micro-LEDs?

faster response? multi-channel output? Visible-light communications using micro-LEDs Bandwidth of micro-LEDs Bare pixels individually-addressed using a high-speed probe Bandwidth strongly dependent on current density Bandwidth of micro-LEDs

General trend that smaller micro-LEDs have higher maximum bandwidths. Attributed to higher maximum current densities for smaller pixels (reduced current crowding and device self-heating). Data transmission demo. Single micro-LED addressed using high-speed probe. Emission imaged onto Si photodetector. NRZ modulation (modulation depth 2V, DC bias ~7V). Data transmission demo. 155 Mbit/s

622 Mbit/s 1.2 Gbit/s 520nm-emitting micro-LED, diameter 34m i = 35mA, output power 0.2mW Error-free up to 1.1 Gbit/s Visible-light communications using CMOS-controlled microLEDs CMOS-driver array

Primarily designed for generating intense (sub)ns-duration pulses for OSL pumping 1616 array of individually-addressable drivers, 100100m2, 100m pitch Multiple modes of operation CW, pulsed, NRZ modulation 1.6mm Each of the 16 columns may be modulated with independent data inputs (MIMO data transmission) CMOS and micro-LED chips integrated by

flip-chip bonding process Bandwidth of CMOS-micro-LEDs NRZ signal from BERT used to trigger CMOS drivers. Micro-LEDs bias voltage modulated between 0V and LED_VDD (variable) Increasing V = higher bandwidth. Higher bandwidths obtained with smaller diameter pixels. Max bandwidth from single pixel 185MHz (450nm device)

Error-free data transmitted at up to 512 Mbit/s (450nm device) Data transmission over POF Work done in collaboration with O. Ziemanns group, POF-AC, Nrnberg 450nm-emitting CMOS-controlled micro-LED device used Micro-LED emission butt-coupled to 1m of 1mm diameter SI-POF Passive equalisation, low-pass filter and electrical amplifier used Data transmission over POF Up to -3dBm of coupled CW power Error-free (BER 110-9) data transmission at 1Gbit/s from pixel diameters

ranging from 34 to 84m Error-free data transmission also achieved using 520nm-device at up to 500Mbit/s Received power (a.u.) 84m diameter pixel, 1Gbit/s Time (0.2ns/div) Multi-channel transmission

Existing CMOS device has up to 16 data inputs potential MIMO transmitter for highthroughput parallel data transmission Data transmission using two channels has been investigated. Using two 450nm-emitting 34m diameter pixels, error free parallel transmission has been achieved up to 600Mbit/ s (300Mbit/s per channel) Data rate per channel limited due to EMI issues between the two channels this issue appears to be primarily caused by the design of the interface board, not the CMOS or micro-LED arrays themselves.

Conclusions Micro-LED pixels have been shown to have modulation bandwidths of up to ~450 MHz, with peak emission at wavelengths suitable for transmission over POF. >1Gbit/s single pixel transmission demonstrated with no equalisation CMOS control arrays have been shown to provide convenient control over micro-LED arrays, with bandwidth of up to 185MHz possible. With up

to 16 independent data channels, these devices are potential MIMO transmitters for VLC. Key Publications Jonathan McKendry, Richard P. Green, A. E. Kelly, Zheng Gong, Benoit Guilhabert, David Massoubre, Erdan Gu and Martin D. Dawson High Speed Visible Light Communications Using Individual Pixels in a Micro Light-Emitting Diode Array Photon. Tech. Lett., Vol 22, No.18, pp 1346-1348, Sept 2010. McKendry, J. J. D.; Massoubre, D.; Zhang, S.; Rae, B. R.; Green, R. P.; Gu, E.; Henderson, R. K.; Kelly, A. E.; Dawson, M. D.; , "Visible-Light Communications Using a CMOSControlled Micro-Light- Emitting-Diode Array," Lightwave Technology, Journal of , vol.30, no.1, pp.61-67, Jan.1, 2012

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