The success of GaN as a substrate for high performances applications, in terms of a very large spectrum of working frequencies, is the result of an intense research activity focused on the possibility of integrating GaN-based devices with CMOS devices. Let’s consider, for example, LEDs built with GaN as a substrate described in an interesting article published in the JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 1, JANUARY 1, 2012 (see Figure 1):
“…, the modulation bandwidths of pixels from 8 x 8 arrays of individually-addressable micro-light-emitting diodes, with pixel diameters ranging from 14 to 84 m and peak emission wavelengths of 370, 405, 450 and 520 nm have been reported. The highest optical -3dB bandwidth observed are in excess of 400 MHz for a single emitter, achieved using standard epitaxial LED wafers and photolithography processes. The modulation bandwidth of a particular micro-LED pixel was found to increase with increasing injected current densities, which has been attributed to a reduction in the differential carrier lifetime as the current density (carrier density) within the micro-LED active region increases. Smaller area micro-LEDs were found to have higher maximum modulation bandwidths than their larger area counterparts, which has been attributed to their ability to operate at higher injected current densities. These high bandwidths were observed for ‘bare’ micro-LEDs, addressed via a high-speed probe. As a step towards a more practical multi-emitter optical data transmitter, a 450 nm-emitting micro-LED has been integrated with a CMOS driver array chip allowing each pixel within the array to be controlled via a simple computer interface and control board. The modulation bandwidth of the micro-LEDs under CMOS control was found to be up to 185 MHz, with error-free data transmission using on-off keying being demonstrated at bit rates of up to 512 Mbit/s. Although this represents a reduction in the frequency response compared to the measurements on the bare micro-LED devices, a good compromise is achieved by the additional functionality available from the CMOS-controlled micro-LEDs, including convenient computer control of each pixel within the array and the potential for high-throughput parallel data transmission by independently modulating up to 16 columns of micro-LEDs.” (Source: Visible-Light Communications Using a CMOS-Controlled Micro-Light-Emitting-Diode Array by Jonathan J. D. McKendry, David Massoubre, Shuailong Zhang, Bruce R. Rae, Richard P. Green, Erdan Gu,Robert K. Henderson, A. E. Kelly, and Martin D. Dawson, Fellow, IEEE)
“LIGHT-EMITTING diodes based on the AlInGaN alloy system promise energy-efficient light generation across the visible spectrum and beyond” (Source: ResearchGate.net)
Another good example of how research activity led to the success of GaN adoption in electronics is represented by the activity of Boon Chirn Chye as Associate Professor at the Nanyang Technological University (NTU) (see Figure 2):
The research activity of professor Boon Chirn Chye focused on RFIC in GaN and CMOS (Source: ntu.edu)
The result of the intense activity with GaN substrates has hit the market of semiconductors. GaN and CMOS integration, indeed, is going to gain importance for large companies in the field of semiconductors. In the next part of this blog series we will explore this interesting market and the actors involved in this project.
Do you think a GaN and CMOS combination could benefit electronics technologies?