Study and design of a driving circuit for GaN LED microdisplays ; Exploration, conception et mise en œuvre de circuit de pilotage pour micro-écrans à LED GaN

Recent advances in the field on inorganic LEDs, allow for manufacturing of GaN LEDs at micrometer scale. These optical devices, which were initially only manufactured with large dimensions, can be associated to a CMOS driving circuit to form micro-displays. GaN based micro-LEDs offer a maximum brightness and a commutation speed, well above other LEDs technologies used at micrometer scale. However, they also have specific electrical characteristics, such as reduced efficiency and large dispersion of behavior, when used with a reduced current. Consequently, driving methods commonly used with other types of LEDs are not appropriate for the control of such devices.This thesis focusses on the design of pixel driving circuits suitable for micro GaN LEDs, both in terms of implemented driving method and footprint compliance with the size of used LEDs. The first part of this work focusses on display applications, with a compact pixel matrix exploiting LEDs high brightness, while offering a large resolution. A PWM driving scheme, which implies sporadic operation of the LEDs under high current, is chosen to deal with LEDs specificities. In order to insure low silicon footprint despite the relatively high complexity of PWM driving, a 3D manufacturing of the circuit is introduced. A derivative of the CoolCube 3D technology that is developed by CEA Leti, is considered to manufacture a micro-display on three superposed levels. The driving circuit is split between the two first levels, made a CMOS circuit with different types of transistors. An array of GaN LEDs form the third level for the display.The second part of this thesis focusses on exploiting the reduced commutation time of the GaN LEDs. The ability to generate a high frequency optical signal is appropriate for building visible light communication emitters. Several free space optical communication emitters reported in the literature use a single GaN LED to transmit data at several Gb/s. Although, these single LED emitters are very fast, they are cumbersome and complex ...